Research On The Manufacturing Technology Of Ternary Boride Base Cemented Carbides

The high hardness and wear resistance were obtained in the ternary boride base cemented carbides of WC-Co/TiB₂. In this dissertation, the ternary boride base cemented carbides were prepared by vacuum sintering, and the mechanical properties of cemented carbides were improved by sinter-hot isostatic pressing. The relationship among manufacturing process, composition, microstructure and mechanical properties had been systematically investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy dispersive spectrdmeter (EDS) and scanning electron microscopy (SEM).The phase and microstructure transformation during sintering of the ternary boride base cemented carbides of WC-Co/TiB₂, and the influences of the sintering temperature and time on microstructure and mechanical properties were studied. The sintering technique of cemented carbides was identified preliminarily. The conclusions were obtained as follows: WCoB was only obtained in solid phase sintering. WCoB decomposed in the liquid sintering, and the cemented carbides consisted of W₂CoB₂, TiC and little TiB₂ by liquid phase sintering. The best mechanical properties were obtained for cemented carbides sintered at 1400℃for 60min.The influences of Co content and WC/TiB₂ ratio in main composition on the phase composition, microstructure and mechanical properties were studied. The conclusions were obtained as follows: the TiB₂ content decreased with the increasing of Co content, and the brittle phase of Co₂B appeared when Co content exceeded ₂₂.4wt%. The sintering properties of cemented carbides decreased when WC/TiB₂ ratio was too small, and the best mechanical properties were obtained when WC/TiB₂ ratio was 0.5.The influences of Mn and Mo on microstructure and mechanical properties of the ternary boride base cemented carbides were studied. The conclusions were obtained as follows: the wettability between hard phase and liquid phase was improved by Mn addition, which refined the grains and increased the transverse rupture strength of cemented carbides. The (W, Mo) ₂CoB₂ solid solutions were generated by Mo addition. Mo was enriched in the core of (W, Mo) ₂CoB₂ solid solutions, and the double layer structure with light gray core formed. At the same time, the mechanical properties of cemented carbides increased with appropriate Mo addition.The influences of sinter-hot isostatic pressing on microstructure and mechanical properties of the ternary boride base cemented carbides were studied. The conclusions were obtained as follows: smaller grain size and fewer pores were obtained in the cemented carbides prepared by sinter-hot isostatic pressing, and the mechanical properties of cemented carbides were improved.