Ti60 titanium alloy is a nearly α-type high-temperature titanium alloy that can be employed for long-term service even at a temperature of 600 °C. As an important material used in aero-engine blades and compressors, it needs to withstand complex loads and high-friction and -wear conditions. For example, fretting wear will occur between the root of the rotor blade and the disc mortise due to the centrifugal force caused by the rotor blade rotating at high speeds or when the engine becomes overexcited. Due to vibrations, thermal expansion, and other factors during high-speed rotations, the blade tip will accidentally scrape the sealing coating on the inner wall of the casing, resulting in adhesive and abrasive wear. When the engine is used in an environment with desert dust or volcanic ash suspended at high altitudes, the hard particles in the air will impact the high-speed rotating blades, resulting in erosion wear. This highlights that the Ti60 titanium alloy also has some shortcomings, such as a low hardness (340 HV) [
1] and insufficient friction and wear resistance; however, currently, no relevant studies have attempted to improve the wear resistance of Ti60 alloy.
However, many studies have reported the use of laser cladding technology to improve the wear resistance of other types of titanium alloys. For instance, Di et al. [
2] prepared a high-entropy alloy coating of AlCoCrFeMoVTi on the surface of a TC4 titanium alloy via laser cladding technology. The experimental results show that the highest microhardness of the coating HV
0.2 was 10,990 MPa, which was 3.29 times that of the substrate, and the wear volume of the coating was only 12.01% that of the substrate. Qin et al. [
3] used laser cladding technology to prepare a NiCrCoAlY-Cr
3C
2 composite coating on the surface of a TC4 titanium alloy. The results show that the highest microhardness of the composite coating was 1344 HV, which was about 3.8 times that of the substrate (350 HV), and the wear loss of the coating was 24% that of the substrate. Jiang et al. [
4] prepared a WC-Co composite coating using laser cladding to significantly improve the wear resistance of a TC4 substrate, making the maximum microhardness of the coating as high as 1536 HV
0.5 and the wear rate as high as 1.5 g/h. Huang et al. [
5] used laser cladding technology to prepare a Ti
5Si
3/Ti
3Al composite coating on a TA2 titanium alloy. The average microhardness of the coating was about 668 HV
0.1, which was 3.34 times that of the matrix, and the mass wear rate of the coating was 1/5.79 that of the matrix. Yu et al. [
6] used a semiconductor laser to laser clad a Ti-Ni-Si
3N
4-ZrO
2 mixed powder onto the surface of a TA15 alloy to prepare a ZrO
2/Ti
5Si
3/TiN/Ti
2N composite coating. The results show that the microhardness of the composite coating was 835–1050 HV, which was about three times that of the substrate. Under dry sliding friction and wear, the wear of the coating was about 1/6 that of the substrate. Feng et al. [
7] used laser cladding technology to prepare a TiB-TiC co-reinforced TiNi-Ti
2Ni intermetallic compound composite coating on the surface of a TA15 titanium alloy, with a Ti-Ni-B
4C powder mixture as the raw material. The highest microhardness value of the coating was about 700 HV, which was about 2.07 times that of the matrix (340 HV), and the wear quality of the coating was only 0.47% of the matrix. Chen et al. [
8] used laser cladding technology to clad TiN powder onto the surface of a TC9 titanium alloy to prepare a TiN coating. The results showed that the wear of the TiN coating under 10 kg and 30 kg loads was about 1/100 and 1/30 of the matrix, respectively, which indicates that the wear resistance of the coating greatly improved. Hu et al. [
9] used a YAG laser to laser clad a Ti-based Cr
2C
3 alloy powder onto the surface of a Ti600 alloy to prepare a functional gradient coating, with TiC as the enhanced phase, making the average friction coefficient and wear rate of the coating only 0.3–0.5 times that of the Ti600 matrix, indicating that the wear resistance of the coating significantly improved. Cheng et al. [
10] used laser cladding technology to prepare a NiCr/TiAl coating on the surface of a Ti600 titanium alloy. Their experimental results showed that the average microhardness of the coating was 832 HV, and the wear rate of the coating at room temperature was 27% that of the substrate.
In short, the current research on improving the wear resistance of titanium alloys mainly focuses on the preparation of metal–alloy composite coatings and ceramic coatings using laser cladding technology, while few studies have been conducted on the preparation of high-entropy boride coatings using laser cladding technology [
11]. However, high-entropy borides have attracted much attention due to their comprehensive properties, such as their high melting point, excellent mechanical properties, and high thermal stability. For example, high-entropy diborides are considered candidate materials for components such as the leading edge of supersonic aircraft and metal-melting crucibles [
12,
13]. Since 2015, high-entropy boride ceramics dominated by high-entropy diborides have been widely studied [
14,
15,
16,
17]. According to the mixing rule, the theoretical hardness of high-entropy ceramic materials should be the sum of that of the single-phase materials of each component, but the actual values are often higher, particularly in high-entropy boride ceramics [
18]. For example, Gild et al. [
14] reported that the hardnesses of the ceramic blocks for six high-entropy borides—(Ti
0.2Zr
0.2Nb
0.2Ta
0.2Hf
0.2)B
2, (Ti
0.2Zr
0.2Hf
0.2Ta
0.2Mo
0.2)B
2, (Ti
0.2Zr
0.2Nb
0.2Hf
0.2Mo
0.2)B
2, (Ti
0.2Zr
0.2Nb
0.2Ta
0.2Cr
0.2)B
2, (Ti
0.2Zr
0.2Nb
0.2Ta
0.2Mo
0.2)B
2, and (Ti
0.2Hf
0.2Nb
0.2Ta
0.2Mo
0.2)B
2—were higher than those obtained using the mixing rule at 17.5 GPa, 19.1 GPa, 21.9 GPa, 19.9 GPa/23.7 GPa, and 22.5 GPa, respectively.
In view of the abovementioned excellent hardness properties of high-entropy borides, laser cladding was used in this study to obtain a composite coating containing the high-entropy (Ti0.2Zr0.2Mo0.2Ta0.2Nb0.2)B2 boride phase on a Ti60 alloy with the Ti, Zr, Mo, Ta, Nb, and B powders as the raw materials. The microstructure and dry sliding friction and wear behavior of the coating were studied to provide a basis for the application of Ti60 alloy in wear-resistant environments.