Microstructures of binderless tungsten carbides sintered by spark plasma sintering process

Abstract

Pure WC was sintered by spark plasma sintering (SPS) process for a binderless cemented carbide application. The relative density of spark plasma sintered WC was over 98% when the SPS temperature was 1700 degreesC under 50 MPa pressure. Grain growth of WC could be suppressed with full densification by shortening sintering time. When the initial WC powder size was varied from 0.57 to 4.06 mum, the sintered density decreased with decreasing WC powder size. However, WC with an initial powder size of 0.57 mum could be sintered to densification by addition of free carbon. The higher amount of surface oxide in the finer WC powder is considered to have caused decarbonization during the sintering process. For WC powders of 4.06 mum, abnormal grain growth occurred when the sintering time was over 1 min if the sintering temperature was over 1700 degreesC. Also, with the sintering temperature and sintering time where no abnormal grain growth occurred, abnormal grain growth occurred by addition of carbon. This result shows that the abnormal grain growth in WC sintered by SPS process can be controlled by carbon addition. The abnormal grain growth in sintered WC somewhat increased fracture toughness by crack deflection. (C) 2003 Elsevier Science B.V. All rights reserved.