Short Tungsten Research Articles

Enhancing the toughness of Wf/W composites by modifying the fiber/matrix interface utilizing AlN-covered Wf

In this study, short tungsten fibers (Wf) were covered with AlN to modify the fiber/matrix interface in short tungsten fiber-reinforced tungsten matrix composites (Wf/W) fabricated by Fe-activated sintering. During the densification process, an intact and continuous AlN interlayer formed at the fiber/matrix interface through the effective sintering of the AlN powders covering the Wf surface. The AlN interlayer stably existed between the fibers and the matrix without any significant interfacial reactions, leading to relatively weak bonding at the fiber/matrix interface. Based on the extra energy dissipation mechanisms, the composite exhibited typical pseudo-ductile behavior and an increase of 80.35 % in fracture toughness compared to the W(Fe) material. The pseudo-ductile behavior increased the fracture surface area and reduced the stress intensity at the crack tip, resulting in a remarkable toughening effect on the composite.

Interfacial microstructure and mechanical property of the discontinuous short tungsten fiber-reinforced tungsten matrix composites

For tungsten fiber-reinforced tungsten matrix (Wf/W) composites, the interface between W matrix and W fiber has a dominant effect on the mechanical properties. In this study, the interfacial microstructure in the Wf/W composites with or without Y2O3 coating deposited on W fiber is investigated. The crystal structure of the Y2O3 coating composed of nano-sized columnar grains on the W fibers is cubic. And the crystal structure of Y2O3 coating changes to be face centered cubic after sintering in the Wf/W composites. Two kinds of interfaces, including the interface between W matrix and Y2O3 coating, the interface between W fiber and Y2O3 coating, are present in the Wf/W composites. Different orientation relationships are observed in these two kinds of interface. The stable orientation relationship with 111Y2O3 // 01¯1W have the lowest interfacial energy. The Y2O3 interface is essential for improving the toughening behavior of Wf/W composites and impeding the abnormal grain growth on the surface of W fiber sintering at low temperature. The recrystallization nucleus is developed by the bonding between W powder and W fiber during sintering, and then grow fast into W fiber. The apparent activation energy of abnormal grain growth of W fibers is about 242.7 KJ/mol sintering at temperature between 1500 and 1800 °C. The abnormal large grains usually show intergranular brittle fracture and make the W fiber be brittle.

Supplementary comparison - calibration of gauge blocks by mechanical method

Main textComparison of short tungsten gauge blocks and steel long gauge blocks by comparison method.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Tensile behavior of hybrid tungsten composites with zirconium carbide nanoparticles and tungsten fibers

Hybrid tungsten composites reinforced with zirconium carbide (ZrC) nanoparticles and tungsten fibers were developed by the conventional powder metallurgy process (ball-mill mixing of powders and fibers followed by spark plasma sintering). The synergistic and mutual influences of the fibers and nanoparticles on tungsten were investigated in tensile behavior and fracture-energy tests. Aided by the ZrC nanoparticles, up to 30% of the fibers could be embedded in the tungsten matrix. The fracture energy was maximized by co-introducing 0.2 wt% ZrC particles with 20 wt% short tungsten fibers. The fracture-energy enhancement of the short fibers is contributed by pseudo-toughness from the fiber–matrix interface, inherent toughness from the fibers themselves, and grain refinement (by 50%) of the tungsten matrix. The fracture energy of the composite is very sensitive to the ZrC content, because the two-way action of ZrC weakens the pseudo-toughness of the interface energy.

Infiltrated tungsten-copper composite reinforced with short tungsten fibers

To achieve an enhancement of mechanical properties, the WCu composite reinforced with short tungsten fibers was advocated. Characteristics including phase constituents, microstructure and mechanical properties (tensile, compressive and frictional behaviors) of the Wf reinforced WCu composite have been systematically investigated. The magnetron sputtered Ti layer on the surface of Wf effectively improved the sinterability of the composite, leading to excellent electrical conductivity of 56.55% IACS and hardness of 182 HB. Cross sectional EBSD results clearly reveals the sharp <110> fiber texture according to the {110} pole figure of the Wf part, indicating a reserved texture structure although after high-temperature sintering and infiltration, which ensures the fiber strengthening effect. Further tests confirmed the enhancement of mechanical properties including high tensile strength of 549.0 MPa and compressive strength of 1047.8 MPa with large plasticity, as well as low friction coefficient of 0.494. A three dimensional model via numerical simulation further revealed that the smaller the angle between the axial direction of the inserted fibers and the loading direction, the easier it was to bear a higher stress, and the middle part of the fiber was more vulnerable to the accumulated damage.

Synthesis and property of short tungsten fibre/Zr-based metallic glass composite

ABSTRACTThe short tungsten fibre reinforced Zr41.2Ti13.8Ni10.0Cu12.5Be22.5 bulk metallic glass composites with macroscopic isotropic mechanical properties were prepared by infiltration and rapid solidification. The diameters of the tungsten fibres are 300, 500 and 700 µm with a length of 1000 µm and the fibre volume fraction in three kinds of composites is between 60 and 65%. The room temperature compressive deformation behaviours of these composites were investigated systematically. The results show that the strength and plasticity of the composites increase with the decrease in the tungsten fibre diameter. The maximum compressive strength and plastic strain of the composite with 300 µm fibre, respectively, reach 3079 MPa and 37%. The fracture modes of all the composites are shear fracture. The superior compressive property of the composites with short tungsten fibre is due to the competition among different fracture modes and the inhibition effect of the interface on the shear band extension.

Toughness enhancement of tungsten reinforced with short tungsten fibres

The feasibility and toughening efficiency of the short tungsten fibre reinforcement on tungsten were investigated in Wf/W composites fabricated by powder metallurgy method of spark plasma sintering. Fibres in the composites presented a Z-free laminar structure. Partial recrystallization of fibre grains occurred but fibre crack or damage was not detected. Fracture energy of Wf/W composites was estimated in tensile tests, and the results indicated great toughness improvement over pure tungsten in virtue of frictional pullout and plastic deformation of fibres, and matrix-fibres interfacial debonding since 873K. The specimen with mass fraction of 10% and fibre diameter of 100µm exhibits the largest elongation of 9±1.1% and the highest ultimate strength of 482±13MPa at 873K.

A Strong Metal-to-Metal Interaction in an Edge-Sharing Bioctahedral Compound that Leads to a Very Short Tungsten–Tungsten Double Bond

An ionic edge-sharing bioctahedral (ESBO) species has been prepared having a tetramethylated bicyclic guanidinate with two fused six-membered rings characterized by a fairly flat N-C(N)-N skeleton and abbreviated as TMhpp. The anion has two W(IV) atoms bridged by two oxo groups; the metal atoms are also spanned by two bridging guanidinate ligands, and each has two monodentate chlorine atoms. The complex formulated as (H2TMhpp)2[W(μ-O)(μ-TMhpp)Cl2]2 has the shortest W-W distance (2.3318(8) Å) of any species with a σ(2)π(2) electronic configuration. The anion and cations are connected by hydrogen bonds. To unambiguously ascertain the existence of the double-bonded W2(μ-O)2 entity, density functional theory calculations and natural bond orbital analyses were done on an analogous but hypothetical species with a W2(μ-OH)2 core having trivalent tungsten atoms and a possible σ(2)π(2)δ(2) electronic configuration. The calculations decidedly support the presence of tungsten-oxo instead of tungsten-hydroxo groups and thus the existence of the double-bonded W2(μ-O)2 core. The strong bonding interaction between metal atoms is a clear indication that under certain circumstances the two octahedra in ESBO species do not behave as the sum of two mononuclear compounds.

Wear of rotary instruments: a pilot study

The aim of this study was to assess the wear of tungsten carbide burs and round rotary diamond instruments through measurements of rake angle and visual observations respectively under a field emission scanning electron microscope. Sixty short and long head pear-shaped tungsten carbide burs and 18 round rotary diamond instruments that had been used to complete &lt; 5, &gt; 5 and &gt; 10 cavity preparations (n=10/group) were selected from the 3rd and 4th year dental students, Faculty of Dentistry, University of Malaya. There were two control groups consisting of long and short tungsten carbide burs of ten each. Two-way ANOVA was used to analyse the rake angle data. The data from the two control groups were collectively analysed following multiple paired t-test (p&gt;.05) which showed no significant difference between the two types of tungsten carbide bur (short and long head). The mean rake angle of the control group was significantly higher (p &lt; .05) compared to the &lt; 5, &gt; 5 and &gt; 10 cavity preparation groups. The rake angle of the &gt; 10 cavity preparation group was significantly lower than the other two test groups (p &lt; .05). Round rotary diamond instruments in the &lt; 5 cavity preparation group showed intact diamond particles with distinct cutting facets comparable to the control group. However, diamonds instruments in the &gt; 5 and &gt; 10 cavity preparation groups showed blunt diamond particles. In conclusion, wear of tungsten carbide burs and round rotary diamond instruments were evident after repeated use. Wear was more pronounced when instruments were used to prepare more than ten cavities.

A low-background organic-type GM tube

A low-background, organic-type small GM tube with a short tungsten wire anode of 1 cm length and a cylindrical steel cathode was constructed. Reduction on the background caused by cosmic rays and contamination is achieved by using a short, small GM tube. At the same time, the problem of low counting efficiency caused by the short tube length is overcome. The drop in the field values near the ends of the short cylindrical GM tube below the values required to produce Geiger action, which in turn causes the decrease in the counter efficiency, is corrected using two metallic balls connected to both ends of the tungsten wire anode. The optimum size of these balls corresponding to the minimum capacitance of the counter is determined using a simulation technique. Plateau curves of tubes with different-sized metallic balls are reported. Then, a plateau curve of the tube with optimum ball size is compared with that of an ordinary cylindrical GM tube having the same dimensions to evaluate the effect of using the wire anode with two metallic balls at the ends in order to improve counter performance and efficiency. >

Fracture and fatigue of discontinuously reinforced copper/tungsten composites

The strength, toughness and resistance to cyclic crack propagation of composites consisting of copper reinforced with short tungsten wires of various lengths have been studied and the results compared with the behaviour of continuously reinforced composites manufactured by the same method, i.e. by vacuum hot-pressing. It has been found that whereas the resistance to fatigue crack growth of continuously reinforced composites is very similar to that of continuous Al/stainless steel composites reported elsewhere, the addition of short fibres completely changes the mode of fracture, and no direct comparisons are possible. In effect, short fibres inhibit single crack growth by causing plastic flow to be distributed rather than localized, and although these composites are much less strong than continuous fibre composites, they nevertheless have much greater fatigue resistance. The fracture toughness of the composites is thought to be derived simply from the separate contributions of matrix and fibre plastic flow and, in composites containing fibres near to the critical length, from the very substantial work of fibre pull-out.

Secondary Electron Emission Produced by Positive Caesium Ions

Number of electrons emitted from a Cs covered grid and plate per positive Cs ion striking them.---The source of the positive caesium ions, a short tungsten filament maintained at about 1200\ifmmode^\circ\else\textdegree\fi{}K in the presence of caesium vapor, was mounted on the axis of a long cylindrical grid and plate. The plate current and total positive ion emission current were observed for each of several negative grid potentials as the plate potential was varied from +50 to -650 volts. From these observations the number of electrons that were emitted from the caesium covered grid and plate per positive ion was calculated. This number increased uniformly from 0.01 at approximately 100 volts to 0.15 at 600 volts.Calibration of tube.---After corrections for the emission of secondary electrons were made, the ratio of the positive ion current to the plate to the total emission current was found to be independent of the plate and grid potentials for plate potentials greater than 0.2 of the grid potential. This ratio, 0.72, is the same as the ratio between the total area of the plate less the projected area of the grid, and the total plate area. Assuming the same distribution of electrons as positive ions, we can calculate the ratio of the plate current to the grid current in this type of tube.

An experimental determination of the critical electron velocities for the production of radiation and ionisation on collision with argon atoms

In the ‘Proceedings of the Royal Society’ for 1919 (A, vol. 95, p. 408) we have given an account of an investigation of the effects of electron collisions with helium atoms. The apparatus and method there described have been somewhat modified, and applied to a similar investigation with argon. With this gas Franck and Hertz came to the conclusion that ionisation occurs when the velocity of the colliding electrons is raised to 12 volts, but the method of experimenting used by them was not able to distinguish between ionisation of the gas and the photo-electric effect of radiation produced by the collisions. The main features of the apparatus used in the present research have been described in the earlier paper; the modifications introduced will be seen by reference to the diagrammatic view in fig. 1. A short tungsten filament, F, which could be heated to incandescence by an electric current, was used as the source of electrons. This was supported horizontally and about 1·5 mm. below the top of the platinum thimble, E, which was plane and circular, and had at its centre a circular hole 1·5 mm. in diameter.

The short tungsten filament as a source of light and electrons

The short tungsten filament as a source of light and electrons