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Crystallographic and morphologicalcharacteristics of explosivelycompacted copper under variousdetonation velocitiesAkash Deep Sharma a , A.K. Sharma b & Nagesh Thakur aa Materials Research Laboratory, Department of Physics , HimachalPradesh University , Shimla-171005 , Indiab Terminal Ballistics Research Laboratory , Chandigarh-160030 ,IndiaPublished online: 13 Mar 2012.

To cite this article: Akash Deep Sharma , A.K. Sharma & Nagesh Thakur (2012) Crystallographic andmorphological characteristics of explosively compacted copper under various detonation velocities,Philosophical Magazine, 92:16, 2108-2116, DOI: 10.1080/14786435.2012.669057

To link to this article: http://dx.doi.org/10.1080/14786435.2012.669057

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Philosophical MagazineVol. 92, No. 16, 1 June 2012, 2108–2116

Crystallographic and morphological characteristics of explosively

compacted copper under various detonation velocities

Akash Deep Sharmaa*, A.K. Sharmab and Nagesh Thakura

aMaterials Research Laboratory, Department of Physics, Himachal Pradesh University,Shimla-171005, India; bTerminal Ballistics Research Laboratory,

Chandigarh-160030, India

(Received 9 August 2011; final version received 3 February 2012)

Micro-sized copper powder has been compacted using explosives of variousdetonation velocities. Corresponding crystallographic and morphologicalcharacteristics along with particle size variation have also been compared.Cylindrical configuration has been used for the shock consolidation ofmetal powder. It has been observed that using an explosive mixture ofdetonation velocity 4.2 km/s, the crystallite and micro-structure of thecompacts remains the same with intact dendritic structure accompanied bya small variation in particle sizes. A good order of micro-hardness (88� 4)Hv and density of �94% of the theoretical value has been observed withlesser melting compared to the compacts obtained using explosive mixturewith a high detonation velocity.

Keywords: explosive compaction; detonation; crystallography;morphology

1. Introduction

Copper/ceramic composites have many applications in the electronic, aerospace andautomotive industries [1]. Over the last three decades, shock waves have beenemployed for the rapid solidification of the metal powders and ceramics which areotherwise difficult to compact using conventional techniques such as hydraulic andisostatic pressure techniques [2–5]. Compacted specimens may suffer difficulties dueto the formation of coarse-intermetallic compounds, grain growth and longprocessing time [6,7]. Explosive compaction is an alternative way for the synthesisof micro-sized composites and densification of metal powders to retain thehomogeneity of the compacts. The main advantage of this technique over thetraditional metallurgical process is that it is a micro-second phenomenon andrequires no additional binders for compaction. The rapid time-scale offers anopportunity to consolidate metastable and fine-grained powders, without increasingtheir grain size [8]. Shock waves produce heterogeneous surface heating on theparticle boundaries, high quench rates and interfacial bonding between the particleswhile maintaining a relatively cool temperature in the interior of the particles. Thepreeminent characteristic of explosive shock wave loading to materials is its

*Corresponding author. Email: ads.hpu@gmail.com

ISSN 1478–6435 print/ISSN 1478–6443 online

� 2012 Taylor & Francis

http://dx.doi.org/10.1080/14786435.2012.669057

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controlled detonation pressure which directly transmits shock wave to the material[9,10]. Furthermore, this technique induces localised heating via the intensedeposition of shock energy preferentially on the particle surface, which is deformed,often melted and re-solidified, producing inter-particle bonding without melting thecore of the specimen.

Although considerable work on different consolidation techniques and on themicro-structure of compacts has been reported [11–23], to the best of our knowledge,little information on crystallographic parameters and particle size variation of post-compacts is available in the literature. In this paper, we report crystallographicparameters, such as crystal phase/structure, lattice constants and particle sizeanalysis as well as micro-structural, micro-hardness and density analysis of the post-compacts. The paper describes the shock wave compaction of copper powder usingtrimonite (AN/TNT/Al, 68:25:7) and PEK (a plastic explosive) with a velocity ofdetonation (VOD) of 4.2 and 7.1 km/s, respectively. The aim is to produce fracture-less and crack free compacts of copper powder by keeping the crystalline structure ofthe compacts intact with dendrites oriented in the direction of heat flow.

2. Experimental

A schematic arrangement of the cylindrical geometry used in the experiment isillustrated in Figure 1. Micro-sized copper powder is placed in the cylindricalampoule which is fitted with a conical plug at the top and a plane plug at the bottom.

Figure 1. Cross-section of the explosive compaction assembly.

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The powder-filled ampoule is then placed in a PVC pipe and the space in between istapped with explosive. A wooden plug with an electric detonator and a boostercovers the top of the PVC container. The explosive-filled assembly is placed in anearth pit for easy recovery of the compacted specimen. When the assembly isdetonated from the top, an axi-symmetric shock compresses the copper powder. Twodifferent explosives, viz. trimonite and PEK, were used for compaction of the metalpowder. After the experiment, the compacted specimens are retrieved by machiningthe ampoule.

The crystallographic parameters of the post-compacts were examined using XRDtechnique (X’PERT-PRO, X-ray detector) with CuK� lines of wavelength�¼ 1.54 A with a step-time of 10.33 s and step-angle of 0.02o. Particle sizes wereexamined using a laser diffraction-based particle size analyser (LDPSA, MalvernMastersizer, S-2000). For micro-structural analysis of the post-compacts, a scanningelectron microscope (JEOL JSM6100 at 15 kV) was used. Micro-indentation wasperformed with a micro-hardness tester (Leica 550MW AUTO).

3. Results and discussion

For crystallographic analysis of the post-compacts, an X-ray technique wasemployed. Figure 2 shows the graphic workspace fitted X-ray pattern of thecopper powder before and after compaction. It was observed that the crystal phaseof the post-compacts remained the same, thus satisfying the fcc structure [24]. Theinter-planer spacing and lattice constant for the compacted specimens were reduced.For instance, the lattice constant a111 for a pre-compacted specimen was 3.622 A,whereas the values for low and high VOD compacted specimens were 3.615 and3.607 A, respectively (only a 1.5% variation). The FWHM value increased from0.201 to 0.235� (2�) on explosive loading of the specimen. The values give an insightinto particle size reduction of the post-shock compacts. Astonishingly, it was found

Figure 2. X-ray pattern for the pre- and post-compacts.

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that, for low VOD-compacted specimen, there was an unknown peak (though withlow intensity) at an angle of 36.525�. This peak is due to the formation of Cu2O,which is responsible for the lower density in this case; no such peak was detected forcompacts with high VODs [25].

The particle size of post-compacts was established by laser diffraction-basedparticle size analysis. Figure 3 shows the particle size distribution for pre- and post-compacted specimens. It is evident that there is a wide distribution of particle sizes.The mass moment mean average size of the particles before shock loading is 22 mm.Low VOD compacts possess an average particle size of �15 mm, while the averageparticle size is 55 mm for high VOD compacts. This means that particle sizereduction is directly related to the velocity of detonation.

The micrograph in Figure 4a shows the initial powder morphology and dendriticstructure. Figure 4b and c show the post-compacted specimens of high and lowVOD, respectively. The post-compacts were examined for fracture, micro-cracks/voids and inter-particle melting/bonding using electron microscopy. The micrographof the high VOD-compacted specimen shows that there is a small cavity at the centre,called the Mach cavity/hole. This may be due to entrapped air which remained insidethe powder-filled ampoule at the time of tapping. The same air was concentrated atthe centre during dynamic compaction using high VOD explosives. Since the shockwave is converging, the pressure increases as we move radially inward from theperiphery. This increasing pressure causes local/plastic deformation of the particlesand thus melts the material at the core [26,27]. This also causes the variation inmicro-structure of the compacts from the centre towards the periphery of thecompacted specimen. No such melting was observed in case of low VOD explosive-compacted specimens. This means that by critically choosing the type of explosive,melting at the core can be minimised and the specimen can be further compacted byrepeating the experiment on the earlier compacted ampoule to achieve better results.

The structural effects in the core of the compacts were also analysed. Figure 5aand b show micrographs of the core of high and low VOD-compacted

Figure 3. Particle size distribution for the pre and post compacts.

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Figure 5. SEM micrographs from the inner core of a high VOD-compacted specimen (a) anda low VOD-compacted specimen (b).

Figure 4. SEM micrographs of micro-sized Cu powder showing initial powder morphology(a); a high VOD-compacted specimen (b); a low VOD-compacted specimen (c).

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specimens, respectively. Figure 5a shows comparatively more melted and deformed

grains. It is well known that the pressure in axi-symmetric compaction increases

when shock wave traverses from the periphery to the centre of the compact [28,29].

Melting in the particle interfacial regions may be due to extensive material flow at

high velocities into the voids between the particles during the compaction process.

The molten material entrapped in the cavity exhibits an amorphous grain structure

[30]. On the other hand, the low VOD-compacted specimen shows an almost intact

dendritic structure at the inner core. This is evident from the SEM, where the

particles retain their shape and the grains are bound together with little melting,

which is responsible for bonding. Well-bonded original dendritic structures found at

the periphery can be attibuted to the generation of pressure sufficient to induce

particle bonding.Figure 6a and b show the surface morpholgy of the compacted specimen obtained

using high and low VOD compaction, respectively. No fracture or micro-voids were

observed in the comapcts. The disorder on the surface is due to machining of the

specimen.Figure 6c and d show optical micrographs at an indenter load of 50 gf on high

and low VOD-compacted specimens respectively, obtained by mounting and

polishing. The Vicker’s micro-hardness of the high VOD compact was (102� 6)

Hv, while the low VOD-compacted specimen had slightly larger indent diagonals,

corresponding to a hardness of (88� 4) Hv and indicating a greater micro-hardness

of the high VOD compact. Densities of the post-compacts were also calculated. High

VOD compacts had a density of �97% of theoretical mean value, while low VOD

Figure 6. SEM micrographs showing the surface morphology of a high (a) and low VODcompact (b). Corresponding optical micrographs with indentation of a high (c) and low VODcompact (d).

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Table

1.Dependence

ofvariousexplosiveparametersonthestructuralproperties

ofshock-processed

micro-sized

copper

powder.

Trial

set-up

Explosive

type

Explosive

density

(�ein

kg/m

3)

Detonation

velocity

(Din

km/s)

Detonation

pressure

(Pin

GPa)

Tapped

powder

density

(�i%

TMD)

Compacted

powder

density

(�f%

TMD)

Lattice

constant

(ain

A)

Grain

size

(tin

mm)

Micro-hardness

(Hv)

1Trimonite

1040

4.17

4.52

58

94

3.615

15

(88�4)

2PEK

1500

7.1

8.55

57

97

3.607

5(102�6)

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compacts had a density of �94% of the theoretical value. Variations in criticalexperimental parameters are shown in Table 1.

4. Conclusions

The crystal structure of the post-compacts remained the same, i.e. fcc, after usingexplosives of both low and high velocities of detonation. The particle sizes of thepost-compacts decreased and were proportional to the detonation velocity of theexplosive: 15–22 mm for low and 55 mm for high VOD explosives. At a cost ofdeformation of the grains and dendritic structure, the high VOD explosive lead to theformation of harder and denser compacts compared to low VOD compacts. HighVOD compacts showed a 14% increase in micro-hardness compared to low VODcompacts. The density achieved in high VOD compacts was497% of the theoreticalvalue compared to low VOD compacts, which had density of �94% of thetheoretical value. The greater compaction achieved in high VOD compacts isassociated with some melting of the specimen’s core, whereas no such melting wasobserved for low VOD compacts. Also in case of low VOD compacts, the dendriticstructure remained intact with less melting and less size variation. These techniquesare now being used to produce compacts of hard metal powders/superalloys havingunique strategic and industrial applications.

Acknowledgements

The authors acknowledge Defence Research and Development Organization (DRDO), India,for grant-in-aid support. Thanks are due to Director TBRL, the trial team and CIL/SAIFLaboratory, Chandigarh.

References

[1] N.G. Alba-Baena, W. Salas and L.E. Murr, Mater Charact. 59 (2008) p.1152.[2] D.G. Morris and M.A. Morris, Mater. Sci. Eng. A 104 (1998) p.201.[3] S. Wang, Y. Yang, Z. Sun and D.D. Dlott, Chem. Phys. Lett. 368 (2003) p.189.

[4] D. Raybould, D.G. Morris and G.A. Cooper, J. Mater. Sci. 14 (1979) p.2523.[5] D. Raybould, J. Mater. Sci. 16 (1981) p.589.[6] K. Shiva Kumar, T. Balakrishna Bhat and P. Ramakrishnan, J. Mater. Process. Technol.

73 (1998) p.268.

[7] K. Shiva Kumar, P. Soloman Raj, T. Balakrishna Bhat and K. Hoamoto, J. Mater.

Process. Technol. 115 (2001) p.401.[8] D.J. Benson and W.L. Nellis, Appl. Phys. Lett. 65 (1994) p.418.

[9] J. Henrych, The Dynamics of Explosion and its Use, Elsevier, New York, 1979.[10] W. Hermann, D.L. Hicks and E.C. Young, Shock Waves and the Mechanical Properties of

Solids, Syracuse University Press, New York, 1971.[11] A.A. Bukaemskii and E.N. Fedorova, Combust. Explos. Shock Waves 41 (2008) p.717.

[12] K. Hokamoto, S. Tanaka, M. Fujita, R. Zhang, T. Kodama, T. Awano and Y. Ujimoto,

J. Mater, Process, Technol. 85 (1999) p.153.[13] D.G. Morris, Mater. Sci. Eng. 57 (1983) p.589.

Philosophical Magazine 2115

Dow

nloa

ded

by [

Van

Pel

t and

Opi

e L

ibra

ry]

at 1

3:46

22

Oct

ober

201

4

[14] K. Hokamoto, S. Tanaka, M. Fujita, S. Itoh, M.A. Meyers and H.C. Chen, Physica B 239(1997) p.1.

[15] S. Tanaka, K. Hokamoto, M. Fujita, S. Itoh and T. Mashimo, Physica B 239 (1997) p.16.[16] W. Salas, N.G. Alba-Baena and L.E. Murr, Metall. Mater. Trans. A 38 (2007) p.2928.

[17] S.B. Zlobin, V.V. Pai, I.V. Yakovlev and G.E. Kuz’min, Combust. Explos. Shock Waves36 (2000) p.256.

[18] Z. Zhao, X.J. Li, H.H. Yan and D.H. Liu, Combust. Explos. Shock Waves 44 (2008)

p.119.[19] A.G. Mamalis, G.N. Gioftsidis and A. Szalay, J. Mech. Work Technol. 19 (1989) p.239.[20] L.E.G. Cambronero, E. Gordo, J.M. Torralb and J.M. Ruiz Prieto, Mater. Sci. Eng. A

207 (1996) p.36.[21] Z. Zhao, X.J. Li and T.A.O. Gang, J. Alloy. Compd. 478 (2009) p.237.[22] M.A. Meyers, A. Mishra and D.J. Benson, Prog. Mater. Sci. 51 (2006) p.427.

[23] I. Karman and M. Haouaoui, J. Mater. Sci. 42 (2007) p.1561.[24] B.D. Cullity, Elements of XRD, Addison-Wesley, Boston, 1956.[25] A.R. Frinha, R. Mendes, J. Barada, R. Calinas and M.T. Vieira, J. Alloy Compd. 483

(2009) p.235.

[26] A.G. Mamalis and G.N. Gioftsidis, J. Mater. Process. Technol. 23 (1990) p.333.[27] W.H. Gourdin, J. Mater. Sci. 67 (1984) p.179.[28] K. Sivakumar, K.S. Prasad, T. Balakrishna Bhat and P. Ramakrishan, J. Mater. Sci. 32

(1997) p.5271.[29] T. Rzychon and K. Rodak, Arch. Mater. Sci. Eng. 28 (2007) p.605.[30] S.L. Wang, M.A. Meyers and A. Szecket, J. Mater. Sci. 23 (1988) p.1786.

2116 A.D. Sharma et al.

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