Effects of powder preparation and sintering temperature on consolidation of ultrafine WC-8Co tool material produced by spark plasma sintering

In this study, ultrafine tool materials were produced by spark plasma sintering using three sets of WC-8Co nanopowders mixed by different methods. Effects of powder preparation method and sintering temperature on the consolidation of WC-8Co cemented carbides were investigated. At sintering temperature of 1250 degrees C, cemented carbide sintered from the powder mixed by ultrasonic vibration method exhibited homogeneous microstructure, high relative density (99.1%), small average grain size (280 nm), and excellent mechanical properties (H-v: 18.8 GPa, K-IC: 11.4 MPa.m(1/2)). However, cemented carbide sintered from heavily ball-milled powder (ball milling for 24 h) showed increased grain coalescence and microdefects as well as lower relative density of 94.6%. Moreover, its hardness decreased to 17.7 GPa due to the decrease in relative density. Furthermore, straight cracks along grain boundary became dominant, causing fracture toughness to decrease to 10.5 MPa.m(1/2). Additionally, high sintering temperature caused grain coarsening, which was detrimental to mechanical properties of cemented carbides.