Study of silicon carbide dissociation into Fe and Fe C matrixes produced by die pressing and sintering

Abstract

During the sintering process of self-lubricating steels, the dissociation of Silicon Carbide (SiC) in the iron matrix forms turbostratic graphite nodules which provide the lubricating properties of these materials. Previous works have explored the turbostratic nature of the graphite nodules and the influence of the SiC content in the microstructure and tribological properties of these materials, however, the thermodynamics and kinetics of SiC dissociation have not been fully explored yet. This study uses the versatility of die pressing to study the influence of particle sizes, sintering temperature and carbon content in the dissociation of SiC. The resulting materials were analysed by optical microscopy and scanning electron microscopy (SEM). The evolution of the size and morphology of pores and graphite nodules was investigated through image analysis software and simulations with the DICTRA® software were used to a better assessment of the kinetical aspects of SiC dissociation. Also, the thermodynamic influence of the particle size in the equilibria of the Fe–SiC system is discussed. Results indicate that SiC particle size rather than Fe/SiC size ratio governs the dissociation process, sintering temperature causes coalescence and rounding of pores as well as of graphite nodules. In addition, excessive activity of carbon in the system causes the precipitation of graphite flakes, which are not desired for technological applications.