# Study on Wear Resistance of Ti-6 Al-4V Alloy Composite Coating Prepared by Laser Alloying
## 3 Results and Discussion
### Impact of Temperature Variation on Friction and Wear Properties
#### 3.3.3 Effect on Wear Volume and Specific Wear Ratio  
Tables 6 and 7 show the wear volume and specific wear rate of Ti-6 Al-4V alloy and alloying coating at different temperatures. As shown in Table 6, with the increased in temperature, the wear width narrowed, the wear depth decreased and the wear volume reduced. As shown in Table 7, the wear volume of the alloyed coating decreases as the temperature increases, but the reduction degree is lower than the Ti-6 Al-4V alloy. The specific wear ratio is higher than that of the Ti-6 Al-4V alloy, indicating that the wear resistance ability of alloying coating is relatively poor under high temperature. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature (\({}^{\circ}\)C)** & **25** & **350** & **700** \\ \hline Ti-6 Al-4V alloy (mg) & 1.1 & 0.7 & 0.2 \\ Alloying coating (mg) & 0.7 & 0.5 & 0.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The abrasion loss of Ti-6 Al-4V alloy and alloying coating at different temperatures. According to the wear cross-section trajectory curve of Ti-6 Al-4V alloy at different temperatures, the wear depth and width are decreased with the increase of temperature. As the temperature increases, the surface material softens and the friction resistance decreases. At the same time, the peeled oxide layer is stuck on the grinding surface during the friction and wear reciprocation process, and enters the groove or furrow of the wear scar and adheres to the surface of the titanium alloy, acting as a lubricant to reduce the wear of Ti-6 Al-4V. Figure 14 shows the wear-cross section trajectory curve of Ti-6 Al-4V alloy at different temperatures. The width and depth of wear marks at room temperature are the maximum values at three different temperatures. Figure 15(a), (b) shows that there is a significant furrow and a small amount of debris on the wear surface of the alloyed coating at room temperature. When the temperature rises to 350 \({}^{\circ}\)C, as shown in Figure 15c,d, there is a significant adhesion mark on the wear surface, and the amount of debris increases. As the temperature rises to 700 \({}^{\circ}\)C, the wear width is narrowed, and it is difficult to observe furrow and the adhesion traces of metal. However, serious brittle flaking are found on the wear surface, as shown in Figure 15e,f. At room temperature, the Si\({}_{3}\)N\({}_{4}\) ceramic ball is in contact with the hard phase of the coating surface to produce a normal stress and shear stress. At the same time, under the action of normal stress, the abrasive debris slides on the contact surface and rubs the groove marks. As the temperature increases, the surface metal material softens, the hardness decreases, and the plastic deformation is serious, causing the dislocation slip rate to be less than the plastic deformation rate, and the material continuity is destroyed to form micro-cracks. Micro-cracks continue to spread to the surface of the material to form macro-cracks, and break away from the surface of the material. The wear goes back and forth continuously, and the metal detached from the surface of the material is pressed against the surface of the material again under normal stress. When the temperature rises to 700 \({}^{\circ}\)C, the surface will be severely oxidized, and the resulting oxide film will be detached from the metal surface under the action of normal stress and shear force, causing peeling. Because the oxide layer is thin, the lubrication effect of the oxide film is relatively small, wear continues, not only resulting in poorer wear resistance than Ti6 Al4V alloy. Figure 14: The wear cross-section trajectory curve of Ti-6 Al-4V alloy at different temperatures. It can be seen from Figure 16 that, with the increase of temperature, the wear width and depth of the alloyed coating decreases, and the wear rate decreases. At room temperature, the wear width and depth of alloying coating are smaller than that of Ti-6 Al-4V alloy.