Effect of Si content on microstructure and tribological properties of Ti5Si3/TiC reinforced NiTi laser cladding coatings

Abstract

NiTi98-xSixC2 (x = 0, 4, 8 wt%) coatings were prepared on Ti-6Al-4V substrate by laser cladding to improve the surface mechanical properties of NiTi coatings. The effects of Si content addition on the microstructure, phase composition, microhardness, and tribological properties of the coatings were systematically analyzed. The results show that NiTi98-xSixC2 (x = 0, 4, 8) coatings are mainly composed of NiTi, NiTi2, TiC, and Ti5Si3 phases. The rod-like phase of Ti5Si3 was found in NiTi90Si8C2 coating, while the rod-like phases were found broken. The fragmentation of the rod-like phase is related to the growth of the NiTi phase around it. At the same time, TEM results show that the NiTi (B2) phase and Ti2Si second phase are exited in the NiTi90Si8C2 coating. Ti2Si, which has not been decomposed into Ti5Si3, remains during the laser cladding process. In addition, the eutectic structure in NiTi90Si8C2 coating was observed in some regions. The average microhardness of the NiTi98-xSixC2 (x = 0, 4, 8) coating were at 534.08 HV0.5, 598.06 HV0.5, and 974.08 HV0.5, respectively. The wear resistance of NiTi98-xSixC2 (x = 0, 4, 8) coatings increased with the increased Si content. The NiTi90Si8C2 coating exhibits the highest microhardness (974.08 HV0.5) and wear resistance (friction coefficients, wear trace, widths loss weight, and wear rate are 0.320, ~1.25 mm, 12.2 mg, and 5.78 × 10−6 g/Nm, respectively). In NiTi90Si8C2 coating, Ti5Si3 phase plays a significant role in the second phase strengthening to improve its tribological properties. The above analysis confirms that NiTi90Si8C2 coating has optimal tribological properties.