Structure and properties of the equiatomic CuAu alloy ordered under a tensile stress of 40 MPa

One of the key challenges in materials science is the search for methods to control the structure and properties of various materials. It was previously established that compression during the ordering of the equiatomic CuAu alloy orients the short c-axes of the crystalline lattice (L1₀ superstructure) along the direction of the applied force. However, in practice, thin wires are predominantly used, for which only tensile processing is applicable. This work studied wire specimens of the equiatomic CuAu alloy ordered by cooling from 500 °C at a rate of 12 °C/h under a tensile stress of 40 MPa. A comparison was made with specimens ordered in a free state. For the experiments, miniature grips were designed, and all heat treatments were performed in vacuum. X-ray diffraction analysis revealed that the short c-axes of the tetragonal L1₀ superstructure are predominantly located in the plane of the wire cross-section, perpendicular to the direction of the tensile force. Dilatometric investigation revealed that a specimen ordered under tension subsequently contracts (by approximately ~0.8 %) when heated above the phase transformation temperature, while simultaneously expanding in diameter. This effect is explained by the difference in the volumes of the crystalline lattices of the ordered and disordered phases. It was found that during the heating of a specimen ordered under load, the maxima in the temperature derivatives of electrical resistance change in intensity and shift in temperature. A hypothesis has been put forward that ordering the CuAu alloy under a tensile load increases the disordering temperature and alters the thermal stability of the ordered CuAuI and CuAuII phases. The obtained result is consistent with literature data for the CuAu alloy ordered after compressive deformations.