Time filter

Source Type

Wu C.,Xiamen Tungsten Co. | Wu C.,Xiamen Golden Egret Special Alloy Co.
International Journal of Refractory Metals and Hard Materials | Year: 2011

Ultrafine tungsten powders with a grain size below 0.5 μm are key raw materials for fabricating ultrafine cemented carbides. Conventional hydrogen reduction technique has been utilized to prepare the ultrafine tungsten powders. In the present work, highly pure nano-needles of violet tungsten oxide (WO 2.72) were reduced by dry hydrogen. Nucleation and growth of the metallic tungsten in the early stage of hydrogen reduction have been studied by XRD, FESEM and HRTEM. Mechanism of formation of nano-size tungsten powders is proposed and a concept of in-situ hydrogen of the nano-needle WO 2.72 is presented. Empirical relations between an average diameter of nano-needle WO 2.72 and an average particle size of the resultant tungsten powders in both stage of nucleation and industrial conduction have been established. These empirical relations could be a reasonable guidance for suitably choosing the raw materials of nano-needle WO 2.72 to prepare ultrafine tungsten powders. It has been determined that the BET special surface areas of the in-situ hydrogen-reduced tungsten powders with the average particle size of 0.2 μm and 0.3 μm, which were produced from the raw nano-needle WO 2.72 powders with the average diameter of 60 nm and 80 nm, are 6.03 m 2/g and 4.65 m 2/g, and the oxygen contents are 0.35% and 0.29%, respectively. © 2011 Elsevier Ltd. All rights reserved.


Lin N.,Central South University | Wu C.H.,Xiamen Tungsten Co. | Wu C.H.,Xiamen Golden Egret Special Alloy Co. | He Y.H.,Central South University | Zhang D.F.,Central South University
International Journal of Refractory Metals and Hard Materials | Year: 2012

In this work, the effects of 1.0 wt.% additions of Mo and Co on the microstructure and properties of WC-TiC-Ni cemented carbides were investigated using scanning electron microscope, mechanical properties tests, corrosion resistance and abrasion resistance tests. The results show that 1.0 wt.% Mo addition can refine the WC grains and increase the hardness. Moreover, with the addition of minor Mo, the corrosion resistance and abrasion resistance of alloys improved significantly. The addition of 1.0 wt.% Co can inhibit the growth of WC grains, improve the density and hardness slightly, and enhance the abrasion resistance of cemented carbides. However, the minor Co has negative effect for the corrosion resistance. © 2011 Elsevier Ltd. All rights reserved.


Wu C.-H.,Xiamen Tungsten Co. | Zhang T.-Q.,Xiamen Golden Egret Special Alloy Co.
International Journal of Refractory Metals and Hard Materials | Year: 2013

The characteristics and formation mechanisms of microstructure imperfections in two sets of submicron WC-10wt.%Co cemented carbides, which are fabricated by vacuum and low-pressure sintering, respectively, are deeply analyzed. Main imperfections are pore-Co-pool in the vacuum-sintered samples. The number of pore-Co-pool is obviously reduced by low-pressure sintering, but many porous microstructures with poor-Co or Co-free are easily introduced; the impurity segregation is also easily formed. Transverse rupture strength (TRS) of samples is strongly affected by the characteristics and size of imperfections. Two linear relationships between TRS and pore size are experimentally established, and a critical pore size has been calculated to be 28.8 μm. © 2013 Elsevier Ltd.


Wu C.-H.,Xiamen Tungsten Co. | Wu C.-H.,Xiamen Golden Egret Special Alloy Co.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2011

The continuously dynamic-controlled combustion synthesis (CDCCS) was developed based on the continuous fluidization and combustion synthesis technologies. CoC2O4·2H2O powders were transformed to Co3O4 in a gas-solid fluid bed unit designed and build independently, where the reactant of CoC2O 4·2H2O powders and the reactant of air were poured and introduced from the top and the bottom of the bed at a certain rates respectively. The reagents met in the bed and ignited at a given low temperature, resulting in formation of Co3O4. The results show a significant difference in combustion wave models. In the case of CDCCS, there was an immobile combustion wave, floating in the combustion zone located in the middle of the bed, instead of propagating of the combustion wave. The temperature of the combustion wave can be controlled by adjusting the flow rate of carrier gas. The resultant Co3O4 powders (diameter size ≤0.8 μm) have a narrow particle size distribution and spherical or quasi-spherical shape. This novel technique has many advantages, such as continuation, efficiency, energy conservation and environmental friendly and has been used in mass production. © 2011 The Nonferrous Metals Society of China.


Lai J.,Xiamen Golden Egret Special Alloy Co.
Solid State Phenomena | Year: 2011

Titanium alloys are difficult-to-cut materials, and the rapid wear of cutter is a big problem for machining of these alloys. In this paper, the wear characteristics of seven milling cutters in milling of TC4 (Ti6Al4V) titanium alloys are investigated. The results indicated that the averaged flank wear of each cutter linearly increases as the accumulated cutting length expands. Large radial rake angle as well as axial rake angle is favor for reducing cutter wear .© (2011) Trans Tech Publications, Switzerland.


Zhang S.-Q.,Xiamen Golden Egret Special Alloy Co.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2014

WC-10Co-0.6Cr3C2 cemented carbides was prepared by sinter-HIP. The physical and mechanical properties of the alloys with different carbon contents were tested by OM RHA analysis, magnetic saturation and coercive force analysis. The results show that the hardness, density and coercive force of the alloys decrease with carbon content increase. When the carbon content of the alloy varies from 5.41% to 5.55%, the alloys have a two-phase structure. When the carbon content of the alloys is lower than 5.41%, a carbon deficiency phase, i.e. the θ phase appeares. When the carbon content of the alloys is higher than 5.55%, a free carbon phase appeares.


Zhang S.,Xiamen Golden Egret Special Alloy Co
Fenmo Yejin Jishu/Powder Metallurgy Technology | Year: 2015

A gradient sintered WC-Ti(C, N)-(Ti, W)C-(Ta, Nb)C-Co cemented carbide with three different carbon contents was fabricated by one-step sintering procedure. The microstructure and element distribution of the cemented carbides were investigated by SEM and EPMA. Vickers hardness (HV30) and fracture toughness (KIC) were measured. The aim of this work is to relate the variation in carbon content to the resulting microstructures and to the mechanical behavior of these alloys. The results show that all alloys create a surface zone depleted of cubic carbides containing Ta, Ti, Nb, and ductile binder phase rich Co. The zone width and WC grain size increase with increasing carbon content. Hardness decrease and fracture toughness increase with increasing carbon content. ©, 2015, Beijing Research Institute of Powder Metallurgy. All right reserved.


Zou L.,Xiamen Golden Egret Special Alloy Co Ltd
Fenmo Yejin Jishu/Powder Metallurgy Technology | Year: 2015

A gradient sintered WC-Ti(C,N)-NbC-Co cemented carbides were fabricated with two different Ti(C,N) contents (0.5% and 1.5%) and by one-step sintering procedure, and were coated with the TiN/MT-TiCN/Al2O3 coating using chemical vapor deposition (CVD). The effects of the variation in Ti(C,N) content on the resulting microstructures and the mechanical behavior of gradient cemented carbide and its cutting performance of coated inserts in turning of 45# steel were studied. The results show that both the alloys create a surface zone depleted of cubic carbides, with the increase of Ti(C,N) content, the zone width increases from 11μm to 35μm and the average WC grain size decreases from 1.97 μm to 1.60 μm; meanwhile, hardness (HV30) and coercive force (Hc) increase, while fracture toughness (KIC) and density decrease. The cutting tests demonstrate that the coated gradient inserts with a higher Ti(C,N) content have a slightly decreased wear resistance, but obviously improve impact resistance. ©, 2015, Beijing Research Institute of Powder Metallurgy. All right reserved.


Lin G.-A.,Xiamen Golden Egret Special Alloy CO.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2014

Some selection principles of metal cups used to fabricate poly-crystal diamond (PCD) and poly-crystal cubic boron nitride (PCBN) compacts have been summarized according to the actual production. The selection principle are as follow, 1)higher melting point; 2) higher plasticity, transformation equality and no breaking at high pressure; 3) there is the purification function on cavity body; 4) simple technology. The effects of some common metal cup materials and some assembly modes on the ultra-high pressure-high temperature sintering process have been analyzed in detail in the present paper. Some assistances can be provided to the production of superhard materials.


Chen L.,Xiamen Golden Egret Special Alloy Co. | Chen L.,Harbin Institute of Technology | Leng Y.,Harbin Institute of Technology | Guo H.,Harbin Institute of Technology | And 2 more authors.
Journal of the Franklin Institute | Year: 2012

The problem of ∞ control for a class of discrete-time Markov jump linear systems (MJLSs) characterized by piecewise-constant transition probabilities (TPs) is investigated in the paper. The so-called piecewise-constant TPs mean that the TPs are varying but invariant within an interval. The variation of the TPs considered here is subject to a typical class of slow switching signal, the average dwell time (ADT) switching, i.e., the number of switches in a finite interval is bounded and the average time between two consecutive switchings of TP matrices is not less than a constant. In this paper, the technique is illustrated and its use is exemplified with application to the popular class of multiplier-accelerator macroeconomic model. © 2012 The Franklin Institute. All rights reserved.

Loading Xiamen Golden Egret Special Alloy Co. collaborators
Loading Xiamen Golden Egret Special Alloy Co. collaborators