Wire EDM of WC - ZrO2 composites

Ceramic based composites are considered well suited for heavy tribological applications. Due to their extreme hardness, EDM is the machining method of choice. The interrelationships between the dispersion of the ZrO2 phase, the WC particle size and the Electrical Discharge Machining (EDM) behavior of WC based composites with respectively 0, 5 and 10 vol % of ZrO 2 are investigated. XPS measurements reveal the presence of a nanometric WO3 layer on the EDM surface, confirming oxidation as the major material removal mechanism (MRM). Oxidation of the WC grains is responsible for a difference in the material removal rate between nanometric and micrometer sized WC powder based composites. A higher machining rate is obtained with micrometer sized composites. The surface roughness after final EDM finishing regime was strongly influenced by the presence of ZrO2 agglomerates and could be reduced down to 0. 15 μm (Ra) on an agglomerate free composite. Residual stress measurements indicate that EDM does not introduce significant surface stresses. Three point bending tests show that after the final finishing cut the flexural strength increases slightly from 819 MPa to 926 MPa for 10 vol % of ZrO2. XRD measurements reveal the presence of W2C and ZrC in the surface layer which indicates ZrO 2 depletion and consequentially, a reduced flexural strength compared to ground samples.status: publishe