Effect Of Grain Inhibitors On Microstructure And Mechanical Properties Of WC-Based Cemented Carbides Prepared By SPS

All types of tungsten carbide reinforced materials have been proved to be the most effective materials to strengthen the cone bit, geological core bit and various kinds of downhole fishing tools etc. This suggests a need for the development of cemented carbides with high hardness,high toughness and high intensity. This paper analyzes the microstructure and the properties of advanced commercial milling tools materials, on that basis, new inhibitors combination are developed. High quality cemented carbides are prepared through high-energy ball grinding + SPS technique, so that their microstructure and the properties can exceed those of commercial cemented carbides. It is studied that how these inhibitors to influence the microstructure of cemented carbide by means of EDS, SEM, EPMA, XRD and so on. The properties of cemented carbides are evaluated through the density test, hardness test and 3-point bending test. Finally, action mechanism of these inhibitors combination is discussed.The experimental results show that, advanced commercial WC based cemented carbides include inhibitors TaC,TiC and Cr₃C₂; Because the addition of a small amount of inhibitors will promotes fine grain size, the hardness of commercial cemented carbides are high; however, a lot of grain inhibitors will lead to the precipitation of edges massive phase and the formation of a great deal of pores, so their toughness are not very high.Green powders get refining and activation by way of high energy ball grinding technology. And in this process,a small number of nano-WC powders are synthesized mainly through diffusion reaction mechanism, the crystallite size is 20～30nm. Rare earth elements Y could dramatically reduce pores of microstructure of cemented carbide, make the microstructure uniform and compact, and density gets increased obviously. Rare earth elements Y exerts a little influence on the hardness of alloy,but it enhances the bending capacity of alloy significantly. These two kinds of inhibitors combination TaC/Cr3C2 and VC/Cr3C2 can fine grains obviously and increase the hardness,but there are still pores in the microstructure; Adding carbide inhibitors (TaC/Cr3C2) and rare earth inhibitors (Y) to alloy at the same time, which can not only fine grain size but also make the microstructure dense; the grain is like a long rod commonly, grain size is about 1μm, and the hardness and bending strength of this kind of alloy are higher. Particularly, the microstructure and comprehensive properties of cemented carbide-B2 with combinations of inhibitors ( 0.6 wt % Cr3C2– 4.8 wt %TaC– 0.4 wt %Y ) is the best, its relative density is 99.40%, its hardness is 91.7 HRA, its bending strength is 2847MPa, all of which exceed those of cemented carbide with ordinary carbide inhibitors(VC/ Cr3C2)and advanced commercial milling tools materials.