Formation of long-period ordered CuAuII phase in the non-stochiometric Cu-56 at% Au alloy

A study of the formation of structure and properties during the disorder $\to$ order phase transformation with the formation of a long-period ordered CuAuII phase in a non-stoichiometric Cu-56 at.% Au alloy has been carried out. X-ray diffraction analysis was used in the course of this work. Annealing of deformed and quenched samples of the alloy under study was carried out in the temperature range of 275–375$^\circ$C (every 25$^\circ$C), the annealing duration ranged from 1 hour to 2 months. It has been established that a single-phase state ordered by the CuAuII type is formed in the Cu-56Au alloy at temperatures of 325 and 350$^\circ$C. The ordered CuAuI phase is formed at a temperature of 275$^\circ$C in the alloy, which somewhat diverges from the generally accepted phase diagram. A two-phase (CuAuI + CuAuII) state is formed at a temperature of 300$^\circ$C. Annealing at a temperature of 375$^\circ$C leads to the formation of a two-phase (disorder + order) structure (A1 + CuAuII). Using mathematical processing of X-ray peaks, an assessment of the phase relationship in two-phase states has been carried out. It has been shown that during the formation of the long-period CuAuII structure, the CuAuI superstructure is first formed.