Constrained Recovery Characteristics Research Of Fe-Mn-Si Shape Memory Alloy

In this paper,the recovery stress and the reverse martensitic transformation characteristics under constrained condition by cement composite matrix in the Fe-17Mn-5Si-10Cr -5Ni shape memory alloy have been studied by means of expansion test, recovery stress measure,X-Ray Diffraction(XRD) analysis and metallographic observation.By the expansion test it is found that in the Fe-17Mn-5Si-10Cr-5Ni shape memory alloy, the A_s is almost immovability,the A_f is elevated,and the reverse martensitic transformation temperature space(A_s～A_f) was widened with the increment of pre-strains.By the recovery stress measure it is found that in Fe-17Mn-5Si-10Cr-5Ni shape memory alloy,the recovery stress of the alloy always increases with the increment of the recovery strain,in the same pre-strains;the pre-strains of the alloy increases with the increment of the recovery stress,in the same recovery strain.The relationship between the recovery stress and the recovery strain which measured by the one-way tensile of Fe-17Mn-5Si-10Cr-5Ni shape memory alloy specimens can be approximately expressed with the quadratic parabolic function.The maximum recovery stress of Fe-17Mn-5Si-10Cr-5Ni shape memory alloy was 187MPa when the pre-strained was about 8%on the room temperature,which was later than the maximum recoverable strain about 6%,because improvement of the strength by deformation intensification can increase the recovery stress.From XRD analysis,it is found that the Af ofε→γreverse martensitic transformation of the Fe-17Mn-5Si-10Cr-5Ni shape memory alloy in unrestricted station was about 250℃,the Af ofε→γreverse martensitic transformation of the alloy under constrained condition by cement composite matrix is higher,the temperature space between the A_s and A_f was widened. the reverse martensitic transformation still proceeded when the temperature was 500℃. Compare unrestricted the time of constrainedε→γreverse martensitic transformation in Fe-17Mn-5Si-10Cr-5Ni shape memory alloy lasted longer under the same conditions.It is because that the recovery stress which produced by the reverse martensitic transformation and the constrained effect in cement composite matrix,leading to the stabilization ofεmartensitic and hampering the interface changing from HCP to FCC,when the Fe-Mn-Si shape memory alloy was constrained by the cement composite matrix.