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.

Tensile behavior change depending on the varying tungsten content of w-ni-fe alloys

Abstract: Tungsten heavy alloys (WHAs) are metal–metal composites consisting of nearly pure spherical tungsten particles embedded in a Ni–Fe–W or Ni–Co–W or Ni–Cu–W ductile matrix. In this dual phase alloy, there are several complicated relations between the ductile matrix and hard tungsten particles. The aim of this research was to examine the effect of varying tungsten content on the microstructure and mechanical properties of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity and solid volume fraction) were measured and were found to have a significant effect on the mechanical properties of tungsten-based heavy alloys. The result shows that the binding strength between the W and the matrix phase has a major influence on the ductility of tungsten-based alloys. The larger this binding force is, the better the ductility is.

Adsorption of CO on Tungsten: Field Emission from Single Planes

Abstract: Work‐function and Fowler–Nordheim pre‐exponential changes for incremental oxygen adsorption at 20 and 100°K have been measured on the (120), (111), (100), (211), and (110) planes of a tungsten field emitter. On the (110) plane Δφ = 0.6 eV at full coverage, while Δφ = 1.2–1.4 eV on most other planes. A model of O adsorption based on the partial filling of an affinity band is presented to account for this and other features of the results. Diffusion into various planes was also investigated. It was found that low‐temperature boundary diffusion at 25°K leaves the (110) plane bare. Diffusion in the chemisorbed layer starts at 400°K on (110) with an activation energy of 15 kcal, and on other planes at temperatures of ∼ 500°K.

Method for plasma etching tungsten

Abstract: A process wherein a thin film metal (e.g. tungsten) is anisotropically etched under plasma bombardment conditions by using a feed gas mixture which includes a fluorine source (such as SF 6 ) plus a fluorosilane (e.g. SiF 4 ), plus a bromine source (such as HBr), plus a weak oxygen source such as carbon monoxide. This chemistry provides anisotropic high rate fluoro-etching with good selectivity to photoresist.

Measurement of the Polarizabilities and Field Evaporation Rates of Individual Tungsten Atoms

Abstract: The relative field evaporation rates of tungsten kink site atoms at (110) plane edges and the absolute field evaporation rates of individual tungsten adatoms on tungsten (110) planes have been measured covering nine orders of magnitude. From the experimental data, the effective polarizabilities of the tungsten kink site atoms and the adatoms are found to be 4.6 ± 0.6 and 6.8 ± 1.0 A3, respectively. A theoretical consideration is given to explain why the effective polarizability of metal surface atoms depends on the atom‐to‐surface mirror plane distance, and therefore the atomic sites. The calculation also reveals a first power field dependent energy level shift, which is dependent upon the atom‐to‐surface plane distance. It is further shown that the classical image potential no longer holds at a distance smaller than 1 A from the metal surface.

Clustering of H and He, and their effects on vacancy evolution in tungsten in a fusion environment

Abstract: The behaviours of hydrogen and helium in tungsten are vitally important in fusion research because they can result in the degradation of the material. In the present work, we carry out density-functional theory calculations to investigate the clustering of hydrogen and helium atoms at interstitial sites, vacancy and small vacancy clusters (Vacm, m = 2, 3), and the influence of hydrogen and helium on vacancy evolution in tungsten. We find that hydrogen atoms are extremely difficult to aggregate at interstitial sites to form a stable cluster in tungsten. However, helium atoms are energetically favourable to cluster together in a close-packed arrangement between (1 1 0) planes forming helium monolayer structure, where the helium atoms are not perfectly in one plane. Both hydrogen and helium prefer to aggregate stably in vacancy and small vacancy cluster forming VacmXn (X = H, He). The concentrations of VacmHn (m = 1) clusters relative to temperature are evaluated through the law of mass action. The present calculations also show that the emission of a 〈1 1 1〉 dumbbell self-interstitial atom (SIA) from Hen to form VacHen and from VacHen to form Vac2Hen may take place for n > 5 and n > 9, respectively. According to the present results, we predict that a helium monolayer structure could nucleate for He atom platelet lying on (1 1 0) plane in tungsten, and the helium platelet formation on (1 1 0) plane in molybdenum observed by the experiment may be due to the initial monolayer arrangement of He atoms at interstitial sites. Meanwhile, our results contribute to the understanding for nucleation and the development of the voids and blisters in tungsten that are observed in the experiments.