The tensile behavior of a cold-rolled and reverse-transformed equiatomic TiNi alloy

Abstract

The tensile test shows that the martensite accomodation/reorientation process in the ascold-rolled equiatomic TiNi alloy is depressed due to the hindrance of deformed martensite structures and defects. If the cold-rolled equiatomic TiNi alloy is subjected to a reversed martensitic transformation (RMT) at temperature < 300°C, the strengthening effect induced by cold-rolling can significantly improve the alloy's characteristic shape memory effect (SME) and pseudoelasticity (PE) by raising the critical shear stress for slip. The σ y M can improve from 380 MPa of solution treated specimen to 1000 MPa of 31% cold-rolled RMT specimen. Meanwhile, for its PE characteristic, a cold-rolling RMT process can also increase significantly the stored mechanical energy and the energy storage efficiency. Experimental results show that, even in up to 20% thickness-reduced RMT TiNi alloy, the specimen still has 20% elongation at fracture. If the cold-rolled specimens are subjected to an annealing at temperature ⩾400°C, the martensite accomodation/reorientation process can recover gradually due to the nullification of deformed martensite structures and defects. Finally the recrystallization occurs at annealing temperature ⩾600°C.