Electric discharge machining of zirconia toughened alumina ceramic with an optimized assistive electrode method

Abstract

Zirconia toughened alumina (ZTA) ceramics are commonly used in prosthetic hip implants because of their excellent mechanical properties and wear/corrosion resistance. Surface texturing can improve the lubricity and longevity of hip implant bearing surfaces, but precision machining of ceramics such as ZTA is difficult with traditional machining techniques. This work studies electric discharge machining (EDM) – a process usually reserved for conductive metals – to machine holes into the ZTA surface. EDM is enabled through the assistive electrode method (AEM), in which a combination of metal and carbon is first applied to the ceramic surface, and machining is conducted in a carbon-based dielectric oil. Voltage, current, and electric discharge time were varied to find the optimal parameter combination that minimized cracks and defects and maximized accuracy, repeatability, and quality of holes. The results identify an optimal parameter set (voltage of 71 V, current of 2.4 A, electric discharge time of 80 µs) to machine ZTA with high repeatability and dimensional accuracy and avoid cracking of the tool or workpiece. The combination of a gold–palladium, carbon, and copper assistive electrode layer, with the optimal parameter set and multi-pronged electrode, led to successful machining of ZTA using EDM. These results will facilitate reliable surface texturing in ZTA materials, which could enhance the capabilities of hip replacement manufacturing.