Anisotropy of discharge behavior, removal mechanism, and damage evolution for Cf-HfB2-HfC-SiC composites in EDM drilling

Electrical Discharge Machining (EDM) demonstrates significant potential for deep-hole fabrication in C f -HfB 2 -HfC-SiC composites, which is a typical Carbon fiber-reinforced Ultra-High Temperature Ceramics (C f /UHTCs). However, the anisotropy effects of each component in C f -HfB 2 -HfC-SiC on the EDM behavior and drilling process remain unclear, leading to a low Material Removal Rate (MRR) and unacceptable machining defects. In this study, the discharge behavior, removal mechanism, and damage evolution of EDM drilling of C f -HfB 2 -HfC-SiC were investigated. From the discharge behavior observation, the discharge channel tends to expand along the fiber’s axial direction. With a larger interfacial area between the channel and the fiber axis, it likely forms a heat-affected zone, which is aligned with the fiber orientation. This phenomenon results from the combined influence of the carbon fibers’ higher axial thermal and electrical conductivities, which distinguishes it from the conventional understanding of thermal machining. The morphology of the discharge craters is governed by the fiber orientation, and their edges are notably irregular. Additionally, the morphology and structural characteristics of the surface and subsurface vary with the machining angle of the car-bon fibers. The HfB 2 -HfC-SiC components show a higher MRR and are removed before the C f s. The material removal of C f -HfB 2 -HfC-SiC occurs through the combined effect of mechanics and heat, the surface and subsurface damage also exhibit anisotropy, with microcracks appearing exclusively on the fiber end faces. Besides, the primary forms of machining damage include cracking and fiber–UHTCs debonding. Based on a comprehensive understanding of the removal mechanism and the parameter optimization, micro-holes with a diameter of 0.38 mm and an aspect ratio of 114 were fabricated the C f –HfB 2 –HfC–SiC composites.