H. J. Grabke

Surface cosegregation and surface precipitation on Fe-3%V-C,N(100) single crystals

Abstract Surface cosegregation and surface precipitation has been studied on (100) oriented surfaces of Fe-3%V-C,N and Fe-3%V-C single crystals by means of AES and LEED. Between 450 and 750°C cosegregation leads to the formation of the two-dimensional surface compounds V(C,N) and VC, which are both epitaxially arranged on the substrate surface as indicated by LEED. The stoichiometry of the surface compounds, determined by quantitative evaluation of Auger spectra, is VC 1.2 and V(C x N y ). x + y = 1.2, the composition of the latter varies between V(C 0.6 N 0.6 ) at 450°C and V(C 0.2 N 1.0 ) at 650°C. Saturation is obse to 650°C, at higher temperatures the total surface coverage decreases gradually. Ar + sputtering and room temperature oxidation experiments indicate that the surface compounds form a homogeneous layer on the substrates, the layer thickness is estimated to be less than 2 atomic layers. Upon quenching V(C,N) and VC surface precipitates are growing on clean and sulphur saturated substrate surfaces to a thickness of the precipitates of about 50 A. Sulphur does not prevent the formation of surface precipitates upon quenching but effectively suppresses the formation of V(C,N) and VC surface compounds.

Surface segregation of antimony on ferritic single crystals

Abstract Antimony has frequently been reported to cause temper embrittlement induced by grain boundary segregation in steels containing both nickel and chromium. In order to study the interdependent segregation behaviour of antimony and nickel and the effect of chromium on segregation of these elements, surface segregation was studied on Fe–25% Cr–2%Ni–0.15%Sb and Fe–2.5%Si–2%Ni–0.15%Sb single crystals. Segregation was investigated by means of Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) in the temperature range between 500 and 650°C. On Fe–25%Cr–2%Ni–0.15%Sb, segregation of antimony leading to surface saturation and cosegregation of nickel are observed on (100), (110) and (111) oriented surfaces. LEED investigations yield a complex domain structure which can be derived from a c(2×2) pattern for the (100) oriented surface and a (1×1) pattern for the (111) oriented surface. On the (110) oriented surface, reconstruction occurs. On Fe–2.5%Si–2%Ni–0.15%Sb, the investigated (100) oriented surface is also saturated with segregating antimony. Cosegregation of nickel occurs, but is weaker than on the crystal containing chromium; thus, chromium intensifies cosegregation of nickel with antimony. The LEED pattern exhibits a complex domain structure which is very similar to the structure observed on the (100) oriented surface of the crystal containing chromium.