*2.4.2.2 Adhesive wear*

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

*2.4.2 Classification of wear mechanism*

*2.4.2.1 Abrasive wear*

sives are the major wear mechanisms in the industry.

frictional force. In all the dynamic machine components such as cams, bearings and seals, the wear is almost undesirable one. Those components or machines need to be replaced after a small damage or material loss or if the surface showed with higher roughness. If the system is well defined in tribology, the material removal will be

The wear occurs chemically or mechanically means and is normally induced through frictional heat. Mainly, the wear contains six principal quite distinct phenomena that have only one thing in common; the removal of material from the rubbing interface [24, 25]. The wear can be classified as follows: (1) abrasive; (2) adhesive; (3) fatigue; (4) impact by erosion; (5) corrosive; (6) electrical-arcinduced wear. The other commonly raised wear is fretting corrosion and fretting. However, the wear such as abrasive, adhesive and corrosive are the major combinations of wear. Based on the previously encountered issues, the abrasive and adhe-

The abrasive wear happens while asperities of a rough and hard particles slides on the softer surface and remove the softer material and finally damages the surface through fracture or plastic deformation. Most of the ceramic and metallic materials with high toughness and hard particles result in the plastic stage of the soft material. Even the metal interfaces will deform plastically while applying higher loads. The abrasive wear can be occurred generally in two different situations as shown in **Figure 7**. In the beginning, the hard surface is the harder of two rubbing surfaces like two body abrasion. For example, in cutting, grinding and machining. In another case, the hard surface is the third body. Particularly, this must be small abrasive particle, identified in between the other two surfaces and this may be sufficiently

harder. This may be able to scratch either one or both the sliding surfaces.

*(a) Schematics of hard rough surface mounted with abrasive grits sliding on a softer surface and (b) free* 

very slow and at the same time it must be continuous with steady process.

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**Figure 7.**

*abrasive grits caught between the two surfaces.*

Generally, the adhesive wear can be occurred while two solid body sliding on the flat surfaces with dry or lubrication. The bonding of metals is happening at the asperity contacts at the interface, and these contacts is sheared through sliding process, which may produce the plowing of material from softer surface to harder surface. With continuous sliding process, the transferred wear debris is stop on the transferred surface and the same debris may return to original surface or else this may be loose as wear debris particle. In some cases, the debris may have fractured through fatigue process with continuous loading and unloading process and causes with loose particle formation.

There is some mechanism was explained for the fragment detachment of a material. However, still the well identified mechanism for adhesion is shearing of the two solid bodies or the weakest surface from one of the two surface [27]. The schematic representing the two possible way of metal breaking through shearing process as shown in **Figure 9**. Normally, the interface adhesion strength is assumed to be lesser while compared with breaking strength of nearby regions; hence, the break through shearing arise at the interface regions (path 1) in many cases and there will be no material loss happen during these sliding process. In another case, with lesser fraction of contacts, break may happen in any one of the two solid bodies (path 2) and a minor piece of material (the blue dotted semi-circle) can be attached to the harder other surface.

The SEM picture (**Figure 10**) shows the steel worn out surface with adhesion wear. From the **Figure 10**, it can be seen clearly that the adhesive debris pullout from the softer surface. During the sliding process, the surface asperities severely suffer from fracture or plastic deformation. Further, the subsurface also underwent strain hardening and plastic deformation. The SEM micrograph of worn-out surface shows the severe pull out material with plastic deformation. In the picture, the yellow

**Figure 8.** *SEM picture of steel surface after abrasive wear with dry condition.*

#### **Figure 9.**

*Schematic representing the two possible ways of metal breaking through the shearing process.*

#### **Figure 10.**

*SEM picture of steel surface after adhesive wear under dry condition.*

dotted semi-circle indicates the extensive structural changes by adhesive wear. In addition to that severe type of adhesion wear is called as smearing, galling and scuffing and also this terms are used to describe other type of wear in sometimes.

#### *2.4.2.3 Fatigue wear*

Generally, the fatigue wear on surface and subsurface level can be noticed through continuous sliding and rolling atmosphere. The continuous loading and unloading processes, which will induce the surface and subsurface to form the cracks after critical repeated cycles. Then, the surface of the material will breakup into lager fragments and producing the larger pits on the softer surface. However, the material removed through fatigue wear is not considered as major parameter. There are much relevant is the beneficial life in terms of time or revolutions prior occur the fatigue wear.

#### *2.4.2.4 Erosive wear*

The erosive wear can be occurred due to impingement of solid hard particle with high velocity on the specimen surface. **Figure 11 (a, b)** shows that the hard particle impinging toward the specimen surface and removes the material from the top surface of the specimen. The contact stresses produce from the particle kinetic energy in liquid or air stream as it meets the surface. In erosive wear, the impingement

**197**

*Friction, Lubrication, and Wear*

*2.4.2.5 Corrosive wear*

*surface, (b) material removed by hard particle.*

**Figure 11.**

*DOI: http://dx.doi.org/10.5772/intechopen.93796*

angle and particle velocity combined with abrasive sizes and provide the measure of kinetic energy for the impinging particle. The wear particles/debris are formed in

*Schematic of erosive wear with hard particle hitting on the surface; (a) hard abrasive particle hitting the* 

The corrosive or chemical wear happens while sliding takes place in a chemical atmosphere. The oxygen is considered as a most dominant corrosive medium in air atmosphere. So that the corrosive wear in air atmosphere is normally called as oxidative wear. The corrosive wear is significant in many factories such as slurry handling, chemical processing, mining and mineral processing. The chemical wear can arise due to the electrochemical or chemical interaction of the surfaces with the atmosphere. However, the chemical corrosive wear occurs in extremely high corrosive atmosphere and in high humidity and high temperature atmosphere. The electrochemical corrosive wear can occur with chemical reaction accompanied of an electric current. The potential variations can be observed between those two regions. The high potential region and low potential region is known as cathode and anode, respectively. There will be a current flow between the cathode and anode over an electrolyte conductive medium, the metal dissolve at the anode side in the

While conducting the experiment, the electron transfers via metal to the cathode and minimize the oxygen or ions. After corrosion test, these surfaces changes to some other appearance with corroded region. Further, the electrochemical corrosion is influenced through the electro potential. The aqueous is a most common liquid environment in corrosion atmosphere. In this working atmosphere, the less amount of gases may dissolve, normally carbon dioxide or oxygen may influence the corrosion. **Figure 12** indicates the electrochemical corrosion testing setup and

While the presence of higher potential on the thin air film during the sliding condition, a dielectric breakdown gives that leads to arcing. The higher power density can be produced with short time during the arcing period. The produced

erosion arises as an outcome of repetitive impacts [28].

form of liberates electrons and ions [29].

corroded micrograph with layer formation.

*2.4.2.6 Electrical arc-induced wear*

**Figure 11.**

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

*Schematic representing the two possible ways of metal breaking through the shearing process.*

dotted semi-circle indicates the extensive structural changes by adhesive wear. In addition to that severe type of adhesion wear is called as smearing, galling and scuff-

Generally, the fatigue wear on surface and subsurface level can be noticed through continuous sliding and rolling atmosphere. The continuous loading and unloading processes, which will induce the surface and subsurface to form the cracks after critical repeated cycles. Then, the surface of the material will breakup into lager fragments and producing the larger pits on the softer surface. However, the material removed through fatigue wear is not considered as major parameter. There are much relevant is the beneficial life in terms of time or revolutions prior

The erosive wear can be occurred due to impingement of solid hard particle with high velocity on the specimen surface. **Figure 11 (a, b)** shows that the hard particle impinging toward the specimen surface and removes the material from the top surface of the specimen. The contact stresses produce from the particle kinetic energy in liquid or air stream as it meets the surface. In erosive wear, the impingement

ing and also this terms are used to describe other type of wear in sometimes.

*SEM picture of steel surface after adhesive wear under dry condition.*

**196**

*2.4.2.3 Fatigue wear*

**Figure 10.**

**Figure 9.**

occur the fatigue wear.

*2.4.2.4 Erosive wear*

*Schematic of erosive wear with hard particle hitting on the surface; (a) hard abrasive particle hitting the surface, (b) material removed by hard particle.*

angle and particle velocity combined with abrasive sizes and provide the measure of kinetic energy for the impinging particle. The wear particles/debris are formed in erosion arises as an outcome of repetitive impacts [28].
