Physical_Metallurgy_-_Lesson_1.1

Physical Metallurgy Overview

• Instructor: Assistant Professor Monalisa Pacana-Pongcol

Introduction to Physical Metallurgy

• Definition: Study of metal structures and crystallization.

• Importance: Determines how metals behave under different conditions (heat treatment, mechanical loading, alloying).

Key Concepts in Physical Metallurgy

• **The "PhysMet Triangle"

  • Microstructure: The structure of a material on a microscopic scale.

  • Processing: Methods of shaping and treating materials.

  • Property: Mechanical, thermal, or conductivity characteristics of materials.

Understanding Physical Metallurgy

• Core Focus Areas:

  • Evolution of solid structures from liquid.

  • Effects of alloying elements/impurities on metal transformation processes.

  • Influence of processing techniques on structural evolution.

  • Structure-property relationships in metals and alloys.

• Objectives:

  • Helps in material selection for engineering problems.

  • Understanding structure-property correlation to choose suitable materials for applications.

  • Provides principles underlying the evolution of structures during processing and their properties in service.

Scales of Metallurgy

• Levels of Scale:

  • Atom: Primary unit of matter.

  • Crystal Structure: Arrangement of atoms in a periodic lattice.

  • Microstructure: Consists of phases, defects, residual stress.

  • Components & Phases: Reflexes structural and material composition.

• Types of Structures:

  • Crystal Structure: Arrangement of atoms in a metal.

  • Electromagnetic Structure: Interaction of atoms based on electromagnetic forces.

Defects in Microstructure

• Types of defects include:

  • Vacancies

  • Dislocations

  • Twins

  • Stacking Faults

  • Grain Boundaries

  • Voids

  • Cracks

Atomic Structure of Materials

• The Atom: Composed of a nucleus (protons and neutrons) with electrons orbiting.

• Atomic Dimensions:

  • Protons and neutrons have a charge of 1.6 x 10-19 C.

  • Atomic number (Z): Number of protons/electrons.

  • Atomic mass (A): Sum of proton and neutron mass.

• Isotopes: Atoms of the same element with different neutron counts.

• Avogadro's Number: 1 mol contains 6.023 x 10^23 atoms/morphologies.

• Atomic Weight Definition: 1 amu/atom = 1 g/mol.

Atomic Interactions and Bonding

• Forces Between Atoms:

  • Atoms experience attractive and repulsive forces when close.

  • Equilibrium interatomic distance occurs when attractive and repulsive forces are balanced.

• Types of Atomic Bonds:

  • Primary Bonds:

    • Ionic, Covalent, Metallic.

  • Secondary Bonds:

    • Van der Waals and Hydrogen Bonds.

Ionic Bonding

• Nature of Ionic Bonds:

  • Formed from electrostatic attraction between charged ions (e.g., Na+ and Cl-).

  • Common in metal and non-metal compounds (e.g., NaCl, CaF2).

Covalent Bonding

• Characteristics of Covalent Bonds:

  • Atoms share valence electrons (e.g., methane, CH4).

  • Occurs between atoms with similar electronegativity (e.g., carbon in diamond).

Metallic Bonding

• Understanding Metallic Bonds:

  • Valence electrons are shared across a 'sea' of electrons, creating strong metallic structures.

Crystal Structure Concepts

• Definition of a Crystal: 3D arrangement of atoms in a periodic manner.

• Lattice: Arrangement of points in a periodic structure.

• Motif: Atoms associated with lattice points.

• Unit Cell: Smallest repeating unit in a crystal structure.

Bravais Lattices

• Bravais Lattices: Total of 14 geometrically distinct lattices grouped into 7 crystal systems.

Principal Metallic Structures

• Recognize these three primary metallic structures:

  1. Body-Centered Cubic (BCC)

  2. Face-Centered Cubic (FCC)

  3. Hexagonal Close Pack (HCP)

Density and Packing Calculations

• Atomic Packing Factor (APF):

  • Evaluating the efficiency of atomic packing in unit cells.

• Density Calculations:

  • Example: Density of copper calculated considering atomic radius and structure type.

X-Ray Diffraction Methodology

• Purpose: Investigating atomic or crystal structures.

• Bragg's Law:

  • Governs constructive interference patterns in crystals.

• Interplanar Spacing Calculations: Derived from lattice parameters and angles of diffraction.

Crystalline Structures

• Single Crystals: Perfect atomic arrangements extending throughout the material.

• Polycrystalline Material: Collections of many smaller crystals with grain boundaries.

Isotropy vs. Anisotropy

• Isotropy: Same properties in all directions; independence on crystallographic directions.

• Anisotropy: Varying properties based on crystallographic direction.