Anomalies of deformation behavior and microstructure in CuAu ordered alloy

A polycrystal of the ordered CuAu alloy, which had relatively coarse grains (5 to 10 mu m), without the lamellar structure, was obtained. Tensile test s were performed within the temperature interval from -196 to 350 degrees C . The yield stress sigma(0.2)(T) has a maximum near T-p congruent to 300 de grees C. The sigma(0.2) value at T-p is nearly twice as high as the value a t room temperature. A sharp drop of ductility from 18% at room temperature to 3% at 250 degrees C is found. The TEM analysis revealed the presence of single dislocations, superdislocations and microtwins. Long rectilinear dis locations are observed at 250 degrees C. They have been identified as block ed screw superdislocations with a Burgers vector type < 101]. Numerous curv ed single dislocations are seen, but blocked single dislocations were not d etected in CuAu, unlike in TiAl. The temperature dependence of the yield st ress sigma(0.2) for the fine-grained (0.5 mu m) CuAu alloy was studied too. A temperature peak of sigma(0.2)(T) is still observed. The various models have been discussed to account for the specific deformation behavior of CuA u. (C) 1999 Elsevier Science Ltd. All rights reserved.