Tungsten

About: Tungsten is a research topic. Over the lifetime, 35225 publications have been published within this topic receiving 456213 citations. The topic is also known as: W & element 74.

Quenching and recovery investigations of vacancies in tungsten

Abstract: Resistivity and transmission-electron-microscopy investigations have been carried out on high-purity quenched tungsten These have yielded values for the monovacancy formation and migration enthalpies of HIV F=3·67±0·2 eV and HIVM=1·78 ± 01 eV respectively, Direct observations of voids formed by vacancy precipitation during quenching and subsequent annealing have led to the conclusion that the equilibrium vacancy concentration at the melting point is Cv(Tm=3695 K) ≃ 1 × 10−4 Using this value, the vacancy resistivity and formation entropy, pIV=6·3 × 10−4 Ω cm and SIV F=2·3k respectively, were deduced The results are discussed in relation to self-diffusion in tungsten and difficulties encountered in earlier work on quenched tungsten

Electrochemical behaviour of tungsten-carbide hardmetals

Abstract: Accurate measurements of the polarisation curves of tungsten carbide-cobalt composites as well as those of the individual components (tungsten carbide, pure cobalt and a cobalt-tungsten-carbon alloy representing the composition of the binder phase of the liquid-phase sintered composites) in normal sulphuric acid were carried out. The linear rule of mixtures first proposed by Stern for heterogeneous alloys was re-examined. The corrosion behaviour of the hardmetal composites cannot be predicted from that of tungsten carbide and pure cobalt. Two models were tested, one in which the carbide crystals are separated from the binder alloy by a thin layer of cobalt low in both carbon and tungsten, and one where this layer is not considered. The second model agrees very well with the experimental results while the first one shows significant deviations. Calculations of the relative removal rates show that the binder corrodes faster than the carbide and is leached out in spite of exhibiting a pseudopassive behaviour owing to the formation of a porous corrosion layer. The influence of the carbide grain size and of the cobalt content on the corrosion kinetics is shown to be too small as to be of any practical importance.

Thermomechanical properties of TiC particle-reinforced tungsten composites for high temperature applications

Abstract: Tungsten and tungsten alloys are widely used in high temperature environments where arc ablation or mechanical deformation and damage are the main sources of materials failure. For high temperature critical applications in thermomechanical environments, however, the low strength limits the use of tungsten and tungsten alloys. Hence, new tungsten based materials with good high temperature thermomechanical properties need to be developed in order to extend the use of tungsten. TiC particle-reinforced tungsten based composites (TiCp/W) were fabricated by hot pressing at 2000 °C, 20 MPa in a vacuum of 1.3×10−3 Pa. The composites were examined with respect to their thermophysical and mechanical properties at room temperature and at elevated temperature. Vickers hardness and elastic modulus increased with increasing TiC content from 0 to 40 vol.%. The highest flexural strength, 843 MPa, and the highest toughness, 10.1 MPa m1/2, of the composites at room temperature were all obtained when 20 vol.% TiC particle were added. As the test temperature rose, the flexural strength of the TiCp/W composites firstly increased and then decreased, except in the monolithic tungsten. The highest strength of 1155 MPa was measured at 1000 °C in the composite containing 30 vol.% TiC particles. The strengthening effect of TiC particles on the tungsten matrix is more significant at high temperatures. With the addition of TiC particles, the thermal conduction of tungsten composites was drastically decreased from 153 W m−1 K−1 for monolithic W to 27.9 W m−1 K−1 for 40 vol.% TiCp/W composites, and the thermal expansion was also increased. The new composites are successfully used to make high temperature grips and moulds.