Effect of nitrogen on transformation temperatures of arc-melted, Ti-Ni shape memory alloys)

This paper describes an investigation into the effect of nitrogen on the microstructures and phase transformation temperatures of near-equiatomic, Ti-Ni shape memory alloys arc-melted in Ar-N₂atmospheres. The nitrogen content of the arc-melted samples increases with an increasing melting time and rising nitrogen partial pressure in the atmosphere (arc current of 150 A, arc voltage of 12 V, sample weight of 12 g and melting time of 0–480 sec). The amount of second phase observed in the arc-melted samples increases with an increasing nitrogen content. The second phase is identified as TiN by electron probe microanalysis (EPMA) and X-ray diffraction analysis. Both the Ms and Af temperatures decrease with the increasing nitrogen content of the arc-melted samples. The Ms and Af temperatures are described by functions of the nickel and nitrogen contents.