Influence of the depth of cut on the AM nitinol properties in flood and cryogenic machining

Nickel-titanium alloys, commonly called Nitinol, are known for two fundamental properties, namely the shape memory effect (SME) and the superelasticity effect (SE), which make Nitinol a material of great interest for applications in various fields, such as biomedical, aerospace, automotive, and electronics. Most of the published research studies discuss the Nitinol properties after just one step of fabrication, e.g. forming, casting, additive manufacturing (AM), or machining. On the contrary, this work focuses on a process chain including AM followed by heat treatment and both flood and cryogenic machining. In particular, the depth of cut during the last machining step was varied (0.1, 0.25, and 0.4 mm), to investigate its effects on the AM and heat-treated Nitinol in terms of machined surface finish and transformation temperatures. It was found that when cutting with a depth of cut of 0.25 mm, the workpiece shows the worst roughness, regardless of the material microstructure and machining condition. However, for other depths of cut, there is a clear improvement in terms of surface finish. Machining increases the Nitinol transformation temperatures, but changing the depth of cut does not have a significant effect. Cryogenic machining induces a worse surface finish, but has less effect on the transformation temperatures than flood machining.