Preparation of Giant Pseudo-Single Crystals of Superelastic Alloys and the Mechanism of Grain Growth

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The grain growth of beta(bcc) phase in Cu-Al-Mn base shape memory alloys has been studied. The abnormal grain growth was realized when the Cu-Al-Mn alloys were first quenched from the beta single-phase region at high temperature round 1173K and then was slowly cooled at about 773K, and subsequent heating to the beta single-region. The pseudo-single crystals due to abnormal grain growth were obtained by thermally cycling where beta phase leads to a precipitation and subsequent dissolution of the alpha phase. This abnormal grain growth phenomenon results from the formation of subgrain structure introduced through phase transformation, where the subgrain-boundary energy might be one of the driving force. These findings provide a method of fabricating a single-crystal or large-grain structure important for superelastic properties.