Facetting of Fe-15% Cr-N, Fe-3% V-C and Fe-3% V-C,N (111) surfaces

Summary Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning electron microscopy (SEM) have been used to study the surface chemistry of crystallographically open bcc (111) surfaces of Fe-15% Cr-N, Fe-3% V-C and Fe-3% V-C,N alloys. The binary and ternary surface phases CrN, VC and V(C,N) were formed at temperatures ranging from 450 to 750°C depending on the alloy. On Fe-15% Cr-30ppmN (111) two-dimensional surface compounds CrN were formed at temperatures above 600°C according to the bulk phase diagram of the Fe-Cr-N system, whereas on Fe-15% Cr-N samples with nitrogen contents of more than about 100 ppm the precipitation of three-dimensional CrN took place at temperatures below 600°C. Optical and SEM micrographs as well as oxidation experiments at room temperature indicated that the substrate surfaces are inhomogeneously covered by the surface phases. Facetting of the bcc (111) surfaces induced both by cosegregation of the solutes and by surface precipitation was observed in real space (SEM) as well as in reciprocal space (LEED). It is shown that the surface phases are epitaxially arranged on (100) facets of the substrate.