Thermodynamically‐controlled processes on multicomponent alloy surfaces

AbstractThe chemical composition of alloy surfaces is subject of segregation processes at elevated temperatures. In multicomponent alloy systems the joint surface enrichment of different solute atoms (cosegregation) is possible. Under thermodynamic control, i.e. when the temperature is sufficiently high to allow rapid bulk diffusion of the components, cosegregation may cause the formation of thermodynamically stable two‐dimensional chemical compounds (surface compounds), which are epitaxially arranged on alloy surfaces of suitable structure and orientation. The cosegregation‐induced surface confined formation of two‐dimensional chemical compounds must be distinguished from the precipitation of three‐dimensional compounds at surfaces (surface precipitates). According to the Gibbs phase rule, three‐dimensional precipitates can be formed upon oversaturation in coexistence with the saturated solid solution.In this contribution the cosegregation‐induced growth of two‐ and three‐dimensional surface compounds and surface precipitates on several multicomponent alloy single crystals will be described and discussed.