Phosphorus in iron alloys surface engineering

This study explores the role of phosphorus in the surface engineering of iron alloys, focusing on the growth parameters of iron phosphides during phosphorising, phosphorcarburising, and phosphonitriding processes, and their influence on structure and properties. The methodology involves generating phosphide layers on Armco iron and a 0.4%C, 1.1%Cr steel through annealing in specific atmospheres of argon and phosphorus vapours at temperatures ranging from 700 to 1170 K, with varying phosphorus partial pressures and process durations. The resulting diffusion layers are analyzed using metallographic techniques, X-ray structural analysis, microanalysis, and Vickers and wear dry friction resistance tests. Findings indicate the formation of a compact phosphide layer with an adjustable ratio of Fe3P to Fe2P, elucidating the kinetics of phosphide layer growth and establishing that the presence of iron phosphides enhances the hardness and wear resistance of steel surfaces. Research limitations reveal that nucleation of Fe3P crystals begins at specific distances from iron grain boundaries, leading to growth-related interface degradation as the diffusion process progresses. The practical implications highlight the potential of these new composite diffusive layers generated by various thermochemical treatments, which exhibit promising tribobiological properties.