Engineering Materials: Properties, Types, and Applications
Classification of Engineering Materials
Ferrous Materials
These are materials that contain iron as their primary constituent.
Examples: Cast iron, steel, wrought iron.
Characteristics: High strength, magnetic properties, prone to corrosion unless treated (e.g., stainless steel).
Non-Ferrous Materials
These materials do not contain iron as a major component.
Examples: Aluminum, copper, titanium, brass, bronze.
Characteristics: Lightweight, corrosion-resistant, good electrical conductivity.
Alloys
A mixture of two or more elements where at least one is a metal.
Ferrous Alloys
Stainless steel, high-speed steel.
Non-Ferrous Alloys
Brass (copper + zinc), bronze (copper + tin), duralumin (aluminum + copper + magnesium).
TTT Curve
Definition: A time-temperature-transformation diagram that shows the transformation of austenite into other microconstituents at different cooling rates.
Importance: Helps predict the microstructure and properties of steel after heat treatment.
Effect of Alloying Elements on Steel
- Chromium (Cr): Improves corrosion resistance, hardenability.
- Manganese (Mn): Improves toughness, wear resistance, and hardness.
- Nickel (Ni): Enhances toughness, corrosion resistance.
- Vanadium (V): Increases strength, wear resistance.
- Molybdenum (Mo): Enhances high-temperature strength, corrosion resistance.
Properties of Engineering Materials
Thermal Properties
Heat capacity, thermal conductivity, thermal expansion, melting point.
Importance in applications like heat exchangers and thermal insulation.
Chemical Properties
Corrosion resistance, oxidation, chemical stability.
Relevant in harsh environments, chemical processing industries.
Electrical Properties
Conductivity, resistivity, dielectric strength.
Used in electrical wires, capacitors, semiconductors.
Magnetic Properties
Permeability, retentivity, coercivity.
Mechanical Properties
Strength, hardness, ductility, toughness, fatigue, creep.
Material Reliability and Safety
Reliability: The ability of a material to perform its intended function consistently over time without failure.
Safety: Ensures that the material does not fail catastrophically under specified conditions.
Babbitt Metals
White metal alloys typically containing tin, antimony, and copper.
Characterized by low melting points and excellent anti-friction properties.
Used as bearing materials to reduce wear and tear in machinery.
Solders
Alloys, usually of tin and lead, used to join metals.
Special Types of Materials
Ceramics
Inorganic, non-metallic materials with high hardness, thermal resistance, and brittleness.
Applications: Refractory materials, cutting tools, biomedical implants.
Composites
A combination of two or more materials with distinct properties.
Examples: Carbon fiber-reinforced polymer, glass fiber composites.
Applications: Aerospace, automotive, sports equipment.
Polymers
Organic materials with high flexibility and low density.
Examples: Polyethylene, PVC, nylon.
Applications: Packaging, insulation, consumer goods.
Nano Materials
Materials with particle sizes at the nanometer scale, exhibiting unique physical and chemical properties.
Applications: Electronics, medical devices, coatings.
Smart Materials
Materials that respond to external stimuli.
Shape Memory Alloys (SMA)
Alloys that return to their original shape upon heating after deformation.
Examples: Nitinol (Nickel-Titanium).
Applications: Medical devices, aerospace, robotics.
Electro-Rheological (ER) Fluids
Fluids whose viscosity changes with the application of an electric field.
Applications: Clutches, dampers, brakes.
Sources of Iron Ore and Its Availability
Major Types of Iron Ores
- Hematite (Fe₂O₃): High-grade ore with ~70% iron.
- Magnetite (Fe₃O₄): Contains ~72% iron and magnetic properties.
- Limonite (Fe₂O₃·nH₂O): Hydrated iron oxide, contains 40-60% iron.
- Siderite (FeCO₃): Contains ~48% iron.
Major Sources
- India: Odisha, Jharkhand, Chhattisgarh, Karnataka, Goa.
- Australia: Pilbara
Crystal Imperfections
Point Defects
- Vacancies: Missing atoms in the lattice.
- Interstitials: Extra atoms positioned between lattice points.
- Substitutional Atoms: Foreign atoms replace host atoms in the lattice.
Effect: Alter density, thermal and electrical conductivity, and strength.
Line Defects (Dislocations)
- Edge Dislocation: An extra half-plane of atoms in the lattice.
- Screw Dislocation: A helical distortion in the lattice.
Effect: Reduce strength and cause plastic deformation.
Surface Defects
Grain boundaries, phase boundaries, and stacking faults.
Effect: Affect corrosion resistance, toughness, and strength.
Volume Defects
Larger voids, cracks, and inclusions.
Effect: Act as stress concentrators, reducing material strength.
Types of Iron and Steel
Pig Iron
Composition: 3-4% carbon, impurities like Si, S, P, and Mn.
Properties: Brittle, low tensile strength.
Applications: Raw material for steelmaking and casting.
Wrought Iron
Composition: Pure iron with <0.1% carbon.
Properties: Ductile, malleable, corrosion-resistant.
Applications: Decorative gates, chains, agricultural tools.
Cast Iron
Composition: 2-4% carbon, Si, Mn, and trace impurities.
Properties: High compressive strength, brittle, wear-resistant.
Applications: Engine blocks, pipes, machine bases.
Steel
Composition: Iron-carbon alloy with controlled impurities and alloying elements.
Applications: Widely used across industries, from construction to automotive.
Special Cutting Tool Materials
High-Speed Steel (HSS)
Properties: Retains hardness at high temperatures.
Applications: Cutting tools, drills, taps.
Diamond
Properties: Hardest known material, excellent wear resistance.
Applications: Precision cutting, grinding tools.
Stellites
Composition: Cobalt-based alloys with Cr, W, and Mo.
Properties: Wear and corrosion-resistant.
Applications: Cutting tools, valve seats.
Furnaces Used for Iron and Steel Making
Blast Furnace
Definition: A large, cylindrical furnace used to produce pig iron from iron ore, coke, and limestone.
Purpose: Extracts iron from iron ore by a chemical reduction process.
Induction Furnace
Definition: A furnace that uses electromagnetic induction to heat electrically conductive materials.
Purpose: Melting and refining metals, particularly for high-quality steels.
LD (Linz-Donawitz) Furnace
Definition: A type of basic oxygen furnace (BOF) used to convert molten pig iron into steel.
Purpose: Rapidly refines pig iron by blowing pure oxygen through the molten metal.
Electric Arc Furnace (EAF)
Definition: A furnace that uses an electric arc to generate intense heat for melting scrap metal.
Purpose: Recycling scrap metal into steel, producing specialty steels.
Cupola Furnace
Definition: A vertical cylindrical furnace used to melt iron for casting.
Selection Criteria for Engineering Materials in Industries
- Application-specific requirements: Mechanical, thermal, electrical, or magnetic properties.
- Cost-effectiveness: Includes material cost, manufacturing cost, and lifecycle cost.
- Availability: Easy procurement and supply chain considerations.
- Environmental impact: Recyclability, energy consumption in production, and sustainability.
Metal Structure and Its Relation to Properties
Metal Structure: Metals have a crystalline structure with atoms arranged in a regular, repeating pattern. The arrangement of atoms affects their mechanical, electrical, thermal, and magnetic properties.
Relation to Properties
- Strength: Depends on the crystal structure and bonding between atoms.
- Ductility: Atoms’ ability to slide past each other determines malleability and ductility.
- Conductivity: Closely packed atoms and free electrons make metals good conductors of heat and electricity.
Arrangement of Atoms in Metals
Metals are characterized by a metallic bond, where free electrons move through a lattice of positively charged ions.
Common Atomic Arrangements (Lattices)
- Body-Centered Cubic (BCC): Less densely packed; higher strength but lower ductility (e.g., iron at room temperature).
- Face-Centered Cubic (FCC): Densely packed; high ductility and toughness (e.g., aluminum, copper).
- Hexagonal Close-Packed (HCP): Densely packed but limited slip systems; low ductility (e.g., magnesium, zinc).
Electroplating
Depositing a thin layer of metal (e.g., chromium, nickel, zinc) onto the surface of a substrate using an electrochemical process.
Improves corrosion resistance, wear resistance, and aesthetics.
Galvanizing
Applying a zinc coating to steel by dipping it in molten zinc.
Deformation of Metals
Deformation: The process of changing the shape or size of a metal under applied stress.
Slip
The sliding of one plane of atoms over another.
- Primary mechanism for plastic deformation.
- More prominent in FCC metals due to multiple slip systems.
Twinning
Atoms shift in a mirrored fashion across a plane.
- Common in HCP metals with limited slip systems.
Effect of Deformation
- Increases dislocation density.
- Enhances strength (work hardening) but reduces ductility.
Classification of Steel and Alloy Steel
Based on Carbon Content
Low Carbon Steel (Mild Steel)
Carbon Content: <0.25%.
Properties: Ductile, weldable, low strength.
Applications: Structural components, pipelines, car bodies.
Medium Carbon Steel
Carbon Content: 0.25-0.60%.
Properties: Balanced strength and ductility.
Applications: Gears, shafts, railway tracks.
High Carbon Steel
Carbon Content: 0.60-1.25%.
Properties: Hard, wear-resistant, brittle.
Applications: Cutting tools, springs, dies.
Alloy Steel
Low Alloy Steel
Alloy Content: <8%.
Applications: Bridges, pressure vessels, pipelines.
Corrosion
Corrosion: The deterioration of materials, typically metals, through chemical reactions with their environment.
Factors Influencing Corrosion
Material Properties
- Composition: Pure metals are generally more susceptible than alloys.
- Microstructure: Grain boundaries, inclusions, and other microstructural features can act as sites for localized corrosion.
- Passivity: Some metals form protective oxide layers (passivity) that hinder further corrosion.
Physical Conditions
- Temperature: Higher temperatures generally increase corrosion rates.
- Humidity: Moisture is essential for most corrosion reactions.
- pH: Acidic and alkaline environments can accelerate corrosion.
- Presence of Corrosive Agents: Saltwater, acids, bases, and oxidizing agents promote corrosion.
- Stress: Stresses can concentrate corrosion at specific points.
Corrosion Control Methods
Material Selection
- Use corrosion-resistant materials: Stainless steel, aluminum alloys, titanium, and certain plastics offer good corrosion resistance.
Impact of Hot and Cold Working on Metal Structure
Hot Working
- Grains deform but recrystallize, resulting in uniform grain size.
- Reduces residual stresses.
Cold Working
- Grains become elongated in the direction of working.
- Increased residual stresses and dislocations.
Effect of Deformation on Material Properties
Cold Working (Below Recrystallization Temperature)
- Effects:
- Increases hardness and strength (strain hardening).
- Reduces ductility and toughness.
- Applications: Rolling, drawing, bending.
- Impact on Structure: Increases dislocation density, creating a more strained lattice.
Hot Working (Above Recrystallization Temperature)
- Effects:
- Enhances ductility and toughness.
- Reduces strength due to dynamic recovery.
- Applications: Forging, extrusion, rolling.
- Impact on Structure: Recrystallization removes dislocations, forming new grains.
Crystalline Structure of Metals
Definition: A crystalline structure is an orderly and repetitive arrangement of atoms in a metal.
Classification of Crystals
- Single Crystals: Entire material has a continuous and unbroken lattice.
- Polycrystalline: Composed of many small crystals (grains) with grain boundaries.
- Amorphous: Lack long-range order (not common in metals).
Ideal Crystal
A perfect lattice with no defects.
Crystal Imperfections
Deviation from the ideal arrangement of atoms.