Evolution of the Structure and Properties of Cu-56Au (at %) Alloy during L10-Type Atomic Ordering

The ordered gold-copper alloy Cu–56 at % Au is widely used in instrument engineering as conductors of weak electrical signals in control devices. However, microstructural evolution and changes in the physicomechanical properties of the alloy during the disorder → order phase transformation (A1 → L10) are still poorly understood. In the present paper, we study the evolution of the microstructure and properties of the quenched Cu–56 at % Au alloy during the disorder → order phase transformation. The annealing time at 250°C ranged from 10 min to 4 months. Microstructural studies were performed using transmission electron microscopy, the ratio of volume fractions of the ordered and disordered phases was determined using X-ray diffraction analysis and resistometric measurement, and material properties were measured in mechanical tensile and microhardness tests. The fraction of the ordered phase, strength properties, and specific electrical resistivity were plotted as a function of the annealing time. It is found that the maximum strength properties correspond to the two-phase state (A1 + L10) of the alloy with an approximately equal phase ratio. It is shown that, with an increase in the fraction of the ordered phase, the tensile strain hardening coefficient almost doubles.