Spangold

Spangold is a family of shape memory-effect alloys (SME) of gold, copper, and aluminum in either 18K or 23K. The name of the family is a play on the word "spangled".^[1]

Spangold is a beta-phase alloy with a nominal stoichiometry of Au₇Cu₅Al₄ and a nominal composition by mass of 76% gold, 18% copper, and 6% aluminum. The texture is caused by the induction of a martensitic-type phase transformation on a polished surface.^[2][3]

Spangold undergoes a martensitic-type phase transformation when properly treated.^{[citation needed]} This phase transformation is induced on a polished surface of the alloy.^{[citation needed]} Martensitic transformations are a common feature in shape memory alloys, and they involve a reversible change in crystal structure that allows the material to recover its original shape when subjected to specific temperature changes.^{[citation needed]}