THE EFFECTS OF ORDER ON THE CRITICAL RESOLVED SHEAR-STRESS OF CU-10 AT-PERCENT AU SINGLE-CRYSTALS

Heat treating copper-10 at.% gold single crystals in the temperature r ange 473-723 K resulted in various states of order. They have been cha racterized in X-ray diffraction experiments. Since the 100-superlattic e reflections were always very sharp, it has been concluded that all s ingle crystals were long-range ordered. The long-range order parameter S varied between 0.14 and 0.23. The critical resolved shear stress (C RSS) was measured between 90 and 500 K. Ar all temperatures the CRSS d ecreased slightly as S increased, i.e. there was order softening which amounts to up to 3%. This result is interpreted on the basis of the e lastic interaction forces between gold solute atoms and edge dislocati ons. If S is high, the forces that are due to the gold atoms' lattice mismatch tend to average out. (C) 1997 Acta Metallurgica Inc.