Week 2 enginerring materials

ID 2322 Materials & Production - Week 2

• Course: Materials & Production
• Institution: National University of Singapore
• Division: Industrial Design
• College: Design and Engineering
• Level: BA(ID) 2
• Semester: 1
• Module Leader: Kouo Wai Chiau
• Email: [email protected]

Engineering Materials

• Engineering materials are classified into four categories: Metals, Polymers, Ceramics, Composites.
• These materials differ significantly in structure, properties, and applications.

Metals

• Structure: Crystalline (atoms arranged in a regular pattern).
• Appearance: Opaque, lustrous (shiny).
• Conductivity: Good electrical and thermal conductors.
• Shape Change: Capable of changing shape permanently under external forces (ductility).
• Strength & Stiffness: Relatively high strength and stiffness.
• Alloy: Formed when two or more metals are combined.
• Common Examples: Copper, Aluminum, Gold, Steels, Brasses, Bronzes (copper + tin), Bell metal (copper + tin), Sterling silver (silver + copper), Nichrome (nickel + chromium), Super alloys.
• Applications: Car bodies, tin cans, construction, rails, engine blocks, wires, cabinets, valves.

The Nature of Metals

• Metals are defined as solids made up of atoms held together by an electron matrix.

Structure of Metals

• Molten state: atoms arranged randomly.
• Solid state: atoms arrange in a regular 3D pattern (space lattice).
• Unit cell: the smallest repeating unit in the space lattice.
• Common unit cells: body-centered cubic (BCC), face-centered cubic (FCC), hexagonal close-packed (HCP).

Types of Unit Cells (Lattice Structures)

• BCC: High melting point, high yield strength, but low ductility. Examples include tungsten, molybdenum, vanadium.

• FCC: More open-spaced arrangement, ductile and easily deformed. Examples include copper, aluminum, lead, nickel, silver, gold, and iron.

• HCP: Found in less common metals (beryllium, zinc, titanium, magnesium, zirconium). Wide spacing between basal planes leads to low plasticity. Brittleness readily arises upon deformation at room temperature.

• Electrical properties: Electrons are free to move throughout the crystal, making them good conductors.

• Other properties: Malleability (ability to deform plastically), opacity (light cannot pass through), and ability to be strengthened.

• Cleavage failure: Crystalline solids subjected to loads may try to split atoms apart when bonds are very strong.

• Atomic slip: In metals, loading can cause slip rather than cleavage.

• Dislocations: Atomic in size, observed with microscopic and etching techniques. Sources include crystal mismatch in solidification, external stresses (like plastic deformation), phase transformations, and alloying elements.

• Strengthening Mechanisms: Dislocation interactions, solid solution strengthening (adding impurity atoms), mechanical working (multiplicating dislocations), and precipitation hardening.

Additional Metal Types

• Precious Metals: Rhodium, Sterling silver, 14k/18k yellow/rose gold, 14k nickel/PD white gold, palladium, platinum.
• Ferrous Metals: Iron based metals.
• Nonferrous Metals: Not based on iron (i.e. copper, aluminum, magnesium, zinc)

Steel

• Steel: An alloy of iron and carbon (typically 0.06% to 2.0% carbon).
• Pure Iron: Soft, ductile, relatively weak. Used for applications like magnetic devices and enameling.
• Cast Iron: Contains more than 2% carbon, too brittle for rolling, forming, shearing, or other fabrication techniques. Primarily used for castings.

Steel Production & Processing

• Refining iron ore and limestone is heated with coke in a blast furnace; removes impurities.
• Molten iron is transported to steel-making furnaces.
• Ingot teeming, soaking, pits, continuous casting, shaping (billets, slabs, blooms, skelp), rolling, drawing are part of steel product processing.

Different Forms of Steel Products

• Sheet, Bar, Coil, Flat wire, Shapes, Tin plate, Wire, Free machining, Drawing quality, Merchant quality, Pickling.

Stainless Steel

• A minimum of 10.5% chromium is the key alloying element.
• Categorized by microstructure: austenitic, ferritic, martensitic, precipitation hardening.

Types of Nonferroous metals

• Aluminum.
  • High strength-to-weight ratio, good formability.
  • Corrosion resistance due to an oxide coating.
  • Electrical conductivity.
• Copper
  • Ease of forming, joining, good electrical and thermal conductivity, attractive color, high corrosion resistance.
• Brass and Bronze: Copper alloys used extensively in plumbing and fine art casting.
• Magnesium:
  • Excellent combination of low density and good mechanical strength, giving high strength-to-weight ratio.
  • Commonly used in transportation, power tools, etc.
• Zinc alloy: Used for die-cast components in a wide range of products (automotive, building hardware, industrial tools, and toys). Also used as a coating for steel (galvanized steel) to prevent corrosion.

Powdered Metallurgy (P/M)

• Provides new processes and alloys for weight reduction and enhanced mechanical properties.
• Applications include sports, electronics, office equipment, automotive parts, and off-road vehicles.
• Steps involve atomization of molten metal, mixing, compacting, and sintering.

Metal Injection Moulding (MIM)

• Hybrid technology combining plastic injection molding and powder metallurgy.
• Economical method for mass manufacturing of small intricately shaped components.
• Results in components with 95-98% of wrought properties at reduced cost.

Polymers

• Structure: Long molecular chains of carbon atoms.
• Weight: Typically light weight.
• Conductivity: Low electrical and thermal conductivity.
• Common Examples: Polyamide, polyvinyl chloride (PVC), polystyrene, ABS, rubber, nylon.
• Applications: Carrier bags, plumbing pipes, hoses, tires, domestic items.
  • Specific applications often involve thermosets, thermoplastics, or blends thereof.
• Types: Thermoplastics, Thermosets, and Composites.

Types of Polymers

• Thermoplastics: Can be melted and reshaped repeatedly.
  • Amorphous (no long-range order), Crystalline (long-range order), Liquid Crystalline Polymers (LCPs).
• Thermosets: Can be molded only once. - These, with their cross-linking, inhibit crystallizations.

Copolymers and Blends

• Copolymers: Polymers composed of two or more different monomers.
  • Types: Random, Alternating, Block, Graft.
  • Applications can differ significantly from the homopolymers.
• Blends: Mechanical mixing of two or more polymers.
  • Applications include polymers with balanced characteristics such as strength and flame resistance.

Terpolymers

• Polymers with three different repeating units. Tailored for wide ranges of properties.
  • Example: ABS - acrylonitrile, butadiene, styrene.

Molecular Weight

• Sum of weights of the atoms that make up the polymer molecule.
• Indicates the average length of polymer chains.
• Variation in molecular weight affects plastic properties, including viscosity and performance.

Additives

• Fillers (glass, minerals) - change properties (aesthetic, resistance, conductivity).
• Plasticizers - reduce stiffness and increase flexibility.
• Flame retardants - comply with safety regulations.
• UV stabilizers - counteract degradation from UV light.

Factors Affecting Mechanical Properties

• Weld lines: Grooves in molded parts due to flow front join; they weaken the part.
• Residual Stress: Uneven cooling, differential shrinkage cause stresses in parts.
• Ultimate Strength: Property related to the alignment of polymer chains; may vary depending on the direction.

Ceramics

• Formed from metal and nonmetal (oxygen, nitrogen, or carbon).
• Brittle, high compressive strength.
• Good heat resistance. insulating properties. Common examples: refractories, glasses, concrete, silica, magnesium oxide, and fireclays.
• Applications include: cookware, electrical insulators, cutting tools, and building materials.

Composites

• Combo of two or more materials, creating unique properties not found in individual materials.
• One material (matrix) holds another material (reinforcement).
• Examples include fibrous (e.g., roof covers) and particulate (e.g., cermets) composites.
• Benefits often include strength and light weight, but varies with types (fiber, matrix, and manufacturing process).