Rietveld Analyses on Hydrogenated TiNi Shape Memory Alloy and Multiple-Stage Transformation

Abstract

Hydrogenated TiNi alloy were investigated by X-ray diffraction and the Rietveld refinements from the view of transformation behavior. Small expansion of lattice constants indicated that hydrogen atoms located at interstitial sites in parent and martensite phases were small amount. The refinements also indicated that the amount of hydride TiNi(H) was approximately 0.1%, which was small. These refinements and optical microscopic observations indicated most of hydrogen atoms were located around grain boundaries or martensite variant boundaries. DSC measurements showed that hydrogenated TiNi displayed multiple-stage transformation behavior and thus hydrogen atoms around grain boundaries may cause mutiple-stage behavior of the transformation.