Effect of High Temperature and High Stress-Assisted Austenite Aging on Martensitic Transformations in High-Strength Ti – 51.8 ат.% Ni Single Crystals

Abstract

High-strength materials containing dispersed Ti3Ni4 particles (d ~ 800 nm) and exhibiting superelasticity (SE) in a wide temperature range from 200 to 450 K were designed by aging at 823 K, 1 h of nickel-rich [001]-oriented Ti–51.8 at.% Ni single crystals. The influence of the stress-assisted austenite aging in different regimes (temperature, applied stress, and time) on the stability of the shape memory effect (SME) and SE is studied. It is shown that the single crystals are stable to stress-assisted austenite aging in the entire SE temperature range at T < 523 K under a stress of 0.8σcr. An increase in the temperature to 523–573 K for stress-assisted (1400 MPa) and stress-free aging time 1–10 h leads to precipitation of nanosized Ti3Ni4 particles and changes the SE and SME evolution. The largest effect of increase in the Ms temperature by 22–27 K during SME, decrease in the critical stress σcr during SE (by 10–34%), and increase in the deformation hardening coefficient θ = dσ/de and the coefficient of critical stress growth with temperature α = dσ/dT was observed after aging at 573 K for 10 h (0 and 1400 MPa).