Nitridation of Fe-2.3 wt.% Al alloy powder and its compaction by spark plasma sintering

Abstract

Development of nanosized alloying element nitride particles in ferrite matrix of steels is known to drastically enhance the mechanical properties of steels. In this study we have investigated the nitriding induced phase transformations in Fe-2.3wt.% Al alloy powder followed by further investigation on spark plasma sintering (SPS) of this nitrided powder. Microstructure of the specimens was characterized employing Light microscopy, Hardness measurements and X-ray diffraction. Nitriding was carried at 560°C in a flowing ammonia gas in an industrial scale gas nitriding facility. After the nitriding treatment the entire powder particles got transformed to iron-nitrides (γ'-Fe4N1-x and ϵ-Fe3N1+y) and some iron-oxides (Fe2O3 and Fe3O4) have also developed. During SPS of the nitrided powder, all iron-nitrides got dissociated into iron and N2 gas which has been attributed to the metastable nature of iron-nitrides. Additionally, the initially present iron-oxides have transformed to FeO which has been ascribed to FeO being stable oxide at sintering temperature of 900°C and the rapid cooling of sample after sintering. Although a significant increase in hardness has occurred due to the application of nitriding treatment to powders before SPS, the SPSed compacts are brittle due to the presence of iron-oxides and the porosity. © 2018 Elsevier Ltd.