FACETING OF FE-15-PERCENT CR-N, FE-3-PERCENT V-C AND FE-3-PERCENT V-C,N (111) SURFACES

Auger electron spectroscopy (AES), low energy electron diffraction (LE ED) and scanning electron microscopy (SEM) have been used to study the surface chemistry of crystallographically 'open' bcc (111) surfaces o f Fe-15% Cr-N, Fe-3% V-C and Fe-3% V-C,N alloys. The binary and ternar y surface phases CrN, VC and V(C,N) were formed at temperatures rangin g from 450 to 750-degrees-C depending on the alloy. On Fe-15%Cr-30ppmN (111) two-dimensional surface compounds CrN were formed at temperatur es above 600-degrees-C according to the bulk phase diagram of the Fe-C r-N system, whereas on Fe-15%Cr-N samples with nitrogen contents of mo re than about 100 ppm the precipitation of three-dimensional CrN took place at temperatures below 600-degrees-C. Optical and SEM micrographs as well as oxidation experiments at room temperature indicated that t he substrate surfaces are inhomogeneously covered by the surface phase s. Facetting of the bcc (111) surfaces induced both by cosegregation o f the solutes and by surface precipitation was observed in real space (SEM) as well as in reciprocal space (LEED). It is shown that the surf ace phases are epitaxially arranged on (100) facets of the substrate.