Zhang Chuan-fu

Phase composition, transition and structure stability of functionally graded cemented carbide with dual phase structure

The phase composition, phase transition and phase structure transformation of the wire-cut section of functionally graded WC-Co cemented carbide with dual phase structure were investigated by XRD phase analysis. It is shown that the composition of η phase in the core zone is Co3W3C (M6C type). The structure of cobalt based solid solution binder phase is fcc type. At the cooling stage of the sintering process, the phase transition of η phase, i.e. M6C→M12C and the martensitic phase transition of the cobalt based solid solution binder phase, i.e. fcc→hcp are suppressed, which facilitates the strengthening of the alloy. Because the instantaneous temperature of the discharge channel is as high as 10 000 °C during the wire cutting process, the processed surface is oxidized. Nevertheless, the oxide layer thickness is in micro grade. In the oxide film, η phase is decomposed into W2C and CoO, and cobalt based solid solution binder is selectively oxidized, while WC remains stable due to the existence of carbon containing liquid organic cutting medium.

Computer model of copper smelting process and distribution behaviors of accessory elements

A computer model has been developed to simulate the distribution behaviors of Ni, Co, Sn, Pb, Zn, As, Sb, Bi, Au and Ag in copper smelting process. The model assumes that the copper smelting furnace is in thermodynamic equilibrium. As many as 21 elements (Cu, S, Fe, Ni, Co, Sn, As, Sb, Bi, Pb, Zn, Au, Ag, O, N, C, H, Ca, Mg, Al, and Si) and 73 compounds are considered. This model accounts for physical entrainment in the melts. The predictions by the present computer model are compared with the known commercial data from Guixi Smelter in China. Horne Smelter in Canada and Naoshima Smelter in Japan. The agreements between the computer predictions and the commercial data are excellent, so that the present computer model can be used to monitor and optimize the actual industrial operations of copper smelting. It is applicable to simulation of almost all copper pyrometallurgical processes.

Cerium enrichment on sinter skin of mischmetal doped WC-Co cemented carbide

Rare earth-doped WC-Co cemented carbides with low carbon-containing level were prepared by adding mischmetal (mainly containing lanthanum and cerium) in the form of cobalt pre-alloyed powder during ball-milling. After sintering, the sinter skin (exterior) was observed and analyzed by scanning electron microscopy (SEM) and energy disperse X-ray spectroscopy (EDXS). The results show that during the sintering process lanthanum and cerium are separated and cerium predominantly migrates towards the surface forming precipitates containing oxygen. Thermodynamic analysis and polarization of cerium atom caused by the strong interaction between cerium atoms and high energy carbon atoms were used in explaining the observed phenomenon.

The Effect of Sintering on the Properties of Ultrafine Rhenium Powders Prepared by CVD Method

A novel CVD method of preparing ultrafine rhenium powders was investigated in this paper. The Re2O7 gas obtained by decomposing NH4ReO7 was transported to the reduction chamber and then reduced by H2 to form rhenium powders. In order to evaluate the effects of sintering on properties of rhenium particles, such as crystal size, morphology, surface conditions and particle size, the samples of rhenium powders prepared at different reduction temperatures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser particle size analyzer. The experimental results show that the sintering effect among particles is enhanced with increasing of reduction temperature, resulting in larger crystal size, smoother surface and larger average particle size of the rhenium powder.

A new method of computing multi-component E-pH diagrams

Aqueous E-pH Diagram is an essential tool for analyzing hydrometallurgical and corrosion processes. Due to the requirements for environmental protection and energy saving in recent years, waste water processing and hydrometallurgical process of concentrate have been greatly developed. The construction of E-pH diagrams has turned to multi-component systems. However, there are some limits in plotting such diagrams. There is only one diagram for one multi-component system, which can not reflect the truth of the aqueous reaction. In the paper, a new computation method is proposed to construct E-pH diagrams. Component activity term is used to determine the boundary of stable areas. For the multi-component systems, different atom ratios of elements have been taken into account. M-S-H2O system is chosen to study since it is of importance in metallurgical solution. Compared with conventional methods, the algorithm is simple and conforms to real conditions.

Microstructural evolution of TiAl base alloy during three-stepped thermo-mechanical treatment

A TiAl base alloy ingot with a height-to-diameter ratio of 2.2 was broken down by multiple step canned forging. The microstructures after every deformation and subsequent recrystallization were observed by optical microscopy. Results show that at the first step the reduction should be carefully controlled in case of double-bulge and crack of the ingot. After the first annealing, recrystallization occurred at the deformed grain boundaries and inside the grain. The recrystallized microstructure is favorable for further deformation. After the second deformation and annealing, coarsening of the lamellae occurred and the microstructure became equiaxed. By the final deformation and subsequent recrystallization, the coarse lamellar colony can be refined to about 20 µm, and homogeneous microstructure was obtained from the ingot with a large initial height-to-diameter ratio.