Yield stress in titanium nickelide-based alloys with thermoelastic martensitic transformations

Abstract

It is shown that in alloys with thermoelastic martensitic transformations, shape memory and superelasticity effects, the real yield stress (τ0.3) can be determined only by a joint analysis of “stress-total strain” and “plastic deformation-total strain” dependences. We suggest to determine of the dependence of the “plastic deformation – total deformation” from isothermal cycles of “loading at successively increasing values of the applied external stress – unloading” and the subsequent heating of unloaded specimens up to finish of the return of inelastic martensitic deformation. The residual deformation equals to the plastic deformation in this case. Using Ti49.2Ni50.8 (at%) binary alloy specimens whose structure was changed from coarse-grained to micro- and submicrocrystalline by means of warm rolling, the yield point τ0.3 in torsion of specimens was demonstrated to be localized on “τ-γ” dependence at the end of pseudo- yield plateau or at the beginning of the subsequent linear section of deformation development under loading. The development of plastic deformation at τ > τ0.3 was also studied.