Materials Science Phase Diagrams Introduction

Introduction to Phase Diagrams

• A phase diagram is a graphical representation of the equilibrium relationships between phases in a system
• It is used to identify the phases present in a system at a given temperature and composition
• Phase diagrams can be unary (one component), binary (two components), or ternary (three components)

Components of a System

• A system consists of independent chemical species, which can be elements, ions, or compounds
• Examples:
  • Au-Cu system: components are Au and Cu (elements)
  • Ice-water system: component is H2O (compound)
  • Al2O3-Cr2O3 system: components are Al2O3 and Cr2O3

Phases

• A phase is a physically homogeneous and distinct portion of a material system
• Phases can be classified based on:
  • State: gas, liquid, solid
  • Atomic order: amorphous, quasi-crystalline, crystalline
  • Band structure: insulating, semiconducting, semi-metallic, metallic
  • Property: para-electric, ferromagnetic, superconducting
  • Stability: stable, metastable, unstable
  • Size/geometry of an entity: nano-crystalline, mesoporous, layered

Phase Transformations

• Phase transformation is the change of one phase into another
• Examples:
  • Solid → Liquid → Gas

Solvent and Solute

• Solvent: the component present in a greater extent in a solution
• Solute: the component present in a lesser extent in a solution

Phase Diagrams

• Unary phase diagram: a phase diagram with one component
• Binary phase diagram: a phase diagram with two components
• Isomorphous phase diagram: a phase diagram with complete solid and liquid solubility
• Eutectic phase diagram: a phase diagram with limited solid solubility and one composition at which the liquid freezes at a single temperature
• Peritectic phase diagram: a phase diagram with complete liquid solubility and a reaction between the liquid and a solid to produce another solid

Tie Line and Lever Rule

• Tie line: a horizontal line drawn at a specified temperature to determine the chemical composition of phases in equilibrium
• Lever rule: a method to determine the relative amounts of each phase in equilibrium

Eutectic and Peritectic Phase Diagrams

• Eutectic reaction: a reaction where the liquid freezes at a single temperature
• Peritectic reaction: a reaction where the liquid reacts with a solid to produce another solid
• Characteristics of eutectic and peritectic reactions:
  • Complete liquid solubility
  • Limited solid solubility
  • Formation of a new solid phase

Allotropic Transformations

• Allotropic transformations: changes in crystal structure of a metal with temperature
• Examples:
  • Iron: B.C.C. to F.C.C. structure
  • Tin: diamond cubic to tetragonal structure

TTT Diagrams

• Time-Temperature-Transformation (TTT) diagrams: diagrams that show the kinetics of isothermal transformations
• Determination of TTT diagrams: using molten salt bath techniques combined with metallography and hardness measurements
• Utility of TTT diagrams: predicting microstructures and kinetics of phase transformations

Composite Materials

• Composite materials: engineered materials made from two or more constituent materials with different physical or chemical properties
• Advantages of composite materials:
  • High strength-to-weight ratio
  • Tailored properties
  • Corrosion resistance### Benefits of Composites
• Offer designers greater flexibility in creating complex shapes and structures that would be difficult or impossible to achieve with traditional materials like metals
• Exhibit excellent fatigue resistance, making them suitable for applications subjected to cyclic loading
• Have good electrical insulation properties, making them suitable for electrical and electronic applications

Applications of Composite Materials

Aerospace Industry

• Extensively used due to high strength-to-weight ratio
• Components made from composites include aircraft fuselages, wings, and engine components

Automotive Industry

• Used to manufacture body panels, chassis components, and interior parts
• Contribute to weight reduction and improved fuel efficiency

Marine Industry

• Widely used for boat hulls, decks, and other structural components
• Chosen for corrosion resistance and high strength

Construction

• Used in bridges, buildings, and infrastructure components
• Valued for durability, corrosion resistance, and design flexibility

Sports and Recreation

• Prevalent in sports equipment such as tennis rackets, golf clubs, bicycles, and skis
• Lightweight nature and ability to enhance performance make them ideal

Wind Energy

• Wind turbine blades are often made from composite materials
• High strength and fatigue resistance enable efficient energy generation

Medical Industry

• Used in medical applications such as prosthetics, orthopaedic implants, and dental materials
• Biocompatibility and tailored mechanical properties make them suitable

Electronics

• Composite materials with excellent electrical insulation properties are used in electronic components, circuit boards, and insulation materials