improvement of machinability of tungsten by copper infiltration technique

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International Journal of Refractory Metals & Hard Materials 26 (2008) 530–539

Improvement of machinability of tungsten by copperinfiltration technique

Jiten Das *, A. Chakraborty, T.P. Bagchi, Bijoy Sarma

Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500 058, India

Received 17 September 2007; accepted 29 December 2007

Abstract

Infiltration of liquid copper in partially sintered tungsten was undertaken to improve machinability of tungsten. Initial skeleton oftungsten was prepared by pressing commercial tungsten powder in cold isostatic press to near-net shapes. The green compacts are thensubjected to controlled sintering to about 85% theoretical density. This leaves adequate amount of open channels which are filled sub-sequently with liquid copper by infiltration. The resulting composite material exhibits reasonable strength coupled with desired level ofmachinability. Some pilot samples were made with �99% density and were subjected to in-house characterization (e.g., density, shrink-age and porosity). Microstructural study has been carried out to compare the theoretically calculated porosity levels with the observedporosity level. X-ray diffraction studies revealed presence of elemental tungsten and copper with no mutual solubility. Mechanical prop-erties (e.g., ultimate tensile strength, tensile elongation and hardness values) of the composite were also evaluated and reported.� 2008 Elsevier Ltd. All rights reserved.

Keywords: Copper infiltration; Machinability; Porous tungsten

1. Introduction

Tungsten metal has received much attention due to itsvery high density (19.3 g/cc) [1], melting point (3420 �C)[2], elastic modulus (410 GPa) [3], strength (minimum800 MPa, at room temperature) [4], and good c-ray shield-ing [5] properties (as compared to lead). It also has reason-ably good erosion resistance [6] and retains reasonablestrength (345 MPa at 1000 �C) and elastic modulus(390 GPa at 1000 �C) [3] at elevated temperature. But oneinherent drawback of tungsten—its poor machinabilityand formability—hinders its shaping to complicated partscommercially. Powder Metallurgy (P/M), however, offersa reasonably good solution to tungsten fabrication prob-lems exploiting its near net-shaping capability [7]. This alsowill not solve all the problems as modern technology

0263-4368/$ - see front matter � 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.ijrmhm.2007.12.005

* Corresponding author. Tel.: +91 9989178700; fax: +91 4024344535.E-mail address: [email protected] (J. Das).

demands components of intricate shape which cannot beaddressed through P/M route alone.

It has been observed in practice that good machinabilitymay be imparted to tungsten when coupled with copper.Copper additionally improves thermal conductivity of thecomposite [1]. Tungsten–copper composite can be used athigh-temperatures (for short time durations, normally lessthan 1 min) where copper is used to impart ablative coolingto the tungsten substrate (heat of evaporation = 4800 kJ/kg) [8]. As a result of all these combinations, tungsten–cop-per composites are used for a variety of commercial prod-ucts like—arc runners, current carrying members, hightemperature erosion resistant materials, CG adjusters, bal-lasts of different shapes and sizes, jet vanes, c-ray shields,etc.

Copper can be mechanically alloyed with tungsten byhigh-energy milling [9] or attrition as it is otherwise immis-cible to tungsten (heat of mixing is highly positive i.e.,+35.5 kJ/mol) [10]. However, the process is very costly.Purity of the product and powder handling are two

mailto:[email protected]

Fig. 2.2. SEM (secondary electron) image of as received tungsten powderutilized in this study.

J. Das et al. / International Journal of Refractory Metals & Hard Materials 26 (2008) 530–539 531

important technological issues for mechanical alloying.From this viewpoint, simple infiltration of liquid copperin partially sintered tungsten (porous) may prove to beanother acceptable option for production. Advantage ofthis process is that after machining the material to compli-cated shape, copper can be also removed through the openpore channels, if desired. This opens up another option forproduction of tungsten parts of any machinable shape withcontrolled level of open porosity depending on the neces-sity. At present, in our laboratory, the copper is being triedto leach out by dipping the P/M part (i.e., Cu-infiltratedtungsten) in 50% HNO3 solution. Appearance of blue col-our in the solution (as soon as the part is being dipped intothe solution) indicates successful copper removal by follow-ing reaction:

3CuðsÞ þ 8HNO3ðaqÞ ! 3CuðNO3Þ2ðaqÞþ 2NOðgÞ þ 4H2OðlÞ ð1Þ

The blue colour solutions is being replaced several timeswith freshly made diluted (50%) HNO3 solution. Comple-tion of copper leaching operation is indicated by the disap-pearance of blue colour solution. This leaching processtakes about 3 days. The remaining copper can be removedby vacuum distillation at �1500 �C.

2. Experimental technique

2.1. Determination of porosity, density and shrinkage of the

composite made in this study

Seven green compacted pure tungsten blocks havingdimensions 270 mm length � 70 mm breadth � 32 mmwidth have been made from finely divided tungsten powder(Alldyne) using Cold Isostatic Press (Make: NationalForge, Belgium: maximum pressure 5.2 kbar) at 2.5 kbarpressure. The properties of tungsten powder is shownin Figs. 2.1 and 2.2 and in Table 2.1. The densities ofthese green compacts have been measured by measuringtheir volume from their dimensions and measuring theweight by precision electronic balance (Make: Sartorius

0102030405060708090

100

0 10 20 30 40Particle size, micron

Volu

me

freq

uenc

y (c

umul

ativ

e) %

50

Fig. 2.1. Particle size distribution of pure tungsten powder.

BP34000-P, maximum 34,000 g, d = 0.1 g for 8000 g,d = 0.2 g for 16,000 g and d = 0.5 g for 34,000 g). Thesegreen compacted blocks are then pre-sintered at 1300 �Cfor 1.5 h in hydrogen atmosphere in Pusher type sinteringfurnace (Make: FHD Furnace Limited, England; Maxi-mum temperature 1800 �C). Densities of these pre-sinteredblocks are measured by measuring their volume by waterdisplacement method and mass by precision electronic bal-ance. These pre-sintered blocks are then controlled sintered(at 1790 �C for 5 h) in hydrogen atmosphere to achievecontrolled porosity (�15 v/o). The 15 v/o porosity ensuresfree escape of water molecule during hydrogen cleaning ofpores [11] and adequate amount of open porosity as well asinterconnected porosity for facilitate copper infiltration.The densities and shrinkages have been measured afterfinal sintering treatment. At every stage porosity valueshave been calculated by the formula

v=o porosityat any stage ¼ 100� fðdensityat that stage � 100Þ�

=pore free densityg� ð2Þ

where pore free density of tungsten is 19.3 g/cc.The copper infiltration in porous tungsten blocks have

been carried out by dipping it in packed copper powderswhich are kept inside a graphite boat and heating theassembly in FHD furnace at 1400 �C for 2 h in hydrogen

Table 2.1Properties of pure tungsten powder

Properties

Source Alldyne Powder TechnologiesApparent density (g/cc) 4.7Tap density (g/cc) 7.0Particle shape CuboidFlow rate Time taken 30 s for flow of 50 g of

powder in Hall flow meterChemical composition W-99.9 wt%

532 J. Das et al. / International Journal of Refractory Metals & Hard Materials 26 (2008) 530–539

atmosphere. While hydrogen atmosphere clean the pores aswell as copper powders, high temperature causes melting ofcopper powder. This molten copper infiltrates inside theporous labyrinth of controlled sintered tungsten by capil-lary pressure from all the sides by virtue of its reasonablewettability to tungsten [12]. This situation is illustratedschematically in Fig. 2.3. The capillary pressure is inverselyproportional to radius of pores (capillary pressure =2*adhesion tension/radius of pores) [13]. Therefore, thesmaller the pore radius, the higher is the capillary pressure.However, infiltration time is very high in case of pores withnarrow length (height to diameter (H/D) ratio high). Lar-ger radius pores with low H/D ratio, on the other hand,facilitate easy penetration of molten copper inside the por-ous labyrinth. Very large radius pores with low H/D ratio,however, become unable to retain the infiltrant in the poresdue to insufficient capillarity. Therefore, optimum radius ofpores with optimum H/D ratio has to be maintained toobtain maximum infiltration. It was found, by trial anderror process, that average pore radius between 1 and4 lm with H/D ratio between 1 and 8 renders maximummolten copper infiltration. Copper powders are heated at1400 �C to reduce the viscosity of the molten copper. Low-

PorousTungstenblock before infiltration

Heating of Cu powder to obtain molten CuCover around the porous W block

PorousLabyrinth

Copper infiltration

Cu Filled pores after infiltration

Machining to remove excess Cu

Excess Cu aftercompletepore filling

Fig. 2.3. Schematic diagram of molten copper infiltration inside theporous tungsten block.

ering of viscosity causes faster filling of molten copperinside the porous labyrinth as filling time is given by theequation [13]:

Filling time ¼ 2l2l=r coshrlg ð3Þwhere l = pore length, l = viscosity, r = pore radius,rlg = liquid–gas surface tension, h = contact angle.

Generally holding the molten copper around the tung-sten block for 2 h (at 1400 �C) completes the pore fillingprocess. Gravity aids the filling process from the top sur-face of the porous tungsten blocks while, gravitational pullworks against the capillary rise of molten copper from thebottom surface of the block. Remaining molten copper,after complete pore filling will reside around the surfacesof tungsten block and will solidify once the graphite boatassembly is taken out from the furnace.

After removal of solidified copper from the surface, den-sity of copper infiltrated blocks have been measured and v/o porosity at this stage measured using Eq. (2). Here, The-oretical density (TD) of pore free Cu–tungsten compositehas been estimated using equation:

TD ¼ 100=Rðw=o constituent element

=density of the constituent elementÞ ð4Þ

Here, w/o copper in the composite has been estimated bywet chemical analysis.

Depth of cut

Depth

of

cut

Feed

rate

Rotating Work piece

Shape of Chips

Depth of cut

Feedrate

cuttingdirection

Tool

Fig. 2.4. Schematic diagram illustrating the correlation of the dimensionsof the unbroken turning chips with the machining parameters: breadthand thickness of the unbroken chips are equal to depth of cut and feed raterespectively.

Fig. 2.5. Schematic diagram [14] of surface roughness measuring instru-ment (skidded gages, the sensitive diamond-tipped stylus is containedwithin a probe).

Table 3.2Calculated values of lattice parameters of W and Cu from 2h values of the peaks obtained from the X-ray Diffraction pattern (using CuKa, k = 1.54056 A)(Fig. 3.4) of W–Cu composite made in this study

2h h sin2h (h k l) (h2 + k2 + l2) c = sin2h/(h2 + k2 + l2) Average c Lattice parameters a = k/2p

c (A)

For element tungsten

40.37 20.19 0.119 (110) 2 0.059558.34 29.17 0.238 (200) 4 0.059473.25 36.63 0.356 (211) 6 0.0593 0.0593 3.16387.00 43.50 0.474 (220) 8 0.0592For element copper

43.48 21.74 0.137 (111) 3 0.045750.56 25.28 0.182 (200) 4 0.0456 0.0456 3.60790.00 45.00 0.500 (311) 11 0.0455

Table 3.1Density, shrinkage and porosity values of seven tungsten blocks after green compaction, pre-sintering, controlled sintering and Cu-infiltration operation

BlockNo.

Greencompa-ctionoperation

Greendensity(g/cc)

Pre-sinteringoperation

Density (g/cc)after pre-sintering

Controlledsinteringoperation

Totalshrinkage(%) aftercontrolledsintering

Density (g/cc)after controlledsintering

Copperinfiltrationoperation

Amount ofanalyzedCu in Cu-infiltratedW

Density afterCu-infiltration(g/cc)

1 CIP/2.5 kbar 1300 �C/1.5 h/H2

12.745 1790 �C/5 h/H2

16.512 1400 �C/2 h/H2

17.78

2 CIP/2.5 kbar 1300 �C/1.5 h/H2

11.740 1790 �C/5 h/H2

16.477 1400 �C/2 h/H2

17.66

3 CIP/2.5 kbar 1300 �C/1.5 h/H2

12.580 1790 �C/5 h/H2

16.459 1400 �C/2 h/H2

17.575

4 CIP/2.5 kbar 1300 �C/1.5 h/H2

12.240 1790 �C/5 h/H2

L = 7.55 16.577 1400 �C/2 h/H2

7.2 w/oor

17.538

5 CIP/2.5 kbar 11.574(Porosity40 v/o)

1300 �C/1.5 h/H2

12.426 1790 �C/5 h/H2

W = 5.30 16.474 1400 �C/2 h/H2

14.55 v/o 17.636

6 CIP/2.5 kbar 1300 �C/1.5 h/H2

12.036 1790 �C/5 h/H2

T = 6.66 16.479 1400 �C/2 h/H2

17.533

7 CIP/2.5 kbar 1300 �C/1.5 h/H2

12.310 1790 �C/5 h/H2

16.452 1400 �C/2 h/H2

17.622

Averagevalue

12.380(Porosity = 36.3v/o)

16.490(Porosity = 14.6v/o)

17.620(Porosity = 1.0v/o)

Table 3.3The hardness and tensile properties of copper-infiltrated tungsten block

Hardness 280 VHN

Tensile strength 432 MPaElongation 2%


Alternatively, v/o of infiltrated copper was calculatedfrom the w/o of copper (wet chemical analysis data) usingthe equation:

v=o Cu ¼ fðw=o Cu=8:9Þ � 100g=fðw=o Cu=8:9Þþ ðw=o W=19:3Þg ð5Þ

Now, v/o porosity after copper infiltration is calculatedusing equation;

v=o porosityat Cu-infiltration ¼ v=o porositybefore infiltration

� v=o Cuat Cu-infiltartion ð6Þ

2.2. Microstructural study

The microstructural observation using Leo scanningelectron microscope has been carried out for the final sin-tered porous tungsten blocks as well as Cu-infiltrated tung-sten blocks to compare the observed porosity with thecalculated porosity (measured using Eq. (3)).

2.3. X-ray diffraction study

X-ray diffraction study using CuKa radiation (wavelength k = 1.54056 A) of the tungsten–copper compositemade in this investigation has also been carried out usingPhillips XRD Machine. The data obtained from XRDpattern of this composite has been analyzed manually toknow the phases present and lattice parameter of thosephases.


2.4. Hardness and tensile properties evaluation

The tensile specimen (ASTM E8 M: T-11) has beenmachined from the block and tested using Tensometer(Make: Masanto, UK, Maximum load 2 tones). Hardnessalso measured using Wolpert Vicker Hardness Tester using10 kg load.

11.574 12.38 16.49 17.62

40.0 36.314.6

1.0

0

10

20

30

40

50

60

Green Compaction (CIP/3000bar)

Presintering(1300C/1.5h/H2)

Sintering(1790C/5h/H2)

Post sintering (Cu infiltration) (1

400C/2h/H2)

Average Porosity(volume%)

Average Density (g/cc)

Fig. 3.1. Average density and porosity values of tungsten block aftervarious operations such as green compaction, pre-sintering, controlledsintering and Cu-infiltration operations.

2.5. Machinability study

Machining (turning) of porous tungsten cylindricalsample as well as Cu-infiltrated cylindrical sample wascarried out, (using Lathe Enterprise-1550, Kirloskar,Mysore, India, Capacity: 1000 mm bed length,3.73 kW), in identical condition to compare machinabilityof both the materials. The turning operation was carriedout at identical condition (i.e., at 420 rpm speed, at0.04 mm/revolution feed rate and at 0.5 mm depth ofcut) for both the materials. The turning operation is sche-matically illustrated in Fig. 2.4. Initial shape of both thematerials was cylindrical and initial diameter was 8 mm.The turning was carried out for 25 mm length of thesecylindrical samples in dry condition and chips were col-lected, weighed and observed using Leo electron micro-scope. Tungsten carbide tool (K-20: Sandvik make) toolwith a rake angle 14� was used for the turning operation.The Chips dimensions are dependent on the machiningparameters such as depth of cut and the feed rate. Thebreadth and thickness of the unbroken chips would beequal to the depth of cut and feed rate, respectively (referschematic diagram Fig. 2.4). The surface roughness of theporous tungsten and Cu-infiltrated tungsten, after turningoperation, was measured using MITUTOYO SURF-TEST-211, JAPAN. The schematic diagram of surface

Table 3.4Comparison of machinability of porous tungsten and Cu-infiltratedtungsten

Material Tungsten Copper-infiltratedtungsten

Feed rate 0.04 mm/rotation

0.04 mm/rotation

Depth of cut 0.5 mm 0.5 mmMachine RPM 420 420Ease of machining Difficult EasyTool Tungsten

carbide tip (K-20)

Tungstencarbide tip (K-20)

Tool tip wear Heavy, tool gotblunted

Negligible

Chipping out of material fromselected pocket/partialfragmentation

Observed Not observed

Surface roughness Non-uniform(3.8 ± 2.4 lm)

Uniform(3.0 ± 0.6 lm)

Metal removal rate 0.04 g/s 0.06 g/sTime taken for turning of 25 mm

length of the cylindrical sample80 s 78 s

roughness measuring instrument is shown in Fig. 2.5[14]. Surface roughness/average roughness (Ra) is deter-mined by comparing all the peaks and valleys to themean line, and then averaging them all over the entirecutoff length of 0.8 mm (cutoff length is the length thatthe stylus is dragged across the surface). The stylus is dia-mond tipped and having tip radius 5 lm. The average of5 Ra readings of the machined surfaces is taken andrecorded in Table 3.4.

The machined surfaces were also observed using scan-ning electron microscope.

Fig. 3.2. The back scattered image of pure tungsten block made by coldisostatic compaction at 2.5 kbar pressure and pre-sintering at 1350 �C for1.5 h and controlled sintering at 1790 �C for 5 h in hydrogen atmosphere.Around 15 v/o porosity is seen in tungsten matrix.

Fig. 3.3. Pore free microstructure of Cu-infiltrated tungsten composite.(a) Back scattered image of Cu-infiltrated tungsten block, (b) X-raymapping of tungsten, and (c) X-ray mapping of Cu.


3. Results and discussion

Density and calculated porosity values at green compac-tion, pre-sintering, controlled sintering and at copper infil-

tration stage have been estimated and tabulated in Table3.1 and shown as bar chart in Fig. 3.1. It was observed thatwhile density value at green compaction stage was only�11.6 g/cc, its density significantly improved to �16.5 g/cc after final sintering operation. Calculated porosity valueat green compaction was 40.0 v/o and it reduced to only14.6 v/o after final sintering operation. Back scatteredimage (Fig. 3.2) of controlled sintered tungsten blocks alsorevealed that the porosity value was around 15 v/o. Wetchemical analysis of the Cu-infiltrated blocks showed onan average �7.2 w/o copper went inside the porous tung-sten. According to Eq. (5), 7.2 w/o copper is equal to14.55 v/o copper. This indicates that nearly all pores havebeen filled up by the copper. This may be due to the opti-mum volume % as well size distribution of porosity, highcopper infiltration time and temperature adopted in thisinvestigation. High temperature increases fluidity(decreases viscosity) of molten copper, enhances the fillingof copper into tungsten. The back scattered image of cop-per infiltrated tungsten block as well as X-ray mapping oftungsten and copper (shown in Fig. 3.3) revealed thatnearly pore free microstructure of tungsten–copper com-posite was obtained. However, v/o porosity calculatedusing Eq. (2) indicates that there is still 1.0 v/o porosityremained. The pore free density of copper infiltrated tung-sten was calculated using Eq. (4).

X-ray diffraction pattern (shown in Fig. 3.4) was ana-lyzed and found that only elemental tungsten and copperpeaks were found. Calculated (Table 3.2) lattice parametervalues of tungsten and copper (i.e., 3.163 A, 3.607 A,respectively) from the data obtained using XRD technique,exactly matching with the lattice parameters of pure tung-sten and copper i.e., 3.1648 A and 3.6150 A, respectively.This indicates that very negligible/nil mutual solubilityexists between tungsten and copper metals in the compositedeveloped in this study (as expected).

The hardness and tensile properties of copper infiltratedtungsten block has been evaluated and shown in Table 3.3.Tensile strength of the composite is lower than the puretungsten P/M product. However, owing to their very lowhardness and tensile strength the blocks are having verygood machinability.

The comparative machinability features of porous tung-sten and Cu-infiltrated tungsten are demonstrated in Table3.4. Porous tungsten was very difficult to machine, and thisfact is supported by heavy tool (tungsten carbide) wear.The carbide tool got blunted during turning a length of25 mm of the cylindrical sample made of porous tungstenand while reducing its diameter from 8 mm to 7 mm (i.e.,depth of cut 0.5 mm). The surface roughness was observedto be of non-uniform nature throughout the machinedsample. The reason for observing non-uniformity in sur-face roughness of machined porous tungsten is demon-strated schematically in Fig. 3.5a. Rough surface in themachined piece might originate due to fracture of theridges, which experience non-uniform kind of cutting force(due to inhomogenity in the porous tungsten material,

Fig. 3.4. X-ray diffraction Pattern of tungsten–copper composite.

Fig. 3.5. Schematic diagrams illustrate the variation of surface roughness after machining along AB for (a) porous tungsten and for (b) Cu-infiltratedtungsten in case of porous tungsten (c) isolated ridges will experience non uniform impact kind of cutting force, whereas incase of Cu-infiltrated tungsten(d) ridges will be supported by ductile copper and ridges will experience uniform kind of cutting force.


Fig. 3.6. SEM images of machined surfaces of (a, b) porous tungsten (secondary electron image), (c) tungsten–copper composite (secondary electronimage), (d) tungsten–copper composite (back scattered electron image) as well as (e) EDAX obtained from point 1 in (d).


which happens to be a mixture of solid tungsten + 15 v/oporosity) during turning.

During machining, individual particles or bunch oftungsten particles were scooped out from porous tungsten.This resulted in obtaining a very rough surface finish in themachined piece (Fig. 3.6a). The tungsten carbide tools pos-sibly got blunted due to continuous abrasion combinedwith rubbing action with the rough surface of porous tung-sten (which is highly wear resistant). This blunted toolcould not machine the remaining material (due to very highcontact area between the tool edge and the work piece) andsubsequently, only abrasion and rubbing action of tool onthat portion of work piece took place without any signifi-cant material removal (Fig. 3.6b). Sometimes, the porousrod also exhibited partial fragmentation while machining.Heavy porosity (15 v/o) observed in Fig. 3.2 is probably

responsible in causing fragmentation behaviour of theparts during machining.

The successive machining marks separated by a distanceof 40 lm are visible in the machined surface of poroustungsten (Fig. 3.6a). This is related to the feed rate (indi-cated in Fig. 3.6a), which happens to be 40 lm per revolu-tion in this study. Secondary electron image (Fig. 3.7a–d)showed that the turning chips, generated while machining,appear to be like powders (which were fractured in a pre-dominantly brittle manner) having average size between50 and 100 lm.

On the other hand, machining of Cu-infiltrated tungstenrod was comparatively easier. This is supported by theabsence of any tool wear and presence of a very uniformsurface finish in the machined piece (Fig. 3.6c and d).The reason for the good surface finish in case of Cu-infil-

Fig. 3.7. SEM (secondary electron) image of machining chips of (a–d) porous tungsten and (e–h) tungsten–copper composite at different magnifications.The thickness and breadth of the unbroken chips are equal to feed rate and depth of cut respectively.


trated tungsten is schematically described in Fig. 3.5b. Softcopper completely filled the porosity present in poroustungsten and after machining, a very uniform surface finishwas observed. As in this case, tungsten ridges are supportedby the ductile copper, most of the shocks (imparted by thetool) on the ridges would be absorbed by the ductile cop-per. Uniform cutting force imparted by the cutting toolcause very smooth surface.

Back scattered image (Fig. 3.6d) and EDAX (Fig. 3.6e)at point 1 showed clearly that copper in between tungstenpores helps in easier metal removal by shearing. Thisessentially occured due to high ductile nature of copper,which finally resulted into easy clevability followed byeasy material removal from the work-piece. The succes-sive machining marks separated by a distance of 40 lm

are visible in the machined surface of Cu-infiltrated tung-sten (Fig. 3.6c and d). This is related to the feed rateemployed in the present study. Presence of copper alongthe machining mark clearly prove that 40 lm thick and�500 breadth chips sheared easily from the rod duringmachining. Secondary electron image (Fig. 3.7e–h)showed that the turning chips, generated while machining,were having very smooth surface (refer Fig. 3.7f and g)having breadth of 100–500 lm and thickness of about40 lm.

4. Conclusions

Nearly full density copper infiltrated tungsten blockshave been made in this study.


The tungsten–copper composite shows very goodmachinability owing to their very low hardness andstrength. Tungsten–copper composite exhibits easier metalremoval, lesser tool wear and smoother surface finish ascompared to porous tungsten during machining.

Mutual solubility between tungsten and copper is negligi-ble/nil in the tungsten–copper composite made in this study.

Acknowledgements

Authors wish to thank Dr. G. Malakondaiah, Director,Defence Metallurgical Research Laboratory, Hyderabadfor allowing the authors to publish this manuscript in theJournal. Authors also gratefully acknowledge financialsupport provided by DRDO.

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improvement of machinability of tungsten by copper infiltration technique

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