Microstructure and wear resistance of NiTiNb ternary alloy coatings fabricated in situ by laser cladding

Abstract

In this study, (NiTi)100-xNbx (x = 5, 10, 15 wt%) ternary alloys with different Nb contents were synthesised in situ by directed energy deposition. Microstructure analysis shows that the (NiTi)100-xNbx ternary alloy possess a typical dendritic structure. With the increase of Nb content, eutectic regions were formed between Nb and NiTi alloy, and TiNb intermetallic compounds were segregated at the eutectic. The NiTiNb ternary alloy formed a good metallurgical bond with the substrate at all different Nb contents, and no cracks or unfused areas were observed. (NiTi)85Nb15 demonstrated excellent elasticity at varying loads, especially at a load of 800 mN, with a modulus of elasticity of only 57.37 GPa. Meanwhile, the in situ synthesised (NiTi)85Nb15 demonstrated excellent wear resistance compared to other materials, with a minimum specific wear rate of 0.96 ∗ 10−4 mm3/Nm. The superelasticity of NiTiNb alloys plays a role in alleviating the effect of normal loads during sliding wear, which is the key to improving wear resistance. The wear mechanism of NiTiNb ternary alloys is dominated by furrowing with a small amount of adhesive wear. This work reveals the influence of Nb element content on the microstructure and wear resistance of NiTi alloys, providing insights into in-situ alloying of NiTiNb ternary alloys through laser cladding. In future research, it is recommended to enhance the functional properties of NiTiNb ternary alloys, such as memory properties or superelasticity by heat treatment.