Features of the Structure and Properties of an Equiatomic Cu-Au Alloy Ordered in the External Force Field

Abstract

Atomically ordered gold-copper alloys have technological applications, which makes the search for ways to improve their mechanical properties an urgent scientific and practical task. The present paper studies the effect of tensile and compressive stresses on the formation of an ordered structure, texture, and physicomechanical properties of an equiatomic CuAu alloy. All experiments were carried out on Ø1.5 mm wire specimens, which were initially disordered by quenching from 600°C or plastic deformation by 75%. An ordered structure was formed at a temperature of 350°C for 24 h; compressive stresses during annealing were 7 and 11 MPa; tensile stresses were 7 and 20 MPa. Comparison was made with the specimens ordered in a free state. It is shown that annealing in the compressive stress field causes a significant part of the short c axes of the ordered lattice to align along the force direction. Annealing under tension forms a different texture, i.e. most of the short c axes lie in the cross section of the specimen. The estimation of the degree of long-range order (S) showed that the specimens annealed in a free state had the maximum atomic order (S ≈ 0.95). According to the dilatometric study, the specimen quenched and then ordered in the compressive stress field demonstrates a sharp (by ~0.7%) increase in the length at the temperature of order → disorder phase transformation. It is found that compressive loads during ordering of the quenched specimens increase their strength and ductility, while tensile loads decrease these characteristics. It is shown that the mechanical properties of the specimens ordered after preliminary deformation are almost independent of the load direction. This phenomenon is explained by the absence of a clear texture (small loads do not cause rotation of c domains during ordering of high-strength deformed specimens).