Research Themes
Keywords:
metal matrix composite,
in-situ composite, casting, melting and solidification
process, cast iron, aluminum alloy, magnesium alloy
1.
Fabrication of
short potassium titanate fiber reinforced aluminum
alloy composite and its properties
– Development of new machinable aluminum alloy
composite –
The use
of aluminum alloys has increased in many industrial applications because the
reduction in the weight and size of the products, such as automobile parts, has
recently been promoted. These applications often require the improvement in the
strength, rigidity, heat resistance and wear resistance of the aluminum alloy.
To satisfy these requirements, the reinforcement of the aluminum alloy with
ceramic fibers or particles has been presented. The aluminum alloy composites
reinforced with the ceramic fibers or particles have been not only studied
fundamentally but also made by way of trial or put into practical use. However,
there is a concern about a decrease in machinability of the aluminum alloy by
reinforcing with ceramics, because ceramics are generally difficult to machine.
Therefore, it is very important to clarify the machinability of the composites.
To develop a machinable aluminum alloy composite
having low thermal expansion rate, we have noticed the potassium titanate as the reinforcement because it has low thermal
expansion and hardness. Although several investigations have been conducted on
the aluminum alloy composites reinforced with the potassium titanate
whisker, the whiskers are considered harmful to the respiratory organs. The
short potassium titanate fiber, having greater
diameter and length than the whisker, was developed to reduce this concern.
Based on these findings, we fabricated aluminum alloy composites reinforced
with the short potassium titanate fibers by squeeze casting, and clarified that the
thermal expansion coefficient of the composite was lower than that of the
aluminum alloy.
In
the present study, short potassium titanate fiber
reinforced aluminum alloy composites are fabricated, and the effects of the
fiber volume fraction in the composite and cutting conditions on the
machinability are clarified by measuring the cutting resistance and tool wear,
and observing the machined surface and chip forms.
丂
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Optical micrograph of the composite (亊100丆dark phase: potassium titanate fiber) |
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2.
Fabrication of
short alumina fiber reinforced aluminum alloy composite and its properties – Development of aluminum alloy composite
with heat and wear resistance –
Aluminum alloys have been used in many
industrial applications as the lightweight material instead of steel or cast
iron, because it is lightweight and its strength can be improved by alloying or
heat treatment. However, their use in parts that require heat resistance or
wear resistance is still limited because their high temperature strength and
wear resistance are insufficient. In order to improve these properties, the
reinforcement of the aluminum alloy with ceramic fibers has been presented. The
alumina fiber would be most suitable for improving the properties of the
aluminum alloy, because its high temperature strength and hardness are
superior. The alumina fiber-reinforced aluminum alloy composites have not only
been fundamentally studied but also made in trials or put into practical use.
From the viewpoint of the practical use of such composites, it is very
important to clarify their machinability. There is a concern about a decrease
in machinability of the aluminum alloy by reinforcing with alumina fibers,
because alumina is generally difficult to machine. However, the machinability
of the composite has not yet been sufficiently clarified. In addition, there
are many chemical compositions and crystal structures of alumina fibers, and
the properties of the fiber strongly depend on its composition or structure.
There are no reports regarding the effect of the properties of alumina fibers
on the machinability of a composite.
In the present study, short alumina fibers
having different properties are used as the reinforcements of the aluminum
alloy, and a fiber preform is infiltrated with the aluminum alloy melt by
squeeze casting in order to fabricate the composite. The effects of the fiber
reinforcement on the machinability of the aluminum alloy are then clarified.
丂
|
Scanning electron image of alumina fibers |
3.
Fabrication of
carbon fiber reinforced aluminum alloy composite and its properties – Development of aluminum alloy
composite with high thermal conductivity –
These
applications often require the improvement in the strength, rigidity, heat resistance
and wear resistance of the aluminum alloy. To satisfy these requirements, the
reinforcement of the aluminum alloy with ceramic fibers or particles has been
presented. In recent years, the performances of machines and electronic
equipment have been drastically improved. At the same time, these components
tend to be exposed to the severer environment. For example, high temperature
leads to an incorrect action or damage of the
equipment. It is important to release the heat from the components as soon as
possible. High thermal conductive materials are required to satisfy this.
Although aluminum is known as a metal with high thermal conductivity and low
density, higher thermal conductivity has been required recently to apply for
the machines
and electronic equipment
with high performance. Carbon fiber, which has a high thermal conductivity, is
one of the candidates. To our knowledge, however, it is not easy to obtain the
high thermal conductivity by the reinforcement with the carbon fibers.
Additionally, aluminum reacts with carbon at elevated temperature and leads to
the formation of aluminum carbide harmful to its properties. Needless to say,
it is very important to prevent from the reaction progressing.
The purpose of
this work is to solve these problems that obstruct the practical application of
the carbon fiber- reinforced aluminum alloy composite.
4.
Microstructure of
Niobium silicide based in situ composites – Development of future superalloy –
New
high temperature structural materials are required for the next generation of
advanced aircraft engines. Many intermetallic
compounds have been studied as candidate materials that could replace the
conventional nickel-based superalloys. Niobium silicide based in situ composites are
very promising candidates for future application in airfoils. While these in situ composites
exhibit excellent creep strength at elevated temperatures, they lack oxidation
resistance and suffer from poor fracture toughness at room temperature. From the viewpoint of the practical use of
these composites, we need to solve these drawbacks.
The
purpose of this work is to understand the effects of transition metal,
refractory metal and free electron metal additions on the microstructure of the
in situ composites based on Nb-18Si and the oxidation of these alloys.
|
BEI image of the composite (dark
phase: niobium silicide) (bright phase: niobium solid solution) |
5.
Effect of tramp elements on microstructure of thin wall
spheroidal graphite cast iron
Cast iron has been produced in quantity as the castings for automobile parts and industrial
machines, because it has excellent castability, good
wear resistance and damping capacity. Recent years, reduction in weight and
size of the machine products has been promoted to reduce the energy
consumption, use of raw material and exhausting of greenhouse gas. This trend
leads to the promotion of thinning of the spheroidal graphite cast iron
castings. However, the cast iron melt in thin wall is exposed to the rapid
cooling, and the cementite (chill) tends to increase out in the matrix. The
chilling causes the decrease in the mechanical properties of the castings. For
the spheroidal graphite cast iron, it is reported that the increase in graphite
nodule in the matrix is effective for preventing the chilling without any heat
treatment. It is also reported that the addition of some tramp elements is
effective for increasing the graphite nodule count. However, the effect of these elements on
the graphite and matrix structure of the thin wall spheroidal graphite cast
iron
has not yet been sufficiently clarified.
In this study, the effects of tramp elements on the
microstructure of thin wall spheroidal graphite cast iron are examined.
Some of researches shown above are collaborated
with some companies or carried out by grants-in-aid.