**5. Wear behavior**

*Mechanics of Functionally Graded Materials and Structures*

*Hardness along the depth of the modified layer for various Ni coating thickness.*

*Hardness values—substrate, surface refined and Ni surface alloyed specimen.*

**Depth (mm) Hardness for various Ni coating thickness (HV0.1)**

0 326 379 418 485 0.25 289 361 410 478 0.5 268 347 389 431 0.75 248 311 365 399 1 201 289 321 347 1.25 189 240 266 314 1.5 166 201 227 269 1.6 154 182 213 244 1.8 140 162 197 223 1.85 120 147 184 120 1.9 120 120 120 120

**80 μm 120 μm 160 μm 200 μm**

**86**

**Figure 12.**

**Table 4.**

**Figure 11.** *Hardness profile.*

A typical height loss vs. time plot for the Cu-10Sn modified alloy is shown in **Figure 13**. It can be observed that the height loss increases linearly with the sliding time. This behavior is in agreement with the results reported by Singh et al. [9] in the bulk alloys.

The wear results obtained for the substrate and the Ni surface alloyed samples are reported in **Table 5**.

It can be observed that the wear rate reduced significantly after surface alloying with Ni. The reduction in the wear rate is attributed to the increase in the hardness after Ni addition.

**Figure 14** is a bar chart showing the variation in the wear rate with the Ni concentration. It can be observed that the wear rate decreases with an increase in the Ni concentration. The minimum wear rate was obtained for the 17.8 wt % Ni. It can be concluded that the wear rate of the Cu-Sn bronze alloy can be reduced by surface alloying with Ni. The increased hardness due to the Ni addition is the reason behind the reduction in the wear rate.

**Figure 15** is a bar chart showing the wear rate obtained for the substrate, surface refined and the Ni surface alloyed specimens.

It can be observed from **Figure 15** that the surface refining process decreases the wear rate marginally and the surface alloying process remarkably decreases the wear rate of the Cu-10Sn bronze alloy. The reduction in the wear rate observed in the surface refining process is due to the increase in the hardness as a result of the grain refinement due to the faster cooling rate experienced. Further, it is to be noted that the refinement in the grain structure also occurs in the surface alloying process

**Figure 13.** *A typical wear plot.*

as discussed earlier. However, the Ni addition significantly contributes to the increase in the hardness that reduces the wear rate of the surface alloyed specimen. Hence, the reduction in the wear rate is attributed to both the grain refinement occurring in the surface alloying process and the Ni addition.

A typical image showing the wear tracks after the dry sliding test on pin-on-disc wear tester for the Ni surface alloyed specimen is shown in **Figure 16**.

It can be observed from **Figure 16** that the wear mechanism is of adhesive type. Zhang et al. [10] studied the dry sliding wear behavior in the bulk Cu-15Ni-8Sn alloy. They reported that the adhesive wear took place under the dry sliding test


**Table 5.**

*Wear rate results.*

**Figure 14.** *Variation in wear rate with Ni concentration.*

**89**

**Figure 17.**

*Frictional force vs. time plot.*

*Development of Functionally Gradient Cu-Sn-Ni Alloy Using GTA Heat Source*

conditions. It is to be noted that the compositions of the modified layer in this study are similar to the Cu-15Ni-8Sn alloy that was used in the study of Zhang et al. Therefore, the observation in the present study is consistent with that of Zhang et al. [11].

Frictional force vs. time plot of Ni Surface Alloyed Cu-10Sn alloy is shown in **Figure 17**. The same trend was found for all the other Ni Surface alloyed specimens. It can be noticed that the frictional force becomes constant after a short period of time and remains as such. The rapid increase in frictional force found initially is due to the uneven contact between the modified specimen and counter face material. The frictional force remains constant once perfect contact is achieved. A typical plot of coefficient of friction vs. time for the surface alloyed Cu-10Sn alloy is shown in **Figure 18**. The plot shows both transient period and single steady-state regime. The reasons for the transient behavior may be the effect of work-hardening

The coefficient of friction obtained in this study for the substrate and the surface alloyed Cu-10Sn alloys are reported in **Table 6**. An average value of 0.23 was

and/or accumulation of debris as reported by Singh et al. [9].

obtained as frictional coefficient after surface alloying process.

*DOI: http://dx.doi.org/10.5772/intechopen.86315*

**Figure 16.** *Wear tracks.*

**6. Coefficient of friction**

**Figure 15.**

*Wear rate—substrate, surface refined and surface alloyed specimens.*

*Development of Functionally Gradient Cu-Sn-Ni Alloy Using GTA Heat Source DOI: http://dx.doi.org/10.5772/intechopen.86315*

**Figure 16.** *Wear tracks.*

*Mechanics of Functionally Graded Materials and Structures*

occurring in the surface alloying process and the Ni addition.

wear tester for the Ni surface alloyed specimen is shown in **Figure 16**.

**Substrate alloy Ni coating thickness (μm) Wear rate (×10<sup>−</sup><sup>4</sup>**

as discussed earlier. However, the Ni addition significantly contributes to the increase in the hardness that reduces the wear rate of the surface alloyed specimen. Hence, the reduction in the wear rate is attributed to both the grain refinement

It can be observed from **Figure 16** that the wear mechanism is of adhesive type. Zhang et al. [10] studied the dry sliding wear behavior in the bulk Cu-15Ni-8Sn alloy. They reported that the adhesive wear took place under the dry sliding test

Cu-10Sn 80 18.40 13.70 Cu-10Sn 120 18.40 8.40 Cu-10Sn 160 18.40 4.5 Cu-10Sn 200 18.40 2.2

A typical image showing the wear tracks after the dry sliding test on pin-on-disc

 **mm3 /m)**

**Substrate Surface alloyed**

**88**

**Figure 15.**

**Table 5.** *Wear rate results.*

**Figure 14.**

*Variation in wear rate with Ni concentration.*

*Wear rate—substrate, surface refined and surface alloyed specimens.*

conditions. It is to be noted that the compositions of the modified layer in this study are similar to the Cu-15Ni-8Sn alloy that was used in the study of Zhang et al. Therefore, the observation in the present study is consistent with that of Zhang et al. [11].
