The effect of thermomechanical training on the shape memory effect and mechanical properties of an Fe-Mn-Si ternary shape memory alloy

摘要

The shape memory effect of the Fe-Mn-Sialloy investigated was significantly improved bythermomechanical training, with the efficiency oftraining being a function of the number oftraining cycles, the training strain, and therecovery annealing temperature. Generally, theshape memory effect increased with increasingtraining clcle number, and reached a saturationvalue after 4 to 6 training cycles. An excessivetraining strain induces slip deformation whichdoes not contribute to the recovery strain. Therecovery annealing temperature was found to becrucial to the thermomechanical training, and thecurrent study indicated that annealing at about873K was most effective for improving the shapememory effect. Thermomechanical training makesstress induced martensitic transformation easier,because the training process creates dislocationstructures which promote the nucleation ofmartensite. Training resulted in a finermartensite plate size, reducing the localtransformation shear and volume strains which needto be accommodated in the austenite.Thermomechanical training also influenced ε→γreverse transformation, with the Af temperaturedecreasing with number of training cycles. Incontrast, the Ms and As temperatures remainednearly constant. Therefore, the improvement ofshape memory effect on training is due to thefacilitation of both stress induced martensitictransformation and its reverse transformation.