Machining Effect On The Surface Integrity And SE Of Additively Manufactured And Heat-Treated Nitinol

Nitinol belongs to the class of smart materials that have attracted the attention of researchers in recent decades due to their new promising industrial applications. Because of the austenite/martensite phase transformation, nitinol offers unique properties: superelasticity and shape memory effect. The former ability can be exploited for sensing, actuating, and damping applications. On the other hand, additive manufacturing of nitinol has started kicking off unimaginable applications exploiting the complexity-for-free characteristics offered by the 3D printing processes. Although stand-alone research on additive manufacturing of nitinol is available, the impact of different manufacturing steps, such as machining and heat treatment, on its superelasticity is severely lacking. This work used a powder bed fusion process using a laser beam to manufacture a Ni50.4Ti49.6 austenitic alloy, which was subsequently heat-treated at different aging temperatures. Subsequently, turning operations were carried out at varying cutting speeds under cryogenic cooling conditions. An in-depth characterization of the surface integrity and SE alterations induced by manufacturing was conducted before and after machining. The outcome of the work provides the best combination of heat treatment and machining parameters that allow for maximum surface integrity and SE.