XRD characterization of mechanically alloyed high-nitrogen nanocrystalline Fe–Cr system

Abstract

The effect of milling time on defect structure and phase composition of nanostructured Fe–25Cr–10Mn–1N (wt%) alloy powders processed by mechanical alloying (MA) in the high energy planetary ball mill under argon atmosphere was investigated using X-ray diffraction (XRD) and Mössbauer spectroscopy. For this purpose the powder mixture of iron, chromium and manganese nitride Mn2N was used. The consecutive deformation dissolution of chrome and manganese nitride in bcc Fe and phase transformation from bcc (ferrite) to fcc (austenite) with the formation of fully austenitic structure for 8h of MA took place. Using the differential scanning calorimetry it was shown that the chromium nitride Cr2N precipitates and a partial reverse fcc to bcc transformation occurs during the heating of mechanically alloyed austenite in the temperature range of 600°C. The anisotropic (hkl-dependent) position shifts of Bragg bcc reflections increasing with MA duration were observed. These anisotropic shifts together with the observed anisotropic broadening of reflections were reasonably attributed to the appearance of certain type of stacking faults on {211} and {310} planes of bcc phase during MA. It was assumed that the stacking faults play an important part in the deformation bcc to fcc transformation under MA of high-nitrogen Fe–Cr system.