In-Situ Study of Phase Transformation and Microstructural Evolution of Ni45Mn37In13Co5 Metamagnetic Shape Memory Alloy

This paper aims to study the phase transformation and microstructural evolution of Ni45Mn37In13Co5 metamagnetic shape memory alloy during heating and cooling in terms of differential thermal analysis, thermo-magnetic analysis, and temperature-variable optical Kerr microscopy. It has been found that two-stage phase transformation occurs for the alloy during heating. The first stage is magneto-structural transition from low-magnetic martensite to ferromagnetic austenite with a transformation entropy change of about 30.5 Jkg(-1)K(-1), and the other is pure magnetic transition from ferromagnetic austenite to paramagnetic austenite. In-situ observation of microstructural evolution at one given position during heating shows that the austenite transformation begins at 359 K (inferred as A(s)), reaches a peak value at about 6 K above the As and ends at 375 K. Meanwhile, the temperature when the lath-like martensite begins to disappear (or appear) differs at different region, suggesting that various degrees of superheat (or supercool) and nucleation energy barriers are needed for different martensitic variants. However, one common feature in transformation at these different regions is that the collective formation of a series of austenite (martensite) plays a dominant role.