Understanding Engineering Materials
Classification of Engineering Materials
Metals
- Ferrous (e.g., steel, cast iron)
- Non-ferrous (e.g., aluminum, copper)
Ceramics
- Oxides, nitrides, carbides (e.g., alumina, silicon carbide)
Polymers
- Thermoplastics (e.g., polyethylene)
- Thermosets (e.g., epoxy)
Composites
- Fiber-reinforced materials (e.g., fiberglass, carbon fiber)
Semiconductors
- Silicon, germanium, used in electronics
Smart Materials
- Shape memory alloys, piezoelectric materials
Thermal, Electrical, and Mechanical Properties
Thermal Properties
- Thermal conductivity
- Thermal expansion
- Specific heat
Electrical Properties
- Electrical conductivity
- Resistivity
- Dielectric strength
Mechanical Properties
- Strength (tensile, compressive)
- Hardness
- Ductility
- Toughness
- Fatigue resistance
Smart Materials
Definition
Materials that respond to external stimuli (temperature, pressure, electric field) with a significant change in properties.
Types
Shape Memory Alloys (SMA)
Return to original shape when heated (e.g., Nitinol).
Piezoelectric Materials
Generate electricity under mechanical stress (e.g., Quartz).
Magnetostrictive Materials
Change shape in the presence of a magnetic field (e.g., Terfenol-D).
Electroactive Polymers (EAPs)
Change shape in response to an electric field.
Types of Metal Structures
- Body-Centered Cubic (BCC): Strong but less ductile (e.g., iron at room temperature).
- Face-Centered Cubic (FCC): More ductile (e.g., aluminum, copper).
- Hexagonal Close-Packed (HCP): Less ductile, high strength (e.g., titanium, magnesium).
Types of Crystal Defects
- Point Defects: Vacancies, interstitials, substitutional atoms.
- Line Defects: Dislocations (edge, screw).
- Surface Defects: Grain boundaries, phase boundaries.
- Volume Defects: Voids, precipitates.
Hot-working vs Cold-working
- Hot-working: Performed above recrystallization temperature, less hardening, better ductility, used for large deformation.
- Cold-working: Performed below recrystallization temperature, increases strength through strain hardening, less ductile.
Types of Cast Iron and Steel
- Cast Iron:
- Gray Cast Iron: High carbon content, good machinability.
- White Cast Iron: Hard and brittle, used in wear-resistant applications.
- Ductile Iron: Nodular graphite, high ductility.
- Steel:
- Carbon Steel: Low, medium, and high carbon content, used in construction and machinery.
- Alloy Steel: Contains alloying elements (e.g., chromium, vanadium) to improve properties like hardness and corrosion resistance.
Types of Alloy Steels
- Low-Alloy Steel: Less than 5% alloying elements (e.g., molybdenum, manganese).
- High-Alloy Steel: More than 5% alloying elements, like stainless steel (contains chromium, nickel for corrosion resistance).
Types of Cutting Tool Materials
- High-Speed Steel (HSS): Tough, wear-resistant.
- Carbides: Extremely hard, used for high-speed cutting.
- Ceramics: Heat resistant, brittle, used for high-temperature applications.
- Cubic Boron Nitride (CBN): Harder than carbide, used for hard materials.
- Diamond: Hardest material, used for precision cutting.
Polymers
- Thermoplastics: Re-moldable, recyclable (e.g., polyethylene, PVC).
- Thermosets: Once set, cannot be remolded (e.g., epoxy, bakelite).
- Elastomers: Rubber-like elasticity (e.g., natural rubber, silicone).
Nano Materials
- Definition: Materials with structures on the nanometer scale (1-100 nm).
- Properties: High surface area, quantum effects, increased strength, electrical properties.
- Applications: Medicine (drug delivery), electronics, energy storage.
Effect of Alloying Elements on Steel
- Carbon: Increases strength, hardness, reduces ductility.
- Chromium: Improves corrosion resistance, hardness.
- Nickel: Increases toughness, improves corrosion resistance.
- Molybdenum: Increases strength at high temperatures, corrosion resistance.
- Vanadium: Refines grain size, increases toughness.