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Basics of Materials Science & Engineering – Complete Study Notes

IES / ESE GATE PSU

Complete Study Notes for IES ESE Paper I

Ch 1 · Crystal Structure Ch 2 · Mechanical Properties Ch 3 · Metals & Alloys Ch 4 · Ceramics & Polymers Ch 5 · Composites Ch 6 · Failure & Testing Quick Revision

1Crystal Structure and Atomic Bonding►

The properties of engineering materials are determined by their atomic structure and bonding. Understanding crystal geometry explains why metals are ductile, ceramics brittle, and polymers flexible.

Atomic Bonding Types

Bond Type	Nature	Strength	Example
Ionic	Electron transfer; cation + anion attraction	Strong	NaCl, MgO, Al₂O₃
Covalent	Electron sharing; directional	Very strong	Diamond (C), Si, SiC
Metallic	Sea of free electrons; non-directional	Moderate–strong	Fe, Cu, Al
Van der Waals	Weak dipole attractions; secondary bond	Weak	Polymers, noble gases
Hydrogen	H between electronegative atoms	Moderate	Water, nylon, DNA

Crystal Structures — Unit Cells

Structure	APF	Atoms/cell	CN	Examples
Simple Cubic (SC)	0.52	1	6	Po (only metal)
Body-Centred Cubic (BCC)	0.68	2	8	Fe(α), Cr, W, Mo, V
Face-Centred Cubic (FCC)	0.74	4	12	Fe(γ), Cu, Al, Ni, Au, Ag
Hexagonal Close-Packed (HCP)	0.74	6	12	Zn, Mg, Ti, Co

APF = Atomic Packing Factor; CN = Coordination Number

APF = (Number of atoms per unit cell × Volume of one atom) / Volume of unit cell

Miller Indices

Used to identify crystallographic planes and directions
Procedure for plane: Intercepts on axes → reciprocals → clear fractions → (hkl)
Plane (100): intercepts at 1,∞,∞ → reciprocals 1,0,0
Plane (110): intercepts at 1,1,∞ → reciprocals 1,1,0
Family of planes: {hkl}; family of directions: ⟨uvw⟩

Crystal Defects

Defect Type	Examples	Effect on Properties
Point defects	Vacancy, interstitial, substitutional, Frenkel, Schottky	Affect diffusion, electrical, mechanical
Line defects (dislocations)	Edge dislocation, screw dislocation	Control plastic deformation, yield strength
Planar defects	Grain boundaries, twin boundaries, stacking faults	Affect strength, corrosion, diffusion
Volume defects	Voids, inclusions, precipitates	Affect toughness, fatigue

ESE Tip: FCC metals (Cu, Al) are more ductile; BCC metals (Fe at room temp) are stronger but less ductile. APF of FCC and HCP = 0.74 (highest packing). Iron changes BCC→FCC at 912°C (allotropic transformation).

2Mechanical Properties of Materials►

Mechanical properties determine how materials respond to applied loads. Selection of materials for engineering applications requires thorough knowledge of stress-strain behaviour, hardness, toughness, and fatigue.

Stress-Strain Curve (Mild Steel)

Elastic region: Linear; Hooke's law holds (σ = Eε); fully reversible
Proportional limit: Last point obeying Hooke's law
Elastic limit: Last point of fully elastic behaviour
Upper yield point: Sudden drop in stress before plastic flow
Lower yield point: Stable plastic flow begins
Ultimate Tensile Strength (UTS): Maximum engineering stress
Fracture point: Material breaks
% Elongation and % Reduction in area measure ductility

σ = F/A₀ (Engineering stress) | ε = ΔL/L₀ (Engineering strain) | E = σ/ε (Young's modulus)

Elastic Constants Relationships

E = 2G(1+ν) = 3K(1−2ν) | where E = Young's, G = Shear, K = Bulk, ν = Poisson's ratio

Poisson's ratio ν = –(lateral strain)/(axial strain); typically 0.25–0.35 for metals
Steel: E ≈ 200 GPa, G ≈ 80 GPa, ν ≈ 0.3
Aluminium: E ≈ 70 GPa, ν ≈ 0.33
Concrete: E ≈ 25–35 GPa (compression only, brittle)

Hardness Tests

Test	Indenter	Load	Scale	Application
Brinell (BHN)	10 mm steel ball	3000 kg (steel)	BHN	Soft–medium materials; UTS ≈ 3.4 × BHN (MPa)
Vickers (VHN)	Diamond pyramid 136°	1–120 kgf	VHN (HV)	All materials; wide range
Rockwell	Diamond cone / ball	Minor + major load	HRC, HRB	Fast; production testing
Shore (Scleroscope)	Rebound height	—	Shore hardness	Finished parts; non-destructive

Toughness and Impact Testing

Toughness: Energy absorbed per unit volume before fracture = area under stress-strain curve
Charpy test: Notched specimen; horizontal; hammer impact; specimen supported at both ends
Izod test: Notched specimen; vertical cantilever; hammer impact
Impact energy decreases at lower temperature — ductile-to-brittle transition temperature (DBTT)
BCC metals (steels) show DBTT; FCC metals (Al, Cu) do not — no brittle fracture at low T

Fatigue

Failure under cyclic loading at stresses below static fracture stress
Endurance limit (S_e): Stress amplitude below which infinite life; ~0.5 UTS for steels
S-N curve: log(stress amplitude) vs. log(cycles to failure)
Crack initiates at surface defects, notches, or inclusions
Improvement: surface finishing, shot peening, case hardening

Creep

Time-dependent plastic deformation under constant load at elevated temperature
Significant above ~0.3–0.4 × melting point (in Kelvin) = homologous temperature
Three stages: primary (decreasing creep rate), secondary/steady-state, tertiary (accelerating, fracture)
Applications: turbine blades, boiler components, nuclear reactor parts

ESE Tip: BHN–UTS relation: UTS (MPa) ≈ 3.4 × BHN. Endurance limit ≈ 0.5 UTS for steel. Charpy test uses simply-supported beam; Izod uses cantilever. FCC metals have no DBTT.

3Metals, Alloys and Phase Diagrams►

Metals and alloys form the backbone of structural engineering. Phase diagrams map the stable phases as a function of composition and temperature — essential for understanding heat treatment and alloy design.

Iron-Carbon Phase Diagram — Key Points

Point/Line	Temperature	Carbon %	Significance
Eutectic point	1148°C	4.3% C	L → Austenite + Cementite (Ledeburite)
Eutectoid point	727°C	0.8% C	Austenite → Pearlite (α-ferrite + Fe₃C)
Peritectic point	1493°C	0.16% C	δ-Fe + L → Austenite
A1 line (PSK)	727°C	—	Lower critical temperature
A3 line (GS)	910°C (at 0% C)	—	Upper critical temperature (hypoeutectoid)
Acm line (SE)	—	—	Upper critical temperature (hypereutectoid)

Steel Microstructures

Microstructure	Formation	Properties
Austenite (γ-Fe)	FCC; above A1; up to 2.14% C solubility	Non-magnetic, tough
Ferrite (α-Fe)	BCC; <0.022% C; room temp	Soft, ductile, magnetic
Cementite (Fe₃C)	6.67% C; iron carbide	Hard, brittle
Pearlite	Eutectoid: α-Fe + Fe₃C lamellae	Medium strength, medium ductility
Bainite	Intermediate quench; finer than pearlite	Good combination of strength+toughness
Martensite	Rapid quench; distorted BCT; trapped C	Hardest, most brittle; tempered for use

Heat Treatment of Steel

Process	Cooling	Purpose
Annealing	Furnace cool (very slow)	Soften; relieve stress; improve machinability
Normalising	Air cool	Refine grain; uniform microstructure
Hardening (Quenching)	Water/oil quench (rapid)	Form martensite; increase hardness
Tempering	Reheat 150–650°C after quench	Reduce brittleness of martensite; improve toughness
Case hardening	Surface treatment	Hard surface + tough core (carburising, nitriding)

Non-Ferrous Alloys

Alloy	Composition	Key Properties	Applications
Brass	Cu + Zn (10–40%)	Good machinability, corrosion resistance	Fittings, valves, musical instruments
Bronze	Cu + Sn (3–20%)	High strength, wear resistance	Bearings, gears, coins
Duralumin	Al + Cu(4%) + Mg + Mn	Age-hardenable; high strength/weight	Aircraft structures
Stainless steel	Fe + Cr(≥10.5%) + Ni	Corrosion-resistant (Cr₂O₃ passive layer)	Food equipment, surgical, chemical
Ti alloys	Ti + Al + V	High strength/weight; biocompatible	Aerospace, biomedical implants

ESE Tip: Eutectoid point = 0.8% C, 727°C → forms Pearlite. Eutectic = 4.3% C, 1148°C → forms Ledeburite. Martensite is hardest, forms by rapid quenching. Stainless steel needs ≥10.5% Cr for corrosion resistance.

4Ceramics and Polymers►

Ceramics and polymers are non-metallic materials with distinctive structure-property relationships. Together with metals, they form the three major classes of engineering materials.

Ceramics

Inorganic, non-metallic materials — ionic/covalent bonding
Properties: High hardness, high melting point, brittle (no dislocation motion), low thermal/electrical conductivity (except SiC/Si₃N₄), chemical inertness, good compressive strength
Failure mode: Fracture due to stress concentrations at pores/cracks; no yielding

Types of Ceramics

Type	Examples	Applications
Oxide ceramics	Al₂O₃, ZrO₂, MgO	Cutting tools, refractories, dental implants
Non-oxide ceramics	SiC, Si₃N₄, TiN, BN	Hard coatings, turbine blades, cutting tools
Glass	SiO₂-based	Windows, optical fibres, laboratory equipment
Glass-ceramics	Pyroceram, Macor	Cookware, telescope mirrors, dental
Cement/Concrete	Portland cement + aggregate	Construction; high compressive, low tensile
Piezoelectric ceramics	PZT (PbZrTiO₃), BaTiO₃	Sensors, transducers, actuators

Polymers

Long chain macromolecules of repeating monomer units; mainly C-H backbone
Degree of polymerisation (n): Number of repeat units in chain
Properties determined by chain length, branching, cross-linking, and crystallinity

Polymer Classification

Type	Structure	Behaviour	Examples
Thermoplastics	Linear/branched; van der Waals bonds between chains	Soften on heating; recyclable	PE, PP, PVC, nylon, PTFE (Teflon)
Thermosets	Cross-linked network; covalent bonds	Cannot re-melt; permanent shape	Epoxy, phenolic, polyester, silicone
Elastomers	Loosely cross-linked; high extensibility	Large reversible deformation (>200%)	Natural rubber (NR), SBR, neoprene, silicone rubber

Glass Transition Temperature (Tg)

Temperature below which polymer behaves as glassy solid; above which rubbery/viscous
Below Tg: stiff, brittle; above Tg: flexible (amorphous polymers)
Crystalline polymers melt at Tm > Tg; amorphous polymers only show Tg

Important Polymers

Polymer	Abbreviation	Key Property
Polyethylene	PE (HDPE/LDPE)	Chemical resistance; pipes, packaging
Polyvinyl chloride	PVC	Rigid or flexible; pipes, wire insulation
Polypropylene	PP	Lightweight; high chemical resistance
PTFE (Teflon)	PTFE	Lowest friction coefficient; non-stick coatings
Nylon (Polyamide)	PA	Strong, tough; gears, bearings, textiles
Epoxy	EP	Excellent adhesion; composites matrix

ESE Tip: Thermosets cannot be remelted (cross-linked); thermoplastics can. PTFE has lowest friction coefficient (~0.04). PZT = lead zirconate titanate — piezoelectric ceramic used in sensors and sonar.

5Composite Materials►

Composites combine two or more distinct materials to achieve properties superior to any single constituent. They are increasingly used in aerospace, automotive, civil, and sports engineering.

Composite Classification

Classification Basis	Type	Example
Matrix material	Polymer Matrix Composite (PMC)	CFRP, GFRP
	Metal Matrix Composite (MMC)	Al/SiC
	Ceramic Matrix Composite (CMC)	SiC/SiC
Reinforcement type	Particle-reinforced	Concrete, cermets
	Fibre-reinforced	CFRP, GFRP, Kevlar
	Structural (laminates, sandwich)	Plywood, honeycomb panels

Rule of Mixtures

Longitudinal (isostrain): E_c = V_f × E_f + V_m × E_m

Transverse (isostress): 1/E_c = V_f/E_f + V_m/E_m

V_f = fibre volume fraction; V_m = matrix volume fraction; V_f + V_m = 1
Longitudinal modulus is fibre-dominated (fibre alignment with load)
Transverse modulus is matrix-dominated

Common Reinforcing Fibres

Fibre	Tensile Strength (GPa)	Density (g/cm³)	Application
E-glass (GFRP)	3.5	2.54	Boat hulls, wind turbine blades, pipes
Carbon (CFRP)	3.5–7	1.75–2.0	Aerospace, racing cars, sports equipment
Aramid (Kevlar)	3.6	1.44	Bulletproof vests, helmets, ropes
Boron fibre	3.4	2.36	Military aircraft, sports equipment
Basalt fibre	3.0	2.7	Construction reinforcement, insulation

Advantages of Composites

High specific strength (strength/density) and specific stiffness
Design flexibility — anisotropic properties can be tailored
Good fatigue and corrosion resistance (PMC)
Near-net-shape manufacturing possible

Limitations of Composites

High cost of fibres and manufacturing
Difficult to inspect for internal delamination (NDT required)
Brittle failure modes; limited recyclability of thermoset composites
Anisotropy can be a disadvantage if load direction is uncertain

ESE Tip: Carbon fibre has best specific stiffness; Kevlar has best toughness/weight. Rule of mixtures — longitudinal = isostrain (parallel springs); transverse = isostress (series springs). CFRP specific strength exceeds steel.

6Failure Analysis and Non-Destructive Testing►

Understanding how and why materials fail is essential for safe engineering design. Non-destructive testing (NDT) allows inspection without damaging the component — critical for quality control and maintenance.

Modes of Fracture

Mode	Mechanism	Fracture Surface	Materials
Ductile fracture	Plastic deformation; void nucleation and coalescence	Fibrous, dimpled, cup-and-cone	Metals above DBTT
Brittle fracture	Rapid crack propagation; little plastic deformation	Flat, granular, often with chevron marks	Ceramics, metals below DBTT, glass
Fatigue fracture	Cyclic loading; crack initiates at surface; beach marks	Beach marks + final rough zone	All materials under cyclic load
Creep fracture	High temperature + sustained stress	Intergranular; neck formation	Metals at T > 0.3Tm

Fracture Mechanics

K_I = σ √(πa) × Y | Critical: K_I = K_IC (plane strain fracture toughness)

K_I = stress intensity factor; σ = applied stress; a = crack half-length; Y = geometry factor
Fracture occurs when K_I ≥ K_IC
High K_IC = high fracture toughness = tolerates larger cracks before fracture
Metals: K_IC high; Ceramics: K_IC very low (0.7–5 MPa√m); CFRP: intermediate

Non-Destructive Testing (NDT) Methods

Method	Principle	Detects	Limitations
Visual Inspection (VT)	Direct/aided visual examination	Surface cracks, corrosion, deformation	Surface only; skill dependent
Liquid Penetrant Testing (PT)	Coloured/fluorescent dye drawn into cracks by capillary action	Surface-open cracks	Surface only; clean surface needed
Magnetic Particle Testing (MT)	Magnetic field + iron particles reveal flux leakage at defects	Surface/near-surface cracks in ferromagnetic materials	Ferromagnetic materials only
Ultrasonic Testing (UT)	High-frequency sound waves; reflections indicate discontinuities	Internal defects, thickness measurement	Couplant needed; operator skill required
Radiographic Testing (RT)	X-rays/gamma rays; denser areas absorb more	Internal voids, inclusions, cracks	Radiation safety; 2D image of 3D flaw
Eddy Current Testing (ET)	Induced eddy currents disturbed by defects	Surface/near-surface defects in conductors	Conductive materials only
Acoustic Emission (AE)	Stress waves from crack growth detected	Active crack growth; overall structural monitoring	Background noise; source location complex

Corrosion Types and Prevention

Corrosion Type	Mechanism	Prevention
Uniform / general	Even metal loss over surface	Coatings, inhibitors, cathodic protection
Galvanic	Two dissimilar metals in electrolyte; anodic metal corrodes	Use same/similar metals; insulate; sacrificial anode
Pitting	Localised attack forming pits; autocatalytic	Higher alloy content; avoid stagnant conditions
Crevice	Differential oxygen concentration in gaps/crevices	Design to avoid crevices; seal gaps
Stress corrosion cracking (SCC)	Combined stress + corrosive environment	Remove stress (anneal), use resistant alloy, change environment
Intergranular	Grain boundary attack (sensitisation in SS)	Low-carbon SS; solution anneal

ESE Tip: Galvanic series — Mg, Zn, Al, Fe, Ni, Cu, Ag, Au (active → noble). More active metal = anode (corrodes). Sacrificial anode protection uses Zn or Mg for steel structures. NDT: UT = internal; PT = surface cracks; MT = ferromagnetic only.

★Key Facts & Exam Essentials►

Topic	Key Fact
FCC atoms/cell	4; APF = 0.74; CN = 12; Examples: Cu, Al, Fe(γ), Ni
BCC atoms/cell	2; APF = 0.68; CN = 8; Examples: Fe(α), Cr, W, Mo
HCP APF	0.74 (same as FCC); Zn, Mg, Ti
Eutectoid point	0.8% C, 727°C → Pearlite (α-Fe + Fe₃C)
Eutectic point	4.3% C, 1148°C → Ledeburite
Martensite	Hardest steel microstructure; formed by rapid quench; BCT
Steel E modulus	~200 GPa
BHN–UTS	UTS (MPa) ≈ 3.4 × BHN
Endurance limit	~0.5 UTS for steels
Charpy test	Simply supported; horizontal specimen; impact energy measurement
Izod test	Cantilever; vertical specimen
DBTT	BCC metals only; FCC metals have no brittle-to-ductile transition
Creep threshold	T > 0.3–0.4 Tm (homologous temperature)
PTFE friction coeff	~0.04 — lowest of any solid
Stainless steel	≥10.5% Cr; passive Cr₂O₃ layer
Rule of mixtures (longitudinal)	E_c = V_f×E_f + V_m×E_m (isostrain)
Kevlar property	Best toughness/weight ratio; bulletproof vests
NDT: internal flaws	Ultrasonic Testing (UT) and Radiographic Testing (RT)
NDT: surface only	Liquid Penetrant (PT) and Visual (VT)
Galvanic series	Mg → Zn → Al → Fe → Ni → Cu → Ag → Au (active → noble)
SCC	Stress Corrosion Cracking — requires both stress AND corrosive environment

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Basics of Materials Science & Engineering – Complete Study Notes

Atomic Bonding Types

Crystal Structures — Unit Cells

Miller Indices

Crystal Defects

Stress-Strain Curve (Mild Steel)

Elastic Constants Relationships

Hardness Tests

Toughness and Impact Testing

Fatigue

Creep

Iron-Carbon Phase Diagram — Key Points

Steel Microstructures

Heat Treatment of Steel

Non-Ferrous Alloys

Ceramics

Types of Ceramics

Polymers

Polymer Classification

Glass Transition Temperature (Tg)

Important Polymers

Composite Classification

Rule of Mixtures

Common Reinforcing Fibres

Advantages of Composites

Limitations of Composites

Modes of Fracture

Fracture Mechanics

Non-Destructive Testing (NDT) Methods

Corrosion Types and Prevention