Phase transformation behavior and superelasticity of nanocrystalline Ti50Ni50_xCox shape memory alloys

The phase transformation behavior and superelasticity of nanocrystalline Ti50Ni50_xCox (x = 3, 5, 9) alloy wires were investigated. The results showed that the starting temperature of the B2 -> R phase transformation gradually decreased with the Co content, while the superelastic temperature range of the alloy wires shifted toward cryogenic temperatures as the Co content increased. The superelastic temperature range appeared from 100 to -45 degrees C for the Ti50Ni47Co3 alloy wire and from 80 to -90 degrees C for the Ti50Ni45Co5 alloy wire. The Ti50Ni41Co9 alloy wire exhibited excellent superelasticity over a temperature range from _ 40 to _ 196 degrees C and ultra-high superelastic stresses from 1200 to 960 MPa.