Austenite-Martensite Phase Transformation of Biomedical Ni_50.8Ti_49.2 Alloy by Ball Burnishing

Nitinol alloys have received considerable attentions in biomedical and aerospace applications. They can exhibit both austenite and martensite phases at room temperature. Austenite can transform to martensite by applied stress or temperature. Ball burnishing is a very promising technique to modify surface integrity via plastic deformation on the workpiece surface. Phase transformation of Nitinol by burnishing may occur at certain load, which results in the mechanical property change on the workpiece. A burnishing experiment has been conducted in this research at different burnishing loads. The burnishing tracks are characterized and microstructures in the subsurface are studied. A corresponding simulation is also performed to shed light on phase transformation mechanism of Nitinol in burnishing.