Research On The Ultrafine WC-TiC-TaC-Co Cemented Carbides For Spraying

The ultrafine WC-Co cemented carbide was prepared by the process of powder metallurgy with large additions of TiC and TaC. The hardness and transverse rupture strength (TRS) were measured by HVS-30ZB/LCD sclerometer and GADABINI SUM5 electronic testing machine. The density and coercive force were measured by Mettler-Toledo AL/AB-N analytical balance and YSK-1 coercive force meter. The phases of the cemented carbides were detected by DX-2000 X-ray Diffractometer (XRD). The microstructure was observed by Zeiss optical microscope and TESCAN-W and JSMLV-5610 Scanning Electron Microscope (SEM). All the results was used to analyse the effect of TiC/TaC inhibitor.On the basis of results, the best formula was determined. And then change the content of Co and measure the density, coercive force, hardness, TRS and microstructure of the alloys. Research the influence of the content of Co on the microstructure and properties of the ultrafine WC-TiC-TaC-Co cemented carbides In the end, the influence of the nitridation was investigated.The results as follow:(1) The content of TiC/TaC inhibitor has great effect on the properties of alloys. The properties of the alloys is best as the formula is WC-1.4TiC-1.5TaC-6Co. The hardness is HV (30)=1863.2; the TRS is 2318 MPa; the coercive force is 29.3 KA/m; the density is 98.69%.(2) For the TiC has high hardness, the addition of TiC is conducive to the hardness of the cemented carbides. But the TaC has great inhibiting effect, the addition of TaC is conducive to inhibit the growth of WC grains. Appropriate formula can control the growth of WC grains effectively, and get more hard alloys. In our experiment, when the formula is WC-1.5TiC-1.4TaC-6Co, the hardness of the alloy is the best, HV (30)=1999.6.(3) Compare with the TiC, the TaC has a more better wettability with the Co. And the TaC can inhibit the growth of WC more effectively. So the appropriate TaC can increase the TRS of the alloys. But superfluous TaC will deteriorate the wettability between the hard phase and binder phase, and is not conducive to the TRS.(4) The tendency of the coercive force is similar with the hardness:the numerical values increase with the fine of the WC grains. Because the composition of the hard phase is complex, the coercive force is only an indirect parameter to reflect the mean WC grain size.(5) The tendency of the density is similar with the TRS:the numerical values increase with the improve of the wettability between the hard phase and the binder phase.(6) The increase of the content of Co can increase the TRS and density and reduce the hardness and coercive force of the alloys.(7) The nitridation can modify the microstructure of the surface. The nitridation treatment introduced a surface zone enriched in titanium and deficient in cobalt.