Hot pressing of oxides of refractory metals

Conclusions A study was made of the sintering process in the hot pressing of several powdered oxides of transition metals, namely, TiO₂, ZrO₂, V₂O₅, Nb₂O₅, and Cr₂O₃. It was established that, at any given treatment duration, raising the temperature steadily increases the rate of densification and density of specimens. At each temperature, the densification process is characterized by a specific final density.Translated from Poroshkovaya Metallurgiya, No. 11 (107), pp. 22–25, November, 1971.     

Interaction of tungsten with tungsten carbide in a copper melt

The chemical interaction between tungsten and tungsten carbide in a copper melt with the formation of W₂C at 1300°C is studied. It is shown that the mechanical activation of a composition consisting of copper melt + W and WC powders by low-temperature vibrations initiates not only the chemical interaction of its solid components but also their refinement.     

钨和碳化钨纳米线的研究进展

新型纳米材料———钨和碳化钨纳米线,以其特殊的一维纳米结构、优异的物理和化学性能而具有重要的学术研究价值和实用意义。该文首先综述了钨和碳化钨纳米线的最新研究进展,介绍了其几种典型的制备方法,即化学气相沉积法、物理气相沉积法、诱导气相沉积法、化学蚀刻法、自催化法、介孔层状结构卷曲法,进而分析了其生长机理,探讨了其存在的问题,并展望了未来的研究趋势。指出:现有各种制备钨和碳化钨纳米线的方法仅限于基础研究和小批量生产应用,而寻找某种简便、经济、能规模生产的新型制备方法,包括现已初获成功的锥形钨及碳化钨纳米线制备法,仍将是今后很长一段时间内的研究重点。     

Dispersion strengthening titanium with refractory oxides

Abstract

Thorium oxide and cerium zirconate were alloyed with pure titanium and with two titanium alloys by arc melting. The refractory compounds apparently dissolved during melting and precipitated as dispersed phases on cooling. Although room-temperature and high-temperature (540°C) tensile strengths were improved at the expense of ductility, the refractory particle size and interparticle spacing were larger than recommended for maximum dispersion strengthening. Heat treating increased the size of the refractory particles.

Résumé

Des additions d'oxyde de thorium et de zirconate de cérium ont été faites à du titane pur et à deux de ses a1liagesfondus à l'arc électrique. Les composés réfractaires se sont apparemment dissous lors de la fusion et ont précipité de fa?on dispersée au refroidissement. La résistance à la traction s'est améliorée au détriment de la ductilité; toutefois, la grosseur des particules et l'espacement des partictiles excédaient la limite recommandée pour un durcissement maximum. Le traitement thermique a augmenté la grosseur des particules réfractaires.     

High-temperature synthesis of tungsten carbide in a methane-hydrogen gas medium

Tungsten carbide synthesis in a methane-hydrogen medium have been studied and the conditions for obtaining WC power with no free-carbon impurity determined. Hard alloys based on a “gas” carbide have been shown to exhibit high ductility. The results of the study have been used to develop a commercial process to produce high-ductile hard alloys for high-pressure equipment, stamping dies, and drilling tools.     

Reaction of titanium carbide with water

Summary Contrary to the generally held view that carbides of the transition metals of groups IV and V are inert with respect to water, the authors show on the example of titanium carbide that the carbides are decomposed by water, although the extent of attack is not more than 5–30 atomic layers, i. e., not more than 100–150 A.The hydrolysis of TiC proceeds according to the reaction: TiC+xH₂O CH₄ + TiO₂ · xH₂O.Methane is the principal constituent of the gaseous hydrolysis products, and consequently it is possible to regard carbides of the transition metals of groups IV and V as methane derivatives. Hydrogen evolution in both carbides of group V and nonstoichiometric carbides of group IV is believed to take place as a result of the presence of free electrons in the carbides. The complex polymer acid TiO₂ · xH₂O undergoes dissociation, which becomes intensified in the course of time and results in a rise of hydrogen ion concentration. TiC powder particles are negatively charged. With the results obtained it is possible to choose suitable dispersion media for such powder metallurgical operations as fine milling, slip casting, and others.Translated from Poroshkovaya Metallurgiya, No. 6(54), pp. 53–57, June, 1967.     

Interaction of a mixture of oxides of tungsten and silicon with carbon

Translated from Poroshkovaya Metallurgiya, No. 3(327), pp. 72–75, March, 1990.     

High temperature hardness of tungsten carbide

The effect of crystallographic orientation and test temperature on hardness of WC single crystals was investigated along with the hot hardness of poly crystalline tungsten carbide. Also investigated was the effect of carbide grain size and the amount of binder phase on the hot hardness of some cemented tungsten carbides. The hot hardness of single crystal WC on all major crystallographic orientations evaluated decreases very rapidly for increasing temperature, and the single crystal hardness on its hardest orientation is only about half of the polycrystalline material depending on the test temperature. Because of its polycrystalline character, some cobalt bonded cemented tungsten carbides can be harder than single crystal WC over some intermediate temperature range.