Understanding mechanical infusion of nitrogen into iron powders

Abstract

Nitrogen alloying of iron-based metals greatly improves mechanical and corrosion properties. However, nitrogen solubility is less than 0.1 weight percent (wt%) in b.c.c iron. In this study nitrogen concentrations in excess of 1 wt% were obtained by high-energy milling of pure iron powders in a nitrogen gas environment. The nitrogen concentration in the powder, the grain size, and internal strain in the mechanically processed iron powder were determined as functions of processing time in both nitrogen and argon gas environments. The contributions of plastic deformation and interstitial nitrogen to changes in lattice d-spacing, and the distribution of nitrogen between interstitial sites and defect sites were estimated. Approximately 25% of the incorporated nitrogen was contained in interstitial sites, with the remainder associated with defect structures and surfaces.