Effect Of Ca, Al On Structure And Properties Of Tungsten Products

As one of the important strategic resources around the world, tungsten has beenwidely used in many industrial areas, for its natures of high melting point, goodthermal and electrical conductivity. The contents of Ca, Al, Mo and other impurityelements are so high that will have effect on the quality of tungsten-based materials.It carries great significance for the high efficient utilization of tungsten resources tohave a deep research on the effect mechanism of impurities on tungsten products.With the solution doping process, the raw materials APT powder with differentcontents of Ca, Al experiences four stages: the calcination of ammoniumparatungstate(APT), reduction of tungsten oxide(WO3), carbonization of tungsten(W)and Sintering of tungsten carbides (WC+Co). The phase transformations anddistribution of element Ca, Al during the process of preparation of tungsten productswere investigated by XRD, SEM and HRTEM. The effect mechanism of Ca, Al to themicro-morphologies and particle sizes of W and WC powder were discussed. Therelationship between Ca, Al and the microstructure and properties of cementedcarbide were also studied. The research presented important references for practicalindustrial production. The main conclusions are summarized as following:1. The raw materials APT powder with50-10000ppm Ca was prepared by theliquid-solid doping method. Ca was mainly in the form of CaWO4in the tungstenoxide(WO3) after the calcination of ammonium paratungstate(APT); mainly in theform of CaWO4and Ca4.26W10O30in the tungsten (W) after the reduction of tungstenoxide(WO3); mainly in the form of CaC2and Ca4.26W10O30in the tungstencarbide(WC) after carbonization of tungsten(W). Ca had little effect on the particlesize of tungsten powder. Second phases enriched calcium distributed in and out of thetungsten powder particles. The average size of undoped WC particles was0.57μm,and that of WC particles doped with10000ppmCa was only0.36μm. The secondphases enriched Ca and WC had volume difference during the carbonization,accelerating the fragmentation of WC particles, thus resulted in the decrease of grainsize.Ca was mainly in the cobalt binder phase of YG6alloy. The density and hardness of alloy doped with10000ppmCa was obviously decreased.2. The raw materials APT powder with50-10000ppm Al was prepared by theliquid-solid doping method. Al was mainly in the form of Al2(WO4)3in the tungstenoxide(WO3) after the calcination of ammonium paratungstate(APT); after thereduction of tungsten oxide(WO3), most of the Al2(WO4)3experienced the phasetransformation of Al2(WO4)3-AlWO4, so Al mainly in the form of AlWO4andAl2(WO4)3in the tungsten (W); mainly in the form of Al4C3in the tungstencarbide(WC) after carbonization of tungsten(W). The average size of undoped Wparticles was1.14μm, and that of W particles doped with10000ppmAl was only0.51μm. It might be that the second phases enriched Al restricted the growth of W. Theaverage size of undoped WC particles was0.57μm, and that of WC particles dopedwith10000ppmAl was only0.34μm. The carbonation rate of the second phasesenriched Al was higher than W, and the Al4C3restricted the growth of WC. Al wasmainly in the cobalt binder phase and the collection region of small WC particles ofYG6alloy. The density and hardness of alloy doped with10000ppmAl was decreasedslightly.