Die sink electrodischarge machining of zirconia based composites

Four zirconia based composite groups with conductive secondary phase additions of TiB₂, TiN, TiC, and TiCN have been developed with the objective of allowing shaping by spark erosion. Each composite was subjected to die sink electrodischarge machining (EDM) using a standard predetermined set of sparking parameters, and an assessment of machining performance was made by comparing volumetric material removal rates (VMRRs), surface finish, and tool wear. Optimum machining conditions for each ceramic composite were found to be polarity dependent. The more electrically conductive composites with higher secondary phase content generally gave higher VMRR values. Erosion rates were further improved by increasing energy and frequency of sparking while maintaining stable machining with no arcing. Bend testing showed an overall reduction of about 20% in the strength the materials after EDM under non-optimised conditions, when compared with conventionally sawed specimens. Despite the reduced strength, a sizeable bending strength of about 800 MPa was maintained after die sinking. Microstructural investigation revealed that the original microstructure of the more conductive composites with 40 vol.-% secondary phase was maintained when die sinking was carried out under optimised conditions. Significant tangential and radial subsurface cracking was however observed under unstable machining conditions in the least conductive composites, with 30 vol.-% secondary phase.