Evaluation of microstructure and contiguity of W/Cu composites prepared by coated tungsten powders (original) (raw)
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Materials & Design, 2009
Fabrication of tungsten-copper net-shapes has become an important issue in recent years due to their unique properties which make them suitable for a wide variety of applications. In this investigation, W-Cu composite powders containing 20 wt.% and 30 wt.% Cu were processed by powder metallurgy technique using two types of prepared powders, namely, Cu-coated tungsten and mixtures of elemental powders. The coating method of tungsten powders was carried out using electroless coating technique. The investigated powders were cold compacted and sintered in vacuum at two sintering temperatures, 1250°C and 1400°C.
International Journal of Science and Research (IJSR), 2016
By using the infiltration method at a temperature of 1250°C and a holding time of 2h in H 2 atmosphere, W-Cu composites with different Cu content (5, 10, 15, 20, 25 and 30 Wt %) have been elaborated. In this study, a Tungsten porous substrate was prepared with cold uniaxial pressing. The results show that 25 Wt% Cu is the maximum cupper content that can be infiltrated. In order to enhance the composites properties, Ni has been added as activator of W matrix. In this case, it was found that (W-5Wt%Ni)-25Wt% Cu gives the most interesting result in terms of density, hardness and microstructure.
Improvement of machinability of tungsten by copper infiltration technique
International Journal of Refractory Metals and Hard Materials, 2008
Infiltration of liquid copper in partially sintered tungsten was undertaken to improve machinability of tungsten. Initial skeleton of tungsten was prepared by pressing commercial tungsten powder in cold isostatic press to near-net shapes. The green compacts are then subjected to controlled sintering to about 85% theoretical density. This leaves adequate amount of open channels which are filled subsequently with liquid copper by infiltration. The resulting composite material exhibits reasonable strength coupled with desired level of machinability. Some pilot samples were made with $99% density and were subjected to in-house characterization (e.g., density, shrinkage and porosity). Microstructural study has been carried out to compare the theoretically calculated porosity levels with the observed porosity level. X-ray diffraction studies revealed presence of elemental tungsten and copper with no mutual solubility. Mechanical properties (e.g., ultimate tensile strength, tensile elongation and hardness values) of the composite were also evaluated and reported.
International Journal of Refractory Metals & Hard Materials, 2009
a b s t r a c t W-30 wt%Cu composite powders were prepared by a novel precipitation process using ammonium meta tungstate and copper nitrate as precursors. The initial precipitates were obtained by adding aqueous ammonia to a mixture of ammonium meta tungstate and copper nitrate solutions and then heating the solution up to 95°C. In order to synthesis W-Cu composite powders, the dried precipitates were calcined in air at 500°C and then reduced by hydrogen. The calcination temperature was determined by thermogravimetry analysis. The powders were characterized by X-ray diffraction technique and scanning electron microscopy analysis. The effect of sintering temperature was investigated on densification of the synthesized powders. Relative density over 98% was achieved for the samples which were sintered at 1150°C. Good electrical conductivity and relatively high hardness were achieved for the samples which sintered above melting point of copper.
International Journal of Refractory Metals and Hard Materials, 2012
The properties of W-15 wt.%Cu composites were investigated by preparing two distinct composites of micrometer and nanoscale structures. Micrometer composite was produced by mixing elemental W and Cu powders and nanometer one was synthesized through a mechanochemical reaction between WO 3 and CuO powders. Subsequent compaction and sintering process was performed to ensure maximum possible densification at 1000-1200°C temperatures. Finally, the behavior of produced samples including relative density, hardness, compressive strength, electrical conductivity, coefficient of thermal expansion (CTE) and room temperature corrosion resistance were examined. Among the composites, nano-structured sample sintered at 1200°C exhibited better homogeneity, the highest relative density (94%) and mechanical properties. Furthermore, this composite showed superior electrical conductivity (31.58 IACS) and CTE (9.95384× 10-6) in comparison with micrometer type. This appropriate properties may be mainly attributed to liquid phase sintering with particle rearrangement which induced by higher capillary forces of finer structures.
Properties of W–Cu composite powder produced by a thermo-mechanical method
International Journal of Refractory Metals and Hard Materials, 2003
In order to improve the process of co-reduction of oxide powder, a new thermo-mechanical method was designed to produce high-dispersed W-Cu composite powder by high temperature oxidation, short time high-energy milling and reduction. The properties of W-Cu composite powder are analyzed in terms of oxygen contents, BET specific surface (BET-S), particle size distributions, morphology of final powder and their sintering behaviors. The results show that the oxygen content of W-Cu composite powder decreases with the increase of milling time, while the BET-S of final powder increases with the milling time. The distributions of final powder are more uniform after reduction at 630°C than at 700°C. After milling of the oxide powder for about 3-10 h, W-Cu composite powder with very low oxygen content can be achieved at the reduction temperature of 630°C owning to the increasing of BET-S of W-Cu oxide powder. The particle size of W-Cu powder after reduction is lower than 0.5 lm and smaller than that reduced at 700°C. After sintering at 1200°C for 60 min, the relative density and thermal conductivity of final products (W-20Cu) can attain 99.5% and 210 W m À1 K À1 respectively.
Synthesis and consolidation of W–Cu composite powders with silver addition
International Journal of Refractory Metals and Hard Materials, 2012
Homogeneous and nanostructured W-19 wt.%Cu-1 wt.%Ag and W-10 wt.%Cu-10 wt.%Ag composite powders were prepared via a chemical precipitation method, with the aim of surveying the effect of silver on the properties of tungsten-copper composites. For this purpose, ammonium metatungstate, copper nitrate and silver nitrate with predetermined weight proportion were separately dissolved in distilled water. Furthermore, W-20 wt.%Cu composite powders were provided for comparison. The initial precipitates were obtained by reacting a mixture of the mentioned solutions under certain pH and temperature. The precursor precipitates were then washed, dried, and calcined in air to form oxide powders. In the next step, the reduction was carried out in hydrogen atmosphere to convert them into the final nanocomposite powders. The resulting powders were evaluated using X-ray diffraction (XRD), thermogravimetry (TG) and scanning electron microscopy (SEM) techniques. The effect of sintering temperature was investigated on densification and hardness of the powders compacts. The results showed that at all sintering temperatures, by increasing in the amount of silver, powders showed better sinterability compared to W-20 wt.%Cu powders. Maximum relative densities of 97.7%, 98.2% and 99.6% were achieved for W-20 wt.%Cu, W-19 wt.%Cu-1 wt.%Ag and W-10 wt.%Cu-10 wt.%Ag compacts sintered at 1200°C, respectively. Moreover, maximum hardness of 359, 349 and 255 Vickers were resulted for W-20 wt.%Cu, W-19 wt.%Cu-1 wt.%Ag and W-10 wt.%Cu-10 wt.%Ag compacts sintered at 1200°C, respectively.
Mechanical Alloying Effects in Ball-Milled Tungsten-Copper (W-Cu) Composites
Fine-grained, high-density (97%+ of theoretical density [TD]), 80 tungsten-20 copper weight-percent (80W-20Cu [58W-42Cu atomic-percent]) composites have been prepared using nonconventional alloying techniques. The W and Cu precursor powders were combined by high-energy ball milling in air. A second set of W+Cu mixtures was prepared in hexane to reduce contamination of the powders. The mechanically alloyed W+Cu powder mixtures were then coldpressed into green compacts and sintered at 1,250 °C. The effects of varying the milling medium and milling time were examined with density measurements. Longer milling increased product densities with a concomitant order-of-magnitude decrease in grain size; air was found to be a more effective medium than hexane. Residual impurities were identified with energy-dispersive x-ray spectroscopy (EDS), and their effects on sample properties were evaluated with microhardness measurements. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses demonstrated that the as-milled W-Cu alloy structures were metastable, decomposing into the starting W and Cu components upon heating at or above 450 °C.
Journal of Materials Science, 2012
Cu-coated W nanocomposite powder was prepared by a combination of high-energy ball-milling of a WO 3 and CuO mixture in a bead mill and its two-stage reduction in a H 2 atmosphere with a slow heating rate of 2°C/min. STEM-EDS and HR-TEM analyses revealed that the microstructure of the reduced W-Cu nanocomposite powder was characterized by *50-nm W particles surrounded by a Cu nanolayer. Unlike conventional W-Cu powder, this powder has excellent sinterability. Its solidphase sintering temperature was significantly enhanced, and this led to a reduction in the sintering temperature by 100°C from the 1,200°C required for conventional nanocomposite powder. In order to clarify this enhanced sintering behavior of Cu-coated W-Cu nanocomposite powder, the sintering behavior during the heating stage was analyzed by dilatometry. The maximum peak in the shrinkage rate was attained at 1,073°C, indicating that the solid-phase sintering was the dominant sintering mechanism. FE-SEM and TEM characterizations were also made for the W-Cu specimen after isothermal sintering in a H 2 atmosphere. On the basis of the dilatometric analysis and microstructural observation, the possible mechanism for the enhanced sintering of Cu-coated W composite powder in the solid phase was attributed to the coupling effect of solid-state sintering of nanosized W particle packing and Cu spreading showing liquid-like behavior. Homogeneous and fully densified W-20 wt% Cu alloy with *180 nm W grain size and a high hardness of 498 Hv was obtained after sintering at 1,100°C.
Thermal–mechanical process in producing high dispersed tungsten–copper composite powder
International Journal of Refractory Metals and Hard Materials, 2008
In order to improve the process of co-reduction of oxide powder, a new thermo-mechanical method was designed to produce high-dispersed W-Cu composite powder by high temperature oxidation, short time high-energy milling and reduction. The properties of W-Cu composite powder are analyzed in terms of oxygen contents, BET specific surface (BET-S), particle size distributions, morphology of final powder and their sintering behaviors. The results show that the oxygen content of W-Cu composite powder decreases with the increase of milling time, while the BET-S of final powder increases with the milling time. The distributions of final powder are more uniform after reduction at 630°C than at 700°C. After milling of the oxide powder for about 3-10 h, W-Cu composite powder with very low oxygen content can be achieved at the reduction temperature of 630°C owning to the increasing of BET-S of W-Cu oxide powder. The particle size of W-Cu powder after reduction is lower than 0.5 lm and smaller than that reduced at 700°C. After sintering at 1200°C for 60 min, the relative density and thermal conductivity of final products (W-20Cu) can attain 99.5% and 210 W m À1 K À1 respectively.