| The shape recovery behavior in Ni-A1 base shape memory alloy whose ductility is improved with Fe and Mn alloying has been investigated by using DSC, XRD and TEM. On heating, the deformed alloys were experienced a double-stage recovery process before they returned to the original shape : The first-stage recovery occurred at lower temperature and the second-stage recovery take place at higher temperature. Increase of bending or tensile strain affected total shape recovery such that it leaded to an increase of the second-stage shape recovery. The shape re-covery at a higher temperature, i.e., second-stage shape recovery was attributed to the hinderance of β` →β transformation by the dislocations in β` martensite introduced during deformation. Possibly, the elastics stress field associated with dislocations would hinder the motion of β`/β boundary. When the alloys were bended at the same strain the second shape recovery increased with annealing at higher temperature because of the increase of volume fraction of the β` martensite in the alloys consisted of β` martensite and β phase. |
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