Constitutive study for tungsten alloy under high pressure

Asymmetric plate impact experiments are conducted on LY12 aluminium alloy in a pressure range of 85–131 GPa. The longitudinal sound speeds are obtained from the time-resolved particle speed profiles of the specimen measured with Velocity Interferometer System for Any Reflector (VISAR) technique, and they are shown to be good agreement with our previously reported data of this alloy in a pressure range of 20–70 GPa, and also with those of 2024 aluminium reported by McQueen. Using all of the longitudinal speeds and the corresponding bulk speeds calculated from the Gruneisen equation of state (EOS), shear moduli of LY12 aluminium alloy are obtained. A comparison of the shear moduli in the solid phase region with those estimated from the Steinberg model demonstrate that the latter are systematically lower than the measurements. By re-analysing the pressure effect on the shear modulus, a modified equation is proposed, in which the pressure term of P/η1/3 in the Steinberg model is replaced by a linear term. Good agreement between experiments and the modified equation is obtained, which implies that the shear modulus of LY12 aluminium varies linearly both with pressure and with temperature throughout the whole solid phase region. On the other hand, shear modulus of aluminium in a solid-liquid mixed phrase region decreases gradually and smoothly, a feature that is very different from the drastic dropping at the melting point under static conditions.

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First-principles study on adsorption mechanism of hydrogen on tungsten trioxide surface

Jiang¹,

Zheng-Bing²,

Yong-Bo³

2017

Acta Phys. Sin.

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With the development of modern industrial technology, tungsten products prepared from normal tungsten powder cannot meet the demands of industry. The tungsten product produced from ultra-fine tungsten powder exhibits high strength, high toughness, and low metal plasticity-brittleness transition temperature, which greatly improves the performance of materials. Hence, it is necessary to carry out theoretical research on the micro adsorption dynamics during hydrogen reduction of tungsten trioxide to prepare ultra fine tungsten powder. In order to understand crystal characteristics of WO3 and WO3(001) surface characteristics, and to provide beneficial theoretical support for reaction law of hydrogen reduction on the WO3(001) surface, the mechanisms of H atom adsorption on cubic WO3 and WO3(001) surface are studied by the first-principles calculation based on the density functional theory (DFT) plane wave pseudo-potential method. The results show that theoretically calculated band gap of the cubic crystalline WO3 is 0.587 eV. There are two kinds of WO3(001) surfaces, WO-terminated (001) surface and O-terminated (001) surface. The W-O bond length and the bond angle of W-O-W structure change after the geometric optimization of the surface, and thus the surface relaxation is realized. The WO-terminated (001) surface shows n-type semiconductor characteristics while the O-terminated (001) surface shows p-type semiconductor characteristics. Four adsorption configurations of H atoms on the WO-terminated (001) surface and the O-terminated (001) surface, including H-O2c-H, H-O2 cH-O2c, H-O1c-H, and H-O1cH-O1c, are calculated. Among them, the adsorption energy of the H-O1c-H configuration is the smallest (-3.684 eV) with the shortest bond length of H-O bond (0.0968 nm), and hydrogen atoms lose the most of electrons (0.55e), which indicates that the H-O1c-H adsorption configuration is the most stable one. The band gap of the H-O1c-H configuration increases from 0.624 eV to 1.004 eV after adsorption, while the bandwidth of valence band is almost unchanged. The results about the density of states (DOS) reveal that 1s state of the H atom interacts with 2p and 2s states of the O atom. Strong isolated electron peaks are formed to be at about -8 and -20 eV. The outermost O1c atoms of O-terminated (001) surface contain an unsaturated bond, facilitating the bonding between two H atoms and one O1c atom. Thus, two H atoms and one O1c atom form chemical bonds respectively, and an H2O molecule is generated, leaving an oxygen vacancy on the surface after adsorption reaction. By combining experimental observations with simulation results, the mechanism of hydrogen reducing tungsten trioxide can be elaborated profoundly from a micro view.

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Constitutive study for tungsten alloy under high pressure

Cited by 4 publications

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A study of the hydrogen adsorption mechanism of W18O49 using first-principles calculations

A study of the hydrogen adsorption mechanism of W18O49 using first-principles calculations

Shear modulus of shock-compressed LY12 aluminium up to melting point

First-principles study on adsorption mechanism of hydrogen on tungsten trioxide surface

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