Roosta et al. International Journal of Industrial Chemistry 2012, 3:10http://www.industchem.com/content/3/1/10

RESEARCH Open Access

An experimental investigation on the fabricationof W-Cu composite through hot-pressMostafa Roosta1*, Hamidreza Baharvandi1 and Hossein Abdizade2

Abstract

In this paper the feasibility of fabricating W-Cu composite by hot-press has been studied and the best parametersfor hot-pressing were acquired. W/20 vol%Cu composite was successfully prepared by this process, in which atfirst the powder of tungsten and copper, containing 20% vol copper were mixed in a ball mill for 3 h at rotationspeed of 200 rpm. Then the mixed powders were hot-pressed for 3 h at a compact pressure of 30 MPa andtemperatures of 1,250°C, 1,350°C, and 1,450°C. The composites made have been investigated and revealed themaking W-Cu composite with good properties included density, hardness, modules of elasticity, flexural strength,and microstructure. Also, the sample made at 1,450°C possesses better properties, and its microstructure showedthe tungsten matrix and the copper reinforcement separately; the X-ray diffraction patterns showed that nocompound has been formed between W and Cu.

Keywords: Tungsten-copper, Composite materials, Hot-press

BackgroundComposite materials are engineered or naturally occur-ring materials made from two or more constituent mate-rials with significantly different physical or chemicalproperties which remain separate and distinct at themacroscopic or microscopic scale within the finishedstructure. W-Cu composites are made by mixing a re-fractory phase called tungsten, which possess highstrength and low coefficient of thermal expansion, and aCu-phase having high thermal and electrical conductivity[1]. The combination of these elements optimizes someproperties such as ductility, strength, and corrosion andwear resistance. In the recent years, W-Cu compositeshave gained great importance in automotive, electrical,and military industry because of their high thermal con-ductivity, low thermal expansions, high wear resistanceand excellent electrical conductivity. They are used aselectrical contacts, resistance welding electrodes, heatsinks, electro-forging dies, packaging materials, and soon [2,3].The fabrication of a full density W-Cu composite is

very difficult. Because of the big difference between

* Correspondence: mostafa_rosta@yahoo.com1Malek-Ashtar University of Technology, P.O. Box 13336–95711, Tehran, IranFull list of author information is available at the end of the article

© 2012 Roosta et al; licensee Springer. This is anLicense (http://creativecommons.org/licenses/byprovided the original work is properly cited.

melting points of tungsten (approximately 3,400°C) andcopper (approximately 1,083°C), there is no overlap ofsintering temperature ranges. Also, tungsten-copper sys-tem has no mutual solubility which means poor sinterability [1]. The infiltration of a porous-sintered tungstenskeleton by liquid copper is one of the most commonmethods for producing W-Cu composite. However, inthis method defects like pores, copper lakes, and tungstenagglomerates form easily, so this technique results in apoor quality [2-4]. Other methods to fabricate W-Cucomposites include the following: thermal-mechanicalprocess [2], metal powder injection molding [5], hot ex-trusion [6], liquid sintering and hot-hydrostatic extrusion[7-9], microwave sintering [10], resistance sintering [11],vacuum plasma spray [12,13], mechanical alloying, andother new methods [14-18].Although one of the most important methods in pro-

ducing composites is hot-press, in which the mixedpowders will be subjected to high pressure and hightemperature at the same time, this method has not beenused as sole way for making W-Cu composite. Of allthe advantages that this method contains, increasingthe properties of row and sintered material such asdensity, strength, and fatigue properties is the mainone. In this experiment, we use hot-press to produceW-Cu composite because of its simplicity and low cost.

Open Access article distributed under the terms of the Creative Commons Attribution/2.0), which permits unrestricted use, distribution, and reproduction in any medium,

Figure 1 Optical micrographs of W/20 vol%Cu prepared byhot-press with 30 MPa pressure at 1,400°C.

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Results and discussionPhysical propertiesThe bulk density of pieces made at 30 MPa and tempera-tures of 1,250°C, 1,350°C and 1,450°C was measured about15.21, 15.76, and 16.25 g/cm3 respectively. Also, the poros-ity of specimens can be measured through this method.For example, the apparent porosity which does not includethe volume of the sealed pores was evaluated about 0.78%for composite made at 1,450°C.Since in Brinell hardness test method, the diameter of

ball indenter is big and pressure is applied to the bulk ofsample, this method was used to calculate the hardness ofthe work pieces. According to the results, the hardnessesof the samples made at 30 MPa and temperatures of1,250°C, 1,350°C and 1,450°C were equal to 131, 149, and163 HB respectively.For calculating modulus of elasticity in accordance

with ASTM C769 test standard (ASTM International,West Conshohocken, PA, USA), the speed of sound inthe sample must be calculated first. In this way, a2.5 × 2.5 cm sample is made and then an ultrasonic pulsewith frequency of 4 MHz will be sent to the surface ofsamples and then will be received. By recording the re-turn time of sound and sample thickness, the speed ofsound (v) passing the sample was obtained; by using thefollowing relations, modulus of elasticity (E) in GPa wasobtained:

E ¼ ρv2 ð1Þ

Thus according to calculated density for the com-posite, the modulus of elasticity are 312.5, 325.4, and341.8 GPa for samples made at 1,250°C, 1,350°C and1,450°C, respectively.Flexural strength of samples is obtained based on

the ASTM C1161 test standard. According to this teststandard, specimens with dimensions of 3 × 4 × 45 mmare made and the surfaces are prepared by polishing.Then the load was applied by flexural strength ma-chine with speed of 0.5 mm/min and distance (l) of40 mm between two bases of applying load. By draw-ing the force-strain diagram, the maximum fractureforce (F) is recorded. Using the following relation,flexural strength or modulus of rupture (MOR) is cal-culated in MPa,

MOR ¼ 3Fl2bd2

ð2Þ

where F is fracture force (N); B is sample width(mm); D is thickness of sample (mm); and L is thedistance between two bases of applying load (mm).Correspondingly, the flexural strength of composite made

at 1,250˚, 1350˚ and 1450°C is 381.2, 350.7 and 343.8 MPa.

The study of microstructureSince it is clear that the best result was obtained fromthe sample made at 30 MPa pressure and temperaturesof 1,450°C, we perform the microstructure study justfor this sample. After preparation and polishing, theparts as a result were seen under optical microscopyand scanning electron microscopy. The etching of workpieces is done according to ASTM 98 C standard, inwhich 10 g of ferrocyanide potassium (K3Fe(CN)6) and10 g of NaOH is added to 10 ml distilled water. Asshown in Figure 1, the optical micrographs of W-Cucomposite made in 1,450°C and 30 MPa copper andtungsten phases are visible. The porosity in the com-posite is also seen, one of the main defects that exists inhot-press.Also by secondary scanning electron microscopy

(SEM) and back scattered electron (BSE) the morph-ology of samples and their particle size and shape arestudied. Figure 2 shows the SEM, and Figure 3 showsthe BSE micrographs of the W/20 vol%Cu compositeprepared by hot-press at 1,450°C and 30 MPa.In Figure 4, the elemental analysis map of composite

can be seen. It is clear in the picture that the compositeis made of tungsten, copper, and nickel.On the other hand, as it is clear in the back-scattered

electron images, the composite is made of dark phase andbright phase. According to the feature of back-scatteredelectron images, the bright phase is related to heavierelements because heavier elements reflect more light.However, to prove this issue, energy dispersive X-rayspectroscopy (EDX)-line scan and elemental analysis ofboth phases can be used. As shown, the dominantbright phase is about 80% volume and the dark phase ofcopper can also be seen in the image. To prove that

Figure 4 Map of composite W/20 vol%Cu; red parts representW and green parts represent Cu.

Figure 2 SEM micrographs of W/20 vol%Cu prepared byhot-press with 30 MPa pressure at 1,400°C.

Roosta et al. International Journal of Industrial Chemistry 2012, 3:10 Page 3 of 6http://www.industchem.com/content/3/1/10

bright phase belongs to tungsten and dark phasebelongs to copper, an EDX-line scan from a bright grainand EDX-line scan from the dark grains are taken andshown in Figures 5 and 6.Also, the fact that the bright phase belongs to tungsten

and dark phase belongs to copper can be shown by elem-ental analysis of the bright and dark phases. Figure 7shows the elemental analysis of bright and dark phases.Figure 8 shows the XRD patterns of starting tungsten

and copper powders before production of composite. Alsothe XRD result of W/20%volCu is present in the image. Asclearly seen in the pictures for the pure powders beforemaking composite, only peaks related to copper and

Figure 3 BSE micrographs of W/20 vol%Cu prepared byhot-press with 30 MPa pressure at 1,400°C.

tungsten are seen. However, in the XRD patterns of com-posite made from tungsten and copper, there are onlypeaks related to these two elements, which show that nocompound between these two elements has been formed.Furthermore, because of the low amount of copper in thecomposite, about 10 weight percent, peaks related to cop-per have a low intensity in comparison with peaks relatedto tungsten.

MethodsThe elemental tungsten powder and copper powder wereused as raw materials. In order to make W/20vol%Cu com-posite, weight percent of powders must be calculated first.For this purpose, the weight percent of copper and tungstenin the desired composite by Equation 3 is calculated,according to density and volume percent of Cu and W, intopercent WtCu=10.34 and percent WtW=89.66.

%WtCu ¼ W1W1þW2

� 100 ¼ ρ1V1ρ1V1þρ2V2

� 100 ð3Þ

On the other hand, the theoretical density of composite iseasily calculated by adding up the mass of each component:

m ¼ mf þmm

m ¼ ρ V

ρV ¼ ρf V fþρmVm ð4ÞρV ¼ ρf f V þ ρm 1−fð ÞVρ ¼ f ρf þ 1−fð Þρm

Figure 5 EDX-line scan of bright grains, showing that the bright grains belong to tungsten.

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Where f is the volume fraction of fibers or the secondphase, ρ is density, m is mass,V is volume, mf is mass ofsecond phase and mm is mass of matrix. According tothese equations, the theoretical density of composite isequal to ρ= 17.22 g/cm3.

Figure 6 EDX-line scan of dark grains, showing that the dark grains b

The required amount of powders is calculated consider-ing the density of composite and size of the piece. In thisexperiment, we attempt to produce a piece with dimensionsof 12×12×0.4 cm, so the volume will be 57.6 cm3 andm=991.87 g. Hence, we need 991.872 g of tungsten-copper

elong to copper.

Figure 7 Elemental analysis. a) bright phase b) dark phase.

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powder to make the piece, and the value of each of thesetwo components is calculated as follows:

WCu ¼ 10:34=100� 991:87 ¼ 102:56g

WW ¼ 991:872–102:56 ¼ 889:3g

Thus to fabricate a piece with aforementioned dimensionsfrom W/20% volCu composite, it must be seen how muchtungsten and copper powder is required. Therefore at firststage, the required amount of each powder was weighedand then mixed for 3 h in a ball mill, with rotation speed of200 rpm. A 2%wt of nickel powder was added to the com-posite as well as to reduce the composite density, consider-ing the low density of nickel (approximately 8.9 g/cm3), incomparison with the composite (approximately 17.22 g/cm3). The mixed powders, after being dried, were per-formed at room temperature under 80 MPa pressure andthen hot-pressed for 3 h with the compaction pressure of30 MPa at three different temperatures of 1,250°C; 1,350°C;and 1,450°C to obtain the optimum temperature. The heat-ing rate was chosen at 10°C/min. The sintering process isshown in Figure 9. The hot-pressing was also done under

2 T40

W/Cu composite

Cu powder

W powder

Figure 8 XRD patterns of starting powders and the produced compos

high-purity argon (99.99%) atmosphere to avoid the powderfrom being oxidized.The density of composite was measured through Archi-

medes test, according to ASTM B311 standard. This teststandard is mostly used to determine the density of powdermetallurgy parts and is based on the water displacementmethod. The hardness was evaluated in accordance withBrinell hardness test method ASTM E10. In addition, thebending strength of the composite has been measured bybending test according to ASTM C1161, and the modulusof elasticity was measured as well by ASTM C769 teststandard method, in which the modulus of elasticity is eval-uated by the help of sound velocity in the work piece.Lastly, the microstructure of made specimens was investi-gated by optical microscopy and scanning electronmicroscopy.

ConclusionIn this study, the feasibility of fabricating W/Cu compositevia hot-press was studied. The W/20 vol%Cu compositeswere made at 30 MPa pressure and temperatures of

heta60 80

W

Cu

ite after being hot-pressed.

Figure 9 The sintering process.

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1,250°C, 1,350°C and 1,450°C showed good properties,including density, hardness, modulus of elasticity, andflexural strength. The microstructure showed the tungstenmatrix and the copper reinforcement distinctly, and theXRD patterns showed that no compound has been formedbetween W and Cu. The best results were obtained for thesample made at temperatures of 1,450°C.

Competing interestsThe authors declare that they have no competing interests.

AcknowledgmentThe authors would like to express their gratitude to Dr. Ebrahim Afshari forproviding language help and useful suggestion in writing the article.

Author details1Malek-Ashtar University of Technology, P.O. Box 13336–95711, Tehran, Iran.2School of Metallurgy and Materials Engineering, University of Tehran I. R.,Tehran, Iran.

Authors’ contributionsMR, the first author, carried out making the composite and testing it. HB,participated in the design of tests and coordination . HA, conceived of thestudy, and helped to draft the manuscript. All authors read and approved thefinal manuscript.

Received: 7 February 2011 Accepted: 2 July 2012Published: 2 July 2012

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doi:10.1186/2228-5547-3-10Cite this article as: Roosta et al.: An experimental investigation on thefabrication of W-Cu composite through hot-press. International Journal ofIndustrial Chemistry 2012 3:10.

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