Structural-Phase State, Mechanical and Inelastic Properties of Ti49.8Ni50.2 Alloy after Severe Plastic Deformation by abc Pressing at 573 K

Abstract

The structural-phase state, mechanical and inelastic properties of Ti_49.8Ni_50.2 alloy after severe plastic deformation by abc pressing at 573 K were investigated. It was found that abc pressing of the Ti_49.8Ni_50.2 alloy specimens at a relatively low temperature (573 K) to high true strain (e = 7.43) did not affect the start temperature of B2→R martensite transformation (MT). At the same time, the start and finish temperatures of direct MT to the B19' phase and reverse MT decreased by only 14 ± 2 degrees. After abc pressing at 573 K to е = 7.43, the martensitic shear stress τ_m sharply decreased (from 230 MPa to 100 MPa), and the pseudo-yield plateau significantly shortened (from 7.5 to 3.5%). In addition, the stress of transition from the strain hardening stage to the active plastic deformation stage sharply increased (from 835 to 1300 MPa). It was found that the dependences of the shape memory effect γ_SME, superelasticity γ_SE, and plastic strain component γ_pl on the total strain γ_t both in the initial state and after abc pressing had a similar pattern and were close in magnitude. It was shown that abc pressing to e = 7.43 induced the total inelastic strain γ_TIS = γ_SE + γ_SME of about 8% in the specimens, which recovered after unloading due to the superelasticity and shape memory effects.