X-ray diffraction of high nitrogen face centred cubic phase formed on nitrogen modified austenitic stainless steel

Abstract

High nitrogen face centred cubic phase formed on the nitrogen modified Fe–Cr–Ni austenitic stainless steel, which is named by γN phase, has a combined wear and corrosion resistance. X-ray diffraction (XRD) patterns of the γN phase on the stainless steel depict a set of broad and asymmetry diffraction peaks with a peak shift to low Bragg angles and a decrease in intensity, even disappearing of some peaks of high index planes, from each austenite peak for the γ matrix. The peak shift of the XRD patterns was first explained by Warren's XRD theory by Blawert et al. (Surf. Coat. Technol., 2001, 136, 181). In this paper, a systematic study of XRD on the peak shift, peak asymmetry, peak broadening and peak intensity of the γN phase has been carried out, based on a fault induced scattering geometry in diffraction to imperfect crystals by Warren's theory and Wagner's method. Both the higher deformation faults density α in a range of 0·02–0·25 and the lower twin faults density β of 0·01–0·1 were successfully used to describe the line profiles in the XRD patterns of the γN phase formed on plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel. A novel stacking faults factor Sαβ dependent on α and β described, in good agreement, the peak intensity of the γN phase. The calculated XRD patterns of the γN phase using the imperfect crystals model of a face centred cubic phase with a higher deformation faults density and a lower twin faults density were associated with the experimentally structural characteristics.