Material removal mechanism of RB-SiC ceramics in dry impulse electrical discharge machining

Reaction-bonded silicon carbide (RB-SiC) is a high hardness ceramic material with two-phase Si matrix and SiC particles so it is very difficult to machine due to their different electrochemical and mechanical properties. Electrical discharge machining (EDM) provides an effective alternative regardless of its hardness. However, the relationship between machining efficiency and machining quality is difficult to coordinate because the material removal mechanism of EDM has not been understood. In this paper, the dry single impulse EDM is proposed to machine RB-SiC to reveal the material removal mechanism based on the viewpoints of topographies and phase components of the machined surface. The material removals of Si matrix and SiC particles were analyzed using scanning electron microscopy (SEM), energy dispersion spectrum (EDS), and Raman spectroscopy. Five levels of discharge energy by setting pulse-on time were used to investigate the variation of material removal. The results reveal that short pulse-on time mainly caused material removal of Si matrix due to its lower electrical resistivity and melting temperature. The material removal mechanism of SiC particles was attributed to spalling induced by thermal shock and decomposition at high temperatures. Material migration and oxidation were also found on the electrical discharged machined (EDMed) surface.