X-RAY-DIFFRACTION AND COMPUTER-SIMULATION STUDIES OF THE STRUCTURE OF[001] TWIST BOUNDARIES IN AU-AG ALLOYS

A combined X-ray diffraction and Monte Carlo simulation study of the s tructure of SIGMA 13 [001] twist boundaries in gold-silver alloys, as a function of silver concentration is presented. Five alloy concentrat ions corresponding to 0, 25, 50, 75, and 100 at.% silver are studied. For the 50% alloy, a large number of absolute grain boundary structure factors are measured, both in the plane of the grain boundary and nor mal to it. At the other compositions fewer structure factors are measu red. However, their magnitudes are found to be useful in setting limit s on the extent of interfacial segregation. Generally good agreement i s found between all measurements and calculations. For the 50% alloy i t is concluded that the alloying with silver produces only very slight boundary segregation and changes in the positions of the substitution al sites in the boundaries (relative to that in pure gold) and that th e gold and silver atoms are distributed on these sites almost randomly . Detailed information on atomic vibrations and individual site occupa tion probabilities is presented.