Vacuum Induction Melting of Low Inclusion Nitinol Ingots

ASTM Standard 2063-18 specifies allowable impurity element and inclusion size levels for medical grade Nitinol. For most medical device applications, this standard serves well as a common denominator. However, for high end devices its minimum requirements are no longer sufficient. In state-of-the-art implant grade devices cyclic fatigue and corrosion properties are of utmost importance. Expensive raw materials and the modification and combination of melting processes have been applied to improve these properties. However the availability of materials and cost considerations have to be taken into consideration. In this work we demonstrate that management and control of the single step vacuum induction melting process yields promising results. Impurities are kept on a low level. Inclusion sizes and distributions are compared with previous results and found to be comparable if not improved. The stability and repeatability of the process makes it suitable for challenging Nitinol implants with improved fatigue and corrosion resistance.