Mechanical Behavior of Sintered Cu-15%W Nano Composite

International Journal of Production Technology and Management TECHNOLOGY–AND
INTERNATIONAL JOURNAL OF PRODUCTION (IJPTM), ISSN 0976 6383
MANAGEMENT (IJPTM)
(Print), ISSN 0976 – 6391 (Online) Volume 3, Issue 1, January- December (2012), © IAEME

ISSN 0976- 6383 (Print)
ISSN 0976 - 6391 (Online)
Volume 3, Issue 1, January-December (2012), pp. 54-60 IJPTM
© IAEME: www.iaeme.com/ijptm.asp
Journal Impact Factor (2012): 1.5910 (Calculated by GISI)
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©IAEME

INVESTIGATION OF MECHANICAL BEHAVIOUR IN FORMING OF
SINTERED COPPER-15%TUNGSTEN NANO POWDER COMPOSITE

N.Vijayponraj1, Dr.G.Kalivarthan2, Vetrivel.S.C3
1
Research Scholar, CMJ University, Meghalaya, Shillong, India
2
Principal/Dept of Mech. Engg, PSN Institute of Technology and Science, Tirunelveli,
Tamilnadu, India, Supervisor CMJ University, Shillong.
3
Asso.Prof/Dept. of Mech. Engg, PET Engineering College, Tirunelveli, Tami nadu, India,
E mail: vijay_ponraj@yahoo.com , Sakthi_eswar@yahoo.com

ABSTRACT

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
Keywords: Metal-Matrix Composites (MMCs), Nano-structures, Preform, Mechanical
properties, Sintered copper-15% Tungsten

1. INTRODUCTION

Composite material is the combination of two or more materials which are having
different phases and the properties superior to the base materials. Composite materials are
produced by casting and powder metallurgy methods. By means of casting methods,
composite materials reinforced by dispersion particles [1, 2], platelets [3], non-continuous
(short) fibres and continuous (long) fibres [4-5] as well as composite materials with hybrid
reinforcement composed of particles and fibres [6] are produced by powder metallurgy
methods, composite materials reinforced by dispersion particles [7-9], platelets [13], non-
continuous fibres [10-11] and continuous fibres [12] are manufactured.
High-energy mechanical ball milling can be used to produce nano powders from
micron size. When mechanical milling is used in the traditional sense, the process does not
generate a new material, since the microstructure of the powder does not change. Particulate
composites are prepared by mixing reinforcement and matrix material in powder form and

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International Journal of Production Technology and Management (IJPTM), ISSN 0976 – 6383

cold pressing to near theoretical density. An important aspect of composites is their
fabricability to near-net shapes. To develop and improve near-net shape forming process the
study on analyzing the fabrication process is necessary as well as experimental study on
fabrication of composites.
Most of the authors were reported the deformation behaviour of various powder
composites in micro and nano particle sizes except Cu-W. The material properties of the
sintered compacts were ascertained from the uniaxial compression test with 15% Tungsten
with copper three aspect ratios 0.40, 0.60 and 0.80. Graphite was used as surface preform
lubricant. From this study, it was also attempted to establish the relationship between the
fractional theoretical density, the Poisson’s ratio and other parameters namely the stress,
strain and strain factor under Cu-10%W preform compositions.

Table 1 Characteristics of powder
(a) Copper Powder
Test IS 5461 ASTM B-417 ASTM B- ASTM E-
Standard 213 194
Property Sieve analysis, % Apparent Flow rate Acid
+75µm +45µm -45µm density (g/cc) Sec(50g-1) Insoluble
EC/86 Grade 0.40 5.40 94.20 1.56 Nil Nil

(b) Tungsten Powder
Characteristics Test Standard Value
Sieve analysis : - 45 µm ASTM D-185 99.00
Average Particle Size, Fisher ASTM B-330 3.90
Number
Oxygen Content (Hydrogen Loss) ASTM E-159 1.87
Other Impurities AAS 0.22
Purity 97.90

2. EXPERIMENTAL DETAILS

2.1 Materials and characteristics

Copper and Tungsten powders were used in the present investigation. These powders
were purchased from M/s. Metal Powder Company (P) Ltd., Tirumangalam, Madurai,
Tamilnadu, India. Electrolytic copper and atomised tungsten were obtained with 100% and
99.00% purity respectively. The characteristic of the copper and Tungsten powder is shown
in Table 1 (a-b). The individual powders were pulverized in a high energy ball mill (Fritsch,
Germany - Pulverisette - 6) for four hours after that it was mixed on weight basis with 5%
Tungsten and rest Copper powder. These composite powders were pulverized in a high
energy ball mill and after 10 hours milling, the obtained particle size was approximately
below 400nm. SEM was used for evaluation of morphological changes of the particles after
milling and is shown in Fig. 1(a-c). Fig. 1(a) shows the SEM image of the Cu particles at
9500X magnification and has a structure of a cluster of tiny particles and like small flattened
flake particles due to severe plastic deformation of copper, micro-welding and fracture of the
large flakes due to typical mechanical milling. Fig. 1(b - c) shows the SEM image of the W
powders at 6000X and 2000X magnification respectively, It is in the formation of flattened
particles with pancake structure. Fig. 1(d) shows the SEM image of the Cu-10%W Powder

55

January

Composite at 8000X particles. It shows the morphological changes of Cu 10%W powder
Cu-10%W
mixture after 10 hours milling. No significant difference between the Cu morphology in the
significant
composite and the monolithic W powder is observed at low milling times; that means the fine
W elements distributed throughout the Cu matrix and represents the particle size in the range
between 200-400nm.

(a) (b)
Fig. 1 SEM micrograph after ball milling (a) Cu powder 9,500 X (b) W powder 6,000X
.

2.2. Compacting

Cylindrical compacts of 20 mm diameter with an aspect ratio of 0.40, 0.60 and 0.80
were prepared. The compacts were prepared using ball milled Cu-10% W composite. The
mi 10%
composite powders were compacted by using suitable punch and die set assembly on a
Universal Testing machine having 1 MN capacity. Compacting pressure was applied
gradually and it was 1.2 GPa for three aspect ratios. Graphite was used to lubricate the punch,
was
die and the butt. When preparing the compacts, the initial density and aspect ratio were
maintained by precisely controlling the mass and accurately monitoring the compacting
pressure employed.

2.3 Sintering
After the compaction, the compacts were immediately taken out from die set
action,
assembly and loaded into the furnace for sintering. To prevent oxidization, the green
compacts were initially covered with inert argon atmosphere in the furnace. The sintering was
carried out in an inert gas circulated electric muffle furnace at 650°C for a holding period of
one hour. As soon as the sintering schedule was over, the sintered preforms were cooled
inside the furnace itself to the room temperature. After the completion of sintering, t the
preforms were cleaned by using a fine wire brush.

2.4 Cold Deformation Experiments
Deformation experiments were carried out by using flat faced dies and a hydraulically
operated compression testing machine of having 1MN capacity. The flat dies were machined
m
and tempered. Flat faces of the dies were ground after heat treatment in a grinding machine,
in order to obtain the final dimensions and surface quality and its hardness was measured as
91 HRB after tempering. Graphite was well applied as lubricant on the ends of preforms and
contacting surfaces of flat dies, which created a situation for almost frictionless ideal
deformation. In general, each compact was subjected to an incremental compressive loading
in steps of 50kN until the appearance of visible cracks on the free surface. Immediately, after
visible
56


the completion of each step of loading, the height, the contact diameters at the top and
bottom, the bulged diameter and the density were measured for each of the deformed
preforms. The density measurements were carried out using Archimedes principle.
Experimental measurements were also used to calculate the various parameters namely the
stresses, the Poisson’s ratio, density ratio and the strain. The Theoretical approach to
calculate the above parameters are discussed in detail under ref. [13].

3. RESULTS AND DISCUSSION

3.1. Deformation Behaviour of Preforms
The results of deformation behaviour of 85% initial fractional density, Cu-15%W
composite preforms are discussed in this section. The following stress strain relationship
concerning the plastic deformation is discussed in detail for the various aspect ratios with
graphite lubricants

3.1.1. Various stresses and axial strain
Using the simple theory of plasticity, the axial stress (σz), the hoop stress (σθ) and the
hydrostatic stress (σm) were calculated and plotted against the axial strain (εz) for different
aspect ratios in Figures 2(a –c) for the Cu-15%W composite preforms. The hoop stress is
tensile in nature because during compressive loading the bulged diameter expands.
Meanwhile, for any deformation level, the increase in the hoop stress due to loading is very
low compared to that of the axial stress. However, the value of the hydrostatic stress is much
less than the other stresses, namely the axial stress (σz) and the hoop stress (σθ) and it is also
compressive in nature, at different strain level. For all preforms, the axial and the hoop stress
level also increases for a given aspect ratio. The values of the axial stress, the hoop stress and
the hydrostatic stress are high for the lower aspect ratio (0.40) than higher aspect ratios
(0.60and 0.80) preforms.

600

400 Initial Fractional Density 0.85
Cu -15%W
Aspect Ratio:0.8
200 Lubricator: Graphite
Stess,Mpa

0
Axial Stress
0 0.5 1 1.5
Hoop Stress
-200
Hydrostatic Stress
-400
(a)

-600
Axial Strain

57


600

Cu -15%W
Aspect Ratio:0.6
Stess,Mpa 200 Lubricator: Graphite

0
Axial Stress
0 0.5 1 1.5
Hoop Stress
-200
Hydrostatic Stress
-400

-600 (b)
Axial Strain

600

Cu -15%W
Aspect Ratio:0.4
200 Lubricator: Graphite
Stress,Mpa

0 Axial Stress
0 0.5 1 1.5 Hoop Stress
-200
Hydrostatic Stress
-400 (C)

-600
Axial Strain

Fig. 2.The Variation of stresses with respect to axial strain for various aspect ratios (a) 0.80
(b) 0.60 (c) 0.40
3.1.2 Axial stress and axial strain
Fig.3 shows the effect of aspect ratio on the characteristic features of the axial stress
(σz) against the axial strain (εz) for a given initial fractional density of 0.85 of Cu-15%W
composite. These plots are similar in nature irrespective of the aspect ratio values. It is
observed that the true axial stress increases rapidly as the true axial strain is increased,
followed by a gradual increase in the true axial stress with further increase in the axial strain.
Further, it is found that the 0.80 preform improved load bearing capacity compared to that for
other aspect ratios, while the initial fractional density remains constant.

58


Initial Fractional Density 0.85
Cu -15%W

1000
800

Axial Stress
600
Aspect ratio 0.4
400
Aspect ratio 0.6
200
Aspect ratio 0.8
0
0 0.5 1 1.5
Axial Strain

Fig.3 The relationship between σz and εz

3.2 Densification Behaviour of preforms
In densification behaviour of preforms the following relationships are discussed in
detail by varying the initial aspect ratio provided the initial fractional density value is kept
constant for Cu-15%W composites.
 ρf 
• Fractional density  ρ  and strain parameter

e (ε z − ε θ )
 th 
3.2.1. Fractional density and strain parameter

Figure 4 has been drawn to establish the relationship between the fractional density
value  f  of the deforming preform and the value of e (ε z − ε θ ) in accordance with the
ρ

ρ  
 th 
theoretically-derived relationship [16] for sintered P/M preforms during cold axial
deformation. The plots show the existence of power law relationship between the fractional
theoretical density  ρ f  and e (ε z
 
−ε θ )
. However the lower aspect ratio shows better
 
 ρ th 
fractional density values because it has lesser porosity.
1.04
1.02 Cu -15%W
Fractional Density

1
0.98
0.96 Aspect ratio 0.4
0.94
Aspect ratio 0.6
0.92
Aspect ratio 0.8
0.9
0.88
0 0.5 1 1.5
Strain Parameter

Fig.4 The relationship between Fractional Density and Strain parameter

59


4. CONCLUSION

The study has been carried out of cold upset forming of sintered Cu-15%W nano
composites performs. The basic conclusions that can be drawn from the present
investigations are as follows.
The axial stress has an increased trend with higher level of deformation till failure. This is
because, at the time of increasing the load, the pores in the preforms are flattened and contact
surfaces are increased. So the load –bearing capacity increasing steeply by increase of strain.
Lower aspect ratio exhibits improved densification and load –bearing capacity compared
to that of higher aspect ratio performs densify uniformly and quite easily due to rapid load
transfer resulting in extensive work-hardening.

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Mechanical Behavior of Sintered Cu-15%W Nano Composite

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