# Study on Wear Resistance of Ti-6 Al-4V Alloy Composite Coating Prepared by Laser Alloying
## 3 Results and Discussion
### Impact of Load Variation on Friction and Wear Properties  
#### 3.2.1 Effect on Coefficient Friction  
At room temperature, the friction coefficient of Ti-6 Al-4V alloy and alloying coating varied with the wear time in the friction and wear test of different loads, as shown in Figure 6. When the load was 3 N, the friction coefficient of Ti-6 Al-4V alloy increased with the wear time in the first 15 min, then stabilized after 15 min and the friction coefficient was kept in the range of 0.47-0.53. When the load was 6 N, the pre-grinding period was reduced to 10 min, then stabilized, and the friction coefficient was kept in the range of 0.40-0.47. When the load increased to 9 N, there was no pre-grinding period, it was directly into the stable period. The friction coefficient decreased and maintained in the range of 0.39-0.44 eventually, indicating that it was the most stable.  
Ti-6 Al-4V alloy was subjected to normal stress and tangential force during the wear process with Si\({}_{3}\)N\({}_{4}\) ceramic balls, and friction first occurs on the bumps that contact each other. When the load was 3 N, the normal stress applied to the surface of Ti-6 Al-4V alloy was small, the squeezing force of the bumps on the surface of Si\({}_{3}\)N\({}_{4}\) and Ti-6 Al-4V alloy was also small, the bumps were difficult to be smoothed in a short time, and the surface of Ti-6 Al-4V alloy remained uneven rough state, so the coefficient of friction was large. When the load was increased, the size and number of contact points of the Si\({}_{3}\)N\({}_{4}\) ceramic ball and the Ti-6 Al-4V alloy also increased, and the bumps on the surface of the Ti-6 Al-4V  
Figure 5: Cross-sectional morphology and point energy spectrum analysis of the wear surface: (**a**) coating cross-section morphology; (**b**) point spectrum analysis.  
Figure 6: Variation curve of friction coefficient of Ti-6 Al-4V alloy and alloying coating under different load: (**a**) Ti-6 Al-4V alloy; (**b**) alloying coating.  
alloy underwent plastic deformation due to the large squeezing force, and even broke and flake to formed abrasive debris. The abrasive particles began to wear, and the shear stress decreased accordingly. At this time, although the contact area of the friction and wear surface increased, when the metal was in the elastoplastic state, the effective contact area was proportional to 2/3 of the applied load, so the friction coefficient decreased.  
From Figure 6b, it can be seen that, when the load was 3 N, the wear of the alloyed coating also had a pre-grinding period, but the time was shorter than that of the Ti-6 Al-4V alloy, about 6 min, and the fluctuation range of the friction coefficient was smaller, from 0.39 to 0.42. When the load increased to 6 N, 9 N, the pre-grinding period was no longer obvious, entering the wear stabilization period faster, and the floating range of the friction coefficient became smaller, and the stability was better. The friction coefficient of the alloyed coating under different loads was lower than that of the Ti-6 Al-4V alloy. Firstly, the hardness of the alloyed coating was much higher than that of the Ti-6 Al-4V alloy, thereby reducing the tangential resistance between the Si\({}_{3}\)N\({}_{4}\) ceramic ball and the alloyed coating. Secondly, the hardness of the titanium alloy was much smaller than that of the Si\({}_{3}\)N\({}_{4}\) ceramic ball. During the contact and wear between the two, the Ti-6 Al-4V alloy was prone to plastic deformation and adhesion, and the intermetallic compound of the alloyed coating can effectively reduce the adhesion resistance [26].