Role of Si in Improving the Shape Recovery of FeMnSiCrNi Shape Memory Alloys

摘要

The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (y) up to 6 pct Si and, beyond that, becomes two-phase ? + ? ferrite. The Fe_5Ni_3Si_2 type intermetallic phase starts appearing in the micro-structure after 7 pct Si and makes these alloys brittle. Silicon addition does not affect the transformation temperature and mechanical properties of the y phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct Si show poor recovery due to the formation of ?-ferrite. The shape memory effect (SME) in these alloys is essentially due to the y to stress-induced s martensite transformation, and the extent of recovery is proportional to the amount of stress-induced e martensite.