The impact of impurities on the Al–Fe–C system phase composition changes during sintering

Abstract

Manufacturing waste can be not only recycled but also utilized as a source of chemical elements and as a component of powder materials. Steel swarf are a complex multicomponent material with a high iron content, while impurities such as carbon can affect the diffusion interaction in the chip and metal powder mixture. In this study, we investigate the diffusion interaction between aluminum and steel swarf using temperature-controlled vacuum sintering. We analyzed the resulting mixture’s microstructure and phase composition, and observed that sintering creates a multiphase structure in which FeAl iron aluminide occupies at least 30 vol. %. Despite the high sintering temperature, we also observed residual aluminum and iron. Incomplete transformation may result form refractory products that inhibit diffusion or impurities that influence the magnitude and direction of the diffusion fluxes. To confirm the impurities’ role in the diffusion interaction kinetics, we developed simulation models of the intermetallic phase growth for a flat and spherical particle embedded in aluminum. The model consider cross-diffusion fluxes in the emerging phase regions and possible effects of impurities on the concentration limit for the new phase’s existence. We derived approximate analytical solutions to analyze the emerging phase growth trends under various model parameters.