TEM study of pre-strain's effect on shape recovery character in an Fe-Mn-Si-Cr-Ni shape memory alloy

摘要

Relationship between amount of recoverable strain and pre-strain in Fe-25%Mn-4.5%Si-1%Cr-2%Ni shape memory alloy (SMA) was measured in tensile tests. The results show that recoverable strain increases with increasing pre-strain lower than 5%, and decreases rapidly when the pre-strain go beyond 5%. By X-ray diffraction, the effect of pre-strain on volume fraction of stress induced ε martensite (εM) was determined and it was found that amount of εM first keeps increasing with pre-strain and then reaches saturation when pre-strain is over 8%. Transmission electron microscope (TEM) observation shows that morphology of stress induced εM for different pre-strain differs greatly and thus has different influence on shape memory effect (SME) of the alloy. Three types of morphology of εM were observed for different pre-strain, which are thin εM plates, wide εM bands of multilayer and intersecting εM variants respectively.