MOLYBDENUM AND NITROGEN COSEGREGATION ON FE-3.5-PERCENT-MO-N(110)

Surface cosegregation phenomena were studied at elevated temperatures on the (110) surface of a Fe-3.5%Mo-N single crystal by means of Auger electron spectroscopy (AES) and low energy electron diffraction (LEED ). Cosegregation of molybdenum and nitrogen, being due to the strong c hemical interactions between the two solutes, was found to cause the f ormation of a two-dimensional MoN surface compound. The stability of t his compound was investigated in the temperature range of 500-700 degr ees C. Above 600 degrees C desorption of molecular nitrogen occurs. Th e maximum surface coverages of the segregants, which were established at temperatures of around 500 degrees C, corresponded to less than a f ull monolayer of the MoN surface compound. LEED investigations reveale d a complex diffraction pattern of the MoN-covered Fe-3.5%Mo-N(110) al loy surface which is not fully understood yet. However, no facetting o f the bcc(110) surface occurred. This finding is in sharp contrast to previous results obtained on (110)-oriented surfaces of ferritic alloy s with various 3d metals, such as Fe-15%Cr-N and Fe-3%V-C, N. It is co ncluded that the maximum MoN surface coverage is too small to induce t he facetting of the bcc(110) alloy surface.