Microstructure And Mechanical Properties Of WC-ZrO₂-SiCw Composites

WC hard alloy which has high hardness,high strength is widely applied on industry,such as wear-resistant tool.At present,WC-Co is most widely used and studied.Although binder Co improves fracture toughness dramatically,Co is harmful for environment and is expensive.What's more,the corrosion resistance of cemented carbide is also reduced.Toughening of hard alloy is focused on by many researchers.This paper studied the effect of SiCw content,sintering temperature and holding time on microstructure and mechanical properties of WC-ZrO₂-SiCw.The synergistic toughening mechanism of SiCw and ZrO₂ is also studied too.The results of research are as follows.The result showed that,with the adding of SiCw,the average grain size increased first and then reduced.WC-ZrO₂-2%SiCw had the largest grain size,0.55?m.Because of coarse grain and small thermal expansion coefficient of SiCw,there was m-ZrO₂ in WC-ZrO₂-4%SiCw.Hardness decreased first and then increased lightly.The hardness of WC-ZrO₂-4%SiCw was 17.8GPa which was the lowest.The fracture toughness increased first and then decreased.The fracture toughness of WC-ZrO₂-2%SiCw was the largest,12.3%higher than WC-ZrO₂?The high sintering temperature improved the average grain size of WC and ZrO₂,but SiCw didn't grow.The large grain size led to the lower hardness.The fracture toughness changed nonlinearly with increasing temperature and the maximum one was 1650?.Due to the large grain of 1650?,the extending path of crack along the grain got farther and the consumption of energy increased a lot.When the temperature was above 1700?,the stabilizer Y₂O₃ failed to keep t-ZrO₂ in room temperature,so there was m-ZrO₂ which reduced the toughening effect.WC-14%ZrO₂-2%SiCw sintered by hot-pressing had perfect wear resistance and there was no obvious polishing scratch on its surface.With the increasing of holding time,the relative density of WC-14%ZrO₂-2%SiCw was improved while the hardness was reduced.The fracture toughness increased first and then reduced.WC-14%ZrO₂-2%SiCw sintered at 1650?and holded for 1h had better mechanical properties with 99.4%relative density,9.21MPa·m^1/2 fracture toughness and 18.68GPa hardness.WC-14%ZrO₂-2%SiCw was sintered by hot-pressing and SPS.At the same temperature,the grain size of composites sintered by SPS was much larger than that by hot-pressing.With the increasing of SPS sintering temperature,hardness decreased drastically.There was no obvious relationship between fracture toughness and SPS temperature.The higher one was1550?and 1650?,while the lowest one was 1700?which was 7.2 MPa·m^1/2.Compared to hot-pressing,the path of crack propagation of SPS was straighter so composites sintered by SPS have higher fracture toughness.What's more,these composites also had good wear resistance.