Structure and Properties of Materials

Course Overview

• Course Content:
  • Classification of materials.
  • Atomic bonding.
  • Crystallinity of materials.
  • Solidification of metals.
  • Phase diagram
  • Iron carbon diagram
  • Polymers
  • Ceramics
  • Mechanical Testing
• Student Activities & Grading:
  • Mid-Term Exam: 25%
  • Practical (Oral) Exam: 25%
  • Final Exam: 40%
  • Assignments: 10%
  • Lab Report: 10%
  • Participation: 5%
• References:
  • W.D. Callister “Materials Science and Eng.- an Introduction” , 7th edition, Wiley.
  • أحمد سالم الصباغ، المیتالورجیا الفیزیائیة، عالم الكتب

Historical Context of Materials

• The use of materials has defined eras in human history:
  • Stone Age: ~3300 BC
  • Bronze Age: ~1200 BC
  • Iron Age: ~600 BC
  • Materials Age: Present
  • Nano Age: Future

Global Relationship: Property-Structure-Processing-Performance

• The performance of a material is dictated by its properties.
• The properties of a material are determined by its structure.
• The structure of a material is a result of its processing.

Importance of Studying Materials Science

• Understanding materials science is crucial for:
  • Understanding capabilities and limitations of materials.
  • Designing better components, parts, and devices.
  • Improving design and fostering innovation.
  • Informed materials selection.
  • Failure analysis.
• Key questions addressed in materials science:
  • How to make something stronger or lighter?
  • How do elements come together to form alloys?
  • Why do some materials have vastly different properties than others?

Case Study: Coffee Cup Design/Materials Selection

• Design Specifications:
  • Avoid burning the user’s hands.
  • Reusable.
  • Environmentally friendly.
• Material Properties Required:
  • Excellent thermal insulation.
  • Reusable.
  • Recyclable.
• Candidate Materials:
  • Ceramics.
  • Polymers.
• Analysis:
  • Polymers (e.g., polyethylene) may become poisonous upon reuse.
  • Disposing of polymers can cause environmental damage due to being unrecyclable.
  • Ceramics can be reused and pose less of a danger to the environment.
• Proposed Material: Ceramics

Structure of Materials

• Structure refers to:
  • The arrangement of parts in a whole.
  • The organization of a substance.
  • The regularity with which atoms or ions are arranged.

Importance of Studying Material Structure

• Significant property differences exist between crystalline and non-crystalline materials with the same composition.
• Non-crystalline ceramics and polymers are often optically transparent, while their crystalline forms are opaque or translucent.

Changing Material Structure

• The structure of a material can be altered through:
  • Chemical composition (alloying).
  • Thermal treatment (heat treatment).
  • Mechanical processes (manufacturing).

Forging Example Demonstrating Structure Change

• Before Forging: Crystal grains of the metal are large and non-uniform.
• After Forging: Crystal grains of the metal are small and uniform, resulting in a tougher structure.
• Structure determines properties, but processing determines structure.

Structure Classification and Length Scales

• Atomic structure: Up to 1 Å $(\text{Å} = 10^{-10} \text{ m})$
• Nanostructure: 1-100 nm $( \text{nm} = 10^{-9} \text{ m})$
• Microstructure: 10 – 1000 nm
• Macrostructure: ~ > 100 μm $( \mu \text{m} = 10^{-6} \text{ m})$
• Atomic structure affects chemical, physical, thermal, electrical, magnetic, and optical properties.
• Microstructure has a larger effect on mechanical properties and the rate of chemical reactions.

Long Range Order vs. Short Range Order

• Long-range order:
  • Atomic positions in a crystal exhibit translational periodicity, repeating in a regular array over a long distance.
• Short-range order:
  • Regular and predictable arrangement of atoms over a short distance (one or two atom spacing’s) without long-range persistence.

Classification of Structure

• Crystalline: Long-range order.
• Amorphous: Short-range order.

Single Crystal, Polycrystalline, and Amorphous Solids

• Single crystals: Infinite periodicity.
• Polycrystals: Local periodicity.
• Amorphous solids (and liquids): No long-range order.

Properties of Materials

• A property gives the same measurement regardless of the size of the material.
  • Example: Density is a property; mass is not.

Physical Properties

• Describe the characteristics of a substance.
• Do not depend on the amount of matter present.
• Include color, texture, shape, smell, state of matter (solid, liquid, gas), sound, and taste.

Chemical Properties

• pH
• Surface energy
• Surface tension
• Specific internal surface area
• Reactivity
• Corrosion resistance
• Oxidation
• UV radiation

Other Properties

• Electrical:
  • Electrical conductivity
  • Permittivity
  • Dielectric constant
  • Dielectric strength
  • Piezoelectric constant
• Magnetic:
  • Permeability
  • Hysteresis
  • Curie Point
• Optical:
  • Absorptivity
  • Reflectivity
  • Refractive index
  • Photosensitivity
  • Transmittance
  • Luminosity
  • Scattering
• Thermal:
  • Thermal conductivity
  • Thermal diffusivity
  • Thermal expansion
  • Emissivity
  • Coefficient of thermal expansion
  • Specific heat
  • Glass transition temperature
  • Melting point

Mechanical Properties

• Tensile strength
• Ductility
• Elastic modulus
• Fatigue limit
• Hardness
• Poisson’s ratio
• Shear modulus
• Yield strength
• Fracture toughness

Materials Engineering

• Engineering Materials:
  • Used in manufacture and become parts or products.
• Non-Engineering Materials:
  • Chemicals, fuels, lubricants, and other materials used in the manufacturing process but do not become part of the product.

Categories of Engineering Materials

• Metals
• Polymers
• Ceramics
• Composites

Metals and Alloys

• Metals are composed of one metallic element (one type of atom): Iron, Aluminum, Copper, Titanium, Gold, and Nickel (pure metal).
• An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal, where the resulting material has metallic properties.
• Alloying usually improves the properties to be better than both.

Polymers

• A group of materials normally obtained by joining organic (Hydrocarbons) molecules into a giant molecular chain or network.
• Examples include:
  • PET
  • PS
  • LDPE
  • HDPE
  • PVC
  • PP

Polymers Classification

• Natural Polymers:
  • Functional: DNA, RNA, Proteins
  • Structural: Fibers, Cellulose, Silk, Wool, Gelatin, Rubber
• Synthetic Polymers:
  • Fibers: Nylon, Acrylic, Polyester
  • Plastics: Polyester, Bakelite, PVC
  • Rubbers

General Properties of Polymers

• Low density
• Low melting point
• Poor conductors of heat and electricity
• Easily affected by environmental factors
• Highly deformable

Ceramics

• Inorganic and non-metallic materials.
• Primarily oxides, but can also be carbides, nitrides, borides, and silicates.
• Examples:
  • Sand
  • Rocks
  • Stones
  • Advanced Ceramics (Sensors, actuators, capacitors, electrical insulation, bricks, glasses, tableware, refractories, abrasives)

General Properties of Ceramics

• Hard but brittle; not deformable
• High resistance to high temperature and harsh environments
• Good insulators to heat and electricity
• Chemically stable
• May be transparent, translucent, or opaque

Composites

• Combinations of two materials:
  • Reinforcing phase (carry the loads) in the form of fibers, sheets, or particles.
  • Matrix phase (transfer force to other phases and protect phases from the environment).
• Classified based on matrix or reinforcement.

Composites vs. Alloys

• Composites are mixtures on a macroscopic level.
• Alloys are mixtures on a microscopic level.

Functional Classification of Materials

• Electronic
• Smart
• Aerospace
• Bio
• Energy
• Functional
• Structural
• Nano-materials & Nanotechnology
• Magnetic
• Environment
• Optical

Textbook Reference

• Chapter 1. Introduction, page 2 to page 17
• Lab: Materials identification