Effect of cyclic deformation on superelasticity of martensitic transformation of nanocrystalline TiNiFe memory alloy
Ti50Ni48Fe2(atomic fraction)memory alloy wire with an average grain size of 15 nm was obtained by drawing deformation and low-temperature annealing.The effect of tensile strain of 6％and 20 cycles of cyclic deformation on stress induced martensitic transformation superelasticity of nanocrystalline TiNiFe memory alloy was studied using a tensile testing machine.The results show that when the number of cyclic deformations increases from 1 to 20,the superelastic stress of martensitic transformation in the nanocrystalline TiNiFe alloy decreases from 871 MPa to 723 MPa,and the residual strain increases from 0.53％to 0.73％.The nanocrystalline TiNiFe alloy in this article exhibits high superelastic stress and small residual strain after cyclic deformation,which is significantly better than the reported TiNi memory alloy.This is mainly due to the fine grain strengthening generated by high-density grain boundaries and the solid solution strengthening generated by Fe element in nanocrystalline TiNiFe alloy,which suppresses the generation of dislocations in the alloy and improves the superelastic stability of martensitic transformation.
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