22-11-2012, 04:34 PM
PRODUCTION AND CHARACTERISATION OF ALUMINIUM-FLY ASH COMPOSITE USING STIR CASTING METHOD
[attachment=40697]
ABSTRACT
Metal matrix composites (MMCs) possess significantly improved properties including high
specific strength; specific modulus, damping capacity and good wear resistance compared to
unreinforced alloys. There has been an increasing interest in composites containing low density
and low cost reinforcements. Among various discontinuous dispersoids used, fly ash is one of
the most inexpensive and low density reinforcement available in large quantities as solid waste
by-product during combustion of coal in thermal power plants. Hence, composites with fly ash
as reinforcement are likely to over come the cost barrier for wide spread applications in
automotive and small engine applications. It is therefore expected that the incorporation of fly
ash particles in aluminium alloy will promote yet another use of this low-cost waste by-product
and, at the same time, has the potential for conserving energy intensive aluminium and
thereby, reducing the cost of aluminium products. Now a days the particulate reinforced
aluminium matrix composite are gaining importance because of their low cost with advantages
like isotropic properties and the possibility of secondary processing facilitating fabrication of
secondary components. The present investigation has been focused on the utilization of
abundantly available industrial waste fly-ash in useful manner by dispersing it into aluminium to
produce composites by stir casting method.
INTRODUCTION
Conventional monolithic materials have limitations in achieving good combination of strength,
stiffness, toughness and density. To overcome these shortcomings and to meet the ever
increasing demand of modern day technology, composites are most promising materials of
recent interest. Metal matrix composites (MMCs) possess significantly improved properties
including high specific strength; specific modulus, damping capacity and good wear resistance
compared to unreinforced alloys. There has been an increasing interest in composites
containing low density and low cost reinforcements. Among various discontinuous dispersoids
used, fly ash is one of the most inexpensive and low density reinforcement available in large
quantities as solid waste by-product during combustion of coal in thermal power plants. Hence,
composites with fly ash as reinforcement are likely to over come the cost barrier for wide
spread applications in automotive and small engine applications. It is therefore expected that
the incorporation of fly ash particles in aluminium alloy will promote yet another use of this
low-cost waste by-product and, at the same time, has the potential for conserving energy
intensive aluminium and thereby, reducing the cost of aluminium products [1-3].
COMPOSITE
Composite material is a material composed of two or more distinct phases (matrix phase and
reinforcing phase) and having bulk properties significantly different from those of any of the
constituents. Many of common materials (metals, alloys, doped ceramics and polymers mixed
with additives) also have a small amount of dispersed phases in their structures, however they
are not considered as composite materials since their properties are similar to those of their
base constituents (physical property of steel are similar to those of pure iron) . Favorable
properties of composites materials are high stiffness and high strength, low density, high
temperature stability, high electrical and thermal conductivity, adjustable coefficient of thermal
expansion, corrosion resistance, improved wear resistance etc.
Metal Matrix Composites (MMCs)
Metal Matrix Composites are composed of a metallic matrix (Al,Mg,Fe,Cu etc) and a dispersed
ceramic (oxide, carbides) or metallic phase( Pb,Mo,W etc). Ceramic reinforcement may be
silicon carbide, boron, alumina, silicon nitride, boron carbide, boron nitride etc. whereas
Metallic Reinforcement may be tungsten, beryllium etc [19]. MMCs are used for Space Shuttle,
commercial airliners, electronic substrates, bicycles, automobiles, golf clubs and a variety of
other applications. From a material point of view, when compared to polymer matrix
composites, the advantages of MMCs lie in their retention of strength and stiffness at elevated
temperature, good abrasion and creep resistance properties [19]. Most MMCs are still in the
development stage or the early stages of production and are not so widely established as
polymer matrix composites. The biggest disadvantages of MMCs are their high costs of
fabrication, which has placed limitations on their actual applications [20]. There are also
advantages in some of the physical attributes of MMCs such as no significant moisture
absorption properties, non-inflammability, low electrical and thermal conductivities and
resistance to most radiations [21]. MMCs have existed for the past 30 years and a wide range of
MMCs have been studied [19].
STRENGTHENING MECHANISM OF FIBRE REINFORCED COMPOSITE
In such type of composite the reinforcing phase carries the bulk of the load and the
matrix transfers the load to the reinforcing phase by the mechanism of seam. The high
strength of the reinforcing phase restrict the free elongation of the matrix especially in
its vicinity, whereas later is free to elongate at some distance away from the former.
This type of non uniform deformation of the matrix leads to a shear stress at the matrix
reinforcement interface which results tensile stress at the reinforcing phase. Thus the
stress is transferred to the reinforcing phase. The fibers either may be continuous or
discontinuous in the matrix. In the former case the load is directly applied to the
reinforcing phase and stress is constant over its entire length. In case of discontinuous
fibers, the stress in the fibre increased from zero value at the end to a maximum value
in the centre and thus average tensile strength developed is always less than those of
continuous fibers. For the same when the fracture of the reinforcing phase, therefore
the strength of the discontinuous fibre reinforced composite increases with increasing
the length of the fibre and artifacts that of the continuous fibre reinforced one. Also the
strength of the fibre reinforced composite will be maximum when the fibres are aligned
in the direction of the applied stress i.e in the isostrain condition. So the strength of this
kind of composite depends on the volume fraction of the reinforcing element present in
the composite, which can be determined by the simple rule of mixtures.
STRENGTHENING MECHANISM OF PARTICULATE COMPOSITE
In the particulate reinforced composite the size of the particulate is more than 1 μm, so
it strengthens the composite in two ways. First one is the particulate carry the load
along with the matrix materials and another way is by formation of incoherent interface
between the particles and the matrix. So a larger number of dislocations are generated
at the interface, thus material gets strengthened. The degree of strengthening depends
on the amount of particulate (volume fraction), distribution, size and shape of the
particulate etc.
[attachment=40697]
ABSTRACT
Metal matrix composites (MMCs) possess significantly improved properties including high
specific strength; specific modulus, damping capacity and good wear resistance compared to
unreinforced alloys. There has been an increasing interest in composites containing low density
and low cost reinforcements. Among various discontinuous dispersoids used, fly ash is one of
the most inexpensive and low density reinforcement available in large quantities as solid waste
by-product during combustion of coal in thermal power plants. Hence, composites with fly ash
as reinforcement are likely to over come the cost barrier for wide spread applications in
automotive and small engine applications. It is therefore expected that the incorporation of fly
ash particles in aluminium alloy will promote yet another use of this low-cost waste by-product
and, at the same time, has the potential for conserving energy intensive aluminium and
thereby, reducing the cost of aluminium products. Now a days the particulate reinforced
aluminium matrix composite are gaining importance because of their low cost with advantages
like isotropic properties and the possibility of secondary processing facilitating fabrication of
secondary components. The present investigation has been focused on the utilization of
abundantly available industrial waste fly-ash in useful manner by dispersing it into aluminium to
produce composites by stir casting method.
INTRODUCTION
Conventional monolithic materials have limitations in achieving good combination of strength,
stiffness, toughness and density. To overcome these shortcomings and to meet the ever
increasing demand of modern day technology, composites are most promising materials of
recent interest. Metal matrix composites (MMCs) possess significantly improved properties
including high specific strength; specific modulus, damping capacity and good wear resistance
compared to unreinforced alloys. There has been an increasing interest in composites
containing low density and low cost reinforcements. Among various discontinuous dispersoids
used, fly ash is one of the most inexpensive and low density reinforcement available in large
quantities as solid waste by-product during combustion of coal in thermal power plants. Hence,
composites with fly ash as reinforcement are likely to over come the cost barrier for wide
spread applications in automotive and small engine applications. It is therefore expected that
the incorporation of fly ash particles in aluminium alloy will promote yet another use of this
low-cost waste by-product and, at the same time, has the potential for conserving energy
intensive aluminium and thereby, reducing the cost of aluminium products [1-3].
COMPOSITE
Composite material is a material composed of two or more distinct phases (matrix phase and
reinforcing phase) and having bulk properties significantly different from those of any of the
constituents. Many of common materials (metals, alloys, doped ceramics and polymers mixed
with additives) also have a small amount of dispersed phases in their structures, however they
are not considered as composite materials since their properties are similar to those of their
base constituents (physical property of steel are similar to those of pure iron) . Favorable
properties of composites materials are high stiffness and high strength, low density, high
temperature stability, high electrical and thermal conductivity, adjustable coefficient of thermal
expansion, corrosion resistance, improved wear resistance etc.
Metal Matrix Composites (MMCs)
Metal Matrix Composites are composed of a metallic matrix (Al,Mg,Fe,Cu etc) and a dispersed
ceramic (oxide, carbides) or metallic phase( Pb,Mo,W etc). Ceramic reinforcement may be
silicon carbide, boron, alumina, silicon nitride, boron carbide, boron nitride etc. whereas
Metallic Reinforcement may be tungsten, beryllium etc [19]. MMCs are used for Space Shuttle,
commercial airliners, electronic substrates, bicycles, automobiles, golf clubs and a variety of
other applications. From a material point of view, when compared to polymer matrix
composites, the advantages of MMCs lie in their retention of strength and stiffness at elevated
temperature, good abrasion and creep resistance properties [19]. Most MMCs are still in the
development stage or the early stages of production and are not so widely established as
polymer matrix composites. The biggest disadvantages of MMCs are their high costs of
fabrication, which has placed limitations on their actual applications [20]. There are also
advantages in some of the physical attributes of MMCs such as no significant moisture
absorption properties, non-inflammability, low electrical and thermal conductivities and
resistance to most radiations [21]. MMCs have existed for the past 30 years and a wide range of
MMCs have been studied [19].
STRENGTHENING MECHANISM OF FIBRE REINFORCED COMPOSITE
In such type of composite the reinforcing phase carries the bulk of the load and the
matrix transfers the load to the reinforcing phase by the mechanism of seam. The high
strength of the reinforcing phase restrict the free elongation of the matrix especially in
its vicinity, whereas later is free to elongate at some distance away from the former.
This type of non uniform deformation of the matrix leads to a shear stress at the matrix
reinforcement interface which results tensile stress at the reinforcing phase. Thus the
stress is transferred to the reinforcing phase. The fibers either may be continuous or
discontinuous in the matrix. In the former case the load is directly applied to the
reinforcing phase and stress is constant over its entire length. In case of discontinuous
fibers, the stress in the fibre increased from zero value at the end to a maximum value
in the centre and thus average tensile strength developed is always less than those of
continuous fibers. For the same when the fracture of the reinforcing phase, therefore
the strength of the discontinuous fibre reinforced composite increases with increasing
the length of the fibre and artifacts that of the continuous fibre reinforced one. Also the
strength of the fibre reinforced composite will be maximum when the fibres are aligned
in the direction of the applied stress i.e in the isostrain condition. So the strength of this
kind of composite depends on the volume fraction of the reinforcing element present in
the composite, which can be determined by the simple rule of mixtures.
STRENGTHENING MECHANISM OF PARTICULATE COMPOSITE
In the particulate reinforced composite the size of the particulate is more than 1 μm, so
it strengthens the composite in two ways. First one is the particulate carry the load
along with the matrix materials and another way is by formation of incoherent interface
between the particles and the matrix. So a larger number of dislocations are generated
at the interface, thus material gets strengthened. The degree of strengthening depends
on the amount of particulate (volume fraction), distribution, size and shape of the
particulate etc.