Copper-tungsten Composites Research Articles

Effect of tungsten contents on the jet penetration performance of shaped charge liner based copper-tungsten composites

Herein, we investigated the effect of W content on the jet penetration performance of W-Cu shaped charge liners by using both simulation and experimental methods. The W-Cu composite liners were prepared directly by using spark plasma sintering (SPS) technique. Microstructural observations showed that W particles were uniformly dispersed within the Cu matrix. The relative density of W-Cu composites decreased slightly from 99.2% to 98.8% with an increase in the W content. The hardness of the W-Cu composite liner increased as increasing W content and reached the highest value of 209.2 HV for the composite reinforced by 60 wt.% W. Besides, the penetration depth increased and reached the maximum value of 80 mm for the composite liner containing 50 wt.% W which is improved by about 11% compared to pure Cu liner. According to simulation and experiment results, the penetration depth of the W-Cu composite liners exhibits a nearly identical trend. W-Cu composite liner containing 50 wt.% W remains the best performance compared to other composites. However, the experimental results are lower compared to the simulation results. This could be because the simulation procedure did not completely account for the actual test conditions.

Mechanical and Electrical Properties of Graphene Oxide Reinforced Copper-Tungsten Composites Produced via Ball Milling of Metal Flakes.

Copper-tungsten (Cu-W) composites are widely used in high-power and -temperature electrical applications. The combination of these metals, however, leads to compromised physical and electrical properties. Herein, we produce Cu-W-graphene oxide (Cu-W-GO) composites to address this challenge. To ensure uniform density composites, the as-received metal powders were flattened into a flake morphology by ball milling and then mixed with up to 0.5 wt.% GO flakes. The green forms were processed using spark plasma sintering. The GO was found to be well-dispersed amongst the metallic phases in the final composite. The addition of GO reduced the relative density of the composites slightly (4.7% decrease in relative density at 0.5 wt% GO loading for the composites processed at 1000 °C). X-ray diffraction confirmed good phase purity and that no carbide phases were produced. GO was found to improve the mechanical properties of the Cu-W, with an optimal loading of 0.1 wt.% GO found for ultimate compression strength and strain to failure, and 0.3 wt.% optimal loading for the 0.2% offset yield strength. Significantly, the electrical conductivity increased by up to 25% with the addition of 0.1 wt.% GO but decreased with higher GO loadings.

Electrode erosion and lifetime performance of a triggered corona-stabilized switch in SF6at a repetition rate of 1 kHZ

This paper describes the work undertaken to investigate the electrode erosion and lifetime performance of an electrically triggered, corona stabilized (TCS) switch. The switch, which had a rod-plane geometry, was filled with SF6 at a pressure of 0.8 bar (1.0bar = 100kPa) absolute and was operated at a pulse repetition frequency (PRF) of 1kHz. The erosion rates of anode and cathode electrode materials such as elkonite (a copper tungsten composite), brass, aluminum and two types of stainless steel was measured, and their surfaces were studied optically, photographed and chemically analyzed. The erosion rate of the anode (rod) electrode materials ranged from 21.39 x 10-6 cm-3C-1 for elkonite to 60.4 x 10-6 cm-3C--1 for brass, whilst a cathode (trigger disc) erosion rate as high as 51.23 x 10-6cm-3C--1 for aluminum was measured. The lifetime of the TCS switch was experimentally determined for each of the electrode material tested, and was found to be inversely proportional to the erosion rate of the rod electrode. The electrode surface morphology and the gas-electrode compound distribution have also been evaluated to address the erosion mechanism in effect. Additionally, the influence of rod electrode surface conditions and gas deterioration has been investigated in respect to the performance and operational behavior of the TCS switch.

Microstructure and Properties of Tungsten Copper Composite Material

The copper-tungsten system in the liquid and solid phase is completely immiscible. In this paper, the powder solid-phase sintering method was used to prepare the copper-tungsten composites of different compositions (CuxWy, x=63, 78, 84, 87, 90, 91, y=37, 22, 16, 13, 10, 9 (x+y=100)). By XRD and SEM analysis of the sample microstructure, the trend of the ratio of the conductivity, density and hardness of the samples with different ratio were determined. The results show that with the increasing tungsten content, the conductivity of the copper-tungsten composite increases, whereas the amplitude reduces. The actual density of the sample is smaller than its theoretical density. The more the tungsten content is, the smaller its hardness value.

Copper-Tungsten Composites Sprayed by HVOF

Copper and copper-tungsten composite coatings were produced by high-velocity oxy-fuel spraying (HVOF). After initial optimization of the spraying parameters, coatings of various compositions were made and their structure, composition, mechanical, thermal, and electrical properties were characterized. The HVOF technique was able to produce rather dense coatings with minimal oxide content and relatively good mechanical and thermal properties compared to, for example, plasma-sprayed coatings; however, the achieved tungsten content was quite low.

Effect of a rigid component (tungsten alloy) on the process of formation of mixtures based on copper powder and the properties of heterogeneous unsintered compacts

We have analyzed the process of structure formation during pressing of copper-tungsten composites. We have established the effect of the amount of the rigid phase (tungsten alloy) in the mix on the pattern of structure formation and the properties (Young’s modulus and bending strength) of unsintered articles made from heterogeneous powder material based on copper. We have experimentally established that despite the substantially higher porosity and high volume fraction of the rigid phase, specimens of composition Cu — 50% Walloy have higher green strength and higher modulus of elasticity. Analysis of the true stress — true strain curves of the porous cold-pressed articles compared with the results of microstructural studies allowed us to determine the effect of the structure formation pattern on the strength properties of articles made from copper-based powder material containing tungsten alloy. By studying the structural features of the porous articles, we determined the mechanism for creation of interparticle contact which determines the strength characteristics of unsintered compacts of heterogeneous composition based on a plastic matrix with different amounts of the rigid phase.

Novel Fabrication Method for Interconnect Materials

A novel method of fabricating thin sheets of metallic and metallic matrix composite materials is described. A near net shape powder metallurgy process is used to roll compact a blend of powders directly into a thin sheet. A sintered bond is subsequently formed and the initially porous sheet is taken to full density, or intermediate density if desired, by a series of thermo-mechanical steps. A number of examples are presented, including an iron aluminide intermetallic composition having excellent high temperature oxidation resistance and creep strength. Properties of copper molybdenum and copper tungsten composites having a range of thermal expansion values according to composition are given. A nickel chromium alloy, difficult to prepare by melt and cast methods, is described.

Copper-niobium and copper-tungsten composites as plasma torch cathodes

This work was performed to screen potential cathode materials for use in arc heaters with cylindrical electrodes. It focused on hot isostatic pressing consolidated copper composites; 10% composites of copper with tungsten and niobium as well as 1.5% niobium were used. The composite cathodes were tested in pure Ar, He and N2 as well as in mixtures of Ar with CO, N2 and H2, at atmospheric pressure and currents up to 150 A. The arc was driven around the circumference of the cathode with an external magnetic field. The results are compared with those using pure copper cathodes. The Cu-W cathode showed a better arc stability and lower erosion rates than copper. The Cu-Nb cathode showed much lower erosion rates and much better arc stability than copper for almost all the different operating conditions and may be considered a promising new electrode material. The experimental results corroborated previous interpretations of the relationships between arc velocity, erosion rate, surface drag and electrode surface composition.

Matrix behaviour in copper-tungsten composites at small strains : Chawla, K.K., Metzger, M. Metallurgical Transactions Vol 8A No 11 (November 1977) pp 1681–1687

Matrix behaviour in copper-tungsten composites at small strains : Chawla, K.K., Metzger, M. Metallurgical Transactions Vol 8A No 11 (November 1977) pp 1681–1687

Matrix behavior in copper-tungsten composites at small strains

Composites with up to 15 pct tungsten wires in a copper crystal matrix prepared by infiltration showed matrix microyield and flow stresses increasing with fiber fraction. Dislocation etch-pit observations showed that the walls of a cell structure in the matrix formed during fabrication were the operative dislocation obstacles and that this initial structure rather than fiber-matrix interaction during straining was responsible for the matrix strengthening.

Dislocation structures in copper matrix after constant stress cycling of coppertungsten composites : Chawla, K. K. Fibre Science and Technology, Vol 8 No 1 (Jan 1975) p 49

Dislocation structures in copper matrix after constant stress cycling of coppertungsten composites : Chawla, K. K. Fibre Science and Technology, Vol 8 No 1 (Jan 1975) p 49

The effect of fibre diameter and interfibre spacing on the tensile properties of copper-tungsten composites

Stress-strain tests have been carried out on continuous fibre-reinforced copper-tungsten composites at a strain sensitivity of 10−6. The material was prepared by the combination of filament winding, electrodeposition and hot-pressing using fibres between 10 and 50 μm diameter and volume fraction in the range 0·1-0·6.The composite elastic modulus, microyield stress, 0·1% proof stress, stress at 1% total strain and fracture stress, all exceeded the values expected from the rule of mixtures, based on the properties of the tungsten wires and unreinforced copper prepared by a similar route to the composites.The difference between the experimental and rule of mixtures modulus values is an order of magnitude greater than predicted by elastic constraint theory, but no satisfactory explanation could be found for this effect.All the remaining parameters which involved matrix plasticity (and fibre plasticity at high strains), showed positive deviations from the rule of mixtures which have been interpreted in terms of matrix strengthening. This strengthening arises from effects due to the matrix grain size, and also to the abnormally high dislocation densities in the matrix as a result of differential thermal contraction on cooling from the pressing temperature. These effects are only likely to be observed in composites containing small diameter fibres, where the interfibre spacing falls below about 50 μm.

The hardening rate of fibre-strengthened materials

The hardening rate of a material reinforced with aligned fibres in stage 2 was calculated by taking into account the change of the elastic energy due to the internal stress and that of the external potential due to the interaction of the internal stress with the applied stress. The result of calculation for the case of a copper-tungsten composite was in good agreement with the experimental data reported by Kelly and Lilholt (1969).

Sintered copper-base composites reinforced with tungsten fibers

1. A study was made of various manufacturing processes, based on powder metallurgy techniques, for reinforcing copper with tungsten fibers. The effect of these fabrication techniques on the density and strength of the resulting composite materials was determined. 2. It is shown that, by combining compaction with extrusion at elevated temperatures, it is possible to produce dense composite materials with satisfactory fiber-matrix bond strength and oriented fiber arrangement. 3. The tensile strength of copper-tungsten composites containing 25 vol.% of fibers exceeds the strength of pure copper by a factor of two at room temperature and by a whole order at 873–1073°K. 4. A comparison of data for composite materials prepared by powder metallurgy techniques and casting shows that the latter method ensures a higher fiber-matrix bond strength.

The failure of copper-tungsten fibre composites in repeated tension

The resistance of typical copper-tungsten composites to repeated tension in the neighbourhood of 10 6 cycles has been investigated. The reinforcement of copper with continuous, brittle tungsten wires was found to be surprisingly ineffective against fatigue, up to volume fractions of 23 per cent tungsten. A detailed study of the behaviour of the composites and their components suggests that fatigue hardening at the tips of cracks in the matrix can build up stress concentrations large enough to break the fibres. It is concluded that a practical composite with continuous brittle fibres should employ a matrix which does not fatigue harden under the conditions of service.