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A Review For Functionally Gradient Materials
Manufacturing And Useful Application
Nabaa S. Radhi
a Lecturer of Materials College engineering, University of Babylon-Hilla-Iraq.
E-mail: dr.nabbaa@gmail.com.
Abstract. In the science of materials the term Functionally Graded Materials (FGMs) which
could be recognized by the gradually changes in structure and composition leading to
variation in the characterization of materials. (FGMs) is considered one of the recent
development of composite materials to enhance the strengths and reduce the weaknesses of
these materials. (FGMs) were used for the first time in Japan in 1984 via an airplane project
because these materials could be used and designed for many roles and applications. The
reasons that make (FGMs) are multi-function materials due to the variation in the chemical
composition, microstructure and design features depending on the requirements. In this
review the functionally graded materials are studied on many different sides such as the
application (the field of implementation) of this new technology and the reason of each use.
Moreover, discuss the manufacturing processes for functionally graded materials and discuss
the reason of choose each processes. On the other hands, discuss the limitation of the using
Functionally graded materials were taking in the consideration.
Keywords: Functionally gradient materials (FGMs), Applications, limitations.
1. Introduction
Day after day, the materials development are continuous to enrich the properties of materials, limited uses
for pure metals and the properties of pure metals cannot controlling to achieve the required properties be
suitable for the new technologies. The materials developed from iron to pure metals to composite
materials which widely in use today. The materials development return to the Bronze Age until now and it
will continuously develop in the future. On the other hands, alloys are considered stronger than pure
metals and multipurpose due to the ability of producing the required properties. Bronze is the first alloy
consists of copper and tin which developed in Bronze age about 4000 BC. After that many researches try
to mix different metallic and non-metallic material to develop their strength, physical and chemical
properties and producing multiple function materials , (Shahistha, et.al., 2014).
Functionally graded materials are one of the revolution technology that happened in the 21st century; they
consist of two-component composite, which properties depend on the compositional gradient of one or
both of the components. Whereas, the conventional composites have A homogeneous composition; hence,
the composition have the desirable properties of their component materials. The need for compromising
the properties is eliminated because the important properties of FGM contain the pure structure for each
component. Additionally, the properties of FGM components can be fully utilised; for instance, the
refractoriness of ceramic can be mated with the toughness of metal, without any requirement to
compromise in toughness of the metal side or the refractoriness of the ceramic side, (Hao, et.al., 2010).
The mechanical characteristics like elasticity modulus, Poisson’s ratio, elasticity modulus for shear, the
density of materials and thermal expansion coefficient are differ smoothly and continuously in preferable
FGMs directions. Due to these various properties, the functionally graded materials used as a biomedical
materials and there are many examples for natural functionally graded materials such as bones, teeth,
skin and bamboo tree. And the first idea to produce functionally gradient material (FGM) was developed
in japan in 1984 by researchers to increase thermal barriers between inside and outside temperature by
using just 10 mm thickness. And the result of this research was standing the space plane the thermal
barrier with outside temperature of 2000 K and inside temperature of 1000K, (Koizumi and Niino,
1995).
After discovering the Functionally Graded Materials (FGMs) in early 1980s in Japan, many researchers
try to study the properties of this new technology, where they found and increasing in the adhesion and
decreasing the thermal stresses in the composite materials (metallic-ceramic) and that help to reuse the
rocket motor, (Koizumi and Niino, 1995). On the other hands, FGM terms open the way for new
researches around the world to investigate the performance of the materials (metals, ceramics and organic
composites) to improve compositions with superior physical characteristic (Mortensen and Suresh,
1995). Based on the area of applying and the load conditions in order to specify varying approaches that
could be used to produce the structure gradients.
Composite materials allow distinct combinations giving hard, wear resistant surface and soft core as per
functional requirement of application. Heterogeneity, anisotropy, symmetry and hierarchy are the main
properties of composite materials reaping particular interest for various applications. High strength to
stiffness rate, give higher resistance to fatigue, wear and corrosion, high reliability and other properties
are the benefits of composites over pure or alloyed metals. Although all these benefits, composite
materials are exposed to sharp transition of properties at the interface which can result in component
failure (by delamination) at risky working conditions, (Malinina, et.al., 2005).
This disadvantage of traditional composites reduced by improved composites form known as functionally
gradient materials (FGMs). In these materials the sharp interface are replaced by gradient interface and
that led to smooth transition of characteristics from one material to the other. These advanced materials
with engineered gradients of composition, structure and specific characteristics in the preferred direction
are superior to homogeneous material composed of similar constituents, (Radhi, 2015)
2. Manufacturing Process For Functionally Graded Materials (FGMs)
The functionally graded materials are usually thin as a surface coatings, so the surface deposition
processes are a wide variety processes to select from them based on the service requirements.
2.1. Vapour Deposition Technique
Vapour deposition method have many different types such as Chemical, Physical Vapour Deposition
(CVD, PVD) respectively and sputter deposit. These different techniques are using to precipitation a
functionally graded coatings on the surface. This coating characterised by thin coating layer and provide
an excellent microstructure to the coated surface. But this techniques are required intensive energy and
generate poisonous gases as a side effect, (Groves, et.al., 1997).
As well as there are another methods that used to precipitation a functionally graded coatings on the
surface of materials such as Self-Propagating High-temperature Synthesis (SHS), electrophoretic, plasma
spraying, electrodeposition, Ion Beam Assisted Deposition (IBAD) and many other methods (Knoppers,
et.al., 2005). All the previous methods cannot be used to achieve bulk FGM due to the speed of these
process are slow and required intensive energy. Thus; these methods are not economic for producing bulk
FGM.
2.2. Powder Metallurgy (PM)
The first production method that producing a bulk functionally graded materials is Powder metallurgy
(PM) the technique of producing Powder metallurgy are generally consist of three steps as following:
firstly the materials should be weighted to mix the powder depending on the previous spatial design to
distribute as a dictate for the requirements of the purpose, loading the premixing-powder that ramming
and then sintering the mixture to become powder, (Nemat-Alla1, 2011). (PM) method increase a structure
stepwise which desired in the continuous structure.
2.3. Centrifugal Method
The second production method that producing a bulk functionally graded materials is Centrifugal
technique is same as centrifugal casting where both of them are using the force of gravity during the
rotation of the mould to produce bulk functionally graded material. The main reason of using this method
to produce the graded materials is return to the difference between the densities of material and the
mould rotation. There are another method which is similar process as centrifugal method, but is known as
gravity method. In spite of Centrifugal method could achieve the grading of materials continuously, but it
has some issues such as the shape that produce is just cylinder. And the second issues that related to this
method, it is a limitation on the product gradient type due to the gradient is produced by a natural process
(centrifugal force and density difference). And many researchers try to solve these problems by using
another manufacturing process called solid freeform, (Watanabe, et.al., 2009).
2.4. Solid Freeform (SFF) Fabrication Method
Solid freeform is an alternative manufacturing method that has many benefits such as the high
production speed, low intensive energy required, optimum utilization of materials, producing
complicated shape with design breeze where the designs drawing on CAD (AutoCAD program) and take
it directly. SFF consists of five essential steps: Drawing the design on CAD (AutoCAD program),
convert CAD data to Standard Triangulation Language (STL) file, then convert (STL) file into 2D
profiles, building of the component layer by layer, and lastly removal and finishing. Solid freeform
fabrcation has many different types of methods technologies, laser process are mainly used to produce the
functionally graded materials. This technology is consists of laser cladding based method, Selective
Laser Sintering (SLS), 3-D Printing (3-DP), and Selective Laser Melting (SLM). Cladding Laser system
and melting
Laser Selective have the ability to produce denser components. Solid freeform considered more flexible
manufacturing process comparison with other process, but the surface finishing is poor, (Kieback, et.al.,
2003).
3. Applications of Functionally Gradient Materials
There are many applications for functionally graded materials (FGMs) and below some of them:
3.1.Aerospace
(FGMs) are used in aerospace industries due to the ability of these materials to stand the high thermal
gradient, the withstanding for extremely high thermal gradient make these materials suitable structures
airplane body the components of rocket motor and many other applications in the space, (Marin, 2005).
3.2. Medical
The human body contains many tissues that characterise as a natural functionally graded materials such as
teeth and bones and during the accidents the human tissues suffering from damages and in the most
conditions these damages are impossible to treat it so it need an alternative parts to replace it. According to
[(MATSUO, et.al., 2001), (Pompe, et.al., 2003), (Watari, et.al., 2004) and (Radhi, 2015)] Functionally
graded materials could use in medical field to replace the damages tissues such as teeth and bones by
biomedical materials.
3.3. Defences
From the properties of the functionally graded materials is well known these materials have an excellent
ability to prevent cracks spreading. This characteristics help to apply these materials in defence specially to
protect soldiers from gun by producing armour plates and bullet-proof vests, (Lu, et.al., 2011).
3.4. Energy
According to [(Müller, et.al., 2003) and (Niino, et.al., 2005)] the functionally graded materials (FGMs)
are using to generate energy because it used to produce solar power, devices energy conversion as well as it
used as a thermal protection to protect the coating of the blades of turbine in gas turbine motor.
3.5. Optoelectronics
Functionally graded materials could use also in Optoelectronics field like low threshold current edge
lasers (GRINSCH), storage media particularly magnetic discs (audio-video) and tuneable photodetectors
due to the graded refractive index for these materials, (Bharti, et.al, 2013).
3.6. Construction field
Construction industry faces many challenges that related to materials performance, cost of materials and
their environmental impact. Also the change of the functionality of the building structures that various
depending on the building location open the way to using functionally graded materials (FGMs) in the
construction field, (Craveiro, et.al., 2012). When using (FGMs) the structure and the composition of
materials will be changed gradually over the volume, and that led to various material characteristic
(Craveiro, et.al., 2011).
3.7. Other applications
In addition to that, there are many field could use (FGMs) as a foundation materials such as coating of
cutting tools (Xing, et.al., 1998), components of engines automobile, components of nuclear reactors,
blades of turbine, exchangers of heat, sensors of fire, Tribology (advance materials), doors retardant and
many other application. Appearance of all these application which are springing up because of the cost of
production and the possibility of controlling and improving the properties of FMGs, (Malinina, et.al.,
2005).
4. The problems of (FGMs)
One of the revolution that happened in the 21st century and will change the manufacturing world is the
Functionally graded materials (FGMs) which is an advanced material used widely. In spite of the (FGMs)
using and applications become so famous, but there are many limitation for achieving the objective of
changing the manufacturing world. The limitations are various depending on the field of applying, but
most of them concentrated on the cost such as the cost that expended on the methods of processing and
fabrication of powder. For Example, Solid Freeform Fabrication (SFF) is one of the techniques that used
to produce (FGMs), but it still has many issues that required an efficient solution. Also many researches
should be conducted to improve the performance of (SFF) in order to create database that controlling on
the properties of Functionally graded materials (FGMs). And finally, (FGMs) process are still manual, so
it need many improvement to make it full automation so as to improve the overall performance of the
process, reduce the cost of (FGMs) and improve reliability of the fabrication process.
5. Conclusions
To sum up, Functionally gradient materials (FGMs) are considered one of the most important materials that
could apply in engineering field and other field, but the cost of (FGMs) producing is so expensive for this
reason it has a limited uses. This piece of paper presents an overview on (FGMs), different manufacturing
methods and focusing on solid freeform method due to the advantages of this method over other processes
and because of the manufacturing flexibility it offers. As well as, it give an overview for various
application fields also presented how the application field can enhance and also extended by reducing the
manufacturing cost via improving the most promising fabrication method (SFF).
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