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Ye N.,Nanchang University | Tang J.,Nanchang University | Wu A.,Nanchang Cemented Carbide Liability Ltd Company | Wei X.,Nanchang University
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2017

Due to the growth of WC particles in the traditional reduction and carbonization process, the method of carbon-hydrogen coreduction-carbonization was adopted to prepare WC nano-powders and the effects of the n(C)/n(W) of precursors and reaction temperature on the properties of WC were studied. The results show that the carbon content of WC is related to the n(C)/n(W) of precursors, and the optimum molar ratio is 3.6. The average particle size of WC is closely related to reduction temperature and carbonization temperature because the transformation of W to WC has structural heredity. With the reduction temperature increasing from 680℃ to 800℃, the pressure of water vapor in the system decreases due to the reaction of H2O and C, which inhibits the volatilization-deposition growth of W particles in the hydrogen reduction process. Therefore, the average particle size of WC decreases with the increasing of reduction temperature. The high temperature can promote the grain boundary migration of WC particles and the combination growth of W nano-particles, and the average particle size of WC increases with the increasing of carbonization temperature. When the n(C)/n(W) of precursor is 3.6, the average particle size of WC powders is 87.3 nm after 800℃ reduction and 1100℃ carbonization. © 2017, Science Press. All right reserved.


Lei C.,Nanchang University | Lei C.,Nanchang Cemented Carbide Liability Company | Wu A.,Nanchang Cemented Carbide Liability Company | Tang J.,Nanchang University | Ye N.,Nanchang University
Xiyou Jinshu/Chinese Journal of Rare Metals | Year: 2014

Tungsten carbide powders with the mean particle size of 109 and 148 nm were prepared at 1180°C in hydrogen molybdenum carbonization furnace by carbonizing the mixture powders of tungsten and carbon black mixed by wet ball milling and dry mixer milling respectively. WC-7%Co (mass fraction) alloys were sintered at 1360°C in the low-pressure vacuum sintering furnace. The effects of morphology of tungsten nano-powders on the properties of tungsten carbide powders and ultrafine cemented carbides were studied. Tungsten nano-powders with the mean particle size of 30 nm were prepared through hydrogen reduction process using ball milling tungsten oxide powder as raw material. The particle size and specific surface of powders were measured by Fisher sizer and specific surface equipment, the phases of carbonization products were analyzed using X-ray diffraction (XRD) and the morphologies and microstructures of powders and sintered alloys were observed by scanning electronic microscope (SEM). The physical and mechanical properties of WC-7Co sintered composites were tested according to related material performance testing standard. It showed that the aggregation of tungsten nano-powders was dispersed by wet ball milling and the distribution of mixtures of tungsten powders and carbon black were improved. High quality tungsten carbide nano-powders were prepared through wet ball milling. The microstructures of ultrafine WC-7Co sintered composites prepared from the powders through wet ball milling method were homogenously and the properties of the alloy were excellent, the hardness and bending strength were HRA 93.7 and 4450 MPa, respectively.


Lei C.,Nanchang University | Lei C.,Nanchang Cemented Carbide Liability Company | Wu A.,Nanchang Cemented Carbide Liability Company | Tang J.,Nanchang University | Liu G.,Nanchang Cemented Carbide Liability Company
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

The effects of a two step carbonization method on properties of tungsten carbide nanopowders and the cemented carbides have been studied. It is shown that the grain aggregation and abnormal coarse grains are mainly due to the sintering combination of agglomerated particles of tungsten or tungsten carbide nanopowders during carbonization process and incomplete carbonization is attributed to the low carbonization temperature. The two step carbonization method (the first step carbonization temperature 1120℃, and the second step carbonization temperature 1180℃) can effectively inhibit the sintering combination phenomenon between nanoparticles, and can carburize the tungsten nanopowders fully. Therefore homogenous tungsten carbide nanopowders are obtained and the content of W2C of the nanopowders is only 0.5%. Microstructures of ultrafine WC-Co sintered composites prepared from the powders through the two step carbonization method are uniform; the properties of the alloy are excellent, and the HRA hardness and bending strength are 93.7 and 4380 MPa, respectively. Copyright © 2014, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.


Tang J.,Nanchang University | Lei C.,Nanchang University | Lei C.,Nanchang Cemented Carbide Ltd Liability Company | Liu G.,Jiangxi Yaosheng Tungsten Co. | Wu A.,Nanchang Cemented Carbide Ltd Liability Company
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

The effect of the morphology structure of tungsten oxide powders on the homogeneity of nanometer W/WC powder was studied during a conventional hydrogen reduction process. The properties of tungsten carbide powder and sintered WC-Co composites were characterized. It is shown that homogenous nanometer tungsten and tungsten carbide powders with loose and porous morphology structure can be prepared from fine tungsten oxide with loose and porous morphology structure. The grain aggregation and abnormal coarse grain are mainly due to the burning binding of agglomeration particle of nano tungsten powder during carbonization process.


Lei C.,Nanchang University | Lei C.,Nanchang Cemented Carbide Liability Company | Tang J.,Nanchang University | Cai D.,Nanchang Cemented Carbide Liability Company | Wu A.,Nanchang University
Xiyou Jinshu/Chinese Journal of Rare Metals | Year: 2013

Medium-size tungsten powders were prepared through high temperature hydrogen reduction process and then mixed homogeneously with carbon by ball milling. The mixtures were carbonized in the H2 atmosphere at 1950 and 1680°C respectively to prepare high temperature medium and normal size tungsten carbide powders. WC-6Co (%, mass fraction) alloys were sintered at 1470°C in a hydrogen protected molybdenum wire furnace. The particle size and particle size distribution of the powders were measured by using Fisher sizer and Malvin particle size distribution equipment, and the phases of carbonization products were analyzed using X-ray diffraction (XRD). The effects of high temperature medium-size tungsten carbide powders on the properties of low cobalt cemented carbide were studied. The performance of WC-6Co sintered alloys were tested and compared with the performance of YG6 cemented carbide produced by normal tungsten carbide powders carbonized at relatively lower temperature. The physical and mechanical properties of WC-6Co sintered composites were tested. The morphology and microstructure of powders and sintered alloys were observed by scanning electronic microscope (SEM). It showed that particle size of high temperature WC powder was larger obviously than that of the original tungsten powder. The grains of high temperature W powder were developed completely and uniform with smooth surfaces. The high temperature WC powder was carbonized completely and its subgrain was coarse, the purity was higher and the lattice defects were lower. The microstructure of WC-6Co alloy was homogenously, crystalline form was integrity, the average grain size of WC crystalline was 2.0 to 2.5 μm, the hardness and bending strength were HRA90.0, 3000 MPa respectively. So the properties of the alloy was better than that of YG6 alloy.


Lei C.,Nanchang University | Lei C.,Nanchang Cemented Carbide Liability Company | Tang J.,Nanchang University | Liu G.,Jiangxi Yaosheng Tungsten Co. | Wu A.,Nanchang Cemented Carbide Liability Company
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2016

The plate-like grain cemented carbides were prepared using W+Co+C (carbon black) as raw materials. Effects of the morphologies of tungsten powders prepared from different raw materials on the microstructures and properties of plate-like grain cemented carbides were investigated. Results show that the morphologies of W powders prepared from blue tungsten oxides (BTO) are spherical polyhedron. However, the W powders prepared from yellow tungsten oxides (YTO) are polyhedral equiaxial, which are easier access to preparation of plate-like tungsten powders by ball milling and plate-like grain WC-Co cemented carbides with large L/D ratio and good grain orientation. © 2016, Science Press. All right reserved.


Wu A.-H.,Nanchang Cemented Carbide Liability Ltd Company | Tang J.-C.,Nanchang University | Ye N.,Nanchang University | Li T.,Nanchang University | And 2 more authors.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2014

The traditional WC powder is generally prepared by heating tungsten and graphite mixture to a certain temperature through radiation, convection and conduction. This process requires both high temperature and a long time, so WC generally has large particle size. Using tungsten nano-powder and activated charcoal as raw materials, nano-structured WC was prepared by microwave carbonization at 1 000℃. The phase composition of samples has been characterized by XRD, the morphology and particle size distribution were observed by SEM and TEM. The results show that a single-phase WC with an average particle size of 86.5 nm can be prepared using W powder with the average particle size of 50 nm by microwave carbonization at 1 000℃ for 10 min. The formation mechanism of nano-WC powders prepared by microwave carbonization was discussed. It is shown that the microwave carbonization process is controlled by diffusion, and the growth rate of WC particle increases with the increase of carbonization temperature. ©, 2014, Central South University. All right reserved.

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