Application of Cos α Method for Analysis of Residual Stress in Hydrogen-Permeable Multi-Phase Nb-TiNi Alloys

The assessment of residual stress in rolled and hydrogenated multiphase Nb-TiNi alloys is important because such materials consist of B2-TiNi and bcc-Nb phases having different mechanical properties. The present work demonstrates that residual stress in cold-rolled and heat treated Nb19Ti40Ni41 (mol%) alloys can be determined using the cos α method, and investigates factors affecting residual stress in hydrogenated and dehydrogenated Nb19Ti40Ni41 alloys. The stress in the sample which was cold rolled and annealed at 1373 K followed by furnace cooling is very low. However, compressive stress was observed in both the Nb and TiNi phases after hydrogenation and dehydrogenation cycling due to the different lattice expansions of the two phases. Variations in total stress and macrostress were found to correlate with the volume change of the Nb phase while variations in pseudo-macro stress were associated with changes in the mechanical properties of this phase.