The fracture property improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile c particles was explained by direct observation of microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable amount of c particles in b grains after the homogenization treatment at 1073 K to 1373 K (800°C to 1100°C). With increasing homogenization temperature, c particles were coarsened and distributed homogeneously along b grain boundaries as well as inside b grains. According to the in-situ microfracture observation, c particles effectively acted as blocking sites of crack propagation and provided the stable crack growth, which could be confirmed by the R-curve analysis. The increase in fracture resistance with increasing crack length improved overall fracture properties of the Ni-Mn-Ga-Fe alloys. This improvement could be explained by mechanisms of blocking of crack propagation and crack blunting and bridging.
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