# Study on Wear Resistance of Ti-6 Al-4V Alloy Composite Coating Prepared by Laser Alloying
## 1 Introduction  
With the development of technology and the requirements of deep space and deep-sea exploration, it is extremely important for equipment and structural parts to be stable, to serve under severe conditions, such as high stress, strong corrosion, and high temperature. The density of titanium is 4.506-4.516 g/cm\({}^{3}\), which is only about 55% of steel, and the strength of titanium alloy can reach 500-1400 MPa, which meets the requirements of aerospace components [1; 2; 3]. In addition, titanium alloys have good performance at both high and low temperatures, and can work for long periods of time at 550 \({}^{\circ}\)C and \(-\)253 \({}^{\circ}\)C, accordingly, titanium alloy is called \"space metal\" [4; 5]. Its application in aerospace engine turbine blades, piston rings, valves, marine heat exchangers, propellers, and other parts with high material performance requirements, is limited [6; 7] due to its large friction coefficient [5], easy adhesion [8], poor wear resistance [9; 10] (Figure 1a), and serious oxidation under high temperature conditions (Figure 1b). Therefore, improving the wear resistance of the titanium alloy is of great significance for broadening its application range in parts and components requiring high performance materials. The surface properties of titanium alloy can be improved by laser surface alloying [11; 12]. Laser surface alloying is a method of local modification of metal surface. It aims to change the composition, phase, and microstructure of the material surface, and then change the performance of the material surface, to meet the performance requirements of wear resistance, corrosion resistance, and oxidation resistance. [PERSON] et al. [13] synthesized TiN coating in situ on Ti6 Ale4V matrix by laser surface alloying, and the results showed that the dendritic structure of TiN increased the hardness of the coating,and its corrosion resistance was significantly improved due to the alloying of Ti-6 Al-4V matrix and TiCN. [PERSON] et al. [14] prepared Ti\({}_{6}\)Ni\({}_{6}\)Si\({}_{7}\), TiB\({}_{2}\), TiNi, and TiN composite coatings by laser alloying on the surface of pure Ti using tin-B-Si-Ni mixed powder as raw material. The study showed that the hardness, wear resistance, and oxidation resistance of the surface of pure Ti were significantly improved. Although the hard phase particles of Ti can enhance the surface strength of the matrix, it will also increase the wear on the matrix. Numerous studies have shown that the addition of silicon elements can improve the wear resistance and high temperature oxidation resistance. [PERSON] et al. [15] studied the microstructure and wear properties of coatings with different silicon contents on the surface of Ti-6 Al-4V titanium alloy. The results showed that the microhardness of the coatings was increased to more than three times that of the substrate. Within a certain range, concerning the carbon content of silicon, the higher the wear resistance, the better[PERSON] [PERSON] et al. [16] used nitrogen and silicon powder laser alloying technology to prepare a composite strengthening coating containing Si\({}_{3}\)N\({}_{4}\), Ti\({}_{5}\)Si\({}_{3}\), Ti\({}_{2}\)N, and other compounds on the surface of titanium alloy Ti-6 Al-4V. The addition of Si not only improves the sliding of the coating the wear resistance, but also makes the coating have good oxidation resistance. Aluminum also plays an important role in improving the high temperature performance of titanium alloys. Ti-6 Al-4V alloy has poor oxidation resistance due to its low aluminum content. Ti-6 Al-4V alloy can only be used for the production of static and rotating parts of the fan low-pressure compressor with the temperature around 315 \({}^{\circ}\)C. [PERSON] et al. [17] prepared high temperature anti-oxidation TiN/Ti\({}_{3}\)Al intermetallic compound composite coating on the surface of Ti6 Al4V titanium alloy by in-situ laser cladding.