Dense Pure Binderless WC Bulk Material Prepared By Spark Plasma Sintering

Compared with the WC-Co cemented carbide, the binderless WC have a higher hardness, better wear resistance and oxidation resistance, which is suitable for the requirements of component with high hardness and high wear resistance, such as the nozzles for the fire high-pressure waterjet. Spark plasma sintering(SPS) is an effective way to sinter the binderless WC with the advantage of lower sintering temperature and finer grains by activating the surface of powder during sintering. In this paper, we studied systematically binderless WC bulk materials prepared by SPS and optimized the sintering parameters to obtain the excellent properties of binderless WC materials.(1) The addition of C was used to reduce or eliminate the impurity phase W2 C which usually accompanied with WC during the sintering. The series of samples WC-x wt.% C with the different addition of C were prepared by high energy ball milling and SPS. The effect of C addition on the phase of the alloy was investigated. Experiments showed that the W2 C impurity phase is disappears in the sample with the addition of 0.65 wt.% C.(2) Based on the above, the WC-0.63 wt.% C mixed powders were used for preparing the sample by SPS to study the influences of the sintering parameters on the mechanical properties. The influences of the sintering temperature, pressure and holding time on the relative density, hardness and grain size of the binderless WC bulk materials were investigated. The results show that the relative density, Vicker hardness and grain size of the material are sensitive to sintering temperature, which increased significantly with increasing sintering temperature, but increase weakly with increasing pressure or sintering time. The sintering parameters were optimized. The binderless WC bulk material with relative density of 99.1%, hardness of 27.5GPa, grain size of 396 nm, fracture toughness of 4.5 MPa m1/2 and flexural strength of 1280 MPa was obtained by SPS at 1800℃ for 6min under 70 MPa.(3) The Cr3C2 and V8C7 were used as grain growth inhibitors in the binderless WC to mitigate grain growth during sintering and increase the fracture toughness of the material in this work. Two series samples with WC-0.63 wt.%C-x wt.% Cr3C2 and WC-0.63 wt.%C-x wt.% V8C7 were prepared by SPS at 1800℃ for 6min under 70 MPa and the effects of the inhibitors on the phase, grain size and mechanical properties were investigated. The results showed that the compound Cr3C2 changed to the Cr C phase while the V8C7 kept the same phase during SPS sintering. The amounts of the inhibitors were optimized to obtain the minimum grain size in the sample, which is 0.7 wt.% for Cr3C2 while 1.5 wt.% for V8C7. The grain size, hardness, fracture toughness and flexural strength are 327 nm, 26.73 GPa, 5.87 MPa m1/2 and 1098 MPa, respectively for the Cr3C2 optimized sample, which decreased by 17% in the grain size, 2.8% in the Vicker hardness, but increased by 30% in the fracture toughness as compared with those of the samples without the inhibitor. The WC grain size, hardness, fracture toughness and flexural strength are 298 nm, 26.62 GPa, 6.90 MPa m1/2 and 950 MPa, respectively for the V8C7 optimized sample, which decreased by 24 % in the grain size, 3.2 % in the Vicker hardness, but increased by 52 % in the fracture toughness as compared with those of the samples without the inhibitor.