FABRICATION OF COPPER - BORON CARBIDE METAL

MATRIX COMPOSITE BY POWDER METALLURGY

P. K. Prajapati, D. Chaira

Department of Metallurgical and Materials Engineering

National Institute of Technology Rourkela

Rourkela, Odisha-769008, India

APMA 2019, 19th -21st February 2019, Pune 1

Motivation

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Copper based ceramic reinforced metal matrix composites (MMCs)

have been the subject of extensive research due to their good

mechanical, thermal and tribological properties.

Boron carbide (B4C) has excellent chemical and thermal stability,

high hardness and low density.

Boron carbide (B4C) cermets and boron carbide-based composites

serve as promising materials for a variety of applications that require

elevated mechanical properties, high neutron absorption cross

section, high melting point, good wear and corrosion resistance.

B4C based cermets and composites are widely used for various

high technology applications, such as light-duty bulletproof

armors, neutron absorber in liquid–metal- cooled fast breeder

reactors, wear-proof parts, and cutting tools.

B4C coating is applied on copper and steel using various methods

which are extensively used in nuclear industries.

One drawback of the boron carbide is lower thermal and electrical

conductivity.

Copper are one of the most important materials for thermal and

electronic applications due to its higher electrical and thermal

conductivities.

The use of B4C particles as reinforcements in copper based

composites is considered very attractive to overcome the drawback

of boron carbide.

3

Objectives

Fabrication of Cu-B4C MMC by cold compaction

followed by conventional sintering.

To study the effect of B4C content in the

composite.

Microstructural characterization, physical,

mechanical and electrical conductivity study of

fabricated composite.

To study interface between Cu-B4C.

4

Experimental Details Blending of Cu and B₄C powder (5, 10 and 15 wt. %)

Cold compaction under pressure of 600 MPa

Conventional sintering at 900o C for 1 hour under Ar gas

Microstructure

analysis Phase Mechanical

property

XRD

Hardness

Electrical

conductivity

Optical

SEM

FESEM

Compressive strength

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Characterization of as received powder

(a) FESEM micrograph of Cu (b) FESEM micrograph of B4C

(a) (b) • Cu-dendritic shape,

electrolytic grade

• B4C-irregular shape

with sharp edge.

• Particles size of B4C

varies from 48 µm to

214 µm.

6

Flowability and density of as received powder

• Compressibility index

(CI)=𝑇𝑎𝑝 𝑑𝑒𝑛𝑠𝑖𝑡𝑦−𝑏𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑥100

𝑇𝑎𝑝 𝑑𝑒𝑛𝑠𝑖𝑡𝑦

• 𝐻𝑎𝑢𝑠𝑛𝑒𝑟 𝑟𝑎𝑡𝑖𝑜 𝐻𝑅 =𝑇𝑎𝑝 𝑑𝑒𝑛𝑠𝑖𝑡𝑦

𝐵𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦

• 𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝑟𝑒𝑝𝑜𝑠𝑒 𝜃 =

tan−1 𝑕𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝑐𝑜𝑛𝑒 𝑓𝑜𝑟𝑚𝑒𝑑

𝑟𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑑𝑖𝑠𝑐 𝑓𝑜𝑟𝑚𝑒𝑑

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Powder Bulk density (gm/cc) Tap density (gm/cc) Compressibility

index (CI)

Hausner ratio (HR)

Copper 1.05 1.28 18.03 1.22

B4C 1.13 1.46 12.90 1.35

• As received copper and B4C powder exhibit angle of repose as 25.770 and 39.200.

• Copper exhibits higher flow ability than B4C.

• Copper shows higher compressibility than B4C.

Pure Cu

5 wt. %B4C

10 wt. %B4C

15 wt. %B4C

Characterization of fabricated Cu-B4C MMC

• Presence of weak peak of

Cu2O with strong peaks of Cu

and B4C

• Uniform distribution of B4C

particles in the Cu matrix.

Optical micrographs

of Cu-B4C composites

sintered at 900 C for

1 hour

XRD spectra of Cu-B4C composites

sintered at 900 C for 1 hour

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Annealing twins

B4C Pores

Cu

B4C

Copper matrix

Cu -B4C interface

(a) (b)

(c) (d) (e)

SEM micrographs of (a) Cu-10 wt. % B4C composite (b) Cu and B₄C

interface of Cu-10 wt. % B4C composite (c) Cu- 5wt. % B4C (d) Cu-10 wt.%

B4C (e) Cu-15wt.% B4C

• Uniform distribution of B4C reinforcements in Cu matrix.

• Good compatibility between Cu and B4C.

• No interfacial product has been formed at Cu-B4C interface.

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1 2 3 4 5 6 7 8

keV

0

2

4

6

8

10

12

14

cps/eV

Cu Cu

El AN Series unn. C norm. C Atom.

[wt.%] [wt.%] [at.%]

-------------------------------------

B 5 K-series 55.58 55.58 58.16

C 6 K-series 44.42 44.42 41.84

------------------------------

Total: 100.00 100.00 100.00

El AN Series unn. C norm. C Atom.

[wt.%] [wt.%] [at.%]

-------------------------------------

Cu 29 K-series 74.52 100.00 100.00

-------------------------------------

Total: 74.52 100.00 100.00

0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80

keV

0

1

2

3

4

5

cps/eV

C B

EDS spectra and elemental composition of B4C

EDS spectra and elemental composition of Cu matrix

10

Elemental mapping of Cu-10 wt. %

B4C composite

Line scan from B4C to Cu matrix

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B4C

Wt.% B4C Density

(g/cc)

Relative

density

(%)

5 7 82

10 6.70 81

15 6.26 78

Pure Cu 7 78

B4C (wt. %) Average Vickers

hardness (VHN)

0 37.88 ± 1.13

5 55.14 ± 1.6

10 65.64 ± 2.96

15 79.06 ± 5.2

Density and hardness study

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Compressive stress- strain graphs for pure

Cu, Cu-5 wt. % B4C, Cu-10 wt. % B4C and

Cu-15 wt. % B4C composites

Compressive strength study

Samples after

compressive test

Maximum compressive strength of 337

MPa is achieved for Cu-10 wt. % B4C

MMC

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Electrical conductivity for Cu-B4C composites

Electrical conductivity

P. K. Prajapati, D. Chaira, Fabrication and characterization of Cu–B4C metal matrix composite by powder metallurgy:

Effect of B4C on microstructure, mechanical properties and electrical conductivity, Trans Indian Inst. Met.,

https://doi.org/10.1007/s12666-018-1518-2 14

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Composition Processing method Density Hardness Strength

Al-5 wt. % Cu alloy

reinforced with B4C (2, 5, 7

wt. %) [9]

Stir casting process followed by

sqeeze casting and then ageing at

200 and 250 C

Average density 99 %

of theoretical

105 VHN for ageing at

250 C for 4 h (Al-5 wt.

% Cu-7 wt. % B4C)

Maximum compressive

strength 143 MPa (Al-5

wt. % Cu-7 wt. % B4C)

Al2024 matrix composites

reinforced by high volume

fraction of B4C (40:60) [10]

Mechanical milling and vacuum

hot pressing followed by hot

extrusion

-------------

----------

Maximum compressive

strength of 1115 MPa with

10 vol. % coarse grained

Al2024

Al-B4C composite (5, 10 , 15

wt. % B4C)[15]

Stir casting at 800 and 1000 C 2.8 g/cc casted at 1000

C

94.7 BHN (Al-15 5

B4C)

Maximum tensile strength

210 MPa

Cu-B4C composites (1, 2, 3

wt. % B4C)[11]

Powder metallurgy method;

sintering at 700 C for 2 h at

open atmosphere

90 % for 3 wt. % B4C 87.5 BHN for 3 wt. %

reinforced B4C

------------------

Cu-8 vol. % B4C surface

dispersion strengthened

composite [12]

Friction stir processing

-------------

99 VHN

-----------------

Cu-B4C composite [16] Friction stir welding ------------------ Average hardness 140

VHN

-----------------

A356-B4C composite [17] Friction stir processing

-------------------

Maximum hardness

74.98 VHN

Maximum tensile strength

399.42 MPa

C-B4C composite [Present

study]

Powder metallurgy; cold

compaction followed by

sintering at 900 C, 1 h

82 % of relative density 79.06 ± 5.2 VHN Maximum compressive

strength 337 MPa

A comparative studies of B4C reinforced composites fabricated by various researchers and the

present research work

Conclusions • Cu-B4C metal matrix composites were successfully fabricated by using powder metallurgy

route taking different weight percentage of B4C powder.

• Optical, SEM and FESEM analysis of pure Cu, Cu-5wt. % B4C, Cu-10 wt. % B4C, and Cu-

15wt. %B4C show that there is uniform distribution of B4C particle in Cu matrix.

• A maximum relative density of 82 % achieved for Cu-5 wt. % B₄C composite. The relative

density decreases with addition of B4C and for 10 and 15 wt. % B4C it is found 80.4% and

78.33% respectively.

• Hardness value increases with addition of B4C in to pure Cu. The Vickers hardness value

for pure copper is 38 VHN, which increases to 79 VHN for 15 wt. % B4C.

• Compressive strength is improved with the addition of B4C powder in Cu matrix. The

maximum compressive strength is found for 10 wt. % B4C, which is 337 MPa. But further

addition of B4C in to Cu makes it brittle and strength decreases.

• Electrical conductivity of pure copper is found to be 4.5×106 S/m which decreases with

increase in B4C content in composites. Electrical conductivity of Cu-5wt.% B₄C is

1.92×106 S/m, Cu-10wt.% B₄C is .75×106 S/m, and Cu-15wt.%B₄C is .32×106 S/m.

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Acknowledgement

• M. Tech student, Pradeep Kumar Prajapati

• Dept. of Metallurgical & Materials Engineering,

NIT Rourkela, Odisha

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