2006 Volume 47 Issue 5 Pages 1328-1331
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 γ (fcc) → ε (hcp) and γ→ε→α′ (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, α′ phase appeared and obviously increased with increasing deformation. Furthermore, TEM observations showed that α′ phase exists in the cross section of the ε martensite and reverses in the different path of γ→ε. 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 γ→ε transformation.
