World Journal Of Engineering
STIR CASTING TECHNIQUE FOR LOW MELTING POINT METAL
MATRIX COMPOSITES AND CHARACTERISTIC STUDY
Jagannath K1, S.S.Sharma2 , N S Mohan3 & P R Prabhu4
1 Profesor,
Dept. of Mechanical Engineering, MIT, Manipal
Professor ,Dept. of Mechanical Engineering,MIT, Manipal
3 Professor ,Dept. of Mechanical Engineering,MIT, Manipal
4 Professor ,Dept. of Mechanical Engineering,MIT, Manipal
2
Email: jagan.korody@manipal.edu
Metal-matrix composites (MMC’s) are now
attracting enormous interest among the
researchers. One of the prime reasons for this is
that significant advances made in recent years
on the development of fabrication routes, which
are economically attractive and generate
material of high micro structural quality. In
particular, it is possible to produce composites,
which are relatively free from gross defects
Among metallic composites low melting point
matrix composites have
the additional
advantages of getting uniform distribution.
Semi-solid forming method is adopted in
industries for the production of metal matrix
composites. This method has an advantage
compared to die casting, squeeze casting or
forging. Because of the well dispersed particles
in metal matrix composites using semi-solid
forming process. This paper describes stircasting method for production of high-density,
low melting point metal matrix composites such
as tin with graphite. The melting is performed in
nitrogen gas environment to avoid oxidation.
Paper presents low cost stir casting technique
for metal matrix production. Micro structural
examination and characteristic study of the
metallic composites are discussed.
the temperature and nitrogen gas purged for
improving the metal yield. A measured quantity
of tin is taken into the crucible. The cap is closed
on the top of the crucible and air is purged out
using nitrogen. Gas burner is turned on to melt
the tin. When it is melted, the stirrer is brought
down and motor is actuated. Stirrer mixes the
molten tin with uniform measured quantity of
graphite. The secondary step involves the
preheating of the graphite particles. The graphite
may contain impurities like water vapor, sulphur
etc. The graphite is heated to the matrix
temperature to remove these impurities. When
the metal melts, heat supplied from the burner is
cutoff and it is allowed to cool, so that it attains a
semi-solid state. In this state, the calculated
amount (wt %) of graphite is slowly added and
stirred continuously for few minutes. The
composite is then allowed to solidify inside the
crucible only. After removing the composite from
the crucible, it is cut into required shapes using
micro-cut machine. The surfaces are then
polished using grinding and polishing machine
for micro structural analysis. The specimens are
made into required shapes for mechanical and
wear testing.
Key words: Metal matrix composites, stir
casting, matrix,stiffness
The stir mechanism designed is shown in Fig.1
which consist of threaded rod carries a four
bladed disc. It can be raised or lowered by
handle depending upon the molten metal solid
or liquid. A thermocouple is provided to measure
511
Figure 1: Stirrer Assembly
.
World Journal Of Engineering
Results and Discussion:
Wear Measurement:
Microstructural Analysis:
The Pin on disc machine is used for wear
measurement of tin-graphite composite. Fig..4
shows the wear rate vs. sliding distance for tingraphite composite under the constant load. It is
observed that wear rate reduces with increase in
the wt% of the graphite. It appears that the
addition of graphite is beneficial in improving the
sliding wear resistance of tin-graphite composite.
The characteristics of the micro structural features
of the composite are shown in the Fig.2 for the
magnification of 100x. The micro structural
examination shows uniform distribution of the
graphite particles in the matrix without dendritic
characteristics. The favorable feature is that the
supply of nitrogen gas avoids oxidation, hence
casting defects such as entrapped gas and
inclusions of slag are eliminated.
Figure.4 Experimental wear rates
for
tin-graphite composite
Figure 2. Microstructure of 5% tingraphite composite (Magnification X 100)
Conclusion:
Mechanical Properties:
a) The tensile stress and hardness is
observed to increase for tin-graphite
composite with wt % of graphite
increases.
b) The wear rate reduces with increase in
wt % of graphite in the tin.
c) Uniform distribution of the particulate in
matrix is observed up to 5 wt % of
particulate.
Fig.3 illustrates the stress-displacement diagram
for tin-graphite composite. Results reveal that
as the wt % of graphite increases in the matrx,
there is increase in the ultimate tensile strength
of the material.
STRESS-DISPLACEMENT DIAGRAM FOR
TIN-GRAPHITE COMPOSITE
30
Reference:
Stress (MPa)
25
20
[1]
15
10
5
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5
Displacement (mm)
1wt% Graphite
3wt% Graphite
[2]
5wt% Graphite
Figure.3. Stress vs. displacement for
tin-graphite composite
512
T.W.Clyne and J.F.Mason, The squeeze
infiltration process for fabrication of metalmatrix
composites,
Metallurgical
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D R. M. K. Young and T. W. Clyne,
Journal of Material Science, Vol.21, 1986,
pp. 1057-1069