The influence of the dispersion technique on the characteristics of the W–Cu powders and on the sintering behavior (original) (raw)
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THE INFLUENCE OF THE MILLING ENVIRONMENT ON THE SINTERED STRUCTURE OF A W-Cu COMPOSITE
Materials Science Forum, 2010
This work reports an investigation about the influence of the environment of milling on the characteristics of the powders and on the structure and density of sintered samples made of these powders. Mixtures of composition W-30wt%Cu were milled for 51 hours in a high energy planetary mill in dry and wet (cyclohexane) conditions. The milled powders have composite particles. The powders were pressed and sintered at 1050°, 1150° and 1200°C under flowing hydrogen. The isothermal times were 0 minutes for the first two temperatures and 60 minutes for the latter. The samples reached around 95% of relative density. The powders were characterized by means of XRD and SEM. The sintered samples were characterized by means of SEM, optical microscopy and density measurement.
International Journal of Refractory Metals & Hard Materials, 2009
Nanoscale dispersed particles of W-20-40%wt Cu were synthesized using a chemical procedure including initial precipitating, calcining the precipitates and reducing the calcined powders. The powders were characterized using X-ray diffraction and map analyses. The effect of sintering temperature was investigated on densification and hardness of the powder compacts. Relative densities more than 98% were achieved for the compacts which sintered at 1200°C. The results showed that in the case of W-20%wt Cu composite powders, the hardness of the sintered compacts increased by elevating the sintering temperature up to 1200°C while for the compacts with 30 and 40%wt Cu, the sintered specimens at 1150°C had the maximum hardness value. The microstructural evaluation of the sintered compacts by scanning electron microscopy showed homogenous dispersion of copper and tungsten and a nearly dense structure. A new proposal for the variation of the mean size and morphologies of W-particles with volume percent of copper melt within the composites has been suggested.
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.
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.
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.
Investigation of nanocrystalline sintered W-25 wt% Cu composite
International Journal of Refractory Metals and Hard Materials, 2021
W and Cu can be found in separate phases in the W-Cu composites since these elements do not dissolve in each other neither in liquid nor in solid phase, but with mechanical alloying it is possible to produce nonequilibrium W-Cu alloys In this work the nanostructured W-Cu composites were produced by planetary ball milling. The nanostructured W-Cu powder was sintered on 900°C and 950°C with 50 MPa pressure applied. The meso-and microstructure of the W-Cu powder and the sintered samples, were investigated with SEM, TEM and XRD. After 50 hours of milling, the size of the W crystallites was ~ 10 nm, and about 10 % of the Cu was solved in the W matrix, producing a W-Cu nonequilibrium alloy layer on the surface of W nano crystallites. During sintering, the Cu atoms left from the W surface to the Cu phases, so the W-Cu nonequilibrium alloy layer disappeared. The size of the W crystallitesafter 60 min of sintering on 950°C-was around 170 nm, and the relative density was ~90% of the theoretical density.
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.
Scripta Materialia, 1998
Introduction Tungsten-copper(W-Cu) composites are promising materials for thermal managing applications such as microelectronic devices because of the low thermal expansion coefficient of tungsten and the high thermal conductivity of copper (1-3). These materials have been produced by conventional Cuinfiltration sintering or by liquid-phase sintering (4, 5). The full densification of W-Cu composites by liquid-phase sintering is attained mainly by the tungsten particle rearrangement due to the capillary force and surface tension of Cu-liquid phase (6, 7) as well as solid-state sintering, because W and Cu have no solubility under equilibrium condition (8). If the constituent phases are extremely fine homogeneous state, the fully dense parts with the homogeneous microstructure can be attained at the stage of particle rearrangement. To promote homogeneity, much works such as the coreduction method of the raw oxide powders (9, 10) or mechanical alloying of the element powders (11, 12) have been studied. The mechanical alloying method is the attractive one from the engineering viewpoint because the nanostructured(NS) materials can be easily synthesized in large quantities. Nevertheless, the studies of nanostructured W-Cu alloys have been focused only on the formation and the fabrication of composite powders by mechanical alloying (11-13). And there were few researches of liquid-phase sintering behavior of NS W-Cu composite powders compared to nanostructure characteristic study. The authors have recently reported on the characteristics of nanostructured W-Cu alloys produced by mechanical alloying method (14, 15). In this study, the new concept of nanosintering was suggested to explain the drastic grain growth of mechanically alloyed NS W-Cu powders during the solid-state sintering. The high sinterabilty of these mechanically alloyed NS W-Cu alloys was also obtained by liquid-phase sintering. In this present work, the enhanced sinterabilty of mechanically alloyed NS W-Cu composite powders with sintering temperature is investigated and evaluated by the combination of nanosintering and conventional liquid-phase sintering. Experimental Elemental W (99.9% purity, 4.28m) and Cu(99.5% purity, 50.42m) powders were used for raw powders in this experiment. The mechanical alloying was carried out in an attrition mill using a stainless steel vial and balls with a speed of 400 rpm. The powder charge was 20g, with balls to powders weight ratio of 60:1. The W-20wt%Cu and W-30wt%Cu composite powders were prepared by milling for 100
Effects of Zn additions on the solid-state sintering of W–Cu composites
Materials & Design, 2000
Full-density W–40vol%Cu composites are prepared by hot-press sintering in a vacuum at 850°C, as Zn is added as activator. Experiments are conducted to evaluate the effects of Zn additive in the range of 0–20wt.% on the densification and mechanical properties of W–40vol%Cu composites. The microstructural characterizations are performed by X-ray diffraction (XRD) and scanning electron microstructure (SEM), and mechanical properties
An experimental investigation on the W–Cu composites
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.