Phase transition of Ni–Mn–Ga alloy powders prepared by vibration ball milling

Effect of heat treatment on martensitic transformation of Ni47Mn40Sn13 ferromagnetic shape memory alloy prepared by mechanical alloying

“…The disordered structure and low level of chemical ordering might be the reasons for the disappearance of MT for 15 and 20 h milled samples. A similar behavior was reported for the ball milled Ni-Mn-Ga alloy, prepared by arc-melting method [14]. By increasing temperature, susceptibility of the 15 and 20 h milled powders showed a decrease at about room temperature, which corresponded to the Curie transition of the austenite (see inset of Fig.…”

“…Grain size is another important parameter in structural transformation for shape memory alloys [13,14,20]. Tian et al studied the effect of grain size on phase transition in Ni-Mn-Ga alloy prepared by MA [14]. Results of this study showed that, by increasing the annealing temperature and consequently the size of grains, an austenite-martensite transformation appeared in the samples annealed at 1073K, while lower temperature annealed samples did not demonstrate any MT [14].…”

“…During annealing, grain size of the powders was increased and internal strain was decreased. The long range atomic order was modified by heat treatment and, as a result of this improvement in atomic ordering, MT appeared [14]. In the XRD pattern of the samples annealed at 823K (S823) and 1023K (S1023), minor additional peaks were observed, which belonged to the martensite phase and indicated the coexistence of martensite and austenite phases at room temperature.…”

“…The presence of structural phase transition could be related to smaller lattice parameter of these samples compared with the one obtained for S823 sample (see Table 1). Grain size is another important parameter in structural transformation for shape memory alloys [13,14,20]. Tian et al studied the effect of grain size on phase transition in Ni-Mn-Ga alloy prepared by MA [14].…”

“…Tian et al studied the effect of grain size on phase transition in Ni-Mn-Ga alloy prepared by MA [14]. Results of this study showed that, by increasing the annealing temperature and consequently the size of grains, an austenite-martensite transformation appeared in the samples annealed at 1073K, while lower temperature annealed samples did not demonstrate any MT [14]. Also, based on the calculations, the nucleation barrier for MT strongly depended on grain size and decreased by increasing the size of grains [13].…”