Overcoming the trade-off between electrical conductivity and densification in Al₂O₃–TiC Ceramics via particle size grading

Electrically conductive composite ceramics face a critical trade-off where increasing the phase domain size ratio between the insulating matrix and the conductive phase theoretically enhances conductivity but practically hinders densification. The resulting porosity inevitably degrades both mechanical and electrical properties. To address this limitation, a matrix particle size grading strategy is proposed using the Al₂O₃–TiC system as a model. The incorporation of nano-Al₂O₃ into a micro-Al₂O₃ matrix triggers a synergistic microstructural evolution. Specifically, nano-Al₂O₃ particles fill interparticle spaces to promote densification and may pin TiC grain boundaries, thereby contributing to the refinement of the conductive phase domains. Concurrently, the micro-Al₂O₃ phase domains coarsen at the expense of nano-Al₂O₃, maximizing the phase domain size disparity and favoring the formation of a continuous three-dimensional TiC network. With 10 vol% nano-Al₂O₃ addition, the calculated effective percolation threshold drops from 15.54 vol% to 10.20 vol%, achieving an electrical conductivity of 4.02 × 10⁴ S/m. Consequently, the composite exhibits enhanced electrical discharge machining (EDM) performance, achieving a material removal rate of 9.50 mm²/min alongside high surface quality. This strategy offers a robust framework for developing advanced conductive ceramics tailored for EDM applications.