Essential Materials Science: Properties, Types, and Processing

Posted on Jun 15, 2025 in Law and Journalism

Polymer Materials: Properties & Types

General Polymer Characteristics

  • Low fabrication cost
  • Excellent strength-to-weight ratio
  • Recyclable
  • Good chemical and environmental resistance

Metal Materials: Characteristics & Types

General Metal Characteristics

  • High strength-to-weight ratio, especially in large applications
  • High rigidity
  • Immune to UV degradation

Ferrous Metals

  • Composed of greater than 50% Iron (Fe)
  • High modulus of elasticity
  • High strength
  • Low cost
  • Quench hardenable

Non-Ferrous Metals

  • Good corrosion resistance
  • Good electrical conductivity
  • Good formability
  • Do not exhibit ductile-to-brittle transition
  • Suitable for precipitation hardening

Precipitation Hardening (PH)

A heat treatment process primarily used for non-ferrous metals, involving:

  1. Heating the material to a single-phase region.
  2. Quenching to a two-phase region.

This process does not involve allotropic lattice transformation.

During the aging (heating) stage, atoms move, but the precipitated particles retain their bond, stretching the surrounding matrix and increasing hardness.

Types of Stainless Steels

Ferritic Stainless Steel

  • Iron-Chromium (Fe-Cr) alloy with a Body-Centered Cubic (BCC) structure.
  • Ductile and formable.
  • Poor high-temperature strength.
  • Non-allotropic and not quench hardenable.
  • Composition: 11-27% Chromium (Cr), up to 0.2% Carbon (C).

Austenitic Stainless Steel

  • Face-Centered Cubic (FCC) structure.
  • Composition: Typically 12% Chromium (Cr), 7-22% Nickel (Ni), up to 0.08% Carbon (C).
  • Offers the highest uniform corrosion resistance.

Martensitic Stainless Steel

  • High carbon levels, resulting in a Body-Centered Tetragonal (BCT) or stretched BCC structure.
  • Composition: 10.5-18% Chromium (Cr), up to 1% Carbon (C).

Duplex Stainless Steel

  • Composed of approximately 50% Ferritic and 50% Austenitic phases.
  • Stronger than both ferritic and austenitic stainless steels individually.

Common Alloying Elements and Their Effects

  • Nickel (Ni): Provides superior strength and erosion-corrosion resistance in high temperatures and corrosive environments (e.g., Monel alloys).
  • Copper (Cu) in Aluminum Alloys: Increases strength, often through precipitation hardening, but can reduce ductility and corrosion resistance.
  • Manganese (Mn): Increases strength and improves strain hardening.
  • Silicon (Si): Reduces melting point and increases fluidity.
  • Magnesium (Mg): Increases strength.
  • Chromium (Cr): Controls grain structure.
  • Lead (Pb): Improves machinability.
  • Zinc (Zn): Increases strength.

Polymer Types: Thermosetting vs. Thermoplastic

Thermosetting Polymers (Step-Growth)

  • Form irreversible cross-linked bonds.
  • Excellent for high-heat applications.
  • Good corrosion resistance.
  • Can withstand high stress.
  • Strong but generally less ductile.

Thermoplastic Polymers (Chain-Growth)

  • Monomers form covalent bonds.
  • Exhibit low toughness at low temperatures.
  • Ductile, recyclable, and re-shapeable.

Ceramic Materials: Properties, Structures & Processing

General Ceramic Characteristics

  • Hard
  • Good compressive strength
  • Excellent electrical insulators
  • Good corrosion resistance

Ceramic Structures

Glasses

  • Silica-based and amorphous.
  • Exhibit high strength and toughness.

Vitreous Ceramics

  • Made from clay.
  • Formed wet, then dried.

Ceramic Processing Steps

  1. Blending: Mixing raw materials.
  2. Forming: Shaping the material (e.g., extrusion, isostatic pressing).
  3. Pre-sintering: Initial heating to remove moisture and bind particles.
  4. Sintering: High-temperature treatment that removes excess moisture, allows for thermal contraction, softens glass phases, and facilitates the fusion of crystal phases.

Types of Engineering Ceramics

  • Oxides: Used as abrasives and insulators.
  • Carbides: Commonly used for cutting tools.
  • Nitrides: Applications in electronics and rocket components.
  • Intermetallics: Utilized for wear coatings.

Key Material Processes & Phenomena

Surface Hardening Techniques

  • Flame Hardening: Heats the material above its A3 critical temperature to form austenite, followed by quenching.
  • Carburizing: Introduces carbon into the surface of low-carbon steel to increase its hardness.
  • Nitriding: Introduces nitrogen atoms into the surface of steel, typically using ammonia (NH3), to enhance surface hardness and wear resistance.

Anodizing

An electrochemical oxidation process that thickens the natural oxide film on a material’s surface. The material is immersed in an acid electrolyte and connected to a DC current. Pores are subsequently sealed by immersion in hot water.

Cross-Linking

A process where individual polymer molecules are chemically linked to other polymer molecules, forming a network structure.

Intergranular Corrosion

A form of corrosion where the boundaries of a crystalline structure are more susceptible to corrosion than the interior of the material.

Sensitization (in Stainless Steels)

Occurs typically between 500-900°C. During this process, carbon migrates to grain boundaries to form chromium carbides. This depletes chromium in the adjacent regions, preventing it from bonding with oxygen to form a protective passive layer. Consequently, corrosion initiates and propagates along the grain boundaries.