Stress Induced R→B2 Transformation and Pseudoelasticity Associated with Twinning in a Ti–Ni Alloy Including Aligned Particles of Ti₃Ni₄

Abstract

A Ti-51 at%Ni alloy including aligned particles of Ti₃Ni₄ precipitate formed by aging under an applied stress exhibits an anomalous transformation, i.e., stress induced R(martensite)→B2(parent) transformation. Confirmation of this transformation was made by tensile tests combined with simultaneous resistance measurements. This alloy also exhibits pseudoelasticity associated with twinning when tensile test is made at a temperature sufficiently below its transformation temperature, i.e., in the R-phase state. The stress induced R→B2 transformation and the pseudoelasticity in the R-phase state are due to the internal stress field formed by the aligned particles of Ti₃Ni₄.