PREDICTION OF BEHAVIOUR IN FORMING OF SINTERED COPPER-10% TUNGSTEN NANO POWDER COMPOSITE (original) (raw)
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iaeme
Experimental investigations are performed in order to predict the mechanism of deformation and densification behaviour during cold upset forming operation on sintered Cu- 15%W Nano composite. High-energy mechanical milling was used to produce Cu and W Nano powder composites. Cylindrical preforms with initial theoretical density of 85% possessing three different aspect ratios of 0.40, 0.60 and 0.80 were prepared using a die and punch assembly with a hydraulic press. The preforms are sintered in an electric muffle furnace at 650°C, and subsequently the furnace was cooled. Cold deformation experiments are conducted in incremental deformation steps. The relationships between various parameters are evaluated
iaeme
Studies were conceded out to evaluate the initially preformed density and initial aspect ratio on the densification behavior of sintered Copper 7% Tungsten composite. The preform possessed 0.85 is the initial theoretical density. Aspect ratio varied from 0.4, 0.6 and 0.8. Properties of Copper Tungsten composites with respect to linear strain, lateral strain and true stress were evaluated and plotted. Studies exposed that higher stress and higher strain values are obtained in composite when compared to the Tungsten powder. The composite of Copper 7%W obtained at 750oC. The Composite obtained at lower aspect ratio acquired the highest stress and strain when compared to the composites preforms obtained at other aspect ratio
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.
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
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.
Materials Science Engineering a Structural Materials Properties Microstructure and Processing, 2007
Nanostructured W-20 wt% Cu composite powder was synthesized by mechanical alloying (MA) in an Attritor ball mill. The morphological changes and structural evolution of the composite powder during MA was studied by employing scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), laser particle size analyzer (LPS), inductively coupled plasma (ICP) spectrometry, atomic absorption spectrophotometery (AAS), and the bulk powder density measurement. The results were compared with those obtained from attrition milling of monolithic W and Cu powders processed at the same condition. Whereas the milling mechanism of the monolithic powders follow the ductile (for Cu) and semi-brittle (for W) systems, the W/Cu powder mixture exhibits different behavior. At the early stage of milling, the copper particles are fragmented and incorporated into the W matrix, resulting in the formation of W/Cu composite with laminar structure. With increasing milling time and due to continuous fracturing, the laminar structure is refined and a homogenous distribution of fine Cu particles (0.3-0.6 m) in the W matrix is formed. The analysis of XRD patterns indicated that the composite powder composes of nanostructured grains with the size of 49 nm for Cu and 23 nm for W. A faster grain refinement in the composite powder compared to the monolithic particles was noticed. The XRD peak intensity also revealed that partial mutual solubility of the constituent elements (≈4-7 at% for Cu in W and ≈2-3 at% for W in Cu) was induced by prolonged mechanical milling.
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.
Effect of heat-treatment on the nanostructural change of W-Cu powder prepared by mechanical alloying
Metals and Materials, 1999
W-30wt.%Cu powder prepared by mechanical alloying (MA) was annealed at various temperatures to investigate the structural change of MA W-Cu powder. From differential scanning calorimeter analysis and transmission electron microscope observation, it was revealed that the recovery of W in MA W-30wt.%Cu powder occurred at 700~ and the W grain started growing also at this temperature. The W grain had grown significantly after annealing at 900~ and the Cu phase in the MA powder was found to act as liquid melt near 900~ The microstructure of the sintered specimen was similar to that of the W-Cu alloy via liquid phase sintering. This microstructure, even at temperatures below Cu melting, was the new feature observed in the MA W-Cu powder. This suggests that such a microstructure is closely related to the inherent high diffusivity of the nanosized W crystallites as well as the liquid-like behavior of the Cu phase.
Materials & Design, 2011
Elemental powders of copper (Cu), tungsten (W) and graphite (C) were mechanically alloyed in a planetary ball mill with different milling durations (0-60 h), compacted and sintered in order to precipitate hard tungsten carbide particles into a copper matrix. Both powder and sintered composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and assessed for hardness and electrical conductivity to investigate the effects of milling time on formation of nanostructured Cu-WC composite and its properties. No carbide peak was detected in the powder mixtures after milling. Carbide WC and W 2 C phases were precipitated only in the sintered composite. The formation of WC began with longer milling times, after W 2 C formation. Prolonged milling time decreased the crystallite size as well as the internal strain of Cu. Hardness of the composite was enhanced but electrical conductivity reduced with increasing milling time.
Densification and structural change of mechanically alloyed W-Cu composites
Metallurgical and Materials Transactions A, 2001
Fine-grained, high-density (97ϩ pct of theoretical density (TD)), 80W-20Cu wt pct (58W-42Cu at. pct) composites have been prepared using nonconventional alloying techniques. The W and Cu precursor powders were combined by a high-energy ball-milling procedure in air or hexane. The mechanically alloyed W ϩ Cu powder mixtures were then cold pressed into green compacts and sintered at 1523 K. The milling medium and milling time were varied to increase product densities with a concomitant order-of-magnitude decrease in grain size. For densification, air was found to be a more effective medium than hexane. From microhardness measurements, it was concluded that the W-Cu alloys were dispersion and solution hardened, but were sensitive to entrapped residual impurities. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) analyses were used to demonstrate that the as-milled and sintered W-Cu alloy structures were metastable, decomposing into the starting W and Cu components upon heating at or above 723 K.