An entropy driven phase transformation in a Au_43.3Cu_31.8Al_24.9 shape-memory alloy

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• 作者：Gianluca  ; Fiore ; Livio  ; Battezzati  ; ;   ; ^{livio.battezzati@unito.it}
• 关键词：A. Intermetallics ; miscellaneous ; B. Phase transformations ; F. Calorimetry
• 刊名：Intermetallics
• 出版年：2011
• 出版时间：December 2011
• 年：2011
• 卷：19
• 期：12
• 页码：1978-1982
• 全文大小：456 K

文摘

The 18-karat Au_43.3Cu_31.8Al_24.9 alloy displays shape memory effect. The parent phase has L2₁ structure which transforms to B2 at high temperature. The B2 phase is retained in metastable state by quenching from the B2 field. It then transforms irreversibly with an endothermic peak in Differential Scanning Calorimetry (DSC) to the stable L2₁ structure in the temperature range between 407 K and 435 K as a function of heating rate. The transformation is, therefore, entropy-driven. Details are reported on the enthalpy of transformation and its temperature dependence. The transformation is discussed with reference to the entropy content of phases as a function of temperature which counteracts austenite stability. The role of vacancy motion is outlined. A comparison is made with analogous transitions occurring in molecular substances and metallic materials.