The effect of thermo-mechanical treatment on the microstructure and properties of NiTiNb shape memory alloys

Because of the wide transformation hysteresis upon proper pre-deformation in martensite state, Ni₄₇Ti₄₄Nb₉ shape memory alloy (SMA) has applied as coupling or sealing components. Actually, in above application situations, the NiTiNb SMA is subjected to a constrained state in the service. In the present work, a thermo-mechanical treatment was applied in attempt to improve the mechanical properties and to enhance the recovery force of NiTiNb SMA under constrained state. A systematical study has made of the microstructure evolution, mechanical properties and recovery force of the NiTiNb SMA upon cooled deformation followed by annealing treatment at different temperature (400 ~ 900 °C). In particular, the dependence of recover force on the raising temperature and the transformation temperature dependence of the pre-deformation were investigated. It was indicated that the thermo-mechanical treatment can significantly improve the mechanical properties and the recovery force of NiTiNb SMA after pre-deformation in martensite state. The relationship between the pre-deformation and the reversed martensitic transformation temperature was reported. In this context, the corresponding mechanisms for the enhancement of the recovery forces and for the transformation temperature change were discussed.
Keywords: NiTiNb, shape memory alloys, thermo-mechanical treatment, mechanical properties
Corresponding author, Ermin Wang, Associated Prof., Email:genlin.yang@biam.ac.cn