Role of Si in improving the shape recovery of FeMnSiCrNi shape memory alloys

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 (γ) up to 6% Si addition and beyond that it becomes two-phase γ+δ-ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing into the microstructure after 7% Si and makes these alloys brittle. The amount of shape recovery increases monotonically till 6% Si addition and is proportional to the amount of stress induced ε martensite. Alloys containing >6% and <4% Si show poor recovery due to formation of δ-ferrite and stress induced α’ martensite respectively. Si addition decreases the stacking fault energy (SFE) of the γ phase and resulted in easier nucleation of stress induced ε martensite. The amount of athermal ε martensite decreases with increase in Si.