Aging effect on a Ti47.25Ni48.75V4 shape memory alloy

Aging effect on a Ti47.25Ni48.75V4 shape memory alloy is investigated. Experimental results reveal that the 400 °C aged Ti47.25Ni48.75V4 alloy exhibits a B2 → R → B19′ two-stage martensitic transformation on cooling, but exhibits a B19′ → B2 one-stage transformation on heating. Two kinds of second phases, (Ti,V)2Ni and V9(Ti,Ni), are observed in the solution-treated Ti47.25Ni48.75V4 alloy. (Ti,V)2Ni exhibits an FCC order structure with a lattice parameter of 11.1 Å while V9(Ti,Ni) exhibits a BCC structure with a lattice parameter of 3.01 Å. There appear lots of fine spherical V9(Ti,Ni) and coherent Ti3Ni4 precipitates after 400 °C aging for the Ti47.25Ni48.75V4 alloy. These precipitates will strengthen the alloy's matrix and improve the shape recovery ability.