Wear behaviour of additively manufactured Nitinol cryogenically machined at different cutting speeds

Nitinol is a distinctive nickel-titanium alloy renowned for its superelasticity, shape memory properties, and biocompatibility, making it highly suitable for applications in the biomedical and aerospace sectors. The performance and service life of Nitinol components are strongly influenced by the process chain and the associated manufacturing parameters. However, existing studies often focus on the effects of individual steps in the process chain, overlooking the combined impact of multiple steps on the material's properties. In this context, the study explores the combined effects of additive manufacturing, heat treatment, and cryogenic machining on the wear performance of a Ni-rich Nitinol alloy. The material was systematically assessed in its as-built and heat-treated conditions for microstructure, transformation temperatures, nano-hardness, superelasticity, and surface roughness. Key findings show that heat treatment following additive manufacturing significantly enhanced the superelasticity and mechanical strength of the alloy, underlining the importance of heat treatment after additive manufacturing of Ni-rich Nitinol. On the contrary, the cryogenic machining step reduced the material superelasticity, with the influence of the cutting speed to be taken into account. Wear tests further demonstrate the superelasticity effect in assessing Nitinol's wear resistance, with surface roughness also playing a significant role. The study underscores the potential of heat-treated NiTi in applications requiring high mechanical strength, wear resistance, and superelasticity, such as biomedical devices and aerospace components.