# Study on Wear Resistance of Ti-6 Al-4V Alloy Composite Coating Prepared by Laser Alloying
## 2 Experiment  
The thickness of Ti-6 Al-4V alloy is 5 mm. The sample size is 120 mm \(\times\) 100 mm \(\times\) 5 mm. Before laser alloying, the surface of the sample is polished with sandpaper to remove the surface oxide film, and then cleaned with acetone and ethanol, then dried for standby. The composite powder in the experiment is Ni60A/TiN/Al/Si, the purity of Al and Si powder is 99.5% and 99.9%, correspondingly, the particle size is 200-400 mesh and 325 mesh. Moreover, the chemical composition and particle size of Ni60A/TiN composite powder are shown in Table 1.  
The test adopts the way of prefabricated powder. The preformed powder was uniformly covered on the surface of the material by air compressor. Then, under the action of high-energy laser beam, the prefabricated powder and Ti-6 Al-4V alloy were melted and mixed at the same time, and then rapidly solidified, forming a good metallurgical combination. Moreover, 0.5% polyvinyl alcohol solution was used as binder and 20 g polyvinyl alcohol powder was weighed and placed in a beaker containing 380 g distilled water. Then the beaker was heated in a constant temperature water bath heating furnace, and continuously stirred until completely dissolved, forming a colorless and transparent viscous liquid, which was cooled to room temperature for standby. The 500 W pulsed Yttrium Aluminium Garnet(YAG) laser was used in the experiment. The laser mode is pulse wave, the rated output power is 500 W, the wavelength is 1.06 \(\upmu\)m, the focal length \(f\) = 80 mm, and the minimum focal spot diameter is 0.8 mm. The parameters used in the experiment are: current I = 200 A, scanning speed v = 5 mm/s, 0 defocus, argon protection. The surface of the laser-alloyed samples was polished and 35.6 mm \(\times\) 25.4 mm \(\times\) 9 mm sample pieces were prepared by wire cutting machine. The friction and wear test was carried out by using multi-function friction and wear test equipment, as shown in Figure 2.  
The Si\({}_{3}\)N\({}_{4}\) ceramic balls with a 6 mm diameter were used as the grinding materials. The load was set to 3 N, 6 N, and 9 N, respectively, and the reciprocating distance was 10 mm. The friction and wear test lasted for 30 min at the speed of 16 m/min. The mass of the sample was measured before and after the test with a balance of precision of 0.1 mg and the amount of friction loss was calculated. Moreover, the working temperature (25 \({}^{\circ}\)C, 350 \({}^{\circ}\)C, 700 \({}^{\circ}\)C) was changed to detect the effect of temperature on the friction and wear properties of Ti-6 Al-4V alloy and coating. It should be noted that 25 \({}^{\circ}\)C is the temperature at room temperature, and 350 \({}^{\circ}\)C is the normal working temperature of Ti-6 AL-4V, which is widely used in aerospace, medical, and other fields [22]. However, 700 \({}^{\circ}\)C is not the normal working temperature of Ti-6 Al-4V, which is obviously higher than the maximum service temperature of Ti-6 Al-4V alloy, but lower than its \(\upbeta\)--transformation temperature (about \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Powder** & \multicolumn{4}{c}{**Chemical Composition (wt.\%)**} & \multicolumn{2}{c}{**Size (Mesh)**} \\ \hline \multirow{2}{*}{Ni60A} & C & Cr & B & Si & Fe & Ni \\  & 0.5–1.1 & 15.0–20.0 & 3.0–4.5 & 3.5–5.5 & \(\leq\)5.0 & others & 150–400 \\ \hline \multirow{2}{*}{TiN} & N & C & O & Fe & Ti & & \\  & \(\geq\)21.5 & \(<\)0.039 & \(<\)0.033 & \(<\)0.020 & others & & 300 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition and particle size of Ni60A/TiN. 995 \({}^{\circ}\)C). At the same time, the temperature is higher than the eutectic temperature of Al Si alloy (about 577 \({}^{\circ}\)C) and the melting point of pure Al (about 660 \({}^{\circ}\)C) [23]. The samples after laser alloying were cut into 10 mm \(\times\) 5 mm \(\times\) 5 mm blocks by wire cutting, and then the samples were inlaid along the direction perpendicular to the laser scanning. The samples were then ground and polished.