Behaviour of the elastic and anelastic properties of Au-47·5 at. % Cd in the vicinity of the cubic-orthorhombic phase transformation

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Abstract
The behaviour of the elastic properties and ultrasonic attenuation of Au-47·5 at. % Cd during the thermoelastic martensitic cubic-orthorhombic phase transition has been determined during cooling and heating transformation cycles. An ultrasonic pulse-technique was used at a frequency of 10 Mhz. Drastic changes in the Young modulus (E), shear modulus (G) and Poisson's ratio (σ), and ultrasonic attenuation (α), were observed in the phase transition region. These changes were of the order of 3·0%, 3·8%, 1·7% and 60%, respectively. In contrast, the adiabatic compressibility exhibits very small discontinuities, of the order of 0·19%, which are due only to the change in the unit cell volume during the cubic-orthornombic transformation. The behaviour of the adiabatic compressibility in Au-47·5 at. % Cd in the proximity of the phase transformation is not typical of a first-order phase change, but rather of a higher-order one. The possibility of an electron transfer mechanism is discussed. The behaviour of the thermoelastic parameters in this alloy and the relative elastic ‘softness’ of the orthorhombie phase, compared with the cubic, appears to be in agreement with such a model.