Effect of Carbon Addition on Recovery Behavior of Trained Fe-Mn-Si Based Shape Memory Alloys

We investigate microstructures and recovery behavior of trained Fe-14Mn-5Si-8Cr-4Ni and Fe-14Mn-5Si-8Cr-4Ni-0.12C alloys under different deformation strains by color optical micrographs, XRD, and SQUID. The training results in the formation of alpha' martensite in Fe-14Mn-5Si-8Cr-4Ni alloy, while introduces Cr23C6 particles besides the alpha' martensite in Fe-14Mn-5Si-8Cr-4Ni-0.12C alloy. The stress-induced emartensite bands are thinner in trained Fe-14Mn-5Si-8Cr-4Ni-0.12C alloy than in trained Fe-14Mn-5Si-8Cr-4Ni alloy. When the deformation strain is below 8%, the recovery strain of trained Fe-14Mn-5Si-8Cr-4Ni-0.12C alloy is slightly lower than that of trained Fe-14Mn-5Si-8Cr-4Ni alloy. This result is attributed to the fact that the M-s temperature of Fe-14Mn-5Si-8Cr-4Ni-0.12C alloy is much below the deformation temperature than that of Fe-14Mn-5Si-8Cr-4Ni alloy. When the deformation strain is above 8%, the recovery strain of trained Fe-14Mn-5Si-8Cr-4Ni-0.12C alloy is higher than that of trained Fe-14Mn-5Si-8Cr-4Ni alloy. The reason for this result is that in trained Fe-14Mn-5Si-8Cr-4Ni-0.12C alloy, both alpha' martensite and Cr23C6 particles prevent stress-induced epsilon martensite bands from colliding each other at large deformation strain, and the width of stress-induced epsilon martensite bands is smaller as compared with trained Fe-14Mn-5Si-8Cr-4Ni alloy. It is concluded that carbon addition can improve the recovery strain of trained Fe-Mn-Si based shape memory alloys at large deformation strain.