STUDY OF A SURFACE CRITICAL PHENOMENON ASSOCIATED WITH SURFACE SEGREGATION IN CU-AG ALLOYS

This paper presents a modified regular solution formalism for surface segregation in substitutional alloys which distinguishes between bond energies at the surface and in the bulk of a solid solution. The differences between surface and bulk energies are ascribed to strain energy effects associated with misfitting solutes. Experimental measurements of surface composition on (111) surfaces of Cu-Ag alloys dilute in Ag are reported and show the existence of a surface phase transition, which manifests itself as an abrupt surface composition change at temperatures below 788 K. Similar measurements on (100) surfaces show no comparable critical phenomena down to temperatures as low as 523 K, indicating a strong anisotropic behavior of the surface phase transition. The data are compared with the model to obtain model-based estimates of the surface critical temperatures and the surface regular solution constants for both surface orientations.