| In this study, training effects in Ni-Al-Fe-Mn shape memory alloys composed with β` and γ phase have been investigated. In particular, effects of the initial bending strain, volume fraction of γ phase and training cycles on shape recovery ability of the alloys were investigated. And the change of transformation temperature with training cycles were also investigated. The results of the training experiments showed that shape recovery ability increased rapidly in the early stage of training. The shape recovery ability of the alloy with low bending strain was poorer than that of the alloy with high bending strain in the first cycle of training, but it was reversed after the second cycle of training. A poor shape recovery ability in the first cycles of training was considered to be caused by the reduction of shape recovery energy of β` phase due to shape recovery of γ phase deformed plastically. The drastic increase of shape recovery ability in the second cycle of training was attributed to the increase of the recoverable detwinning strain of β` phase attained by the reduction of the increase rate in the dislocation density, owing to the strain hardening of γ phase occurred during the first cycle of training. The first-stage shape recovery decreased with increasing number of cycles of training after the second cycle of training, in contrast the second-stage shape recovery increased from the beginning but there was no rapid increase. This seemed to be due to the increase of the number of β` martensite variants transformed to β phase at higher temperature due to introduction of dislocation with training increase. |
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