| The characteristics of constraint stress inducedγ→εmartensitic transformation and reverse transformation in Fe-17Mn-10Cr-5Si-4Ni and Fe-17Mn-2Cr-5Si-2Ni-1V shape memory alloy were studied by the method of analysis observation, constant strain tensile tests and cement constraint tests. The anti-loosing mechanisms and anti-loosing friction torque for Fe-Mn-Si shape memory alloys have been represented and analyzed by means of static anti-loosing tests and repeat performance tests.From tensile tests analysis, it is found that the constant strain suspending loading can make the stress inducedγ→εmartensitic transformation proceed in the tensile deformation of Fe-Mn-Si memory alloys. The amount of stress induced s martensitic and the shape recovery ratio rapidly increases when the suspending loading time is in 0-10 minutes; when the suspending loading time is above 10 minutes, the amount of stress inducedεmartensitic increases slow and gradually stabilized, then the shape recovery ratio decreases. This is owing to the stabilization of the stress induced s martensitic.From the stress relaxation test, it is found that the stress inducedεmartensitic transformation with constant strain constraint at room temperature is the basic reason why the stress relaxation ratio of Fe-Mn-Si memory alloy is much higher than the ordinary materials. When the suspending loading time is in 0-5 minutes, the stress relaxation ratio of Fe-Mn-Si memory alloy rose sharply, then 5 minutes later, relaxation ratio increase slow, that is to say theγ→εmartensitic transformation mainly finishes before 5minutes. The stress relaxation ratio of Fe-17Mn-5Si-2Cr-2Ni-1V alloy is lower than that of Fe-17Mn-5Si-10Cr-5Ni alloy under the same deformation. The reason is that the stress relaxation ratio is representative ofεmartensitic increment, and the s martensitic increment of Fe-17Mn-5Si-2Cr-2Ni-1V alloy is smaller, whose reason is the alloy with C,V and other elements can strengthen parent phase, improved the real yield strength of the material, and make the stress inducedγ→εmartensitic transformation need more driving force, meanwhile, the increase of C,V elements will hinderεmartensitic fellowship intersect and grow up.From XRD analysis, it is found that the finished temperature (Af) of the constraint stress inducedεreverse martensitic transformation is significantly higher than that of the unconstraint one in Fe-17Mn-5Si-10Cr-5Ni alloy, while the start temperature (As) is remained. The results show that constraint s reverse transformation of Fe-Mn-Si memory alloy needs higher transformation driving force. As same as the unconstraint alloy, the temperature range (Af-As) of constraint reverse transformation can widen with the increase of the deformation in Fe-Mn-Si memory alloy. The reason that hard reverse transformation and higher finished temperature (Af) are coordination transformation of reverse transformation in Fe-Mn-Si memory alloy is restrained by the constraint cement matrix.From static anti-loosing test, it is found that the anti-loosing effect of Fe-Mn-Si memory alloy bolt is very obvious. Along with the increase of the temperature recovery, the anti-loosing friction torque of Fe-Mn-Si memory alloy bolt is more and more big, the axial frictional torque and the radial friction torque increase which based on the shape memory effect. The anti-loosing friction torque is 2.97 times of that of the ordinary bolt at 500℃. In the same recovery temperature, the anti-loosing bolt of Fe-Mn-Si memory alloy has changed in the certain deformation range, the anti-loosing friction torque is greater with the increase of the strain, and the axial friction torque and the radial friction torque which based on the shape memory effect make more important contributions to the anti-loosing friction torque.From repeat performance test, it is found that the anti-loosing bolt of Fe-Mn-Si memory alloy has both well anti-loosing performance and repeat performance by controlling the recovery temperature. From dynamic anti-loosing performance test, it is found that the anti-loosing life of Fe-Mn-Si memory alloy bolt is much higher than that of the ordinary bolts under the horizontal loading (vibration, impact and loading).
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