Structural transition of Ni-Mn-Ga ferromagnetic shape memory alloy particles prepared by ball milling

摘要

The size,crystal structure and phase transformation of Ni49.8Mn28.5Ga21.7 alloy particles prepared by planetary ball milling (PBM) and vibration ball milling (VBM) were investigated by SEM,XRD and DSC.The results show that the particles milled by PBM for 4 h exhibit irregular polyhedron,with the size distribution between 5 μm and 40 μm.These particles present disordered fct structure with no phase transformation behaviour.When annealed at 600 °C for 1 h,the crystal structure of the particles evolves from disordered fct to Heusler completely.The particles milled by VBM for 4 h exhibit flaky shape,with the size distribution from 3 μm to 30 μm.The particles present disordered fcc structure with no phase transformation behaviour.However the crystal structure of these particles doesn’t transform from disordered fcc to Heusler completely after annealing at 600 °C for 1 h,for the severe lattice distortion induced in the VBM process is not eliminated entirely.