EFFECT OF Si ADDITION ON THE MICROSTRUCTURE AND SHAPE RECOVERY OF FeMnSiCrNi ALLOYS

摘要

The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The microstructure of these alloys remains single-phase austenite (gamma) up to 6% Si addition and beyond that it becomes two-phase gamma + delta-ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing into the microstructure after 7% Si and makes these alloys brittle. The extent of recovery increases monotonically till 6% Si and is proportional to the amount of stress induced epsilon martensite. Alloys containing >6% and <4% Si show poor recovery due to formation of delta- ferrite and stress induced alpha martensite respectively. Si addition decreases the stacking fault energy (SFE) of the gamma phase and resulted in easier nucleation of stress induced epsilon martensite. The amount of athermal e martensite decreases with increase in Si.