SURFACE-COMPOUNDS AND SURFACE PRECIPITATES ON SINGLE-CRYSTAL SURFACES

The co‐segregation of chromium or vanadium with nitrogen or carbon to (100)‐, (110)‐ and (111)‐oriented surfaces of carbon‐ and nitrogen‐doped Fe–15%Cr, Fe–3%V and Fe–3%Si–0.04%V alloys has been investigated by applying AES, low‐energy electron diffraction and SEM. Two‐dimensional epitaxially stabilized surface compounds CrN, CrC, VC and V(C, N) are formed in the temperature range 500–750°C on (100)‐oriented specimens. The surface compounds CrN, VC and V(C, N) are also formed on (110). The structures of the surface compounds are related to (100) and (110) planes of the corresponding three‐dimensional bulk compounds CrN, VC and V(C, N) and of a hypothetical bulk compoud CrC with a rock‐salt structure. In all cases, the lattice mismatch between the substrate surface and the corresponding crystallographic plane of the bulk compound is <3%. Upon surface compound formation, the (111) surface into (100) facets covered with the surface compounds. At low temperatures and high non‐metal concentrations, heterogeneous nucleation facilitates the formation of three‐dimensional precipitates at the surface. Copyright © 1990 John Wiley & Sons Ltd.