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MATERIAL SCIENCE (NOE047)
SECTION – A
(Attempt All | 10 × 2 = 20 Marks)
(a) Miller Indices
Miller indices are a set of three integers (h k l) used to describe the orientation of crystal planes in a crystal lattice.
(b) Composite Material
A composite material is made by combining two or more materials with different properties to obtain improved performance.
Examples: Fiberglass, Reinforced concrete.
(c) Eutectic and Eutectoid Reactions
Eutectic reaction:
Liquid → Solid α + Solid β
Eutectoid reaction:
Solid γ → Solid α + Solid β
(d) Packing Efficiency
Packing efficiency is the fraction of volume occupied by atoms in a unit cell.
Packing efficiency=Volume of atoms in unit cellTotal volume of unit cell\text{Packing efficiency}=\frac{\text{Volume of atoms in unit cell}}{\text{Total volume of unit cell}}Packing efficiency=Total volume of unit cellVolume of atoms in unit cell
(e) Gibbs Phase Rule
Gibbs phase rule relates phases, components, and degrees of freedom:
F=C−P+2F = C - P + 2F=C−P+2
where F = degrees of freedom, C = components, P = phases.
(f) Hardness vs Toughness
Hardness: Resistance to indentation or scratching
Toughness: Ability to absorb energy before fracture
(g) Refractory Material
Refractory materials can withstand very high temperatures without melting or deformation.
Example: Fire clay
Property: High melting point
Application: Furnace linings
(h) Ferrous vs Non-Ferrous Materials
Ferrous: Contain iron (e.g., steel)
Non-ferrous: Do not contain iron (e.g., aluminium)
(i) Meissner Effect
The Meissner effect is the expulsion of magnetic field lines from a material when it becomes superconducting below its critical temperature.
(j) Classification of Solids (Energy Gap Basis)
Conductors
Semiconductors
Insulators
Semiconductors: Have small energy gap and moderate conductivity (e.g., silicon).
SECTION – B
(Attempt Any Five | 5 × 10 = 50 Marks)
(a) Stress–Strain Diagram & Hardenability
The stress–strain curve of mild steel shows:
Proportional limit Elastic limit
Yield point Ultimate tensile strength
Fracture point
Hardenability: Ability of steel to harden in depth during heat treatment.
Factors affecting hardenability: Carbon content, alloying elements, grain size.
(b) Steel Making & Furnaces
Steel making: Conversion of pig iron into steel by removing impurities.
Furnaces:
Wrought iron: Puddling furnace
Cast iron: Blast furnace
(c) Magnetic Hysteresis
Magnetic hysteresis is the lagging of magnetization behind the applied magnetic field.
Retentivity: Ability to retain magnetism
Coercive force: Reverse field required to demagnetize material
Explained using B–H curve.
(d) Corrosion & Injection Moulding
Corrosion: Deterioration of metal due to chemical or electrochemical reaction.
Control: Coating, cathodic protection, alloying.
Injection moulding: Molten plastic is injected into a mould cavity and cooled to form products.
(e) TTT Diagram
TTT diagram is obtained by isothermal heat treatment experiments.
Importance:
Shows transformation kinetics
More practical than Fe–C equilibrium diagram
Helps in selecting heat treatment processes
(f) Short Notes (Any Three)
(i) Semiconductors: Moderate conductivity, temperature-dependent behavior
(ii) Thermistors: Temperature-sensitive resistors
(iii) Meissner Effect: Magnetic field exclusion in superconductors
(iv) High-Temperature Superconductors: Superconduct above 77 K
(g) Thermoplastics vs Thermosetting Plastics
Thermoplastics: Re-mouldable, soft on heating (PVC)
Thermosetting: Hard, cannot be remoulded (Bakelite)
(h) NDT (Non-Destructive Testing)
NDT tests materials without damaging them.
Types:
Ultrasonic testing
Radiography
Magnetic particle test
Ultrasonic testing: Uses high-frequency sound waves to detect internal flaws.
SECTION – C
(Attempt Any Two | 2 × 15 = 30 Marks)
3) Griffith’s Criterion for Crack Propagation
Griffith proposed that crack propagation occurs when strain energy released ≥ surface energy required.
σc=2Eγπa\sigma_c = \sqrt{\frac{2E\gamma}{\pi a}}σc=πa2Eγ
where
σc = critical stress
E = Young’s modulus
γ = surface energy
a = crack length
This is necessary but not sufficient alone, as real materials have plastic deformation.
4) Superconductivity & Diffusion
Superconductivity:
Property of zero electrical resistance below critical temperature.
Diffusion: Movement of atoms due to concentration gradient.
Why Ni diffuses slower than C in Fe:
Nickel atoms are larger and substitute Fe atoms, while carbon occupies interstitial sites.
Self diffusion: Same atoms
Inter diffusion: Different atoms
5) Short Notes (Any Three)
(i) Gun Metal
Copper–tin–zinc alloy used in bearings and valves.
(ii) Duralumin
Aluminium alloy with Cu, Mg, Mn; used in aircraft structures.
(iii) Babbitt Metal
Soft bearing alloy used for journal bearings.
(iv) Heat Resisting Steel
Alloy steels resistant to oxidation at high temperature.
(v) Cyaniding
Surface hardening process using carbon and nitrogen.