Abstract
The Al–Au–Cu system contains a ternary β electron compound with a nominal stoichiometry of Au 7Cu 5Al 4. At elevated temperatures this compound has a predominantly B2 structure, with some additional next-nearest neighbour ordering of the L2 1 type. The high-temperature phase transforms displacively and reversibly to martensite, with nominal M s and A s temperatures of 23 and 79°C, respectively. It is shown here that the martensite phase is body-centred tetragonal with c/ a<1. The orthogonal lattice is, however, evidently affected by a small degree of additional modulation. This martensite is fundamentally different from the classic 9R and 18R-type martensite of copper-base β phase alloys, and also from the trigonal martensites formed in AuCd and TiNi, and appears rather to be of the same type as the tetragonal martensites of Ni 2MnGa and La 2AgIn.
Published Version
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