X-ray diffraction and Mossbauer characterization of attrition-milled nanostructured iron and iron-nitrogen powders

Publisher Website
Google Scholar
Abstract
To date there has been limited information on the microstructure of mechanically infused interstitial elements in metal powders, and, although interstitials have a limited solubility in iron alloys, they are an important means of increasing tensile strength in large-grained structures. In this study, iron powder was mechanically processed in argon and mechanically alloyed in nitrogen to produce micron-sized particles with nanosized grains. Although the total mechanically infused nitrogen concentration in the milled particles greatly exceeded the thermodynamic equilibrium interstitial solubility limit of iron, no nitrides formed. The nitrogen distribution was determined by a combination of X-ray diffraction (for nanostructure characterization) and Mossbauer spectroscopy (for atomic site characterization). Analysis revealed that the majority of the nitrogen was not intragranular but intergranular, associated with the nanograin boundary as either surface impurities or incorporated into the outer lattice cell of the grain boundary where it distorted the bcc cells to form bet Fe(N) clusters.