Modelling the X-ray powder diffraction of nitrogen-expanded austenite using the Debye formula

Stress-free and homogeneous samples of nitrogen-expanded austenite, a defect-rich f.c.c. structure with a high interstitial nitrogen occupancy (between 0.36 and 0.61), have been studied using X-ray powder diffraction and Debye simulations. The simulations confirm the presence of deformation stacking faults in the structure, while twin or growth faulting can be ruled out. Screw dislocations are abundant and the dislocation density increases with the interstitial nitrogen occupancy. Whether the N atoms are clustered or distributed randomly among the octahedral interstices was found to be indistinguishable to X-ray powder diffraction.