CLASSIFICATION OF MATERIALS

Solid materials have been conveniently grouped into three basic categories: metals, ceramics, and polymers. This
scheme is based primarily on chemical makeup and atomic structure, and most materials fall into one distinct
grouping or another. In addition, there are the composites, which are engineered combinations of two
or more different materials.
Another category is advanced materials—those used in high-technology applications, such as semiconductors,
biomaterials, smart materials, and nanoengineered materials.
Metals
Materials in this group are composed of one or more metallic elements (e.g., iron, aluminum, copper, titanium, gold,
and nickel), and often also nonmetallic elements (e.g., carbon, nitrogen, and oxygen) in relatively small amounts.
- Atoms in metals and their alloys are arranged in a very orderly manner and in comparison to the ceramics and
polymers, are relatively dense.
- With regard to mechanical characteristics, these materials are relatively stiff. and strong, yet are ductile (i.e.,
capable of large amounts of deformation without fracture), and are resistant to fracture, which accounts for their
widespread use in structural applications.
-Metallic materials have large numbers of nonlocalized electrons; that is, these electrons are not bound to particular
atoms. Many properties of metals are directly attributable to these electrons. For example, metals are extremely
good conductors of electricity and heat, and are not transparent to visible light; a polished metal surface has a
lustrous appearance.
- In addition, some of the metals (i.e., Fe, Co, and Ni) have desirable magnetic properties.
Ceramics
Ceramics are compounds between metallic and nonmetallic elements; they are most frequently oxides, nitrides, and
carbides. For example, common ceramic materials include aluminum oxide (or alumina, Al2O3), silicon dioxide (or
silica, SiO2), silicon carbide (SiC), silicon nitride (Si3N4), and, in addition, what some refer to as the traditional
ceramics—those composed of clay minerals (i.e., porcelain), as well as cement and glass.

- With regard to mechanical behavior, ceramic materials are relatively stiff and strong—stiffnesses and strengths are
comparable to those of the metals
- In addition, they are typically very hard.
- Furthermore, ceramic materials are typically insulative to the passage of heat and electricity, and are more
resistant to high temperatures and harsh environments than metals and polymers.
- With regard to optical characteristics, ceramics may be transparent, translucent, or opaque,
- and some of the oxide ceramics (e.g., Fe3O4) exhibit magnetic behavior.
Polymers
Polymers include the familiar plastic and rubber materials. Many of them are
organic compounds that are chemically based on carbon, hydrogen, and other
nonmetallic elements (i.e., O, N, and Si). Furthermore, they have very large
molecular structures, often chainlike in nature, that often have a backbone of
carbon atoms. Some of the common and familiar polymers are polyethylene
(PE), nylon, poly(vinyl chloride) (PVC), polycarbonate (PC), polystyrene (PS), and
silicone rubber.

These materials typically have low densities, whereas their mechanical

characteristics are generally dissimilar to the metallic and ceramic materials—
they are not as stiff nor as strong as these other material types .
Composites
A composite is composed of two (or more) individual materials, which come from the categories previously
discussed—metals, ceramics, and polymers. The design goal of a composite is to achieve a combination of
properties that is not displayed by any single material, and also to incorporate the best characteristics of each of the
component materials. A large number of composite types are represented by different combinations of metals,
ceramics, and polymers. Furthermore, some naturally occurring materials are composites—for example, wood and
bone.
Uses of materials
The properties of a material determine whether it is suitable for a given use. For any given use, certain
properties will be required. There may be more than one suitable material to choose from, and the
advantages and disadvantages of each one must be evaluated. The common use of some materials are
as follows:

Metals: Construction Industry, electronics, Machinery, Refractory and Automobiles, Decorative products

Ceramics: Space industry, cutting tools, refractory materials, thermal insulator, electrical insulator etc.

Polymers: Fabric, Automotive, Aerospace, Medical, Building, Consumer Goods, Packaging

Composites:
Metal matrix composite: cutting tools, driveshaft, electronics, thermal conductivity,
Ceramic matrix composites: Common applications of ceramic matrix composites are Heat exchangers
and burner components, Gas turbine components, Aerospace industry,
Engine exhaust systems, Hypersonic vehicles, Nuclear power industry
Polymer matrix composite: aerospace, transport, construction, shipbuilding
Selection of materials in view of service and fabrication requirements and economics
Material Selection
The basic question is how do we go about selecting a material for a given part?
This may seem like a very complicated process until we realize than we are often
controlled by choices we have already made. For example, if different parts have
to interact then material choice becomes limited. When we talk about choosing
materials for a component, we take into account many different factors. These
factors can be broken down into the following areas.
Material Properties: The expected level of performance from the material
Material Cost and Availability: Material must be priced appropriately (not cheap
but right). Material must be available (better to have multiple sources)
Processing: Must consider how to make the part, for example: Casting Machining
Welding Environment. The effect that the service environment has on the part.
The effect the part has on the environment. The effect that processing has on the
environment
Three important criteria in materials selection are in-service
conditions to which the material will be subjected, any
deterioration of material properties during operation, and
economics or cost of the fabricated piece.
 Selection of materials in view of service and fabrication requirements and economics

ENGINEERING REQUIREMENTS OF MATERIALS

Engineering requirements of a material mean as what is expected of from the material so that the same can be
successfully used for making engineering components such a crankshaft, spanner, etc. When an engineer thinks of
deciding and fabricating an engineering part, he goes in search of that material which possesses such properties as will
permit the component part to perform its functions successfully while in use. For example, one may select high speed
steel for making a milling cutter or a power hack-saw blade.
The main engineering requirements of materials fall under three categories,
(i) Fabrication requirements.
(ii) Service requirements
(iii) Economic requirements.
Fabrication requirements mean that the material should be able to get shaped (e.g., cast, forged, formed, machined,
sintered etc.) and joined (e.g., welded, brazed, etc.) easily. Fabrication requirements relate themselves with material's
machinability, ductility, castability, heat-treatability, weldability, etc.
Service requirements imply that the material selected for the purpose must stand up to service demands, e.g., proper
strength, wear resistance, corrosion resistance, etc.
Economic requirements demand that the engineering part should be made with minimum overall cost. Minimum
overall cost may be achieved by proper selection of both technical and marketing variables.
FACTORS AFFECTING THE SELECTION OF MATERIALS FOR ENGINEERING PURPOSES
(A) Properties of Materials
- The most important factor affecting selection of materials for engineering design is the properties of the materials in
relation to their intended use.
- The properties of the material define specific characteristics of the material and form a basis for predicting behaviour of
the material under different conditions.
- The important properties of materials are :
1. Mechanical: e.g., stresses
2. Thermal: e.g., heat or cold.
3. Chemical: e.g., atmosphere, water, chemicals,.
4. Electrical: e.g., power, current.
5. Radiation: e.g, light, Ultraviolet, Nuclear,

(B) Performance Requirements

- The material of which a part is composed must be capable of embodying or performing a part's function without failure.
For example, a component part to be used in a furnace must be of that material which can withstand high temperatures.
- While it is not always possible to assign quantitative values to these functional requirements, they must be related as
precisely as possible to specified values of the most closely applicable mechanical, physical, electrical or thermal
properties.

(C) Material's Reliability

A material in a given application must also be reliable. Simply stated, reliability is the degree of probability that a product, and
the material of which it is made, will remain stable enough to function in service for the intended life of the product without
failure. A material if it corrodes under certain conditions, then, it is neither stable nor reliable for those conditions.
(D) Safety
A material must safely perform its function, otherwise, the failure of the product made out of it may be catastrophic
(sudden damage) in air-planes and high-pressure systems. As another example, materials that gives off sparks when
struck are safety hazards in a coal mine.
(E) Physical attributes
Physical attributes such as configuration, size, weight, and appearance sometimes also serve functional requirements,
for instance, the functioning of a gyroscope or a flywheel is directly related to the weight of the material used.
(F) Environmental Conditions
The environment in which a product operates strongly influences service performance. Humidity, water, or chemicals
can cause corrosion and subsequent failure of materials.
(G) Availability
Obviously a material must be readily available, and available in large enough quantity, for the intended application. In
times of materials scarcity, this constraint becomes significant. And, in the future, with the projected scarcity of many
material resources, this constraint will assume increasing importance.
(H) Disposability and recyclability
These are the newest of the restrictions and increasingly important factors in materials selection. Example-nuclear
materials.
(I) Economic Factors
- Cost, perhaps more often than any other constraint, is the controlling factor in a given materials application problem. For, in every application, there is a
cost beyond which one cannot go that prescribes the limit that can be paid for a material to meet the application requirements. If it becomes apparent
that this limit will be exceeded, the design will be changed to alter materials requirements. This fact of limiting cost is as true in the aerospace field as in
consumer-products fields. The only difference is that the limiting cost in aerospace systems is considerably higher than for consumer products. The total
original cost of a material for a given application is made up of two components: the cost of the materials and the cost of processing the materials into
the finished part or product.
WHY STUDY MATERIALS SCIENCE
AND ENGINEERING?
Why do we study materials? Many an applied scientist or engineer, whether mechanical, civil, chemical, or electrical,
will at one time or another be exposed to a design problem involving materials. Examples might include a transmission
gear, the superstructure for a building, an oil refinery component, or an integrated circuit chip. Of course, materials
scientists and engineers are specialists who are totally involved in the investigation and design of materials.

Many times, a materials problem is one of selecting the right material from the thousands that are available. The final
decision is normally based on several criteria.
First of all, the in-service conditions must be characterized, for these will dictate the properties required of the material.
On only rare occasions does a material possess the maximum or ideal combination of properties. Thus, it may be
necessary to trade one characteristic for another. The classic example involves strength and ductility; normally, a
material having a high strength will have only a limited ductility. In such cases a reasonable compromise between two
or more properties may be necessary.
A second selection consideration is any deterioration of material properties that may occur during service operation.
For example, significant reductions in mechanical strength may result from exposure to elevated temperatures or
corrosive environments.
Finally, probably the overriding consideration is that of economics: What will the finished product cost? A material may
be found that has the ideal set of properties but is prohibitively expensive. Here again, some compromise is inevitable.
The cost of a finished piece also includes any expense incurred during fabrication to produce the desired shape. The
more familiar an engineer or scientist is with the various characteristics and structure–property relationships, as well as
processing techniques of materials, the more proficient and confident he or she will be in making judicious materials
choices based on these criteria.
ADVANCED MATERIALS
Materials that are utilized in high-technology (or high-tech) applications
are sometimes termed advanced materials. By high technology we
mean a device or product that operates or functions using relatively
intricate and sophisticated principles; examples include electronic
equipment (camcorders, CD/DVD players, etc.), computers, fiber-optic
systems, spacecraft, aircraft, and military rocketry

Semiconductors
Semiconductors have electrical properties that are intermediate
between the electrical conductors (i.e., metals and metal alloys) and
insulators (i.e., ceramics and polymers).

Biomaterials
Biomaterials are employed in components implanted into the human
body to replace diseased or damaged body parts. These materials must
not produce toxic substances and must be compatible with body tissues
(i.e., must not cause adverse biological reactions). All of the preceding
materials—metals, ceramics, polymers, composites, and
semiconductors—may be used as biomaterials.
 Smart Materials
Smart (or intelligent) materials are a group of new and state-of-the-art materials now being developed
that will have a significant influence on many of our technologies. The adjective smart implies that these
materials are able to sense changes in their environment and then respond to these changes in
predetermined manners—traits that are also found in living organisms. In addition, this “smart” concept
is being extended to rather sophisticated systems that consist of both smart and traditional materials.
Components of a smart material (or system) include some type of sensor (that detects an input signal),
and an actuator (that performs a responsive and adaptive function). Actuators may be called upon to
change shape, position, natural frequency, or mechanical characteristics in response to changes in
temperature, electric fields, and/or magnetic fields.
Four types of materials are commonly used for actuators: shape-memory alloys, piezoelectric ceramics,
magnetostrictive materials, and electrorheological/magnetorheological fluids. Shape-memory alloys are
metals that, after having been deformed, revert back to their original shape when temperature is
changed.

Nitinol: A shape memory alloy, Nickel, 40-50% and

Video link: Titanium, 50-60%.ickel, 50-60% titanium
https://youtu.be/QYp9rIJRM8s?si=Dwuscbhxt37Fz_fs
Nanomaterials
One new material class that has fascinating properties and
tremendous technological promise is the nanomaterials.
Nanomaterials may be any one of the four basic types—metals,
ceramics, polymers, and composites.
However, unlike these other materials, they are not distinguished on
the basis of their chemistry, but rather, size; the nano-prefix denotes
that the dimensions of these structural entities are on the order of a
nanometer (10–9 m)—as a rule, less than 100 nanometers (equivalent
to approximately 500 atom diameters).

Classification of Nanomaterials
Currently, the most typical way of classifying nanomaterials is to
identify them according to their dimensions. As shown in Figure 1,
nanomaterials can be classified as
(1) zero-dimensional (0-D),
(2) one-dimensional (1-D),
(3) two-dimensional (2-D), and
(4) three-dimensional (3- D).
Nanomaterials
One new material class that has fascinating properties and
tremendous technological promise is the nanomaterials.
Nanomaterials may be any one of the four basic types—metals,
ceramics, polymers, and composites.
However, unlike these other materials, they are not distinguished on
the basis of their chemistry, but rather, size; the nano-prefix denotes
that the dimensions of these structural entities are on the order of a
nanometer (10–9 m)—as a rule, less than 100 nanometers (equivalent
to approximately 500 atom diameters).

Classification of Nanomaterials
Currently, the most typical way of classifying nanomaterials is to
identify them according to their dimensions. As shown in Figure 1,
nanomaterials can be classified as
(1) zero-dimensional (0-D),
(2) one-dimensional (1-D),
(3) two-dimensional (2-D), and
(4) three-dimensional (3- D).
Ans: There are many ways of making nanoscale materials and structures.
Methods for Making 0-D Nanomaterials
Inert-gas condensation
Inert-gas (free-jet) expansion
Sonochemical processing
Sol-gel deposition
Molecular self-assembly
Methods for Making 1-D and 2-D Nanomaterials
Foil beating
Electrodeposition
Physical vapor deposition (PVD)
Chemical vapor deposition (CVD)
Methods for Making 3-D Nanomaterials
Many bulk materials that we use today derive their properties from
internal structure at the nanoscale.
Top-Down Processes
Rapid solidification
Equiangle extrusion
Intermediate Processes
Milling and mechanical alloying
Micromachining
Bottom-Up Processes
Consolidation of nanoclusters and milled powders
Q. What are the approaches used to synthesis nanomaterials. Briefly describe them. (1 +5)
Ans: Currently one can use either a top–down (comminution and dispersion) or a bottom–up (nucleation and growth)
approach. The decision which to adopt depends, of course, on which can deliver the specified properties, and on cost.
A third approach is bottom-to-bottom mechanosynthesis; that is, “true” nanofacture, according to which every atom
of the material is placed in a predefined position. At present this has no commercial importance because only minute
quantities can be prepared.
Comminution and Dispersion
This top–down approach involves taking bulk material and fragmenting it. Crushing and grinding have typically been
treated as low-technology operations; theoretical scientists seeking to formalize the process beginning with the
formulation of mechanistic phenomenological rules (e.g., the random sequential fragmentation formalism) have
hitherto had little industrial impact. The main advantages are universality (i.e., applicability to virtually any material)
and low cost. Even soft organic matter (e.g., leaves of grass) can be ground by first freezing it in liquid nitrogen to
make it brittle. The main disadvantages are polydispersity of the final particles, the introduction of many defects
(including contamination by the material used to make the grinding machinery—the smaller the particles the worse
the contamination because it is introduced at the surface of the particles) and the impossibility of achieving nanoscale
comminution, depending on the material: as a compressed brittle body is made smaller, its fracture strength increases
until at a certain critical size crack propagation becomes impossible. This explains the well-known size limit to the
crushing of materials—typically above the nanoscale.

Nucleation and Growth

This process involves a first order phase transition from an atomically dispersed phase to a solid condensed phase.
Nucleation and Growth
This process involves a first order phase transition from an atomically dispersed phase to a solid condensed phase.
During the first stage of the transition fluctuations in the homogeneous, metastable parent phase result in the
appearance of small quantities of the new phase. In order to synthesize nanoparticles via nucleation and growth,
firstly the atoms are dispersed (dissolved) in a medium under conditions such that the dispersion is stable. Then, one
or more of the external parameters is changed such that the bulk phase of the material now dispersed is stable. This
could be accomplished, for example, by cooling the vapor of the material. The formation of the new bulk phase is a
first order phase transition involving nucleation. Chance fluctuations will generate critical nuclei.
Piezoelectric materials: An unusual property exhibited by a few
ceramic materials is piezoelectricity, or, literally, pressure electricity:
polarization is induced and an electric field is established across a
specimen by the application of external forces. Reversing the sign of an
external force (i.e., from tension to compression) reverses the direction
of the field. The materials which exhibit such characteristic are known
as piezoelectric materials.

Piezoelectricity is the electric charge that accumulates in certain solid

materials (such as crystals, certain ceramics, and biological matter
such as bone, DNA and various proteins) in response to
applied mechanical stress. Fig. 18.36 (a) Dipoles within a piezoelectric
material. (b) A voltage is generated when
the material is subjected to a compressive
Piezoelectric materials are used in transducers, which are devices
stress.
that convert electrical energy into mechanical strains, or vice versa.
Piezoelectric materials include titanates of barium and lead, lead
zirconate (PbZrO3), ammonium dihydrogen phosphate (NH4H2PO4),
and quartz.

Strain gage
 Lasers and optical fibres
The word "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation.

Most of the radiative electron transitions are spontaneous; that is, an electron falls from a high energy
state to a lower one without any external provocation. These transition events occur independently of
one another and at random times, producing radiation that is incoherent; that is, the light waves are
out of phase with one another. With lasers, however, coherent light is generated by electron
transitions initiated by an external stimulus.

Laser light is used for optical fiber communications because of a single wavelength light source. Ordinary light
contains many different wavelengths of light, differences emerge in speed of transmission, reducing the number of
signals that can be transmitted in any set time.

Figure 21.13 Schematic diagram of

the ruby laser and xenon Coherent light waves Incoherent light waves
Almost all
electronics
transition that
occurs in
atoms, which
involve
photons, fall
into one of this
three
categories
Optical Fibers
One new and advanced ceramic material that is a critical
component in our modern optical communications systems is the
optical fiber. The optical fiber is made of extremely high-purity
silica, which must be free of even minute levels of contaminants
and other defects that absorb, scatter, and attenuate a light
beam.

An optical fiber is a single, hair-fine filament drawn from molten

silica glass. These fibers are replacing metal wire as the
transmission medium in high-speed, high-capacity
communications systems that convert information into light,
which is then transmitted via fiber optic cable.

With regard to speed, optical fibers can transmit, in one second,

information equivalent to three episodes of your favorite
television program. Or relative to information density, two small
optical fibers can transmit the equivalent of 24,000 telephone
calls simultaneously. Furthermore, it would require 30,000 kg (30
tons) of copper to transmit the same amount of information as
only 0.1 kg of optical fiber material.

Fig. Schematic cross section of an optical fiber.

Optical fibers transmit light by total internal reflection
 Optoelectronic materials

Optoelectronics is the study and application of electronic devices and systems that source, detect and
control light.
Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers, or instruments that use
such devices in their operation.

There is a number of materials that can influence light’s properties. However, there are only a few that can
be used together with electronic circuits to generate, detect, and manipulate light signals. The materials
that are capable of integrating optical and electronic functions to produce optoelectronics devices such as
light-emitting diodes, solid state lasers, solar cells, infrared detectors, light modulators, and waveguides
etc. are known as optoelectronic materials.

Optoelectronic devices are predominantly made using III–V semiconductor compounds such as GaAs, InP,
GaN, and GaSb, and their alloys due to their direct-band gap.

Materials based on carbon (such as polymers or fullerenes) are also becoming used in
optoelectronics (such as electroluminescent diodes and photovoltaic cells).
Electronic Materials: From Silicon to Organics
edited by L. S. Miller, J. B. Mullin
 Superalloys
The name “superalloy” refers to metals that have been developed to withstand high
temperatures without deforming (including creep) or corroding.
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of
its melting point. Several key characteristics of a superalloy are excellent mechanical strength,
resistance to thermal creep deformation, good surface stability, and resistance to corrosion or
oxidation.

The superalloys have superlative combinations of properties. Most are used in aircraft turbine
components, which must withstand exposure to severely oxidizing environments and high
temperatures for reasonable time periods.

These materials are classified according to the predominant metal in the alloy, which may be
cobalt, nickel, or iron. Other alloying elements include the refractory metals (Nb, Mo, W, Ta),
chromium, and titanium. In addition to turbine applications, these alloys are utilized in nuclear
reactors and petrochemical-equipment.
Categorization of superalloys
Superalloys are categorized into three, based on the major or principal metal present in the alloy. They are
Ni based superalloys (NBSs),
Fe based superalloys (FBSs) and
Co based superalloys (CBSs)

Ni based superalloys (NBSs)

The NBSs are good corrosion-resistant, high strength, long fatigue life and high-temperature alloys mostly used
at operational temperatures higher than 550 °C. They often contain some alloying elements like carbon or
boron and weighty refractory elements like tungsten and tantalum.
Cobalt (Co) based superalloys (CBSs)
Despite the proven usefulness of nickel-based superalloy materials for significantly high-temperature
applications, CBSs potentially exhibit higher hot corrosion, superior oxidation and better resistance to wear
compared to NBSs.

Iron (Fe) based superalloys (FBSs)

The FBSs are extremely cheaper to produce compared to NBSs and CBSs. Although the use of certain alloys of
steel have shown oxidation and creep resistance alike to that of NBSs. Iron based superalloys exhibit matrix
phase of austenite iron (FCC) just like phase found in nickel-based superalloys. W, Ti, Si, Nb, Al, C, Cr, Ti, Y, Co, Si
and B are the alloying elements commonly found in these stainless steel alloys.
Features of super alloys
- Superalloys are class of nickel (Ni), cobalt (Co) and iron (Fe) based alloys used in jet and marine turbine
engines due to their outstanding dimensional stability at a much higher temperature compared to most
structural and high-temperature materials.
- Superalloys can use a high fraction of their melting point, and this positioned them in the category of high-
temperature application materials.
- They are also reported to exhibit reasonable corrosion resistance and good mechanical properties even at
elevated temperature, which facilitates their suitability for high-stress manufacturing and advance
applications, such as in the production of turbine engines for the marine and aerospace industries.
- The surface of superalloys can be protected using diffusion, overlaying and thermal barrier coatings, which
act as a barrier against oxidation, corrosion, depletion in microstructure and thermal deformation.

Applications of superalloys include:

- Vanes and blades for jet and gas turbine engines
- Heat exchangers
- Components for chemical reaction vessels
- Equipment for heat treatment.
- These alloys are utilized in nuclear reactors and petrochemical-equipment.