| The low temperature relaxation characteristics in two different FeMnSi based shape memory alloys (SMA) (1#: stainless, 2#: high strength, low relaxation) has been systematically studied in this article by thermal expansion, tensile and bending tests, strain circle, XRD, SEM and TEM, after the measurement of shape memory effect (SME) and recovery stress of them, and the smart characteristics of the SMA has also been revealed in brief.It was shown that with the increase of pre-strain, As point (measured by thermal inflation) keep to be remained, Af point increased at first and then reduced; The specimen recovered slowly in both the beginning and the end of recovery course, middle was contrary.From the analysis of the change in structure during transformation, E martensite amount in two alloys increased with the increase of pre-strain (<6%), and they had well orientation property; but when the pre-strain was above 6%, e martensite in 1# alloy began to reduce while those in 2# alloy increased slowly, and ?martensite intersected each other; a' martensite in 1# alloy began to appear at 5% pre-strain, no a' martensite appeared all along in 2# alloy, and the amount of E martensite in 2# alloy was always larger than those in 1# alloy.Unidirectional tensile test was mainly used in this article because of its uniform deformation and accurate result; The recovery rate reduced all along with the increase of pre-strain, and the recovery strain increased first and then reduced too, maximum recovery strain appeared at about 5% strain, about 1.98% and 3% respectively; The SME of 2# alloy was better than that of 1# alloy.From the result of recovery stress, it always increased firstly and then dropped with the increase of the pre-strain, the maximum of the recovery stress appeared at the 6%~7.5% pre-strain, about 166Mpa and 286Mpa respectively, The recovery stress of 2# alloy was better than that of 1# alloy.It was shown that the low temperature relaxation of the two alloys both increased with the increase of the pre-strain. From the result of XRD and TEM, the transformation driving forceincreased with the drop of temperature, and the occurrence of stress induced e and a1 transformation induced the low temperature relaxation. But the relaxation rate of the 2# alloy was much lower than that of l# alloy, mainly because several carbon and carbide elements such as Nb, Zr, Ti, V et al were added in 2# alloy, which could strengthen the parent phase as the composition of solution-strengthen and scatter-strengthen. The carbide separated out during the recovery heating could hinder the stress induced martensitic transformation during the recovery heating.Based on the result of+1.5% circle strain for 20 times, no working hardening occurred in the shape memory alloys; The fatigue life of the SMA was 1300, which improved about a magnitude than that of rail steel, only 110 times. It was founded that through the reversible movement of the interface between the ?-M and the parent phase Y, i.e. stress induced V o e transformation of the shape memory alloys produced strain to accommodate the change of stress, which appeared to be one of the typical smart characteristics- self-accommodation,...
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