Surface enrichment in Cu 3Au and Au 3Cu alloys

Abstract

It is well known that in equilibrated solid alloys surface and bulk compositions can differ appreciably. For homogeneous alloys two theories of surface enrichment are available, which in the present work are checked against new experimental data. One of these theories is based on the regular solution model of liquids and neglects lattice strain effects. It predicts surface enrichment with the component having the lowest heat of atomization. The second theory, which concentrates on differences in atomic radii and is often used to compute grain boundary segregation, predicts enrichment with the atom having the largest radius. Auger electron spectroscopy results are reported for the alloys Au 3Cu and Au Cu 3, for which the two theories predict opposite surface enrichments. It is concluded that the effects due to strain and heats of atomization, which would cause surface enrichments of opposite sign, just cancel out.