Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear and Coefficient of Friction

*Ronaldo Câmara Cozza*

### **Abstract**

The purpose of this work is to study the influence of the micro-abrasive wear modes on the behaviors of the volume of wear (*V*) and of the coefficient of friction (*μ*) of thin films submitted to micro-abrasive wear. Experiments were conducted with thin films of TiN, TiAlN, TiN/TiAlN, TiHfC, ZrN, and TiZrN, using a ball of AISI 52100 steel and abrasive slurries prepared with black silicon carbide (SiC) particles and glycerine. The results show that the abrasive slurry concentration affected the microabrasive wear modes ("grooving abrasion" or "rolling abrasion") and, consequently, the magnitude of the volume of wear and of the coefficient of friction, as described: (i) a low value of abrasive slurry concentration generated "grooving abrasion," which was related to a relatively low volume of wear and high coefficient of friction, and (ii) a high value of abrasive slurry concentration generated "rolling abrasion," which was related to a relatively high volume of wear and low coefficient of friction.

**Keywords:** micro-abrasive wear, grooving abrasion, rolling abrasion, thin films, volume of wear, coefficient of friction

### **1. Introduction**

The micro-abrasive wear test by rotating ball ("ball-cratering wear test") is an important method adopted to study the micro-abrasive wear behavior of metallic, polymeric, and ceramic materials. **Figure 1** presents a schematic diagram of the principle of this micro-abrasive wear test, in which a rotating ball is forced against the tested specimen in the presence of an abrasive slurry, generating, consequently, the called "wear craters" on the surface of the tested material.

Initially, the development of the ball-cratering wear test aimed to measure the thickness of thin films (**Figure 2a** and **b**) [1], which can be made using the equations detailed in Ref. [2]. Because of the technical features, this type of microabrasive wear test has been applied to study the tribological behavior of different materials [3–5], for example, in the analysis of the volume of wear (*V*), coefficient of wear (*k*), and coefficient of friction (*μ*) of thin films [2, 6–10].

As a function of the abrasive slurry concentration, two micro-abrasive wear modes can be usually observed on the surface of the worn crater: "grooving abrasion" is observed when the abrasive particles slide on the surface, whereas "rolling abrasion" results from abrasive particles rolling on the specimen's surface.

**Figure 3a** [11, 12] and **Figure 3b** presents, respectively, images of "grooving abrasion" and "rolling abrasion."

Many works on coefficient of friction (*μ*) during abrasive wear and other types of tests are available in the literature [13–19], but only a few were dedicated to the coefficient of friction in ball-cratering wear tests [2–4, 10, 11]. In particular, Shipway [20] has studied the coefficient of friction in terms of the shape and movement of the abrasive particles, Kusano and Hutchings [21] presented a theoretical model for coefficient of friction in micro-abrasive wear tests with "free-ball" equipment configuration, and Cozza et al. [2–4, 11, 22] measured the tangential force developed during tests conducted in a "fixed ball" equipment configuration, which allowed direct calculation of the friction coefficient by the ratio between the tangential and normal forces. Besides, using a proper electronic instrumentation, Cozza et al. [2, 23–25] have studied and measured the behavior of the coefficient of friction in thin films in ball-cratering wear tests; however, in those works [2, 23–25], the test sphere has reached the substrate.

### **Figure 1.**

*Micro-abrasive wear test by rotating ball: a representative figure showing the operating principle and the abrasive particles between the ball and the specimen; "*h*" is the depth of the wear crater.*

**65**

**Figure 3.**

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear…*

Analyzing and studying important researches regarding to tribological behavior of materials submitted to micro-abrasive wear test conditions [7–9, 26], the purpose of this work is to report the influence of the micro-abrasive wear modes on the behaviors of the volume of wear (*V*) and coefficient of friction (*μ*) of thin films

A ball-cratering wear test equipment with free-ball mechanical configuration (**Figure 4** [27]) was used for the micro-abrasive wear tests, which has two load cells: one load cell to control the "normal force" (*N*) and one load cell to measure the "tangential force" (*T*) that is developed during the experiments. The values of "*N*"

submitted to micro-abrasive wear tests by rotating ball.

*Micro-abrasive wear modes: (a) "grooving abrasion" [11, 12] and (b) "rolling abrasion."*

**2. Equipment, materials, and methods**

**2.1 Ball-cratering wear test equipment**

and "*T*" are read by a readout system.

*DOI: http://dx.doi.org/10.5772/intechopen.86459*

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear… DOI: http://dx.doi.org/10.5772/intechopen.86459*

Analyzing and studying important researches regarding to tribological behavior of materials submitted to micro-abrasive wear test conditions [7–9, 26], the purpose of this work is to report the influence of the micro-abrasive wear modes on the behaviors of the volume of wear (*V*) and coefficient of friction (*μ*) of thin films submitted to micro-abrasive wear tests by rotating ball.

### **2. Equipment, materials, and methods**

### **2.1 Ball-cratering wear test equipment**

A ball-cratering wear test equipment with free-ball mechanical configuration (**Figure 4** [27]) was used for the micro-abrasive wear tests, which has two load cells: one load cell to control the "normal force" (*N*) and one load cell to measure the "tangential force" (*T*) that is developed during the experiments. The values of "*N*" and "*T*" are read by a readout system.

*Friction, Lubrication and Wear*

abrasion" and "rolling abrasion."

**Figure 3a** [11, 12] and **Figure 3b** presents, respectively, images of "grooving

of tests are available in the literature [13–19], but only a few were dedicated to the coefficient of friction in ball-cratering wear tests [2–4, 10, 11]. In particular, Shipway [20] has studied the coefficient of friction in terms of the shape and movement of the abrasive particles, Kusano and Hutchings [21] presented a theoretical model for coefficient of friction in micro-abrasive wear tests with "free-ball" equipment configuration, and Cozza et al. [2–4, 11, 22] measured the tangential force developed during tests conducted in a "fixed ball" equipment configuration, which allowed direct calculation of the friction coefficient by the ratio between the tangential and normal forces. Besides, using a proper electronic instrumentation, Cozza et al. [2, 23–25] have studied and measured the behavior of the coefficient of friction in thin films in ball-cratering wear tests; however, in

*Micro-abrasive wear test by rotating ball: a representative figure showing the operating principle and the* 

*abrasive particles between the ball and the specimen; "*h*" is the depth of the wear crater.*

*Examples of wear craters generated on coated system: (a) multilayer and (b) thin film of TiN.*

those works [2, 23–25], the test sphere has reached the substrate.

Many works on coefficient of friction (*μ*) during abrasive wear and other types

**64**

**Figure 2.**

**Figure 1.**

### **2.2 Materials**

Experiments were conducted with thin films of:


deposited on substrates of cemented carbide. For the counter-body, one ball of AISI 52100 steel with diameter of *D* = 25.4 mm was used.

The abrasive material was black silicon carbide (SiC) with an average particle size of 3 μm; **Figure 5** [4] presents a micrograph of the abrasive particles (**Figure 5a**)

*Ball-cratering micro-abrasive wear test equipment used in this work: free-ball mechanical configuration, able to acquire, simultaneously, the "normal force* N*" and the "tangential force* T*."*

**67**

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear…*

*C*<sup>2</sup> 50% SiC + 50% glycerine

Abrasive slurry concentration (in volume) *C*<sup>1</sup> 5% SiC + 95% glycerine

and the particle size distribution (**Figure 5b**). The abrasive slurries were prepared

**Table 1** presents the values of the test parameters defined for the micro-abrasive

The normal force value defined for the wear experiments was *N* = 0.4 N, combined with two abrasive slurries concentrations (*C*), *C*1 = 5% SiC + 95% glycerine and *C*2 = 50% SiC + 50% glycerine (volumetric values), with the purpose to produce, respectively, "grooving abrasion" and "rolling abrasion" on the surfaces of the

All tests were *non-perforating*, e.g., only the thin films were worn. The normal force (*N*) was constant during the tests; the tangential force (*T*) was monitored and

The volume of wear (*V*) and the coefficient of friction (*μ*) were then calculated using Eqs. (1) [1] and (2), respectively; "*d*" is the diameter of the wear crater, and

**Figures 6** and **7** show examples of worn surfaces obtained in the experiments; in all wear craters, the maximum depth (*h*) observed was, approximately, *h* ≈ 8 μm. **Figure 6** displays the action of "grooving abrasion," characteristic of *C*1 = 5%

<sup>64</sup>*R*,for *<sup>d</sup>* <sup>&</sup>lt; <sup>&</sup>lt; *<sup>R</sup>* (1)

*<sup>N</sup>* (2)

thin films. The ball rotational speed was set to *n* = 70 rpm.

*Test parameters selected for the ball-cratering wear experiments.*

*μ* = \_\_*<sup>T</sup>*

*DOI: http://dx.doi.org/10.5772/intechopen.86459*

Normal force [N] *N* 0.4

Ball rotational speed [rpm] *n* 70

with SiC and glycerine.

**2.3 Methods**

**Table 1.**

wear experiments.

registered during all experiments.

*<sup>V</sup>* <sup>≈</sup> *πd*<sup>4</sup> \_\_\_\_

"*R*" is the radius of the ball:

**3. Results and discussion**

**Figure 5.** *SiC abrasive [4]: (a) scanning electron micrograph and (b) particle size distribution.*

Normal force [N] *N* 0.4 Abrasive slurry concentration (in volume) *C*<sup>1</sup> 5% SiC + 95% glycerine *C*<sup>2</sup> 50% SiC + 50% glycerine Ball rotational speed [rpm] *n* 70

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear… DOI: http://dx.doi.org/10.5772/intechopen.86459*

### **Table 1.**

*Friction, Lubrication and Wear*

Experiments were conducted with thin films of:

AISI 52100 steel with diameter of *D* = 25.4 mm was used.

*to acquire, simultaneously, the "normal force* N*" and the "tangential force* T*."*

*SiC abrasive [4]: (a) scanning electron micrograph and (b) particle size distribution.*

deposited on substrates of cemented carbide. For the counter-body, one ball of

The abrasive material was black silicon carbide (SiC) with an average particle size of 3 μm; **Figure 5** [4] presents a micrograph of the abrasive particles (**Figure 5a**)

*Ball-cratering micro-abrasive wear test equipment used in this work: free-ball mechanical configuration, able* 

**2.2 Materials**

• TiN

• TiAlN

• TiHfC

• ZrN

• TiZrN

• TiN/TiAlN

**66**

**Figure 5.**

**Figure 4.**

*Test parameters selected for the ball-cratering wear experiments.*

and the particle size distribution (**Figure 5b**). The abrasive slurries were prepared with SiC and glycerine.

### **2.3 Methods**

**Table 1** presents the values of the test parameters defined for the micro-abrasive wear experiments.

The normal force value defined for the wear experiments was *N* = 0.4 N, combined with two abrasive slurries concentrations (*C*), *C*1 = 5% SiC + 95% glycerine and *C*2 = 50% SiC + 50% glycerine (volumetric values), with the purpose to produce, respectively, "grooving abrasion" and "rolling abrasion" on the surfaces of the thin films. The ball rotational speed was set to *n* = 70 rpm.

All tests were *non-perforating*, e.g., only the thin films were worn. The normal force (*N*) was constant during the tests; the tangential force (*T*) was monitored and registered during all experiments.

The volume of wear (*V*) and the coefficient of friction (*μ*) were then calculated using Eqs. (1) [1] and (2), respectively; "*d*" is the diameter of the wear crater, and "*R*" is the radius of the ball:

$$V \simeq \frac{\pi d^4}{64R}, \text{for } d < \sim R \tag{1}$$

$$
\mu = \frac{T}{N} \tag{2}
$$

### **3. Results and discussion**

**Figures 6** and **7** show examples of worn surfaces obtained in the experiments; in all wear craters, the maximum depth (*h*) observed was, approximately, *h* ≈ 8 μm. **Figure 6** displays the action of "grooving abrasion," characteristic of *C*1 = 5%

**Figure 6.**

*Occurrence of "grooving abrasion" on the surface of the thin film of TiN.*

**Figure 7.** *Occurrence of "rolling abrasion" on the surface of the thin film of TiN.*

SiC + 95% glycerine; **Figure 7** displays a wear crater under the action of "rolling abrasion," reported for the abrasive slurry concentration *C*2 = 50% SiC + 50% glycerine. These results qualitatively agree with the conclusions obtained by Trezona et al. [28], in which low concentrations of abrasive slurries (<5% in volume of abrasive material, approximately) favor the occurrence of "grooving abrasion" and high concentrations of abrasive slurries (>20% in volume of abrasive material, approximately) favor the action of "rolling abrasion."

The actions of the micro-abrasive wear modes showed an important influence on the volume of wear and on the coefficient of friction of the thin films studied in this research. A significant increase in the volume of abrasive particles from *C*1 = 5% SiC + 95% glycerine to *C*2 = 50% SiC + 50% glycerine (causing, consequently, the micro-abrasive wear transition from "grooving abrasion" to "rolling abrasion") caused an increase in the volume of wear and a decrease in the coefficient of friction.

**Figures 8** and **9** show the behaviors of the volume of wear (*V*) and coefficient of friction (*μ*) as a function of the micro-abrasive wear modes; the maximum errors observed were *V* = 0.4 × 10<sup>−</sup><sup>3</sup> mm3 and *μ* = 0.1, for the volume of wear and coefficient of friction, respectively.

The values of the volume of wear reported under conditions of "rolling abrasion" (high-abrasive slurry concentration, *C*2 = 50% SiC + 50% glycerine) were higher than the values of the volume of wear reported under conditions of "grooving

**69**

**4. Conclusions**

**Figure 8.**

*abrasion."*

**Figure 9.**

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear…*

*Volume of wear (*V*) as a function of the micro-abrasive wear modes' "grooving abrasion" and "rolling* 

abrasion" (low-abrasive slurry concentration, *C*1 = 5% SiC + 95% glycerine), as

The values of the coefficient of friction reported under "grooving abrasion" (low-abrasive slurry concentration, *C*1 = 5% SiC + 95% glycerine) were higher than the values of the coefficient of friction reported under "rolling abrasion" (highabrasive slurry concentration, *C*2 = 50% SiC + 50% glycerine), and this behavior can be explained based on patterns of movements that act on "rolling abrasion" and "grooving abrasion" micro-abrasive wear modes: in "rolling abrasion," the abrasive particles are free to roll between the ball and the specimen, facilitating the relative movement between these elements and, consequently, decreasing the coefficient of friction on the tribological system; however, in "grooving abrasion," the abrasive particles are fixed on the counter-body (in this case, on the ball), limiting their

*Coefficient of friction (*μ*) as a function of the micro-abrasive wear modes' "grooving abrasion" and "rolling abrasion."*

reported by Mergler and Huis in 't Veld [5] and Trezona et al. [28].

movements and requiring higher tangential forces.

The results obtained indicated the conclusions:

*DOI: http://dx.doi.org/10.5772/intechopen.86459*

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear… DOI: http://dx.doi.org/10.5772/intechopen.86459*

### **Figure 8.**

*Friction, Lubrication and Wear*

SiC + 95% glycerine; **Figure 7** displays a wear crater under the action of "rolling abrasion," reported for the abrasive slurry concentration *C*2 = 50% SiC + 50% glycerine. These results qualitatively agree with the conclusions obtained by

approximately) favor the action of "rolling abrasion."

*Occurrence of "rolling abrasion" on the surface of the thin film of TiN.*

*Occurrence of "grooving abrasion" on the surface of the thin film of TiN.*

mm3

Trezona et al. [28], in which low concentrations of abrasive slurries (<5% in volume of abrasive material, approximately) favor the occurrence of "grooving abrasion" and high concentrations of abrasive slurries (>20% in volume of abrasive material,

The actions of the micro-abrasive wear modes showed an important influence on the volume of wear and on the coefficient of friction of the thin films studied in this research. A significant increase in the volume of abrasive particles from *C*1 = 5% SiC + 95% glycerine to *C*2 = 50% SiC + 50% glycerine (causing, consequently, the micro-abrasive wear transition from "grooving abrasion" to "rolling abrasion") caused an increase in the volume of wear and a decrease in the coefficient of

**Figures 8** and **9** show the behaviors of the volume of wear (*V*) and coefficient of friction (*μ*) as a function of the micro-abrasive wear modes; the maximum errors

The values of the volume of wear reported under conditions of "rolling abrasion" (high-abrasive slurry concentration, *C*2 = 50% SiC + 50% glycerine) were higher than the values of the volume of wear reported under conditions of "grooving

and *μ* = 0.1, for the volume of wear and coef-

**68**

friction.

**Figure 6.**

**Figure 7.**

observed were *V* = 0.4 × 10<sup>−</sup><sup>3</sup>

ficient of friction, respectively.

*Volume of wear (*V*) as a function of the micro-abrasive wear modes' "grooving abrasion" and "rolling abrasion."*

### **Figure 9.**

*Coefficient of friction (*μ*) as a function of the micro-abrasive wear modes' "grooving abrasion" and "rolling abrasion."*

abrasion" (low-abrasive slurry concentration, *C*1 = 5% SiC + 95% glycerine), as reported by Mergler and Huis in 't Veld [5] and Trezona et al. [28].

The values of the coefficient of friction reported under "grooving abrasion" (low-abrasive slurry concentration, *C*1 = 5% SiC + 95% glycerine) were higher than the values of the coefficient of friction reported under "rolling abrasion" (highabrasive slurry concentration, *C*2 = 50% SiC + 50% glycerine), and this behavior can be explained based on patterns of movements that act on "rolling abrasion" and "grooving abrasion" micro-abrasive wear modes: in "rolling abrasion," the abrasive particles are free to roll between the ball and the specimen, facilitating the relative movement between these elements and, consequently, decreasing the coefficient of friction on the tribological system; however, in "grooving abrasion," the abrasive particles are fixed on the counter-body (in this case, on the ball), limiting their movements and requiring higher tangential forces.

### **4. Conclusions**

The results obtained indicated the conclusions:


### **Appendix**


**71**

**Author details**

Brazil

Brazil

Ronaldo Câmara Cozza1,2

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear…*

1 Department of Mechanical Engineering, University Center FEI—Educational Foundation of Ignatius "Padre Sabóia de Medeiros", São Bernardo do Campo, SP,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Department of Mechanical Manufacturing, CEETEPS—State Center of Technological Education "Paula Souza", Technology Faculty—FATEC, Mauá, SP,

\*Address all correspondence to: rcamara@fei.edu.br

provided the original work is properly cited.

*DOI: http://dx.doi.org/10.5772/intechopen.86459*

*Thin Films: Study of the Influence of the Micro-Abrasive Wear Modes on the Volume of Wear… DOI: http://dx.doi.org/10.5772/intechopen.86459*

### **Author details**

*Friction, Lubrication and Wear*

concentration.

concentration.

**Appendix**

Greek letter

1.The concentration of abrasive slurry affected the occurrence of "grooving abrasion"—under low concentration—or "rolling abrasion," under high

2.The volume of wear increased with the increase of the abrasive slurry

3.With the low concentration of abrasive slurry, "grooving abrasion" and,

movements and generating high tangential forces.

A list of symbols used in this manuscript is given:

*d* diameter of the wear crater, [mm] *D* diameter of the ball, [mm] *h* depth of the wear crater, [μm] *k* coefficient of wear, [mm3

*n* ball rotational speed, [rpm]

*N* normal force, [N] *R* radius of the ball, [mm] *T* tangential force, [N] *V* volume of wear, [mm3

*μ* coefficient of friction

consequently, high values of coefficient of friction were reported. In this situation, the abrasive particles were incrusted on the counter-body, hindering their

4.On the other hand, when the high concentration of abrasive slurry was used, "rolling abrasion" occurred. In this case, the abrasive particles were free to roll

along the surface of the thin film, causing a low coefficient of friction.

*C* abrasive slurry concentration—in volume, [% SiC + % glycerine]

]

/N m]

**70**

Ronaldo Câmara Cozza1,2

1 Department of Mechanical Engineering, University Center FEI—Educational Foundation of Ignatius "Padre Sabóia de Medeiros", São Bernardo do Campo, SP, Brazil

2 Department of Mechanical Manufacturing, CEETEPS—State Center of Technological Education "Paula Souza", Technology Faculty—FATEC, Mauá, SP, Brazil

\*Address all correspondence to: rcamara@fei.edu.br

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[22] Cozza RC. Wear and coefficient of friction study in micro-abrasive wear tests with rotating ball under conditions of "constant normal force" and "constant pressure" [Ph.D. thesis]. São Paulo, SP, Brazil: Polytechnic School of the University of São Paulo; 2011. p. 327. Available from: http://www.teses. usp.br/

[23] Cozza RC, Wilcken JTSL, Delijaicov S, Donato GHB. Tribological characterization of thin films based on residual stress, volume of wear, microabrasive wear modes and coefficient of friction. In: Proceedings of the "ICMCTF 2017—44th International Conference on Metallurgical Coatings and Thin Films"; 24-28 April 2017; San Diego, California, USA. 2017

[24] Cozza RC, Donato GHB. Study of the influence of the abrasive slurry concentration on the coefficient of friction of thin films submitted to micro-abrasive wear. In: Proceedings of the "PacSurf 2016—Pacific Rim Symposium on Surfaces, Coatings & Interfaces"; 11-15 December 2016; Kohala Coast, Hawaii, USA. 2016

[25] Cozza RC, Wilcken JTSL, Schon CG. Influence of abrasive wear modes on the volume of wear and coefficient of friction of thin films. In: Proceedings of the "CoSI 2015—11th Coatings Science International"; 22-26 June 2015; Noordwijk, The Netherlands. 2015

[26] Batista JCA, Joseph MC, Godoy C, Matthews A. Micro-abrasion wear testing of PVD TiN coatings on untreated and plasma nitride AISI H13 steel. Wear. 2002;**249**:971-979

[27] Cozza RC. Effect of sliding distance on abrasive wear modes transition. Journal of Materials Research and Technology. 2015;**4**(2):144-150

[28] Trezona RI, Allsopp DN, Hutchings IM. Transitions between two-body and three-body abrasive wear: Influence of test conditions in the microscale abrasive wear test. Wear. 1999;**225-229**:205-214

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micro-scale abrasion test on coated substrates. Surface and Coatings Technology. 2004;**183**:312-327

[10] Rutherford KL, Hutchings IM. A micro-abrasive wear test, with

1996;**79**:231-239

2014;**3**(2):191-193

particular application to coated systems. Surface and Coatings Technology.

[11] Cozza RC. Influence of the normal force, abrasive slurry concentration and abrasive wear modes on the coefficient of friction in ball-cratering wear tests. Tribology International. 2014;**70**:52-62

[12] Cozza RC. Third abrasive wear mode: Is it possible? Journal of Materials Research and Technology.

[13] Neville A, Kollia-Rafailidi V. A comparison of boundary wear film formation on steel and a thermal

sprayed Co/Cr/Mo coating under sliding conditions. Wear. 2002;**252**:227-239

[14] Dhanasekaran S, Gnanamoorthy R. Abrasive wear behavior of sintered steels prepared with MoS2 addition.

Wear. 2007;**262**:617-623

[15] Ceschini L, Palombarini G, Sambogna G, Firrao D, Scavino G, Ubertalli G. Friction and wear behaviour of sintered steels submitted to sliding and abrasion tests. Tribology

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Solid Films. 2018;**666**:66-75

Technology. 2019;**357**:626-637

[16] Gheisari R, Polycarpou AA. Threebody abrasive wear of hard coatings: Effects of hardness and roughness. Thin

[17] Atapour M, Blawert C, Zheludkevich ML. The wear characteristics of CeO2 containing nanocomposite coating made by aluminate-based PEO on AM 50 magnesium alloy. Surface & Coatings

[2] Cozza RC. A study on friction coefficient and wear coefficient of coated systems submitted to micro-scale abrasion tests. Surface and Coatings Technology. 2013;**215**:224-233

[3] Cozza RC, Tanaka DK, Souza RM. Friction coefficient and abrasive wear modes in ball-cratering tests conducted at constant normal force and constant pressure—Preliminary results. Wear.

[4] Cozza RC, Rodrigues LC, Schön CG. Analysis of the micro-abrasive wear behavior of an iron aluminide alloy under ambient and high-temperature conditions. Wear. 2015;**330-331**:250-260

[5] Mergler YJ, Huis in 't Veld AJ. Microabrasive wear of semi-crystalline polymers. Tribology and Interface Engineering Series. 2003;**41**:165-173

[6] Cozza RC, Tanaka DK, Souza RM. Micro-abrasive wear of DC and pulsed DC titanium nitride thin films with different levels of film residual stresses. Surface and Coatings Technology.

[7] Batista JCA, Godoy C, Matthews A. Micro-scale abrasive wear testing of duplex and non-duplex (singlelayered) PVD (Ti, Al)N, TiN and Cr-N coatings. Tribology International.

[8] Schiffmann KI, Bethke R, Kristen N. Analysis of perforating and non-perforating micro-scale abrasion tests on coated substrates. Surface and Coatings Technology.

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**References**

2009;**267**:61-70

Chapter 5

Abstract

Walter Holweger

Novel Predictors for Friction and

Wear in Drivetrain Applications

Reliability in a drivetrain is given by the life of its constituents, e.g., gears, clutches, and bearings. Lubrication contributes to the life cycle, preventing wear, friction, and environmental impacts. As lubricants and their additives are chemicals with an expected reactivity in a tribological contact, it comes to the question how surface fatigue phenomena due to loading may be influenced by the reactivity of functional additives and how this might be embedded in construction guidelines. A very basic study based on an elementary gear test rig presents the result that pitting

life of a gear is substantially influenced by the chemical structure of wearpreventing additives. Even under appropriate loading conditions, the lubricant structure comes as a life-limiting factor. A molecular model shows how the release and the approach of the additives toward a surface is essential and related to the

Keywords: drivetrain, gears, bearings, reliability, pitting, wear, gray staining,

Wear is a central topic in tribology. As a system property, it is defined as a continuous loss of material out of a solid surface, caused by mechanical impact, e.g., contact and relative motion of counterpart such as solids, liquids, or gases [1–6]. As such, wear is not a property of a single component. Drivetrain components (e.g., bearings, gears, clutches, etc.) are constructed due to their life expectation in order to come to a predictive reliability in the life cycle. However, in reality they are exposed to wear processes as an incidental or continuous impact. Hence, it is important to know how the entrance of wear in drivetrain components will influence their life expectations and the reliability of the drivetrain as such.

Within a construction, the expected life is a function of the load capacity of the

As reliability is defined yet by the load capacity of the involved materials due to cyclic stress, the question is about how wear relates to fatigue. In a classical view, fatigue is a matter related to stress-strain properties due to the elastic plastic behavior of the load carrying components. If a pressure with no tangential component acts on moving parts, the fatigue phenomena are given by slow changes of the subsurface microstructure due to phase alterations, migration of interstitial atoms, and dislocations. As tangential forces due to slip are coming up, the fatigue processes moves up toward the surface. However, fatigue phenomena near the surface

materials, e.g., their fatigue strength with respect to load cycles and pressure.

reaction processes that occur during the loading.

life cycle, molecular modeling

1. Introduction

75

### Chapter 5

### Novel Predictors for Friction and Wear in Drivetrain Applications

Walter Holweger

### Abstract

Reliability in a drivetrain is given by the life of its constituents, e.g., gears, clutches, and bearings. Lubrication contributes to the life cycle, preventing wear, friction, and environmental impacts. As lubricants and their additives are chemicals with an expected reactivity in a tribological contact, it comes to the question how surface fatigue phenomena due to loading may be influenced by the reactivity of functional additives and how this might be embedded in construction guidelines. A very basic study based on an elementary gear test rig presents the result that pitting life of a gear is substantially influenced by the chemical structure of wearpreventing additives. Even under appropriate loading conditions, the lubricant structure comes as a life-limiting factor. A molecular model shows how the release and the approach of the additives toward a surface is essential and related to the reaction processes that occur during the loading.

Keywords: drivetrain, gears, bearings, reliability, pitting, wear, gray staining, life cycle, molecular modeling

### 1. Introduction

Wear is a central topic in tribology. As a system property, it is defined as a continuous loss of material out of a solid surface, caused by mechanical impact, e.g., contact and relative motion of counterpart such as solids, liquids, or gases [1–6].

As such, wear is not a property of a single component. Drivetrain components (e.g., bearings, gears, clutches, etc.) are constructed due to their life expectation in order to come to a predictive reliability in the life cycle. However, in reality they are exposed to wear processes as an incidental or continuous impact. Hence, it is important to know how the entrance of wear in drivetrain components will influence their life expectations and the reliability of the drivetrain as such.

Within a construction, the expected life is a function of the load capacity of the materials, e.g., their fatigue strength with respect to load cycles and pressure.

As reliability is defined yet by the load capacity of the involved materials due to cyclic stress, the question is about how wear relates to fatigue. In a classical view, fatigue is a matter related to stress-strain properties due to the elastic plastic behavior of the load carrying components. If a pressure with no tangential component acts on moving parts, the fatigue phenomena are given by slow changes of the subsurface microstructure due to phase alterations, migration of interstitial atoms, and dislocations. As tangential forces due to slip are coming up, the fatigue processes moves up toward the surface. However, fatigue phenomena near the surface

will bring up the question at which point fatigue crosses wear and vice versa. While reliability up to now is defined by fatigue properties of the material, the crossing between fatigue and wear, especially those, induced by lubricants is still not solved. Within real applications it might be the case that, due to the operating conditions, fatigue comes to lubricant-induced wear and does not fit with the standard construction guidelines.

We present here a basic study, how fatigue and lubricant-induced wear push each other in a standard gear and bearing test. It comes up that this stimulation is due to the basic behavior of lubricant components, e.g., the reactivity of additives combined with the mechanical loading. As a main and future question of research, it addresses the need of advanced understanding on a molecular scale (10–<sup>9</sup> m), molecular modeling, and in situ spectrometry to embed them in future construction guidelines.

### 2. Gear and bearing life in terms of lubricants

Pitting and gray staining in gears and bearings appear as surface features. In a worst case, they may promote a decay in life expectation, due to their progression in time.

Figure 1.

Figure 2.

Figure 3.

77

Wear rate of lubricants as a function of pitch line speed.

The influence of different oils and additives on gear load cycles referring to the FZG test (DIN ISO 14635) [9].

Novel Predictors for Friction and Wear in Drivetrain Applications

DOI: http://dx.doi.org/10.5772/intechopen.85060

Wear rate (roller) at a cylindrical roller bearing (CRB) from the Schaeffler test rig FE8 (DIN 51819) as a

function of lubricants. While oil 1 and oil 3 do not show any wear, oil 2 is high in wear.

Within the traditional view, they are interpreted by the assumption that loading exceeds the load capacity of the material. Consequently the mating parts will get in touch and come to rupture. As such, lubricants as separating media are only seen as a material to avoid this by separating the surfaces due to viscous effects. However, it is well known that lubricants as a matter of their composition will influence the surface load capacity as well (see Figure 1) [7, 8] as seen for gears in FZG standard test conditions, using SAE 4320 case-hardened material [7–9].

Figure 2 shows the wear rate by the use of different anti-wear and extreme pressure additives base on the FZG test rig (16) as a function of the pitch line speed:

Same as for gears, bearings are impacted also by wear raising from the composition of a lubricant [10, 11] (see Figure 3), using the Schaeffler FE8 test rig as a standard (2100 MPa contact pressure, 80 rpm, 80 h, cylindrical roller bearing, SAE 52100, Martensite):

Within the FZG gear test rig [9, 12–17] (DIN ISO 14635), different lubricants (A, B) differ in wear as a fact of temperature. While oil A shows a decay by raising the temperature, oil B is opposite (see Figure 4).

As a result of those studies, reaction layers with different thicknesses under mechanical influence are created. While thick and uncontrolled layers cause early fatigue and wear, thin oxide layers with a strong bonding to the interface cause no wear, same as reported earlier [1, 11]. It is of interest to describe these effects with respect to their chemical structures of the reactive components and how they undergo a transformation of the tribological contact area by creating those layers. Structure property relationship would lead to predictors for wear derived from the chemical structure of a given lubricant.

As a standard the FZG test rig (DIN ISO 14635) as a back-to-back gear test is used (Figure 5) [7, 18–20]. The gears, type FZG C-PT, are set in a gearbox, fully lubricated. Cylindrical roller bearings (type NJ406, steel cage) are used for the pinion shaft 1 and cylindrical roller bearings, type NJ308, for the motor shaft. Investigations were made on the gears and the cylindrical roller bearings NJ 406.

The test conditions are given in Table 1. The oil temperature is set constant to 90°C and motor speed to 1500 rpm. A running-in period with 1025 N/mm<sup>2</sup> is set for 2 h; the test run at 1700 N/mm<sup>2</sup> till pitting is reached is recorded. The speed at the

### Novel Predictors for Friction and Wear in Drivetrain Applications DOI: http://dx.doi.org/10.5772/intechopen.85060

### Figure 1.

will bring up the question at which point fatigue crosses wear and vice versa. While reliability up to now is defined by fatigue properties of the material, the crossing between fatigue and wear, especially those, induced by lubricants is still not solved. Within real applications it might be the case that, due to the operating conditions, fatigue comes to lubricant-induced wear and does not fit with the standard con-

We present here a basic study, how fatigue and lubricant-induced wear push each other in a standard gear and bearing test. It comes up that this stimulation is due to the basic behavior of lubricant components, e.g., the reactivity of additives combined with the mechanical loading. As a main and future question of research, it addresses the need of advanced understanding on a molecular scale (10–<sup>9</sup> m), molecular modeling, and in situ spectrometry to embed them in future construction

Pitting and gray staining in gears and bearings appear as surface features. In a worst case, they may promote a decay in life expectation, due to their progression

Within the traditional view, they are interpreted by the assumption that loading exceeds the load capacity of the material. Consequently the mating parts will get in touch and come to rupture. As such, lubricants as separating media are only seen as a material to avoid this by separating the surfaces due to viscous effects. However, it is well known that lubricants as a matter of their composition will influence the surface load capacity as well (see Figure 1) [7, 8] as seen for gears in FZG standard test conditions, using SAE 4320 case-hardened material

Figure 2 shows the wear rate by the use of different anti-wear and extreme pressure additives base on the FZG test rig (16) as a function of the pitch line speed: Same as for gears, bearings are impacted also by wear raising from the composition of a lubricant [10, 11] (see Figure 3), using the Schaeffler FE8 test rig as a standard (2100 MPa contact pressure, 80 rpm, 80 h, cylindrical roller bearing, SAE

Within the FZG gear test rig [9, 12–17] (DIN ISO 14635), different lubricants (A, B) differ in wear as a fact of temperature. While oil A shows a decay by raising

As a result of those studies, reaction layers with different thicknesses under mechanical influence are created. While thick and uncontrolled layers cause early fatigue and wear, thin oxide layers with a strong bonding to the interface cause no wear, same as reported earlier [1, 11]. It is of interest to describe these effects with respect to their chemical structures of the reactive components and how they undergo a transformation of the tribological contact area by creating those layers. Structure property relationship would lead to predictors for wear derived from the

As a standard the FZG test rig (DIN ISO 14635) as a back-to-back gear test is used (Figure 5) [7, 18–20]. The gears, type FZG C-PT, are set in a gearbox, fully lubricated. Cylindrical roller bearings (type NJ406, steel cage) are used for the pinion shaft 1 and cylindrical roller bearings, type NJ308, for the motor shaft. Investigations were made on the gears and the cylindrical roller bearings NJ 406. The test conditions are given in Table 1. The oil temperature is set constant to 90°C and motor speed to 1500 rpm. A running-in period with 1025 N/mm<sup>2</sup> is set for 2 h; the test run at 1700 N/mm<sup>2</sup> till pitting is reached is recorded. The speed at the

2. Gear and bearing life in terms of lubricants

the temperature, oil B is opposite (see Figure 4).

chemical structure of a given lubricant.

struction guidelines.

Friction, Lubrication and Wear

guidelines.

in time.

[7–9].

76

52100, Martensite):

The influence of different oils and additives on gear load cycles referring to the FZG test (DIN ISO 14635) [9].

Figure 2. Wear rate of lubricants as a function of pitch line speed.

### Figure 3.

Wear rate (roller) at a cylindrical roller bearing (CRB) from the Schaeffler test rig FE8 (DIN 51819) as a function of lubricants. While oil 1 and oil 3 do not show any wear, oil 2 is high in wear.

to 1.45 m/s, and the sum of speed to 6.29 m/s. As the slip percentage is given by the ratio of sliding speed to the sum of the speed, the slip at the pinion is 23% and at

The material of the bearing accords to the SAE 52100, martensitic hardening,

Two lubricants were tested (Table 3). Lubricant 1 reflects a standard technol-

As a representative of a new ashless additive technology, the lubricant formulation 2

The organic chain length of the phosphorus-sulfur core is given by four C atoms, meaning that during the synthesis of the additives, a C4 (butyl) alcohol component

The structure of the additives are shown in Figures 6 and 7, both looking rather complex. In detail a core of sulfur, phosphorus, and zinc is attached to the carbon

Figure 7 represents the C4NdtP; two structures are held together by an ionic bonding: a sulfur-phosphorus component with two carbon sites, each containing four C atoms and their attached hydrogen and nitrogen component with a positively charged nitrogen at the edge, attached to a carbon site with eight C atoms (C4NdtP). The principal of this substance is similar to ionic liquids, where

opposite-charged atoms create an ionic binding, while the carbon sites are respon-

The test runs by the use of the different additives are given in Table 4 for both gears and bearings (NJ406) as a function of the load cycles. Clearly the table shows how the change in the chemical structure of the additive, despite the same chain lengths on the carbon edge (C4), end up in different load cycles (Table 4):

/s at 40°C.

ogy, using zincdithiophosphates (C4ZndtP) as a sulfur-phosphorus carrier.

The material of the gears applies for a case-hardener SAE 4320. The test specific data of the CRB NJ206 are given in Table 2.

tempered at 180°C, 2 hours, with 10–12% retained austenite.

Novel Predictors for Friction and Wear in Drivetrain Applications

DOI: http://dx.doi.org/10.5772/intechopen.85060

(C4NdtP) is used. The Poly-α-olefine viscosity is 46 mm<sup>2</sup>

sites, containing four C atoms (ZndtPC4) (Figure 6).

the wheel +23%.

was used.

Table 2.

Table 3.

79

Lubricants used for the test.

Data from the CRB NJ206 bearing.

sible for the liquid structure.

### Figure 4. Influence on wear due to temperature.

Figure 5. FZG test rig (DIN ISO 14635).


### Table 1.

Conditions of the test.

pinion is set to 2250 rpm, the torque moment T1 to 372.6 Nm. The tangential speed at the pinion is calculated to 2.42 m/s, at the wheel to 3.87 m/s, the sliding speed at the pinion to 1.45 m/s (reflecting the negative slip), the sliding speed at the wheel Novel Predictors for Friction and Wear in Drivetrain Applications DOI: http://dx.doi.org/10.5772/intechopen.85060

to 1.45 m/s, and the sum of speed to 6.29 m/s. As the slip percentage is given by the ratio of sliding speed to the sum of the speed, the slip at the pinion is 23% and at the wheel +23%.

The material of the gears applies for a case-hardener SAE 4320.

The test specific data of the CRB NJ206 are given in Table 2.

The material of the bearing accords to the SAE 52100, martensitic hardening, tempered at 180°C, 2 hours, with 10–12% retained austenite.

Two lubricants were tested (Table 3). Lubricant 1 reflects a standard technology, using zincdithiophosphates (C4ZndtP) as a sulfur-phosphorus carrier. As a representative of a new ashless additive technology, the lubricant formulation 2 (C4NdtP) is used. The Poly-α-olefine viscosity is 46 mm2 /s at 40°C.

The organic chain length of the phosphorus-sulfur core is given by four C atoms, meaning that during the synthesis of the additives, a C4 (butyl) alcohol component was used.

The structure of the additives are shown in Figures 6 and 7, both looking rather complex. In detail a core of sulfur, phosphorus, and zinc is attached to the carbon sites, containing four C atoms (ZndtPC4) (Figure 6).

Figure 7 represents the C4NdtP; two structures are held together by an ionic bonding: a sulfur-phosphorus component with two carbon sites, each containing four C atoms and their attached hydrogen and nitrogen component with a positively charged nitrogen at the edge, attached to a carbon site with eight C atoms (C4NdtP). The principal of this substance is similar to ionic liquids, where opposite-charged atoms create an ionic binding, while the carbon sites are responsible for the liquid structure.

The test runs by the use of the different additives are given in Table 4 for both gears and bearings (NJ406) as a function of the load cycles. Clearly the table shows how the change in the chemical structure of the additive, despite the same chain lengths on the carbon edge (C4), end up in different load cycles (Table 4):


### Table 2.

Data from the CRB NJ206 bearing.


Table 3. Lubricants used for the test.

pinion is set to 2250 rpm, the torque moment T1 to 372.6 Nm. The tangential speed at the pinion is calculated to 2.42 m/s, at the wheel to 3.87 m/s, the sliding speed at the pinion to 1.45 m/s (reflecting the negative slip), the sliding speed at the wheel

Figure 4.

Figure 5.

Table 1.

78

Conditions of the test.

FZG test rig (DIN ISO 14635).

Influence on wear due to temperature.

Friction, Lubrication and Wear

3. Results for the gear

Novel Predictors for Friction and Wear in Drivetrain Applications

DOI: http://dx.doi.org/10.5772/intechopen.85060

load cycles).

Figure 8.

Figure 9.

81

While the C4-Zincalkyldithiophosphate (C4ZndtP) causes pitting and does not meet the expected load cycles, the test carried out with the C4NdtP was out of failure [7]. Secondary neutral mass spectrometry (SNMS) profiles [21–23] were carried out at the pinion addendum (Position 1: see arrow in Figure 8) (area of positive slip referring to the pinion), the pitch line (Position 2: see arrow in Figure 8) (zero slip referring to the pinion), and tooth dedendum (Position 3: see arrow in Figure 8) (area of negative slip) in order to evaluate how the reaction rate of additives might depend on load cycles. The nature of the reaction was analyzed by secondary neutral mass spectrometry (SNMS). While secondary ion mass spectrometry (SIMS) is sensitive due to the local elements, specifically oxygen, SNMS is less sensitive and allows to track elements quantitatively as depth profiles from the top of the surface down to a few microns. The spatial resolution is around 4 mm<sup>2</sup>

thus averaging local deviations in elements making the results more accurate. The relevant depth profiles were taken at the dedendum of the pinion tooth flank for the additives C4-zincalkyldithiophosphate (C4ZndtP) and C4-aminealkyldithiophosphate (C4NdtP) with respect to load cycles are shown in Figure 9 (C4ZndtP: 9 <sup>10</sup><sup>6</sup> load cycles); Figure 10 (C4ZndtP: 10 <sup>10</sup><sup>10</sup> load cycles); Figure 11 (C4NdtP: 12 <sup>10</sup><sup>6</sup> load cycles); and Figure 12 (C4ZndtP: 16 <sup>10</sup><sup>10</sup>

Gear tooth segment with addendum Position 1 (pitch line), Position 2, and Position 3 as dedendum.

SNMS depth profile: C4ZndtP in FZG pitting test at 9 106 load cycles.

,

Figure 6. Zincalkyldithiophosphate (C4ZndtP).

### Figure 7. Ammoniumdithiophosphate (C4NdtP) as an ionic liquid-like structure.


Table 4.

Test conditions set on the different additive structures.

### 3. Results for the gear

While the C4-Zincalkyldithiophosphate (C4ZndtP) causes pitting and does not meet the expected load cycles, the test carried out with the C4NdtP was out of failure [7]. Secondary neutral mass spectrometry (SNMS) profiles [21–23] were carried out at the pinion addendum (Position 1: see arrow in Figure 8) (area of positive slip referring to the pinion), the pitch line (Position 2: see arrow in Figure 8) (zero slip referring to the pinion), and tooth dedendum (Position 3: see arrow in Figure 8) (area of negative slip) in order to evaluate how the reaction rate of additives might depend on load cycles. The nature of the reaction was analyzed by secondary neutral mass spectrometry (SNMS). While secondary ion mass spectrometry (SIMS) is sensitive due to the local elements, specifically oxygen, SNMS is less sensitive and allows to track elements quantitatively as depth profiles from the top of the surface down to a few microns. The spatial resolution is around 4 mm<sup>2</sup> , thus averaging local deviations in elements making the results more accurate.

The relevant depth profiles were taken at the dedendum of the pinion tooth flank for the additives C4-zincalkyldithiophosphate (C4ZndtP) and C4-aminealkyldithiophosphate (C4NdtP) with respect to load cycles are shown in Figure 9 (C4ZndtP: 9 <sup>10</sup><sup>6</sup> load cycles); Figure 10 (C4ZndtP: 10 <sup>10</sup><sup>10</sup> load cycles); Figure 11 (C4NdtP: 12 <sup>10</sup><sup>6</sup> load cycles); and Figure 12 (C4ZndtP: 16 <sup>10</sup><sup>10</sup> load cycles).

### Figure 8.

Figure 6.

Figure 7.

Table 4.

80

Ammoniumdithiophosphate (C4NdtP) as an ionic liquid-like structure.

Test conditions set on the different additive structures.

Zincalkyldithiophosphate (C4ZndtP).

Friction, Lubrication and Wear

Figure 9. SNMS depth profile: C4ZndtP in FZG pitting test at 9 <sup>10</sup><sup>6</sup> load cycles.

As a result from A1–A2, C4ZndTP causes pitting and increases in layer thickness formation, while B1–B2 C4NdtP does not at prolong load cycles however shows an increase in surface reaction of the phosphorus component while the reaction layer

The calculation of the load distribution is shown in Table 5 and Figure 13. The maximum force is acting on roller nr. 7 with a contact pressure of

The results (see Figures 14 and 15) show an impact of zinc, assumed to be a mixture of phosphates and zinc oxide in the case of the C4ZndtP at 19 <sup>10</sup><sup>6</sup> load cycles (Figure 14), while compared with the oxygen in the case of the C4NdtP stays

The bearing thus gives a different reaction by embedding zinc oxide in the near surface. The results for the C4NdtP are quite similar to the reactions seen in

stays constant.

1481 N/mm<sup>2</sup> [7].

low (Figure 15).

the gear.

Table 5.

Figure 13.

83

Load distribution for the NJ406 bearing.

Conditions at the bearing NJ406.

4. Results for the bearing (NJ406)

DOI: http://dx.doi.org/10.5772/intechopen.85060

Novel Predictors for Friction and Wear in Drivetrain Applications

Figure 10. SNMS depth profile: C4ZndtP in FZG pitting test at 10 106 load cycles.

Figure 11. SNMS depth profile: C4NdtP in FZG pitting test at 12 106 load cycles.

Figure 12. SNMS depth profile: C4NdtP in FZG pitting test at 16 106 load cycles.

Novel Predictors for Friction and Wear in Drivetrain Applications DOI: http://dx.doi.org/10.5772/intechopen.85060

As a result from A1–A2, C4ZndTP causes pitting and increases in layer thickness formation, while B1–B2 C4NdtP does not at prolong load cycles however shows an increase in surface reaction of the phosphorus component while the reaction layer stays constant.

### 4. Results for the bearing (NJ406)

The calculation of the load distribution is shown in Table 5 and Figure 13. The maximum force is acting on roller nr. 7 with a contact pressure of 1481 N/mm<sup>2</sup> [7].

The results (see Figures 14 and 15) show an impact of zinc, assumed to be a mixture of phosphates and zinc oxide in the case of the C4ZndtP at 19 <sup>10</sup><sup>6</sup> load cycles (Figure 14), while compared with the oxygen in the case of the C4NdtP stays low (Figure 15).

The bearing thus gives a different reaction by embedding zinc oxide in the near surface. The results for the C4NdtP are quite similar to the reactions seen in the gear.


### Table 5.

Figure 10.

Friction, Lubrication and Wear

Figure 11.

Figure 12.

82

SNMS depth profile: C4ZndtP in FZG pitting test at 10 106 load cycles.

SNMS depth profile: C4NdtP in FZG pitting test at 12 106 load cycles.

SNMS depth profile: C4NdtP in FZG pitting test at 16 106 load cycles.

Conditions at the bearing NJ406.

Figure 13. Load distribution for the NJ406 bearing.

Figure 16.

of load cycles.

Figure 17.

of load cycles.

Figure 18.

85

C4ZndtP: process of film thickness formation as a matter of load cycles.

SNMS profiles: reaction rate (elements phosphorus and oxygen) in the FZG gear tests for C4ZndtP as a function

Novel Predictors for Friction and Wear in Drivetrain Applications

DOI: http://dx.doi.org/10.5772/intechopen.85060

SNMS profiles: reaction rate (elements phosphorus and oxygen) in the FZG gear test for C4NdtP as a function

Figure 14. SNMS depth profile: rollers, C4ZndtP in FE8 bearing test at 19 106 load cycles.

Figure 15.

SNMS depth profile: C4NdtP in the FE8 wear test, rollers at 29 106 load cycles.

### 5. Gear: reaction rates

For the gear (pinion, dedendum) the reaction turnover stays constant or slightly decreases for the C4ZndtP (Figure 16) but increases in depth by the use of C4NdTP (Figure 17).

The reaction film thickness shows a progression in the case for the C4ZndtP (Figure 18), while the C4NdtP shows a regression in time (Figure 19).

### 6. Gear: nanohardness measurement at the pinion

Nanohardness measurements are shown in Figures 20–22: Figure 20 shows the as-received hardness profile of the dedendum, pitch, and addendum for the asreceived pinion tooth flank material (case-hardener SAE 4320).

Figure 21 shows a steep decrease by the use of the C4ZndtP compared to the asreceived material at the surface.

Figure 22 shows a steep increase by the use of C4NdtP compared to the asreceived material at the surface.

Novel Predictors for Friction and Wear in Drivetrain Applications DOI: http://dx.doi.org/10.5772/intechopen.85060

Figure 16.

SNMS profiles: reaction rate (elements phosphorus and oxygen) in the FZG gear tests for C4ZndtP as a function of load cycles.

Figure 17.

5. Gear: reaction rates

received material at the surface.

received material at the surface.

(Figure 17).

84

Figure 15.

Figure 14.

Friction, Lubrication and Wear

For the gear (pinion, dedendum) the reaction turnover stays constant or slightly decreases for the C4ZndtP (Figure 16) but increases in depth by the use of C4NdTP

The reaction film thickness shows a progression in the case for the C4ZndtP

Nanohardness measurements are shown in Figures 20–22: Figure 20 shows the as-received hardness profile of the dedendum, pitch, and addendum for the as-

Figure 21 shows a steep decrease by the use of the C4ZndtP compared to the as-

Figure 22 shows a steep increase by the use of C4NdtP compared to the as-

(Figure 18), while the C4NdtP shows a regression in time (Figure 19).

6. Gear: nanohardness measurement at the pinion

SNMS depth profile: C4NdtP in the FE8 wear test, rollers at 29 106 load cycles.

SNMS depth profile: rollers, C4ZndtP in FE8 bearing test at 19 106 load cycles.

received pinion tooth flank material (case-hardener SAE 4320).

SNMS profiles: reaction rate (elements phosphorus and oxygen) in the FZG gear test for C4NdtP as a function of load cycles.

Figure 18. C4ZndtP: process of film thickness formation as a matter of load cycles.

Figure 19. C4NdtP: process of film thickness formation as a matter of load cycles.

on 10–<sup>9</sup> till 10–<sup>3</sup> m, e.g., magnitudes of 10<sup>6</sup> in length scale. However, considerable progress in multi-scale modeling has become real in the last years; it is of interest how to predict the observed effects reported here by the use of predictors. Basically predicators are obtained by the properties of a molecule, e.g., coming from the chemical bonding. Exploring molecules by quantitative structure property relationship (QSPR) [24] and the molecular properties by the use of density functional theory (DFT) is a standard [25]. The interaction of molecules with themselves and

C4NdtP: pinion tooth nanohardness as a function of depth (nanometer) and location (dedendum, pitch, and

Figure 24A and B shows the surface of the additive C4ZndtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (A) and the additive C4NdtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (B) energy mini-

Figure 24A shows the surface of the additive C4ZndtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) and the additive C4NdtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (B) attached to an ideal bodycentered cubic (bcc) iron surface as C for the C4ZndtP and D for the C4NdtP,

with surfaces is part of molecular dynamics and ab initio methods.

Novel Predictors for Friction and Wear in Drivetrain Applications

DOI: http://dx.doi.org/10.5772/intechopen.85060

mized by the use of molecular dynamics.

Figure 22.

addendum).

Figure 23.

87

energy minimized by the use of molecular dynamics.

(A) C4ZndtP structure in PAO and (B) C4NdtP structure in PAO.

Figure 20.

Nanohardness measurements for the as-received pinion (from dedendum via pitch to the addendum).

Figure 21.

C4ZndtP: pinion tooth nanohardness as a function of depth (nanometer) and location (dedendum, pitch, and addendum).

### 7. Molecular description

As functional groups in additives determine the reliability of drivetrain components, it is of interest how those processes are to interpret. Coming from the molecular perspective with a size of 10–<sup>9</sup> m, it takes effort to interpret effects

C4NdtP: pinion tooth nanohardness as a function of depth (nanometer) and location (dedendum, pitch, and addendum).

on 10–<sup>9</sup> till 10–<sup>3</sup> m, e.g., magnitudes of 10<sup>6</sup> in length scale. However, considerable progress in multi-scale modeling has become real in the last years; it is of interest how to predict the observed effects reported here by the use of predictors. Basically predicators are obtained by the properties of a molecule, e.g., coming from the chemical bonding. Exploring molecules by quantitative structure property relationship (QSPR) [24] and the molecular properties by the use of density functional theory (DFT) is a standard [25]. The interaction of molecules with themselves and with surfaces is part of molecular dynamics and ab initio methods.

Figure 24A and B shows the surface of the additive C4ZndtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (A) and the additive C4NdtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (B) energy minimized by the use of molecular dynamics.

Figure 24A shows the surface of the additive C4ZndtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) and the additive C4NdtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (B) attached to an ideal bodycentered cubic (bcc) iron surface as C for the C4ZndtP and D for the C4NdtP, energy minimized by the use of molecular dynamics.

Figure 23. (A) C4ZndtP structure in PAO and (B) C4NdtP structure in PAO.

7. Molecular description

Figure 19.

Friction, Lubrication and Wear

Figure 20.

Figure 21.

addendum).

86

C4NdtP: process of film thickness formation as a matter of load cycles.

As functional groups in additives determine the reliability of drivetrain compo-

C4ZndtP: pinion tooth nanohardness as a function of depth (nanometer) and location (dedendum, pitch, and

nents, it is of interest how those processes are to interpret. Coming from the molecular perspective with a size of 10–<sup>9</sup> m, it takes effort to interpret effects

Nanohardness measurements for the as-received pinion (from dedendum via pitch to the addendum).

material by smooth oxides, the C4NdtP creates a thin phosphorus-oxide layer on top on a size of 10 nm. The carbon site exposed to the metal might protect it against oxidation, and as the reactive phosphorus-sulfur site is remote, the hardness at least does not go down. The steep increase could be caused by a hardening process of the surface due to carbide formation at the interface as a degradation process of the carbon site. It is noteworthy to say that this interpretation is related to the positions

Novel Predictors for Friction and Wear in Drivetrain Applications

DOI: http://dx.doi.org/10.5772/intechopen.85060

Hence, the structure of an additive determines how it approaches and how the subsequent reactions take place, either on the site of the functional head or on the site of the carbon, ending up in the reliability of the application with respect to

The reliability of drivetrain with respect to its expected life cycle is of key interest in the value chain of an installation. Each component contributes to this by the matter of load impacting the load capacity of the materials involved. As load capacity is well defined for the construction materials, e.g., gears and bearings, this definition becomes vague for lubricants. Even though a malfunction of a lubricant could cause damage features, like wear, friction, and tribocorrosion, the understanding of the real function and how to judge it by robust predictors is still missing. Lubricants may give malfunction even in the case of a proper application due to the interaction of functional additives with the mating surfaces. Plenty of contributions worldwide show that the "construction" of a lubricant by adding functional additives into a base oil may lead to premature failures given by the interaction of the functional additives with the given surface. Normally additives are readily dissolved in a base oil and as such transported to the points of interacting surfaces, there getting released in order to uptake a function like wear prevention or friction reduction. However, the energy offered by the contact due to sliding and contact pressure makes additives reactive, causing chemical reactions. The chemical reactions with different additives are seen by the use of specific test conditions, presented in the study as an FZG back-to-back gear test rig. The study brings out that a traditional anti-wear additive such as a zincdithiophosphate (C4ZndtP) reacts continuously at a given threshold with the surface, exchanging the nearsurface material. The softening causes continuously material loss over time, ending

up in pitting. In contrast, just by changing the chemical structure from a zincdithiophosphate to an ionic liquid like amine-neutralized dithiophosphate (C4NdtP); it is obvious that the application fulfills the complete life cycle without pitting. Compared to the zincdithiophosphate (C4ZndtP), it comes out that the amine-neutralized dithiophosphate (C4NdtP) hardens up at the area of negative slip at the pinion dedendum. Technical data are not to explain this elementary topic. Hence, it has to be seen in a deeper aspect. As additives are dissolved readily in the base oil, the tribological process makes them approach the surface. This brings up the question how the additive is released from the base oil toward the surface as the initial step. In the given example, a simple molecular model shows that in the case of the zincdithiophosphate, the additive approaches the surface with the reactive site given by the sulfur and phosphorus core, continuously leaching iron out of the surface with a subsequent weakening created by reaction layers with little binding to the core of the material. In the case of ammonium-neutralized dithiophosphate, the molecular model shows that this additive approaches the surface by the carbon site, while the sulfur-phosphorus site is remote. This additive gives a hardness increase during the tribological interaction, and as a speculation, the tribological

of negative slip and speculative.

pitting.

89

9. Conclusions

Figure 24.

(A) Approaching a (A) C4ZndtP and (B) C4NdtP to an ideal bcc, iron surface. Labeled atoms are: red: iron; dark red: oxygen; blue: carbon; gray: hydrogen; and yellow: sulfur.

Figure 23B shows the surface of the additive C4ZndtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42), and the additive C4NdtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (B) attached to an ideal body-centered cubic (bcc) iron surface as C for the C4ZndtP and D for the C4NdtP, energy minimized by the use of molecular dynamics. Approaching this system to an ideal iron surface, it is obvious that the C4Zn is attached with the polar edge (Zn, P, S) to the surface (see Figure 24A), while the C4NdtP is attached via the carbon shell (see Figure 24B).

### 8. Discussion

The results shown here may give a reasoning about the elementary analyses found by SNMS where the C4ZndtP progressively acts in time by increasing the reaction layers toward 50 nm constituted by P, O, and Zn oxides, while the C4NdtP shows an initial reaction in the beginning, but regressing the layer to a constant film at 10 nm [26].

As for the C4ZndtP, the reactive core is near to the surface; the reaction may proceed by continuous load cycling, which is found in the SNMS profiles. Due to the continuous degression of the surface toward oxides, the C4ZndtP shows a decrease in the nanohardness by the fact that the surface gets covered with material softer than the base. Also the reaction rate goes down due to fact that the reaction layers are chemically inert compared to iron. The remote position of the reactive group in the C4NdtP exposes the sulfur-phosphorus core to the environment as oxygen. Tribological impacting may then promote the oxidation of the reactive site, rather than a reaction with the metal surface. This means that in the first step the C4NdtP reacts with oxygen at the reactive site, coming to phosphoric acid specie. Those would turn to the surface as they are not soluble in the base oil and naturally get attracted by the oxide sites at the metal surface. The amine would be dissolved back into the base oil. As a fact those phosphoric acid specie are found to be detached on the surface of the pinion dedendum. The oxidation will continue; hence, it is expected that the phosphorus-oxide layer will increase on top, but no material will be leached out due to the fact that the phosphates and polyphosphates are uniquely covering the surface, not being soluble in the matrix.

While the C4ZndtP obviously causes a successive exchange of near-surface material (e.g., iron), the C4NdtP does not. The hardness profiles might be coherent with the carbon profile (SNMS): while the C4ZndtP converts constantly the surface Novel Predictors for Friction and Wear in Drivetrain Applications DOI: http://dx.doi.org/10.5772/intechopen.85060

material by smooth oxides, the C4NdtP creates a thin phosphorus-oxide layer on top on a size of 10 nm. The carbon site exposed to the metal might protect it against oxidation, and as the reactive phosphorus-sulfur site is remote, the hardness at least does not go down. The steep increase could be caused by a hardening process of the surface due to carbide formation at the interface as a degradation process of the carbon site. It is noteworthy to say that this interpretation is related to the positions of negative slip and speculative.

Hence, the structure of an additive determines how it approaches and how the subsequent reactions take place, either on the site of the functional head or on the site of the carbon, ending up in the reliability of the application with respect to pitting.

### 9. Conclusions

Figure 23B shows the surface of the additive C4ZndtP with one molecule PAO

(A) Approaching a (A) C4ZndtP and (B) C4NdtP to an ideal bcc, iron surface. Labeled atoms are: red: iron;

(as a hydrogenated Di-Dec-1-ene, C20H42), and the additive C4NdtP with one molecule PAO (as a hydrogenated Di-Dec-1-ene, C20H42) (B) attached to an ideal body-centered cubic (bcc) iron surface as C for the C4ZndtP and D for the C4NdtP, energy minimized by the use of molecular dynamics. Approaching this system to an ideal iron surface, it is obvious that the C4Zn is attached with the polar edge (Zn, P, S) to the surface (see Figure 24A), while the C4NdtP is attached via the carbon shell

dark red: oxygen; blue: carbon; gray: hydrogen; and yellow: sulfur.

The results shown here may give a reasoning about the elementary analyses found by SNMS where the C4ZndtP progressively acts in time by increasing the reaction layers toward 50 nm constituted by P, O, and Zn oxides, while the C4NdtP shows an initial reaction in the beginning, but regressing the layer to a constant film

As for the C4ZndtP, the reactive core is near to the surface; the reaction may proceed by continuous load cycling, which is found in the SNMS profiles. Due to the continuous degression of the surface toward oxides, the C4ZndtP shows a decrease in the nanohardness by the fact that the surface gets covered with material softer than the base. Also the reaction rate goes down due to fact that the reaction layers are chemically inert compared to iron. The remote position of the reactive group in the C4NdtP exposes the sulfur-phosphorus core to the environment as oxygen. Tribological impacting may then promote the oxidation of the reactive site, rather than a reaction with the metal surface. This means that in the first step the C4NdtP reacts with oxygen at the reactive site, coming to phosphoric acid specie. Those would turn to the surface as they are not soluble in the base oil and naturally get attracted by the oxide sites at the metal surface. The amine would be dissolved back into the base oil. As a fact those phosphoric acid specie are found to be detached on the surface of the pinion dedendum. The oxidation will continue; hence, it is expected that the phosphorus-oxide layer will increase on top, but no material will be leached out due to the fact that the phosphates and polyphosphates are uniquely

While the C4ZndtP obviously causes a successive exchange of near-surface material (e.g., iron), the C4NdtP does not. The hardness profiles might be coherent with the carbon profile (SNMS): while the C4ZndtP converts constantly the surface

covering the surface, not being soluble in the matrix.

(see Figure 24B).

Figure 24.

Friction, Lubrication and Wear

8. Discussion

at 10 nm [26].

88

The reliability of drivetrain with respect to its expected life cycle is of key interest in the value chain of an installation. Each component contributes to this by the matter of load impacting the load capacity of the materials involved. As load capacity is well defined for the construction materials, e.g., gears and bearings, this definition becomes vague for lubricants. Even though a malfunction of a lubricant could cause damage features, like wear, friction, and tribocorrosion, the understanding of the real function and how to judge it by robust predictors is still missing. Lubricants may give malfunction even in the case of a proper application due to the interaction of functional additives with the mating surfaces. Plenty of contributions worldwide show that the "construction" of a lubricant by adding functional additives into a base oil may lead to premature failures given by the interaction of the functional additives with the given surface. Normally additives are readily dissolved in a base oil and as such transported to the points of interacting surfaces, there getting released in order to uptake a function like wear prevention or friction reduction. However, the energy offered by the contact due to sliding and contact pressure makes additives reactive, causing chemical reactions. The chemical reactions with different additives are seen by the use of specific test conditions, presented in the study as an FZG back-to-back gear test rig. The study brings out that a traditional anti-wear additive such as a zincdithiophosphate (C4ZndtP) reacts continuously at a given threshold with the surface, exchanging the nearsurface material. The softening causes continuously material loss over time, ending up in pitting. In contrast, just by changing the chemical structure from a zincdithiophosphate to an ionic liquid like amine-neutralized dithiophosphate (C4NdtP); it is obvious that the application fulfills the complete life cycle without pitting. Compared to the zincdithiophosphate (C4ZndtP), it comes out that the amine-neutralized dithiophosphate (C4NdtP) hardens up at the area of negative slip at the pinion dedendum. Technical data are not to explain this elementary topic. Hence, it has to be seen in a deeper aspect. As additives are dissolved readily in the base oil, the tribological process makes them approach the surface. This brings up the question how the additive is released from the base oil toward the surface as the initial step. In the given example, a simple molecular model shows that in the case of the zincdithiophosphate, the additive approaches the surface with the reactive site given by the sulfur and phosphorus core, continuously leaching iron out of the surface with a subsequent weakening created by reaction layers with little binding to the core of the material. In the case of ammonium-neutralized dithiophosphate, the molecular model shows that this additive approaches the surface by the carbon site, while the sulfur-phosphorus site is remote. This additive gives a hardness increase during the tribological interaction, and as a speculation, the tribological

energy may crack the molecule to carbon specie, subsequently hardening the surface up by carbides and preventing an excessive penetration of reaction products.

References

13619-3

642-92755-3

83480-017-6

Press; 2001

2001–2003

test\_rig

91

[1] Kragelski IV, Dobycin MN, Kombalov VS. Grundlagen der Berechnung von Reibung und Verschleiß. München, Wien: Carl Hanser Verlag; 1982. ISBN: 3-446-

[2] Bowden T. Friction and Lubrication of Solids. Oxford/Berlin: Clarendon Press/Springer; 1950. ISBN: 978-3-

DOI: http://dx.doi.org/10.5772/intechopen.85060

Novel Predictors for Friction and Wear in Drivetrain Applications

[11] Reichelt M. Mikroanalytische Klärung Des Verschleißschutzes in Langsam Laufenden Wälzlagern. Aachen: Shaker; 2011. ISBN: 978-3- 8440-0424-3; ISSN: 1618-5722

[12] Höhn BR, Oster P. Influence of the Lubricants on Pitting and Micro Pitting in the FZG Gear Test Rig. Hamburg:

Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und

[13] Winter H, Michaelis K. AGMA Technical Paper P291.17, scoring load capacity of gears lubricated with EPoils. In: Fall Technical Meeting; October

17–19; Montreal, Canada; 1983

Mineralöltechnik. 1987;32(6):1-24

[15] Vinogradova IE. Antianrißinhibitoren für Öle. Moskau: Verlag Chimija; 1972.

[16] Ruina A, Pratap R. Introduction to Statics and Dynamics. Oxford: Oxford

University Press; 2002. p. 713

[18] Hibbeler RC. Engineering Mechanics. 11th ed. New Jersey: Pearson/Prentice Hall; 2007. p. 393.

[19] Castro J, Sottomayor A, Seabra J. Experimentals and analytical scuffing criteria for FZG gears. Tribology Series.

[20] Fernandes C, Blazquez L. FZG gearboxes lubricated with different formulations of polyalphaolefin wind

ISBN: 0-13-127146-6

2003;43:651-661

[17] Arun AP, Senthil AP, Giriaj B, Faizur RA. Gear test rig—A review. International Journal of Mechanical & Mechatronics Engineering. 2014;14. No: 05 16 140205-9696-IJMME-IJENS ©

[14] Schönnenbeck G et al.

Kohle e.V.; 1996

p. 272

[3] Zum Gahr K-H. Microstructure and Wear of Materials. Amsterdam: Elsevier; 1987. ISBN: 0-444-42754-6

[4] Rabinowitcz E. Friction and Wear of

Interscience; 1995. ISB-0-471-83084-4

[5] Czichos H, Habig K-H. Tribologie-Handbuch. Wiesbaden: Vieweg & Teubner; 2010. ISBN: 978-3-

[6] Bushan B. Modern Tribology Handbook, Vol. 1(2). New York: CRC

Zusammenhänge zwischen Zahnrad-

[8] Johanssen J. On the Influence of Gear Oil Properties on Pitting Life. Lulea:

[7] FVA Report, 289 I & II.

und Wälzlagerschäden und tribologischen Veränderungen des oberflächennahen Werkstoffbereichs;

University of Lulea; 2015

[10] Geheeb N, Franke J. Forschungsvereinigung

[9] FZG Test Rig. Available from: https://www.researchgate.net/publica tion/235308055\_Testing\_procedures\_ for\_gear\_lubricants\_with\_the\_FZG\_

Antriebstechnik. FVA 126. RWTH Aachen: Vogel Verlag; 2000

Materials. New York: Wiley-

### 10. Summary

Additives are part of a drivetrain reliability. It comes clearly that within a construction, the tribological energy offered by the kinematics, the surrounding temperature and environment plus the material involved, has to be judged in terms of the structure of lubricants in the molecular level and how those structures compete with the offer of tribological energy.

Starting from a very basic and standard molecular model, it is essential to understand how additives dissolve in a base oil and how they get released and redissolved at a tribological contact area. Even though how additives act toward a surface might be a minor question, it turns out to be very essential and at least the limiting factor of an application reliability if the criticality of those processes are unknown and might pop up in a given application as premature failure.

### Abbreviations


### Author details

Walter Holweger1,2

1 Technological Consultant Agency, Epfendorf, Germany

2 Schaeffler Technologies AG & Co. KG, Herzogenaurach, Germany

\*Address all correspondence to: walter.holweger@t-online.de

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Novel Predictors for Friction and Wear in Drivetrain Applications DOI: http://dx.doi.org/10.5772/intechopen.85060

### References

energy may crack the molecule to carbon specie, subsequently hardening the surface up by carbides and preventing an excessive penetration of reaction products.

Additives are part of a drivetrain reliability. It comes clearly that within a construction, the tribological energy offered by the kinematics, the surrounding temperature and environment plus the material involved, has to be judged in terms of the structure of lubricants in the molecular level and how those structures

Starting from a very basic and standard molecular model, it is essential to understand how additives dissolve in a base oil and how they get released and redissolved at a tribological contact area. Even though how additives act toward a surface might be a minor question, it turns out to be very essential and at least the limiting factor of an application reliability if the criticality of those processes are

unknown and might pop up in a given application as premature failure.

C4NdtP isobutyl-dithiophosphoric acid reacted with an alkylamine

PAO poly-α-olefine as a hydrogenated poly-dec-1-ene

1 Technological Consultant Agency, Epfendorf, Germany

\*Address all correspondence to: walter.holweger@t-online.de

provided the original work is properly cited.

2 Schaeffler Technologies AG & Co. KG, Herzogenaurach, Germany

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

10. Summary

Friction, Lubrication and Wear

Abbreviations

Author details

90

Walter Holweger1,2

compete with the offer of tribological energy.

C4ZndtP isobutyl-zincdithiophosphate

FZG gear test rig (DIN ISO 14635) FE8 bearing test rig (DIN 51819)

CRB cylindrical roller bearing bcc body-centered cubic MPa megapascal (10<sup>6</sup> Pa)

SNMS secondary neutral mass spectrometry

[1] Kragelski IV, Dobycin MN, Kombalov VS. Grundlagen der Berechnung von Reibung und Verschleiß. München, Wien: Carl Hanser Verlag; 1982. ISBN: 3-446- 13619-3

[2] Bowden T. Friction and Lubrication of Solids. Oxford/Berlin: Clarendon Press/Springer; 1950. ISBN: 978-3- 642-92755-3

[3] Zum Gahr K-H. Microstructure and Wear of Materials. Amsterdam: Elsevier; 1987. ISBN: 0-444-42754-6

[4] Rabinowitcz E. Friction and Wear of Materials. New York: Wiley-Interscience; 1995. ISB-0-471-83084-4

[5] Czichos H, Habig K-H. Tribologie-Handbuch. Wiesbaden: Vieweg & Teubner; 2010. ISBN: 978-3- 83480-017-6

[6] Bushan B. Modern Tribology Handbook, Vol. 1(2). New York: CRC Press; 2001

[7] FVA Report, 289 I & II. Zusammenhänge zwischen Zahnradund Wälzlagerschäden und tribologischen Veränderungen des oberflächennahen Werkstoffbereichs; 2001–2003

[8] Johanssen J. On the Influence of Gear Oil Properties on Pitting Life. Lulea: University of Lulea; 2015

[9] FZG Test Rig. Available from: https://www.researchgate.net/publica tion/235308055\_Testing\_procedures\_ for\_gear\_lubricants\_with\_the\_FZG\_ test\_rig

[10] Geheeb N, Franke J. Forschungsvereinigung Antriebstechnik. FVA 126. RWTH Aachen: Vogel Verlag; 2000

[11] Reichelt M. Mikroanalytische Klärung Des Verschleißschutzes in Langsam Laufenden Wälzlagern. Aachen: Shaker; 2011. ISBN: 978-3- 8440-0424-3; ISSN: 1618-5722

[12] Höhn BR, Oster P. Influence of the Lubricants on Pitting and Micro Pitting in the FZG Gear Test Rig. Hamburg: Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und Kohle e.V.; 1996

[13] Winter H, Michaelis K. AGMA Technical Paper P291.17, scoring load capacity of gears lubricated with EPoils. In: Fall Technical Meeting; October 17–19; Montreal, Canada; 1983

[14] Schönnenbeck G et al. Mineralöltechnik. 1987;32(6):1-24

[15] Vinogradova IE. Antianrißinhibitoren für Öle. Moskau: Verlag Chimija; 1972. p. 272

[16] Ruina A, Pratap R. Introduction to Statics and Dynamics. Oxford: Oxford University Press; 2002. p. 713

[17] Arun AP, Senthil AP, Giriaj B, Faizur RA. Gear test rig—A review. International Journal of Mechanical & Mechatronics Engineering. 2014;14. No: 05 16 140205-9696-IJMME-IJENS ©

[18] Hibbeler RC. Engineering Mechanics. 11th ed. New Jersey: Pearson/Prentice Hall; 2007. p. 393. ISBN: 0-13-127146-6

[19] Castro J, Sottomayor A, Seabra J. Experimentals and analytical scuffing criteria for FZG gears. Tribology Series. 2003;43:651-661

[20] Fernandes C, Blazquez L. FZG gearboxes lubricated with different formulations of polyalphaolefin wind turbine gear box oils. In: International Gear Conference, Lyon; 2014

[21] Jede RH, Peters RH, et al. Analyse dünner Schichten mittels Massenspektrometrie zerstäubter Neutralteilchen. TM—Technisches Messen. 1986;11:407-413

[22] Passlack S, Kopnarski M. Sekundärneutralteilchen-Massenspektrometrie (SNMS). 2014. Available from: https://onlinelibrary. wiley.com/doi/pdf/10.1002/vipr. 201400569

[23] Vad K, Csik A, Langer G. Secondary neutral mass spectrometry—A powerful technique for quantitative elemental and depth profiling analyses of nanostructures. Chichester, UK: Spectroscopy Europe; 2009:13-16. Available from: https://www.spectrosc opyeurope.com/article/secondary-ne utral-mass-spectrometry-powerful-tech nique-quantitative-elemental-and-depth

[24] Katritzky AR, Lobanov VS, Karelson M. QSPR: The correlation and quantitative prediction of chemical and physical properties from structure. Chemical Society Reviews. 1995;24:279- 287. Available from: https://pubs.rsc. org/en/content/articlelanding/1995/cs/c s9952400279

[25] Bockstedte M, Kley A, Neugebauer J, Scheffler M. Density-functional theory calculations for poly-atomic systems: Electronic structure, static and elastic properties and ab initio molecular dynamics. In: Computer Physics and Communications. Vol. 107. Amsterdam: Elsevier; pp. 187-222. Available from: https://www.sciencedirect.com/science/ article/pii/S0010465597001173

[26] Szlufarska I. Multi-scale modeling of friction and wear. In: 22nd Conference of Wear of Materials; Long Beach, California; 2018. University of Wisconsin, Key Note

**93**

**Chapter 6**

**Abstract**

*Massimo Lorusso*

metallic alloys, wear

**1. Introduction**

manufacturing [2]:

• Prototyping

• Tooling

• Art and jewelry

Tribological and Wear Behavior

Powder Bed Fusion (LPBF)

of Metal Alloys Produced by Laser

Laser powder bed fusion (LPBF) is an additive manufacturing technique for the production of parts with complex geometry, and it is especially appropriate for structural applications in aircraft and automotive industries. Wear is the most important cause of malfunction of mechanical systems. Abrasive wear accounts for 50% of wear in industrial situations, and it is most common in components of machines. LPBF is very attractive due to its extremely high melting and solidification rates that make possible to obtain materials with particular tribological and wear behavior than those by traditional manufacturing routes. The aim of this chapter is to investigate the different behaviors of principal metallic alloys by LPBF.

**Keywords:** additive manufacturing (AM), laser powder bed fusion (LPBF),

of articles per year is increased more than 20 times (**Figure 1**).

According to ASTM F2792-10, additive manufacturing (AM) is defined as "The process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing technologies." The fundamental principle of AM is that a geometric representation, originally generated using 3D-CAD system, can be manufactured directly without a need to process planning [1]. Today AM is receiving a very high attention from the mainstream media, investment community, national governments, and scientific communities. Nearly 10 years ago (2008), only 231 articles were published with AM topic, 5 years ago (2013) about 800 articles, and in 2018 about 4900 articles; in 10 years the number

AM technologies have a strong potential to change the characteristic of manufacturing process, away from mass production in large factories with dedicated tooling and with high costs, to a world of mass customization and distributed manufacture. Everyday new and innovative applications are emerging for the additive

### **Chapter 6**

turbine gear box oils. In: International

[21] Jede RH, Peters RH, et al. Analyse

Massenspektrometrie (SNMS). 2014. Available from: https://onlinelibrary. wiley.com/doi/pdf/10.1002/vipr.

[23] Vad K, Csik A, Langer G. Secondary neutral mass spectrometry—A powerful technique for quantitative elemental and depth profiling analyses of nanostructures. Chichester, UK: Spectroscopy Europe; 2009:13-16. Available from: https://www.spectrosc opyeurope.com/article/secondary-ne utral-mass-spectrometry-powerful-tech nique-quantitative-elemental-and-depth

[24] Katritzky AR, Lobanov VS,

Karelson M. QSPR: The correlation and quantitative prediction of chemical and physical properties from structure. Chemical Society Reviews. 1995;24:279- 287. Available from: https://pubs.rsc. org/en/content/articlelanding/1995/cs/c

[25] Bockstedte M, Kley A, Neugebauer J, Scheffler M. Density-functional theory calculations for poly-atomic systems: Electronic structure, static and elastic properties and ab initio molecular dynamics. In: Computer Physics and Communications. Vol. 107. Amsterdam: Elsevier; pp. 187-222. Available from: https://www.sciencedirect.com/science/

article/pii/S0010465597001173

of friction and wear. In: 22nd

Wisconsin, Key Note

92

[26] Szlufarska I. Multi-scale modeling

Conference of Wear of Materials; Long Beach, California; 2018. University of

Massenspektrometrie zerstäubter Neutralteilchen. TM—Technisches

Gear Conference, Lyon; 2014

Friction, Lubrication and Wear

dünner Schichten mittels

Messen. 1986;11:407-413

201400569

s9952400279

[22] Passlack S, Kopnarski M. Sekundärneutralteilchen-
