Materials Science Flashcards

Gray Iron

• Carbon: 2.5–4.0% C, 1.0–3.0% Si

• Structure: Graphite as flakes in ferrite or pearlite matrix

• Properties:

  • Weak and brittle in tension (flake tips = stress concentrators)

  • Strong under compression

  • Excellent vibration damping

  • High wear resistance

  • Cheap and easy to cast

• Uses: Machine bases, engine blocks, cylinder heads, clutch plates, pipes

Ductile (Nodular) Iron

• Carbon: 3.5–3.8% C, with Mg/Ce addition

• Structure: Graphite as spherical nodules in pearlite or ferrite matrix

• Properties:

  • High tensile strength (414–827 MPa)

  • Good ductility (up to 18% elongation)

  • Approaches steel in mechanical performance

• Uses: Crankshafts, gears, valves, pump bodies, automotive components

White Iron

• Carbon: locked as cementite (Fe₃C), no free graphite; <1.0% Si, fast cooled

• Structure: Cementite dominant, no graphite present

• Properties:

  • Extremely hard and wear resistant

  • Very brittle, virtually unmachinable

  • No plastic deformation

• Uses: Rolling mill rollers; intermediate for malleable iron production

Malleable Iron

• Carbon: 2.3–2.7% C; white iron reheated 800–900°C

• Structure: Temper carbon rosettes/clusters in ferrite or pearlite matrix

• Properties:

  • Better ductility than white iron

  • Good strength

  • Limited to thin sections (must solidify white first)

• Uses: Connecting rods, transmission gears, pipe fittings, railroad components

Compacted Graphite Iron (CGI)

• Carbon: 3.1–4.0% C, 1.7–3.0% Si, lower Mg/Ce than ductile iron

• Structure: Wormlike/vermicular graphite (up to 20% nodules) in pearlite or ferrite matrix

• Properties:

  • Strength between gray and ductile iron

  • Higher thermal conductivity than other cast irons

  • Better thermal shock resistance

  • Lower oxidation at high temperatures

• Uses: Diesel engine blocks, exhaust manifolds, brake discs, flywheels

Ferrous alloy’s

• Ferrite (α iron)BCC (cubic) stable at < 912˚C

• Austenite (γ iron) FCC (cubic) stable at 727 ˚C -1493 ˚C

• Cementite (Fe3C) Compound (orthorhombic ceramic, ratio 3:1)

• Delta iron (δ iron) BCC (cubic) stable at 1394 ˚C -1538 ˚C

• Pearlite (α + Fe3C)

• Ledeburite (γ + Fe3C)

Steel (General)

• Carbon: <2.14% C

• Structure: Iron-carbon alloy, carbon content determines properties

• Properties: High tensile strength, ductile, durable, but rusts/corrodes

• Uses: Structural applications across all industries

Types of Carbon Steel

Low Carbon Steel (<0.25% C)

• Structure: Ferrite and pearlite matrix; cannot form martensite

• Properties:

  • Soft and weak but excellent ductility and toughness

  • Machinable and weldable

  • Least expensive steel

• Uses: Car body panels, I-beams, pipelines, bridges, tin cans

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Low Carbon Steel - HSLA variant

• Structure: Low carbon with added Cu, V, Ni, Mo (up to 10 wt%)

• Properties:

  • Higher strength than plain low carbon

  • Ductile, formable, machinable

  • Better corrosion resistance

• Uses: Bridges, towers, high-rise columns, pressure vessels

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Medium Carbon Steel (0.25–0.60% C)

• Structure: Tempered martensite after heat treatment (austenitize, quench, temper)

• Properties:

  • Stronger than low carbon but less ductile

  • Good wear resistance and toughness

  • Heat treatable with Cr, Ni, Mo additions

• Uses: Railway wheels, gears, crankshafts, machine parts

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High Carbon Steel (0.60–1.4% C)

• Structure: Hardened and tempered; carbide compounds with alloying elements

• Properties:

  • Hardest and strongest of carbon steels

  • Least ductile

  • Excellent wear resistance; holds sharp edge

• Uses: Cutting tools, knives, razors, hacksaw blades, springs, dies

Stainless Steel

• Carbon: Varies; minimum 11% Cr required

• Structure: Martensitic, ferritic, or austenitic depending on composition

• Properties:

  • Highly corrosion and rust resistant

  • Wide range of mechanical properties

  • Strengthened by precipitation hardening

• Uses: Gas turbines, steam boilers, aircraft, nuclear power units, medical equipment

Cast Iron (General)

• Carbon: >2.14% C (typically 3.0–4.5% in practice)

• Structure: High carbon causes graphite formation; type depends on cooling rate and composition

• Properties:

  • Lower melting point than steel (1150–1300°C); easy to cast

  • Some types very brittle

• Note: Parent category for gray, ductile, white, malleable, and CGI

Ceramics (General)

• Structure: Ionic and/or covalent bonding; anions form scaffold, cations fill interstices; anions are larger than cations

• Properties: Hard, brittle, high melting point, chemically inert

• Key concept: The shape and size of interstices (tetrahedral vs octahedral) determines what structures are possible

CsCl

• Structure: Simple cubic (sc); CN = 8 for both ions

• Key concept: Simplest ceramic structure; does not occur in oxides

  

NaCl / Rock Salt (MgO, TiC, PbS)

• Structure: fcc anion arrangement; cations fill all octahedral interstices; CN = 6 for both ions

• Properties: Carbides with this structure are hard, chemically inert, high melting point

• Examples: MgO, CaO, FeO, NiO, TiC

  

GaAs / Zinc Blende (β-SiC)

• Structure: fcc anions; cations fill half the tetrahedral interstices; CN = 4 for both ions; open structure (APF = 0.41)

• Properties: Usually semiconductors due to covalent bonding; band gap increases with more ionic character

• Key concept: Replacing all atoms with same element gives diamond-cubic structure (C, Si, Ge)

CaF₂ / Fluorite

• Structure: fcc cations; anions fill all tetrahedral interstices; Ca CN = 8, F CN = 4

• Properties: Transparent to deep-UV light

• Uses: Semiconductor lithography lenses; cubic zirconia (CZ) is a diamond simulant

• Key concept: UO₂ has this structure; the empty interstice at center can hold nuclear fission byproducts without straining the lattice

  

AlN / Wurtzite (BeO, ZnO)

• Structure: hcp anions; cations fill half tetrahedral interstices; CN = 4; tetrahedra stack ABABAB (vs zinc blende ABCABC)

• Properties: High thermal conductivity (BeO, AlN); ZnO is a semiconductor used in varistors

• Key concept: Same nearest-neighbor environment as zinc blende but only one unique stacking direction [0001]

Types of Polymers

Homopolymer - A-A-A-A-A

Alternating Copolymer - A-B-A-B-A-B

Periodic Copolymer - A-B-B-A-B-B-A-B-B

Statistical Copolymer - A-B-B-B-A-B-A-B

Block Copolymer - A-A-A-A-B-B-B-B

Grafted Copolymer (A-A-A) with side chains of (B-B-B…)

What is a cross-linked polymer?

A polymer where bonds form between chains (usually covalent); requires at least 4 chains to emanate from a junction point

What are examples of complex polymer architectures?

Star, comb, brush, dendronized, dendrimer, and ring polymers

Polyethylene (PE)

• (C₂H₄)ₙ; nonpolar, saturated, thermoplastic; highest global production

• Low strength, high ductility, low friction, prone to creep

• Melts 120–180°C; excellent electrical insulator; resists acids/bases; absorbs almost no water

• Transparency varies with crystallinity level

HDPE vs LDPE

• HDPE (≥0.941 g/cm³): low branching → tight packing → stronger intermolecular forces → stiffer, stronger; used in pipes, jugs, toys

• LDPE (0.910–0.940 g/cm³): high branching → loose packing → weaker forces → flexible, ductile; used in bags, film wrap

PE-X (Cross-linked PE)

• Cross-links convert PE from thermoplastic to thermoset

• Improved heat resistance, chemical resistance, reduced creep/flow

• Methods: peroxide (200–250°C), silane (Si–O–Si bridges), irradiation (β/γ), azo compounds

• Used in plumbing, cable insulation, automotive

Polypropylene (PP)

• Thermoplastic; carbon backbone with CH₃ on alternating carbons; lowest density commodity plastic (0.895–0.92 g/cm³)

• CH₃ group improves mechanical strength and thermal resistance vs PE, but reduces chemical resistance (tertiary carbon is more reactive)

• Isotactic (crystalline, Tm ~171°C) vs atactic (amorphous, lower Tm)

• Resists fats/solvents at room temp; dissolves in xylene/tetralin when hot

• Tough, flexible, good fatigue resistance; translucent to opaque

PVC

• Carbon backbone with Cl on alternating carbons; polar C–Cl bond; thermoplastic; 3rd highest global production

• Rigid (uPVC, 1500–3000 MPa) or flexible (plasticized, 1.5–15 MPa)

• Cl atoms give excellent flame retardancy (LOI ≥45; releases HCl suppressing combustion)

• Poor inherent thermal stability; decomposes at 140°C; requires heat stabilizers

• Electrical insulation inferior to PE/PP due to polarity

• Resists acids, bases, salts, fats; some solvents (THF, acetone) can damage it

PTFE (Teflon)

• Carbon backbone fully surrounded by F atoms; nonpolar fluoropolymer; thermoplastic

• C–F bond = second strongest single bond in organic chemistry → extremely chemically inert

• Lowest coefficient of friction of any solid; hydrophobic due to weak London dispersion forces

• Melts at 327°C; maintains toughness down to −268°C

• Only attacked by alkali metals and strong fluorinating agents

• Used in non-stick coatings, chemical pipework, surgical grafts, catheter coatings

PMMA (Acrylic/Plexiglas) Polymethyl methacrylate

• Atactic, completely amorphous thermoplastic; transparent (no crystalline regions to scatter light)

• Transmits up to 92% visible light; density 1.17–1.20 g/cm³ (less than half of glass)

• Good impact strength vs glass; inferior to polycarbonate

• Ester groups easily hydrolyzed → poor solvent resistance; swells/dissolves in many organics

• Superior UV/environmental stability vs polystyrene and PE → preferred for outdoor use

• Max water absorption 0.3–0.4% by weight; tensile strength decreases with moisture

Ordered region in a polymer

lamellae