Anomalies of deformation behavior and microstructure in CuAu ordered alloy

Abstract

A polycrystal of the ordered CuAu alloy, which had relatively coarse grains (5 to 10 μm), without the lamellar structure, was obtained. Tensile tests were performed within the temperature interval from −196 to 350°C. The yield stress σ 0.2 T has a maximum near T p≌300°C. The σ 0.2 value at T p is nearly twice as high as the value at room temperature. A sharp drop of ductility from 18% at room temperature to 3% at 250°C is found. The TEM analysis revealed the presence of single dislocations, superdislocations and microtwins. Long rectilinear dislocations are observed at 250°C. They have been identified as blocked screw superdislocations with a Burgers vector type <101]. Numerous curved single dislocations are seen, but blocked single dislocations were not detected in CuAu, unlike in TiAl. The temperature dependence of the yield stress σ 0.2 for the fine-grained (0.5 μm) CuAu alloy was studied too. A temperature peak of σ 0.2 T is still observed. The various models have been discussed to account for the specific deformation behavior of CuAu.