X-ray diffraction of high nitrogen face centredcubic phase formed on nitrogen modifiedaustenitic stainless steel

摘要

High nitrogen face centred cubic phase formed on the nitrogen modified Fe-Cr-Ni austenitic stainless steel, which is named by γ_N phase, has a combined wear and corrosion resistance. X-ray diffraction (XRD) patterns of the γ_N 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 Warrens XRD theory by Blawert et at. (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 γ_N phase has been carried out, based on a fault induced scattering geometry in diffraction to imperfect crystals by Warrens theory and Wagners method. Both the higher deformation faults density a 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 γ_N phase formed on plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel. A novel stacking faults factor S_ (αβ)dependent on α and β described, in good agreement, the peak intensity of the γ_N phase. The calculated XRD patterns of the γ_N 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.