Structure and properties of TiNi shape memory alloy after low-temperature ECAP in shells

Abstract

The effect of low-temperature equal-channel angular pressing (ECAP) in shells on the structure formation and mechanical and functional properties of a near-equiatomic titanium nickelide (TiNi) shape memory alloy is studied. ECAP with channel intersection angles of 120° and 110° is carried out at temperatures in the 20 °С to 330 °С range after 1 pass. The optimum material for shells is pure iron, which is not destroyed after ECAP down to room temperature. The optimum deformation temperature of ECAP in a shell is determined to be 200 °С. Deformation at low temperatures leads to the premature destruction of TiNi samples. ECAP of the TiNi core in a shell at 200 °С after 1 pass leads to the formation of an elongated, banded martensite structure with a bandwidth of approximately 100 nm. The best combination of mechanical and functional properties is found after ECAP of a TiNi sample with a diameter of 12 mm in core-shell mode at 200 °С followed by the addition of post-deformation annealing at 400 °С for 1 h.