Influence of annealing temperature on microstructure and shape memory effect in austenite-martensite duplex Ni47Ti44Nb9 rolled sheets

Abstract The evolution of phase composition and microstructure such as grain size, dislocation and crystallographic texture in austenite-martensite duplex Ni47Ti44Nb9 rolled sheets during the annealing was systematically investigated. The influence of annealing temperature on shape memory effect was also examined. The strong {001} fiber texture tested in as-rolled sheets is identified as a wrong result, which is mistakenly introduced by X-ray Diffractometer, due to the interference of martensite. Different annealing temperatures result in variation of phase composition and microstructure. For instance, in the case of 600 °C, the phase fraction of austenite increases and the dislocations develop to form tiny sub-grains due to reverse martensitic phase transformation and recovery. The texture of NiTi austenite mainly concentrates on {111} 〈110〉. In the case of 950 °C,the sub-grains develop to trigger recrystallization, resulting in larger grains and decreasing of dislocations and {111}〈110〉 texture intensity. In addition, the sheets annealed at 600 °C possess higher recoverability than those of 950 °C, which can be attributed to the combined role of grain size, dislocation and crystallographic texture.