SURFACE COSEGREGATION ON FE-3-PERCENT-V-C, FE-3-PERCENT-V-C,N AND FE-15-PERCENT-CR-N(110) SINGLE-CRYSTALS

Surface cosegregation has been studied on (110) oriented Fe-3% V-C, Fe -3% V-C,N and Fe-15% Cr-N single crystals applying AES and LEED. The s urface compounds VC, V(C,N) and CrN are formed upon annealing in the t emperature range from 450 to 750 degrees C depending on the alloy. The stoichiometries of the binary surface compounds correspond to VC1.2 a nd approximately CrN0.8 as determined by quantitative evaluation of Au ger peak height ratios. The composition of the V(C,N) surface compound varies between V(Co0.6N0.6) at 450 degrees C and V(C0.2N1.0) at 640 d egrees C. Three-dimensional precipitates are not formed as indicated b y Ar+ depth profiling, After short annealing times streaking LEED patt erns are observed indicating partial disorder in one direction of the direct space. Upon sufficient annihilation of surface defects sharp (4 x 1) patterns appear. A missing and added row ''model'' is proposed f or the surface compounds on bcc(110) substrate surfaces.