MOLYBDENUM AND NITROGEN COSEGREGATION ON Fe–3.5%Mo–N(110)

Abstract

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 chemical interactions between the two solutes, was found to cause the formation of a two-dimensional MoN surface compound. The stability of this compound was investigated in the temperature range of 500–700°C. Above 600°C desorption of molecular nitrogen occurs. The maximum surface coverages of the segregants, which were established at temperatures of around 500°C, corresponded to less than a full monolayer of the MoN surface compound. LEED investigations revealed a complex diffraction pattern of the MoN–covered Fe–3.5%Mo–N(110) alloy surface which is not fully understood yet. However, no facetting of the bcc(110) surface occurred. This finding is in sharp contrast to previous results obtained on (110)-oriented surfaces of ferritic alloys with various 3d metals, such as Fe–15%Cr–N and Fe–3%V–C, N. It is concluded that the maximum MoN surface coverage is too small to induce the facetting of the bcc(110) alloy surface.