ORDER-SOFTENING OF CU-10AT.PERCENT-AU

The critical resolved shear stress tau(c) of Cu-10at.%Au-single crysta ls has been measured as a function of their state of order. This state has been varied by heat-treatments between 473 and 723 K. X-ray diffr action experiments and the observation of dislocation pairs in the tra nsmission electron microscope led to the interpretation that all speci mens were L1(2)-long-range-ordered; the antiphase domains were, howeve r, small: around 5 nm. tau(c) has been found to decrease as the degree S of long-range order increases; that is, there is order-softening. T his surprising result is interpreted on the basis of the elastic inter action of the large Au-atoms with edge dislocations. If S is high, the resulting interaction forces tend to average out. (C) 1997 Elsevier S cience S.A.