Wire-electrical discharge machinable alumina zirconia niobium carbide composites - Influence of NbC content

Alumina zirconia (ZTA) ceramics can be made electric discharge machinable by addition of a percolating network of an electrically conductive phase. In this study the influence of NbC content on the mechanical and electrical properties as well as the ED-machinability of ZTA-NbC ceramics containing 17 vol.% zirconia and 24-32 vol.% NbC were investigated. Samples were hot pressed from mixed and milled starting powders. Surface morphology and surface roughness of wire electrical discharge machined surfaces were studied by SEM and perthometry. Cutting speed was determined to benchmark the ED-machinability. Rising NbC contents progressively impede sinterability. Maximum strength, Young's modulus and hardness were found at intermediate NbC contents. Conductivity evidently rises with NbC content, the cutting performance showed an adverse tendency. The surface quality of the materials was improved by increasing the content of conductive phase. Additional trimming operations can reduce the mean roughness of machined surfaces to 1 mu m.