Ductility Of Tungsten Research Articles

Effect of alloying elements on stacking fault energy and ductility of tungsten

First principles calculation is conducted to systematically investigate the effects of alloying elements (Mo, Re, Os, Ta, Ti, and V) on phase stability, stacking fault energy, ductility, and restoring force of W. It is found that the addition of Mo, Re and Os would decrease the generalized stacking fault energy (GSFE) of W and increase the ductility of W, while the alloying elements of Ti, Ta, and V could enhance its GSFE and reduce its ductility. The different effects of alloying elements would be mainly attributed to the intrinsic interaction between W and the alloying element, i.e., the repulsive interaction of W-Mo, W-Re, and W-Os with positive heats of formation would increase the interlayer distance of W and facilitate its slip, whereas the attractive interaction of W-Ti, W-Ta, and W-V with negative heats of formation would reduce the interlayer distance of W and impede the slip. The derived results are in good agreement with available observations in the literature, and could provide a deep understanding of the effects of alloying elements on various properties of W.

Ductilisation of tungsten (W): On the increase of strength AND room-temperature tensile ductility through cold-rolling

Here we show that cold-rolling is a method to achieve room-temperature ductility in commercial purity, monolithic tungsten (W). Furthermore, we show that a decrease in rolling temperature concomitantly increases the strength and ductility of tungsten. So cold-rolling is a way to overcome the strength–ductility trade-off.In this work, we assess three different cold-rolled microstructures obtained from rolling at (i) 1000°C (1273K), (ii) 800°C (1073K), and (iii) 600°C (873K). Benchmark experiments were performed on a sintered ingot as well as on a hot-rolled plate. From these plates tensile test specimens were cut by spark erosion and tested at room temperature. The results show an increase of total uniform elongation, Aut, ranging from 1.38% (cold-rolled at 1000°C (1273K), and 800°C (1073K)) up to 1.47% (cold-rolled at 600°C (873K)) and an increase of the total elongation to fracture, At, ranging from approximately 3% (cold-rolled at 1000°C (1273K), and 800°C (1073K)) up to 4.19% (cold-rolled at 600°C (873K)) with decreasing rolling temperature.The microstructure of the plates is analysed by means of scanning electron microscopy (SEM) (grain size, subgrains, crystallographic texture) and transmission electron microscopy (TEM) (bright field imaging, scanning TEM). Furthermore, strain-rate jump tests have been performed at 400°C (673K) to determine the strain-rate sensitivity, m, (sintered ingot m=0.088, cold-rolled at 600°C (873K) m=0.011) and the activation volume, V, (hot-rolled W plate V=191b3, cold-rolled at 600°C (873K) V=111b3) of the tungsten sheets.The question of why cold-rolling increases both strength and ductility is discussed against the background of cold-rolling-induced lattice defects. We speculate that the increase of ductility is caused by the ordered glide of screw dislocations, that move with low deformation incompatibility along the high-angle grain boundary (HAGB) channels (confined plastic slip).

The nature behind the preferentially embrittling effect of impurities on the ductility of tungsten

It is well known that the ductility of tungsten is very sensitive to impurities while the ductility of tantalum is tolerant to them. However, the fundamental reason behind this preferential effect still remains elusive. Here, based on first-principles calculations, we demonstrated that impurities in tungsten are more likely to segregate into the investigated grain boundary region and the vicinity of straight screw dislocation core than in tantalum, thus having more chances to decrease the ductility. In turn, the presence of impurities, if deemed undesirable, will cause a greater reduction in the grain boundary separation energy for tungsten. The analyses of the chemical and mechanical effects of impurities based on an elegant model suggest that, for the deleterious impurities that have similar binding behavior with tantalum and tungsten, if their effect is repulsive at all relevant site, tungsten is more sensitive to them due to its low lattice constant and high elastic modulus despite other possible causes.

Low-Temperature Strengths and Ductility of Various Tungsten Sheets

We used three kinds of tungsten sheets in this study. First, we examined microstructure such as grain size distribution using an optical microscope. Secondly, we carried out three-point bend tests at temperatures between about 290 and 500 K. Then, we examined fracture surface of a failed specimen using a scanning electron microscope. Lastly, by analyzing all these results, we evaluated apparent intergranular and transgranular fracture strengths and discussed strengths and ductility of tungsten. Additionally, we compared mechanical properties of tungsten with those of molybdenum.

Short note Dynamic compression behaviour of tungsten powders consolidated by plasma pressure compaction

It has been generally believed that the ductility of tungsten can be increased by decreasing grain size to ultrafine levels (∼100 nm). Pure ultrafine grain tungsten powders of various average particle sizes (2·0, 0·7, and 0·16 μm) were consolidated using the rapid consolidation technique, plasma pressure compaction (P2C), to minimise grain growth. Preliminary results indicate that tungsten powders can be consolidated to high density without abnormal grain growth at 2000°C and 50 MPa with less than 3 min of iso thermal holding time in the P2C process. The densities of consolidated specimens were measured using Archimedes'method, and the microstructure was analysed using SEM. The mechanical behaviour of the consolidated specimens was investigated using the compression Kolsky bar. Dynamic compression properties were examined to determine the effect of grain size, grain structure, and density on yield stress at various strain rates.

After-annealing strength and ductility of tungsten deposited from a gas medium

Tungsten coatings prepared by the method of deposition from a gas phase onto a graphite substrate have an elevated susceptibility to brittle fracture. In order to increase the ductility and decrease the critical brittleness temperatureT br of parts with such coatings they are subjected to annealing. The present paper studies the changes in the structure and the mechanical properties of coatings of gas-phase tungsten after annealing by various regimes in order to establish the optimum one.

Influence of the critical stage of polygonization on the characteristics of ductility of tungsten in high-temperature mechanical tests

Influence of the critical stage of polygonization on the characteristics of ductility of tungsten in high-temperature mechanical tests

Change in the ductility of tungsten under the influence of electric current

Change in the ductility of tungsten under the influence of electric current

Properties of tungsten-rhenium alloys

1. The W-Re equilibrium diagram has been constructed [Figure 6]. 2. Addition of Re to tungsten raised the temperature of incipient recrystallization of tungsten VCh wire by 200–400°C, depending on the rhenium content. 3. Rhenium improved the strength and ductility of tungsten in the 20–3000°C range. 4. W-Re wire developed a high strength and ductility after annealing at 1400–1950°C. An alloy with 20% Re annealed at 1400–1500°C had a strength of 180–190 kg/sq. mm and 18–20% elongation. 5. W-Re alloys were harder than plain W in the 20–1000°C range. At 800°C, the alloys with 10, 25 and 75% Re had a hardness of about 200 kg/sq. mm while an alloy of W with 2% Re had one of about 110 kg/sq. mm. 6. Alloying of tungsten with rhenium increased several-fold its resistivity at various temperatures. 7. W-Re alloys can be recommended for elements of electric vacuum devices such as cathodes, heaters, radio tube grids, etc. They are also suitable for thermocouples and electrical contacts.