Effect of Nitrogen on Transformation Temperatures of Arc-Melted Ti-Ni Shape Memory Alloys

Abstract

Effects of nitrogen on microstructure and phase transformation temperatures were investigated for near-equiatomic Ti-Ni shape memory alloys arc-melted in Ar-N₂ atmospheres. The nitrogen content in the arc-melted specimens increased with increasing melting time and rising nitrogen partial pressure in atmosphere (arc current 150A, arc voltage 12V, specimen weight 12 g and melting time 0-480 s). With increasing nitrogen content, the amount of second phase observed in arc-melted specimen increased. The second phase was identified as TiN by an electron probe microanalysis and an X-ray diffraction analysis. Both Ms and Af temperatures decreased with increasing nitrogen content of arc-melted specimen. The temperatures of Ms and Af were described by functions of nickel and nitrogen contents.