Investigation of the order -disorder phase transition series in AuCu by in-situ temperature XRD and mechanical spectroscopy

In-situ temperature XRD and mechanical spectroscopy were applied to study phase transitions in AuCu alloy from the disordered FCC state (A1). The phase transition temperature intervals were investigated upon heating and cooling using a rate of 1 K/min in order to be thoroughly determined. The following sequences of phase transitions were recorded upon continuous heating: A1->AuCuI ->AuCuII->A1 and on subsequent cooling: A1 ->A1+AuCuI+AuCuII ->AuCuI+AuCuII ->AuCuI. This transition sequences determine also temperature dependency of elastic and anelastic properties. Mechanical spectroscopy using a forced torsion pendulum shows a peak due to antiphase boundaries motion characterizing the orthorhombic phase AuCuII and a transient peak with the that appears in the tetragonal phase AuCuI together with the classical Zener peak in the A1 phase.