International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)
Effect of Sintering Temperature on Density, Porosity and
Hardness of a Powder Metallurgy Component
Goutam Dutta1, Dr. Dipankar Bose2
1
M. Tech in Manufacturing Technology, Department of Mechanical Engineering, National Institute of Technical Teachers’
Training and Research (NITTTR), Salt Lake City, Kolkata: 700 106, India.
2
Professor of Mechanical Engineering Department, National Institute of Technical Teachers’ Training and Research
(NITTTR), Salt Lake City, Kolkata: 700 106, India.
Porosity can be classified into open and closed
porosities.
In closed porosity, the individual pores are isolated
within the material while interconnected pores represent a
network of pores that are connected with one another and
to the external surface of the component [1]. The total
porosity () present in the sintered component may be
evaluated from the following relation [1].
Abstract - The residual porosity is an unavoidable
phenomenon of the components produced by powder
metallurgy process which in turn largely affects the strength
property of the same. Now a day it is possible to control
porosity of powder metallurgy components and retain them to
desired amount when required. The porosity of a powder
metallurgy component is greatly depends on the sintering
temperature. In this study the porosity variation of a powder
metallurgy component with respect to its sintering
temperature is explored where the fractional porosity of the
powder metallurgy component is being derived from the
sinter density and also observed the hardness variation of the
same with respect to sintering temperature.
Keywords - Density, Hardness,
Metallurgy, Sintering Temperature.
Porosity,
 = 1 – (p / s) ------------------------ (2.1)
Where,  = Fractional porosity of powder metallurgy
component.
p = Density of the sintered component.
Powder
s = Density of the solid material.
Density of sintered component (p) may be evaluated by
the following relation:
I. INTRODUCTION
p = (Mp / Vp) --------------------------- (2.2)
Where, Mp = Mass of sintered component.
Vp = Volume of sintered component.
The residual porosity is unavoidable and is almost
always present in powder metallurgy components and it has
undesirable effects on mechanical properties of the same.
The presence of porosity which acts as a stress raiser has
much greater influence on the elongation, impact and
fatigue strengths and a rapid increase in these is obtained
with the density approaching the theoretical value [2]. Now
a day it is possible to control porosity of powder metallurgy
components and retain them to desired amount when
required. Such tailoring of properties and accurate shaping
of products are great asset of powder metallurgy process
and these have enabled large scale assembly line
production of parts meeting stringent property needs [1].
Density of solid material (s) which is an alloy may be
evaluated by the following relation:
s =  (i . xi) ------------------------------ (2.3)
Where, i = Density of the individual alloying element.
xi = Mass fraction of the individual alloying element
present in the alloy.
III. OBJECTIVE
An experimental approach has been made to study the
porosity variation of a powder metallurgy component with
respect to its sintering temperature where the fractional
porosity of the powder metallurgy component is being
derived from the sinter density and also observed the
hardness variation of the same with respect to sintering
temperature.
II. THEORY
Porosity refers to the open volume in a powder
metallurgy component after sintering. It is very difficult to
produce powder metallurgy component without porosity
even after sintering. Sometime porosity is deliberately
engineered into the component to satisfy certain
requirement as in filters and bearings.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)
IV. SAMPLE PREPARATION
Sintered density (p) and total fractional porosity () of
samples are being evaluated by using the equation: (2.2) &
(2.1) respectively. Density of solid alloy cutting tool
material (s) has been evaluated by using equation: (2.3)
where density of C, Ti, Cr, Co, W, Fe and Zinc Stearate has
been taken 2.25, 4.50, 7.75, 8.86, 19.25, 7.86 and 0.18
gm/cm3 respectively. [3]
A typical alloy cutting tool material having composition
C-2.14%, Ti-2.00%, Cr-4.50%, Co-10.50%, W-19.50% and
Fe-61.36 % is being selected for preparing the samples
through powder metallurgy process.[5][6] Weighing of
individual powdered alloying ingredient has been carried
out in a Digital Balance and mix together with proper
weight proportion where Zinc Stearate powder has been
added as lubricant at proportion of 1% of total weight of
the mixture. Ball Milling Mixing Method has been adopted
to prepare the homogeneous mixture of powdered materials
conforming the proposed composition. Then (12.2mm x
12.2mm) square cross sectional inserts [Fig.1] and
(12mm) cylindrical pins [Fig.2] are prepared by single
ended cold compaction with suitable die punch set at a
pressure of 650 MPa in a 10 Ton capacity UTM and
sintered or pre-sintered at 750C, 1000C and 1250C
respectively with vacuum 10-2 torr in a Vacuum
Furnace.[5][6] After each sintering or pre-sintering each
samples are grinded to desired shape with the help of a
Tool and Cutter Grinder.
VI. EXPERIMENTATION RESULTS
Figure 3: Variation of Mean density, Total Fractional Porosity and
Hardness of Samples (Pins & Inserts) with respect to Sintering
Temperature.
Table 1
Mean Density of Pins at Different Sintering Temperature.
Figure 1: Photograph of Inserts Prepared by Powder Metallurgy
Process
Details
Pins after
Sintering at
750C
Pins after
Sintering at
1000C
Pins after
Sintering at
1250C
Mean Density
(p) in gm/cm3
5.221
5.433
5.825
The Density of solid alloy cutting tool material (s) has
been found 9.87 gm/cm3.
Figure 2: Photograph of Pins Prepared by Powder Metallurgy Process
Table 2
Total Fractional Porosity of Pins at Different Sintering Temperature.
V. EXPERIMENTATION
After each sintering or pre-sintering followed by
finishing process, the detailed dimensions of each sample
has been measured with the help of Vernier Caliper and
Tool Makers Microscope for evaluate volume of the same.
Simultaneously the mass and hardness of each sample are
also being measured with the help of Digital Balance and
Rockwell Hardness Testing Machine respectively.
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Details
Pins after
Sintering at
750C
Pins after
Sintering at
1000C
Pins after
Sintering at
1250C
Total Fractional
Porosity ()
0.4710
0.4495
0.4098
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)
Table 3
Mean Hardness (HRC) of Inserts at Different Sintering
Temperature.
Inserts
after
Sintering
at 750C
Inserts
after
Sintering
at 1000C
Inserts
after
Sintering
at 1250C
Surface: 1
16.94
32.00
56.88
Surface: 2
22.81
35.00
62.50
Details
Mean
HRC
D. It has also been observed that, there having a
significant difference in Hardness (HRC), measured on
Surface: 1 & Surface: 2 of Inserts. Mean Hardness of
Surface: 2 having higher value than that of Surface: 1,
which is mainly due to the reasons of preparing the
Inserts by Single Ended Compaction and non uniform
porosity distribution through out the volume of powder
metallurgy component. (Refer to figure: 3, table 3 &
reference: [1] chapter-5 & 7)
REFERENCES
[1 ] Angelo P.C. “Powder Metallurgy: Science, Technology and
Applications”, © 2008 by Prentice-Hall of India Privet Limited,
New Delhi: 110001.
[2 ] Sinha A.K. “Powder Metallurgy”, © 2003 Dhanpat Rai Publications
(P) Ltd., 67/4, Madras House, Daryagang, New Delhi: 110002.
[3 ] Smith William F., “Foundation of Materials Science and
Engineering” (Second Edition), © 1993 by McGraw-Hill, Inc.
[4 ] Sudhakar B., “An Analytic Study of Porosity Evolution in Powder
Metallurgy Forming Process”, © 1993 IEEE.
[5 ] Dutta Banik Bibhas, the M-Tech. Thesis on “Production of Fe-WCo-Cr-C Alloy Cutting Tool through Powder Metallurgy Route and
Determination Its Suitability”, NITTTR, Kolkata, in the year 2010.
[6 ] Jha Bikash Kumar, the M-Tech. Thesis on “Tribological Testing of
Fe-W-Co-Cr-Ti-C Alloy Used As Cutting Tool Prepared Through
Powder Metallurgy”, NITTTR, Kolkata, in the year 2011.
VII. CONCLUSIONS
A. The total fractional porosity () of pins prepared
through powder metallurgy process is decreasing with
the increase in sintering temperature. (Refer to figure:
3 & table: 2)
B. Mean Density (p) of pins prepared through powder
metallurgy process is increasing with the increase in
Sintering Temperature. It is mainly due to the decrease
in total fractional porosity of the sample with the
increase in sintering temperature. (Refer to figure 3,
table: 1 & reference: [1] chapter: 7)
C. Mean Hardness (HRC) of Inserts prepared through
powder metallurgy process is increasing with the
increase in Sintering Temperature. It is also due to the
decrease in total fractional porosity of the sample with
the increase in sintering temperature. (Refer to figure:
3, table: 3, & reference [1] Chapter-7)
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