Martensite Transformation and Shape Recovery in Pre-Deformed Fe-15Mn-5Si-9Cr-5Ni-(0.5–1.5) NbC Alloys

The shape memory effect (SME) of Fe-15Mn-5Si-9Cr-5Ni-(0.5-1.5)NbC alloys pre-extended at room temperature was investigated. It shows that the pre-deformation result is similar for the SME of three composition alloys, i.e., the SME increased with increasing pre-extension and then decreased when they were over 12-14% pre-extended at room temperature. X-ray diffraction showed that there are two kinds of martensite transformations gamma (fcc) -> (hcp) and gamma -> epsilon -> alpha' (bcc) occurring in the Fe-15Mn-5Si-9Cr-5Ni-(0.5-1.5)NbC alloys when the alloys were deformed at room temperature. It was found by magnetic saturation measurements that when the alloy was 8% extended at room temperature, alpha' phase appeared and obviously increased with increasing deformation. Furthermore, TEM observations showed that alpha' phase exists in the cross section of the epsilon martensite and reverses in the different path of gamma -> epsilon. The effect of pre-deformation and aging on SME was correspondingly explained in view of martensite transformations and its nucleation. i.e., stacking faults and associated contribution of NbC precipitation, for gamma -> epsilon transformation.