Due to rapid heating mechanisms, microwave techniques have been successfully employed to sinter ceramics at reduced temperatures, yielding dense materials with fine grain structures. However, one of the greatest challenges is that the total heat energy generated by the material depends on the electric and magnetic components of microwave energy absorbed, which is dictated by dielectric and magnetic losses. By strategically selecting microwave processing methods and microwave-responsive materials, bulk materials with enhanced properties can be fabricated in shorter times at lower temperatures. From a processing standpoint, single-mode microwave sintering allows for manipulation of electric-to-magnetic field component ratios, providing an influence over heating behavior, and enabling control over densification. From a materials standpoint, internal microwave susceptor can aid in sintering of ceramic materials. By incorporating microwave-susceptible materials as either additives or second phases, rapid localized heating can be achieved in selected regions.
Silicon carbide (SiC), boron carbide (B4C), and composite blends of the two materials, have been investigated because of their chemical compatibility and low densities. Such composites have been identified as suitable candidates for microwave processing, as SiC is a highly microwave-susceptible material. In this study, powders of SiC and B4C were ball-milled to obtain homogenous mixtures, which were then pressed into pellets and cold isostatically pressed. In order to determine the optimum sintering conditions, samples were processed in a single-mode microwave cavity using various electric and magnetic field ratios. Resulting SiC-B4C composites were characterized using scanning electron microscopy and x-ray diffraction, and compared to conventionally hot-pressed composites. By controlling the microwave field components during processing, and designing material compositions based on their microwave characteristics, single-mode microwave sintering enabled the fabrication of dense SiC-B4C composites.