Course Content

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Lecture No. Title Slide

No.

1 Classification of Materials 6

2 Interatomic Bonding 19

3 Crystal Structure 36

4 Phase Diagram (Binary) or Equilibrium Diagram 57

5 Microstructure: Property Relationship 69

6 Mechanical Properties and Their Evaluation (Tensile Test) 79

7 Mechanical Properties and Their Evaluation (Hardness Test) 103

8 Mechanical Properties and Their Evaluation (Creep Test) 121

Course Content

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Lecture No. Title Slide

No.

9 Mechanical Properties and Their Evaluation (Fatigue Test) 134

10 Mechanical Properties and Their Evaluation (Impact Test) 144

11 Magnetic Materials 169

12 Nanotechnology 182

13 Micro Electro Mechanical Systems (MEMS) 198

14 Sensor Technology and Applications 203

15 Metallurgy of Steels and Other Structural Materials:(Plain Carbon Steels and Alloy Steels)

220

Course Content

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Lecture No. Title Slide

No.

16 Stainless Steels 240

17 Polymeric Materials 267

18 Fibre-Reinforced Composites 300

19 Nuclear Materials: Production of U, Pu, and Th Metal 308

20 Nuclear Fuels: Metallic Fuels 329

21 Nuclear Fuels: Ceramic Fuels (Oxides, Mox and MC) 348

22 Zirconium Alloys (Zircaloys and Zr–Nb Alloys) 362

Lecture 1

Classification of Materials

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Classification of MaterialsThe complete range of materials can be classified into the following categories:•Metals and alloys•Ceramics•Composites•Glasses•Polymers (plastics)

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Classification of MaterialsMetals and alloys• In chemistry, a metal is defined as an element with a valence of 1, 2 or 3• All metals possess metallic properties such as luster, opacity, malleability, ductility

and electrical conductivity. Alloys are practically useful for structural or load-bearing applications such as automotives, buildings, bridges, aerospace, etc.

• Although pure metals are occasionally used, combinations of metals called alloys provide improvement in desirable property

• Typical examples of metallic materials are as follows:Iron, copper, aluminum, zinc, gold, silver, etc., and their alloys. Steels are made from iron and carbon, stainless steel is an alloy of iron and chromium (11% minimum), brasses and bronzes.

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Classification of MaterialsCeramics• A ceramic can be defined as a combination of one or more metals with a non-

metallic element. Hence, metal oxides, carbides, nitrides, borides and silicates are considered as ceramics. Ceramics are probably the most ‘natural’ materials. Beach sand and rocks are examples of naturally occurring ceramics.

• They are characterized by high hardness, abrasion resistance, brittleness and chemical inertness and are poor conductors of electricity and heat

• Though they are strong in compression, they are generally weak in tension

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Classification of Materials

Typical examples of ceramics

• Refractories, abrasives, clays, cermets, Al2O3, MgO, SiC, BaTiO3, UO2, PuO2, ThO2

and (U, Pu)O2

• Traditional ceramics are used to make bricks, tableware, sanitaryware, tiles,

refractories (heat-resistant materials) and abrasives. Ceramics are produced in fine

powders and converted into different shapes. Ceramics are also used in consumer

products such as paints, plastics and tyres.

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Classification of MaterialsComposites • A composite is a combination of two or more materials that has properties

different from its constituents. Composites, as a class of engineering material, provide an almost unlimited potential for higher strength, stiffness and corrosion resistance over the ‘pure’ material. Typical examples of composites are as follows:– Steel-reinforced concrete, clad metals (titanium-clad steel), fibre glass,

reinforced plastics, cemented carbide tools, ceramic-metal, oxide dispersion-strengthened steels

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Classification of Materials• With composites, we can produce light-weight, strong, ductile, high temperature

resistant materials or we can produce hard, yet shock resistant, cutting tools that would otherwise shatter. Advanced aircraft and aerospace vehicles, rely heavily on composites such as carbon fibre reinforced polymers. Sports items such as bicycles, golf clubs and tennis rackets which are light and stiff are composed of different kinds of composite materials.

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Classification of MaterialsPolymers• Polymers are organic substances and derivatives of carbon and hydrogen. They are

also known as plastics. Most plastics are light in weight and soft as compared to metals. They possess high corrosion resistance and can be moulded into various shapes by the application of heat and pressure. Just as ceramics provide good electrical and thermal insulation, polymers may be either ductile or brittle depending on their structure, temperature and strain rate. Although they have lower strength, polymers have a very good strength-to-weight ratio. They are typically not suitable for use at high temperatures.

• Applications ranging from bullet-proof vests, compact disks (CDs), ropes, liquid crystals displays (LCDs), coffee cups, etc.

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Classification of MaterialsGlass • An amorphous material produced from the molten state, typically, but not always

based on silica• The term ‘amorphous’ refers to materials that do not have a periodic arrangement

of atoms. Therefore, glass is defined as a super-cooled liquid, for example, optical fibres based on high-purity silica glass. The fibre optics industry is based on the optical fibres

• Glasses are also used in houses, cars, computers, television screens and hundreds of other applications

• They are characterized by brittleness, hardness, transparency and chemical inertness

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Classification of MaterialsGlass ceramics• Glasses are thermally treated (tempered) to make them stronger• Forming a glass and then heat treating it to form small crystals is done by a special

thermal process known as glass ceramics. Examples are mirror substrates for large telescopes

• Glass and glass ceramics are usually processed by melting and casting

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Classification of MaterialsComparison of properties of metals, ceramics and polymers

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Classification of MaterialsSelection of materials•Selection is based on the properties of materials. The designer must decide the properties required for a part under design and then weigh the properties of the candidate materials. There are literally hundreds of properties that are measured in laboratories for the purpose of comparing the materials, however, we shall concentrate on the more important ones•Major categories of properties to be considered in material selection are as follows:

– Chemical – Physical– Mechanical – Dimensional

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Classification of Materials

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Material Properties

Chemical Physical Mechanical Performance

Composition

Oxidation resistance

Corrosion resistance

Stability

Reactivity

Colour

Density

Elasticity

Electrical conductivity Thermal conductivity

Specific heat

Coefficient of thermal expansion

Magnetic

Hardness

UTS

Ductility

Rigidity (modulus of elasticity)

Wear resistance

Fatigue resistance

Creep rate

Damping capacity Work hardening

Service Life

Machinability

Weldability

Reliability

Durability

Absence of toxicity

Capacity for recycling

Availability

Cost Familiarity

Lecture 2

Interatomic Bonding

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Interatomic BondingInteratomic bonding • Solid substances are composed of very large aggregates of atoms and the

properties of these materials derive in part from the manner in which the individual atoms are bonded together and the strength of these bonds.

• The bonding which exists between atoms is not the same for all materials as there are several types of possible interatomic bond.

• Generally, the bonding involves some degree of interaction between the outer shell, or valence electrons and is, therefore, dependent on the number and distribution of electrons within the atom.

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Interatomic Bonding• A completely filled outer electron shell confers a very high degree of stability to an

atom—this being the electronic structure of inert or noble gases.• In the formation of interatomic bonds, atoms of element with incomplete outer

electron shells attempt, in combination with other atoms to achieve filled outer electron shells, thus satisfying the condition of stability.

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Interatomic BondingTypes of bonds1. Primary bonds

The main types of bonds are:a) The ionic bond b) The covalent bondc) The metallic bondThese bonds are relatively strong

2. Secondary bondsThe main types of bonds are:a) The hydrogen bondb) Van der Waal’s bondGenerally, these bonds are weaker and exist between molecules

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Interatomic BondingThe ionic bond• The bond exists between two unlike atoms. If an electron is transferred from a

metallic atom to a non-metallic atom, the two resulting ions are held together by electrostatic attraction.

Examples1. Sodium and chlorine atoms. Sodium atom gives away its valence electron and

becomes a positive ion, while chlorine atom takes the electron to fill its last orbit and becomes a negative ion, as shown in the following figure.

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Interatomic Bonding

Example 1Electron transfer from sodium to chlorine• By losing an electron, the sodium atom has become out of balance electrically, and

said to be in an ionized stateNa Na+ + e-

• Similarly, by gaining an additional electron, the chlorine atom has become ionized Cl + e- Cl-

• The sodium and chlorine ions, being of opposite charge, will be strongly attracted to one another to form one molecule of NaCl

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Interatomic BondingExample 2Calcium and chlorine atoms

Ca Ca2+ + 2e-

2Cl + 2e- 2Cl-

giving one molecule of CaCl2

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Electron transfer from calcium to two chlorine atoms

Interatomic BondingIonic crystals are characterized by having:• Poor electrical conductivity• High hardness• High melting point• Soluble in water.

• In the solution where the ions have mobility, are termed as electrolytes. They will move more preferentially constituting an electrical current in an electrical field. Similarly, when an ionic crystalline substance melts the ions have mobility and the molten salts are electrolytically conductive.

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Interatomic BondingThe covalent bond• The bonding is formed by sharing of electrons between adjacent atoms, rather

than electron transfer, and the stable arrangement of eight electrons in an outer shell is achieved. Covalent bond is the form of bonding in organic molecules which are composed principally of carbon and hydrogen.

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Interatomic BondingExamples 1. Formation of Cl2 molecules – individual chlorine atoms combine to form diatomic

molecules such as2Cl Cl2

– The bond is achieved by the sharing of a pair of electrons. One electron from each atom enters into joint orbit around both nuclei, so giving both nuclei an effective complement of eight outer shell electrons. This is symbolically represented as Cl: Cl or Cl – Cl

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Chlorine molecule Cl2-one pair of electrons shared

Interatomic Bonding2. Formation of O2 molecules

– Two pairs of electrons are shared between two adjacent atoms to give each atom a complement of eight outer shell electrons

O = O

3. Diamond– Where four valence electrons are shared between four neighbouring atoms.

Symbolic representation of covalent bond shown below

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Oxygen molecule O2- two pairs of electron shared

Structure of diamond

Interatomic BondingThe metallic bond• This type of bond results when each atom of the metal contributes its valence

electrons to the formation of an electron cloud, that spreads throughout the solid metal. A characteristic of metallic bond is that the conduction of electricity and heat are produced by the free movement of valence electrons, through the metals. All metal conductors show this type of bond. The resistance to the free movement of electron occurs if it collides with other electrons. This collision of electrons interferes with the flow of electrons and accounts for the resistivity in metals. Metallic crystals are malleable and have variable hardness and melting point.

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Interatomic BondingThe metallic bond

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The metallic state positive ions in an electron cloud

Interatomic BondingSecondary bonds• In additions to the types of primary bond discussed in the preceding sections,

there also exist weaker secondary bonds. These bonds are:1. Hydrogen bond2. Van der Waal’s bond

• The typical bond energies are of the order 0.2 eV for a hydrogen bond and between 0.002 and 0.1 eV for van der Waal’s bonds, as compared with 6.5 eV for the ionic bond in sodium chloride

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Interatomic BondingHydrogen bond• Water molecule is a polar with the two hydrogen atoms being positive relative to

the two non-bonding orbital of the oxygen atom. There is a quite a strong force of attractions between the hydrogen atoms and the negative ends of the adjacent molecules. As shown in the following figure, hydrogen bond can be written as:

H – O – H…..O

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Interatomic Bonding

• The hydrogen bond does not occur only in water and ice, but in a number of polymer materials. Examples of hydrogen bonding in polymers are – N – H….O bonds between polyamide (nylon) molecules and – O – H…O bonds in cellulose and polyvinyl alcohols.

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(a) Representation of a polar H2O molecule

(b) Attraction between neighbouring H2O molecules-the hydrogen bond

Interatomic BondingVan der Waal’s bonds• Many molecular compounds like methane are polarized to some extent and

electrostatic attractive forces exist between the molecular dipoles. These weak electrostatic attractive forces are termed Van der Waal’s bonds. This type of bonds can occur also between atoms. The monatomic inert gases, with full outer electron shells will condense into liquids and solids at extremely low temperatures. This indicates the existence of weak bonding forces. The atom becomes slightly polarized and may be weakly attracted to a similar polarized atom. The momentary uneven electron distribution in atoms giving weak dipoles and weak interatomic attraction is shown in figure:

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Lecture 3

Crystal Structure

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Crystal Structure Space lattice• In a crystal, the atoms are arranged in a periodic and regular geometric pattern in

space. The arrangement of an atom in a crystal can be described with respect to a three-dimensional set of straight lines, as shown below

35Space lattice with a unit cell

Crystal StructureUnit cell and lattice parameter• The unit cell can be regarded as the smallest grouping of atoms still showing the

symmetry of the type.• Shape and size of the unit cell is given by 6 lattice parameters a, b, c, , , and as

shown in the figure. Consider three axes OX, OY, OZ of lengths a, b, c respectively, inclines to one another at angles , and .

36Lattice parameters of a unit cell

Crystal StructureCrystal system • Depending upon the relation between the lattice parameters, the unit cell can be

divided in seven groups as shown in the table given below

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Crystal StructureBravais lattice• The seven different types of crystal systems can be further subdivided into 14

types, depending upon the basic arrangement of the atoms within a unit cell

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Crystal Structure• These 14 space lattices are known as Bravais lattices as

shown in the following table

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Crystal Structure

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Crystal Structure

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Crystal Structure

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Crystal Structure

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Crystal Structure

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Crystal Structure

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Crystal Structure

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Crystal StructureLocation of atom positions and identification of directions and planes in the unit cell•Location of points: Such as atom positions are located by constructing the right-hand coordinates systems. Distance is measured in terms of the number of lattice parameters in the direction of X, Y, Z coordinates to get from the origins to the point of interest as shown in the figure given below.

47Coordinates of selected points in the unit cell

Crystal StructureIdentification of direction • Certain directions in the unit cell are of particular importance. Metals deform more

easily, for an example, in directions along which atoms are in closest packed. Miller indices are use to identify any directions as shown in the figure given below.

48Crystallographic directions and coordinates

Crystal StructureIdentification of planes in the unit cell • Certain planes of atoms in crystal are of particular significance—metals deform

along the planes of atoms that are most tightly packed together. The surface energy of different faces of an crystal depends upon the particular crystallographic planes. Therefore, their properties vary according to the planes or directions along which they are measured.

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Crystal StructureIdentification of planes and directions in the unit cell • It is a desirable to have system of notations to designate different planes and

directions though the crystals. Such a system which designates a set of planes through the crystal is called Miller Indices. These indices are based on the intercepts of a plane with the three crystal axes, i.e., the three edges of the unit cell. The intercepts are measured in terms of the edge lengths or dimensions of the unit cells which are the unit distances from the origin along the three axes. If the plane is parallel to an axis, it intercepts the axis at infinity.

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Crystal Structure

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Designation of crystal planes using Miller Indices

Crystal StructureTo determine the Miller indices of a plane, the following steps are taken:1. Find the intercepts of the plane on the three axes in multiples or fractions of the

axial lengths along each axis2. Take the reciprocals of these numbers 3. Reduce the reciprocals to the three smallest integers in the same ratio as the

reciprocals4. Enclose in the parentheses, e.g., (hkl) • If a plane cuts any axis, e.g., the Y-axis, on the negative side on the origin, the

corresponding index will be negative and is indicated by placing a minus (-) sign in above the index

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l)k(h_

Crystal StructureMiller indices of directions • A direction within the space lattice is represented by line passing though the origin

and any other point P in the space. Then this line may be identified simply by stating the co-ordinates of the point P. The co-ordinates of the point P expressed in terms of the lattice parameters a, b, and c, and reduced to smallest integers, are the Miller indices of directions in question.

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Directions indices though the crystal

Crystal StructureThe distance between the two (hkl) planes • The distance is measured at right angle to them is known as interplaner spacing. It

is a function of plane indices, and crystal system involved, i.e., the lattice parameters, a, b, c, , , and . It is denoted by d(hkl)

• In a cubic crystal:

• The relationship gives the inter planner spacing as a function of the Miller indices and lattice parameters

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222)(lkh

ad hkl