**3. Ni concentration profile**

*Mechanics of Functionally Graded Materials and Structures*

**Figure 4** shows the surface modified Cu-Sn-Ni alloy.

Ni. **Figure 2** shows the experimental setup.

**2. Microstructural examination**

Cu-10Sn alloy is shown in **Figure 6**.

analysis. Microstructural examination, hardness measurement and wear measurements were carried out for the substrate and for the specimen surface alloyed with

**Figure 3** shows the Cu-Sn alloy substrate with and without Ni coating and

A typical dendritic structure was observed in the as-cast substrate of Cu-10Sn bronze alloy as shown in **Figure 5** and the microstructure of the Ni surface alloyed

It can be observed from **Figure 6** that the structure is very fine as opposed to a coarse structure observed in **Figure 5** and therefore it can be concluded that the grain refinement occurs as a result of the surface alloying process [3]. This refinement is due to the fast cooling experienced during solidification in the surface alloying process. A similar fine grained microstructure was observed for all the other Ni alloyed specimens also. Yilbas et al. [4, 5] studied the effect of laser surface modification treatment of aluminum bronze (Cu-9%Al-3%Fe) with

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**Figure 6.**

*Ni surface alloyed Cu-Sn.*

**Figure 5.** *As-cast Cu-Sn.*

The Ni concentration on the surface of the modified layer formed in the surface alloying process was measured using the EDAX analysis. The concentration along the depth of the modified layer was also measured. **Figure 7** shows the points where the Ni concentration was measured. The Ni peaks can be observed in the EDS spectrum for all the surface alloyed specimen and the spectrum for 200 μm Ni is shown in **Figure 8**.

Further, the results obtained by the EDAX analysis are reported in **Table 2**.

The Ni concentration values (wt %) reported in **Table 2** are plotted against the distance along the depth of the modified layer. **Figure 9** shows the Ni profiles for various coating thickness.

It can be observed from **Figure 9** that the Ni concentration is found to be the maximum on the surface of the modified layer for all the coating thickness. The Ni concentration decreases along the depth of the modified layer for all the coating thickness. It can be clearly observed that a gradient exists in the Ni concentration profile.

**Figure 7.** *Ni concentration measurement points.*

#### **Figure 8.**

*EDS spectrum for 200 μm Ni coated samples.*


#### **Table 2.**

*Ni concentration along the depth of the modified layer for four coating thickness.*

## **4. Micro-hardness**

The surface hardness values of the substrate and the surface alloyed specimens with varying Ni concentration were measured. Several readings were taken at

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**Figure 10.**

*Hardness variation with Ni concentration.*

**Table 3.** *Hardness values.*

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

substrate and the Ni surface alloyed specimens are reported in **Table 3**.

different locations and an average value was calculated. The surface hardness increased from 120 HV for the substrate to 485 HV for the specimen surface alloyed with a Ni coating thickness of 200 μm. The average surface hardness values of the

The variation in the surface hardness with the Ni concentration is shown in **Figure 10**. It can be observed that the hardness increases with an increase in the Ni concentration. Ni contributes significantly to the hardness of the Cu-10Sn bronze alloy. The increase in the hardness is attributed to the presence of Ni in the solid solution. Hence, the hardening mechanism is solid solution strengthening.

Hardness values are measured at different points along the depth of the modified layer and are reported in **Table 4** and are represented graphically in **Figure 11**. The hardness is found to decrease along the depth direction for all the surface alloyed specimen as shown in **Figure 11**. It can be concluded that a gradient exists in the hardness profile along the depth direction. The gradient so observed is attributed to the variation in the Ni concentration along the depth of the modified layer (refer to **Table 2**). The hardness is found to be the maximum for a concentration of 17.8 wt % Ni. It can be inferred that the hardness on the surface of the modified layer formed in the surface alloying process can be controlled by controlling the Ni concentration. Kac et al. [6] studied the structure and properties of Cu-10%Al-4%Fe-2%Mn bronze with an addition of Ti on the surface using laser as the heat source. They reported that a gradient exists in hardness along the depth direction of the modified layer. The observation obtained is consistent with that of Kac et al. [6]. **Figure 12** is a bar chart showing the hardness values obtained for the substrate, surface refined and the Ni surface alloyed specimens. It can be observed that the

**Alloy Ni coating thickness (μm) wt % Ni Hardness (HV0.1)**

Cu-10Sn 80 5.03 120 326 Cu-10Sn 120 8.53 120 379 Cu-10Sn 160 13.61 120 418 Cu-10Sn 200 17.81 120 485

**Substrate Surface alloyed with Ni**

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

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

different locations and an average value was calculated. The surface hardness increased from 120 HV for the substrate to 485 HV for the specimen surface alloyed with a Ni coating thickness of 200 μm. The average surface hardness values of the substrate and the Ni surface alloyed specimens are reported in **Table 3**.

The variation in the surface hardness with the Ni concentration is shown in **Figure 10**. It can be observed that the hardness increases with an increase in the Ni concentration. Ni contributes significantly to the hardness of the Cu-10Sn bronze alloy. The increase in the hardness is attributed to the presence of Ni in the solid solution. Hence, the hardening mechanism is solid solution strengthening.

Hardness values are measured at different points along the depth of the modified layer and are reported in **Table 4** and are represented graphically in **Figure 11**.

The hardness is found to decrease along the depth direction for all the surface alloyed specimen as shown in **Figure 11**. It can be concluded that a gradient exists in the hardness profile along the depth direction. The gradient so observed is attributed to the variation in the Ni concentration along the depth of the modified layer (refer to **Table 2**). The hardness is found to be the maximum for a concentration of 17.8 wt % Ni. It can be inferred that the hardness on the surface of the modified layer formed in the surface alloying process can be controlled by controlling the Ni concentration. Kac et al. [6] studied the structure and properties of Cu-10%Al-4%Fe-2%Mn bronze with an addition of Ti on the surface using laser as the heat source. They reported that a gradient exists in hardness along the depth direction of the modified layer. The observation obtained is consistent with that of Kac et al. [6].

**Figure 12** is a bar chart showing the hardness values obtained for the substrate, surface refined and the Ni surface alloyed specimens. It can be observed that the


#### **Table 3.**

*Mechanics of Functionally Graded Materials and Structures*

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**Figure 9.**

**Table 2.**

**Figure 8.**

*EDS spectrum for 200 μm Ni coated samples.*

**4. Micro-hardness**

*Ni concentration profile.*

The surface hardness values of the substrate and the surface alloyed specimens

**Depth from the top surface (mm) Ni concentration for various coating thicknesses (wt %)**

0 5.03 8.53 13.61 17.81 0.3 4.9 8.39 12.92 14.88 0.6 4.48 7.15 10.18 13.65 0.9 3.26 6.46 7.86 10.41 1.2 2.95 5.83 6.85 7.35 1.5 2.15 4.36 5.02 5.89 1.8 0.87 2.48 3.15 4.26

*Ni concentration along the depth of the modified layer for four coating thickness.*

**80 μm 120 μm 160 μm 200 μm**

with varying Ni concentration were measured. Several readings were taken at

*Hardness values.*

**Figure 10.** *Hardness variation with Ni concentration.*

#### *Mechanics of Functionally Graded Materials and Structures*


#### **Table 4.**

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

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

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

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

surface refining process and the surface alloying process significantly increases the hardness of the alloy. Increase in hardness observed in the surface refining process is attributed to the formation of fine grained microstructure due to rapid solidification in the surface refining process. However, the grain refinement occurs in the surface alloying process as shown in **Figure 6**. The addition of Ni in the surface alloying process also contributes to the improvement in the hardness of the alloyed specimen as shown in **Figure 11**. Hence, the increase in hardness is attributed to the grain refinement occurring in the surface alloying process and also to the Ni addition.

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 wear results obtained for the substrate and the Ni surface alloyed samples

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

**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

**Figure 15** is a bar chart showing the wear rate obtained for the substrate, surface

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

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

**5. Wear behavior**

the bulk alloys.

after Ni addition.

are reported in **Table 5**.

the reduction in the wear rate.

refined and the Ni surface alloyed specimens.

**Figure 12.**

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

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

surface refining process and the surface alloying process significantly increases the hardness of the alloy. Increase in hardness observed in the surface refining process is attributed to the formation of fine grained microstructure due to rapid solidification in the surface refining process. However, the grain refinement occurs in the surface alloying process as shown in **Figure 6**. The addition of Ni in the surface alloying process also contributes to the improvement in the hardness of the alloyed specimen as shown in **Figure 11**. Hence, the increase in hardness is attributed to the grain refinement occurring in the surface alloying process and also to the Ni addition.
