(5-6) Physical Metallurgy | Properties of Metal

PHYSICAL METALLURGY

deals with the physical and mechanical properties of metals

PROPERTY

response of a material to any external stimulus such as stress, heat, electricity, magnetic field or the environment

example: strength of a material, which is the response of a material

STRUCTURE

arrangement of the components and at the different level-microscope, atomic, or even subatomic

PROPERTY = f(STRUCTURE)

PROPERTY = f(STRUCTURE)

• CHARACTERIZATION

  • STRUCTURE

  • PROPERTIES

  • PERFORMANCE

  • PROCESSING
    

Material Science Tetrahedron

Atomic Bonding: Net Force

attractive and repulsive force merge at the center = equilibrium (Net Force)

POTENTIAL WELL

• equilibrium will be at the lowest point of well

• the deeper the well, the better the equilibrium

• deeper equilibrium is equal to higher energy needed to overcome that potential

• Primary Bond

  • Ionic Bond

  • Covalent Bond

  • Metal Bond

• Secondary Bond

  • Van der Waals

  • Hydrogen Bond

Types of Bond

IONIC BOND

type of bond where one or more electrons in the valence shell of an atom are transferred to the valence shell of another

between metallic and nonmetallic elements

COVALENT BOND

type of bond that involves sharing of electron

between nonmetallic elements

METALLIC BOND

type of bonding that occurs due to delocalized valence electrons

delocalized electrons can move freely within the solid in response to an electric field, creating a “sea of electrons”

VAN DER WAALS

type of bonding exists between virtually all atoms or molecules that arises from atomic dipoles or molecular dipoles

HYDROGEN BOND

special type of Van der Waals bonding

bond between a hydrogen ion and negatively charged ion

CRYSTALLOGRAPHY

arrangement of atoms within a structure of materials

• Crystalline Solid

• Amorphous Solid

Solid Structure is assembled into two:

CRYSTALLINE SOLID

contains regular and repeating atomic or molecular arrangements

includes metals and some ceramics and polymers

AMORPHOUS SOLID

non-dense, random ordering and packing

LATTICE

the 3D space filling repeating pattern on which atoms are placed

represents the arrangement of atoms, ions, or molecules in a crystalline material.

UNIT CELL

smallest unit and simplest portion of the structure that describes the crystal pattern

LATTICE CONSTANTS

edge length along major axes

INTERAXIAL ANGLES

angles between axes

denoted as α (alpha), β (beta), and γ (gamma)

CRYSTAL SYSTEM

a scheme by which structures are classified according to unit cell geometry

• Simple Cubic

• Face-Centered Cubic (FCC)

• Body-Centered Cubic (BCC)

• Hexagonal Close-Packed (HCP)

Types of Unit Cells

SIMPLE CUBIC

consists of atoms situated only at the (8) corners of a cube

FACE-CENTERED CUBIC (FCC)

• atoms are situated at the corners at the corners of the unit cell as well as the centers of each face

• 8 corner atoms, 6 face atoms

• 2 unit cells

• Al (aluminum)

• Cu (copper)

• Ag (silver)

• Au (gold)

• Pb (lead)

• Ni (nickel)

metals with FCC structure

BODY-CENTERED CUBIC (BCC)

atoms are situated at the corners of the unit cell and at the center of the cube

• Cr (chromium)

• Fe (iron)

• W (tungsten)

Metals with BCC structure:

HEXAGONAL CLOSE-PACKED (HCP)

• has 2 basal planes in the form of a regular hexagon and one atom at the center

• 12 coordination number, 6 atoms

• Cd (cadmium)

• Co (cobalt)

• Ti (thallium)

• Zn (zinc)

Metals with HCP structure:

• Atomic Radius

• Coordination Number

  • number of nearest neighboring atoms

• Number of atoms per unit cell

• Ratio of lattice constant to atomic radius (a:R)

• Atomic Packing Factor

  • fraction of space filled by spherical volume

Unit Cell Parameters

Atomic Packing Factor (APF) formula

Unit Cell Parameters

SINGLE CRYSTAL

• has perfect periodic arrangements of atoms that extends throughout the entire specimen

• exists in nature but is very difficult to grow

• quartz

POLYCRYSTALLINE

• consists of many small crystals or grains

• separated by grain boundaries

POLYMORPHISM

• capability of some material to possess different crystal structures

• Graphite vs Diamond

Polymorphism in Fe (Iron) with Carbon

ANISOTROPY

• dependence of properties with crystallographic direction

• degree increases with low structural symmetry

ISOTROPY

• independence of properties with crystallographic direction

• observed for polycrystalline materials even if individual grains are anisotropic

Stimulus and its Property

MECHANICAL PROPERTIES

external force is applied

• Tension

• Compression

• Shear

• Torsion

Types of Loading (4)

• Tensile Stress

• Shear Stress

• Engineering Stress

• Engineering Strain

Types of Stress (4)

Tensile Stress

Shear Stress

Engineering Stress

instantaneous force divided by the original cross-sectional area

Engineering Strain

instantaneous deformation divided by the original length

the effect of stress

• Universal Testing Machine (UTM)

• Necking

Types of Stress-Strain Testing

Universal Testing Machine (UTM)

used to uniaxially load as sample until material failure

Stress-Strain Diagram

to present data from UTM

Necking

localized reduction in cross-sectional area, begins after UTS

• Elastic Deformation - reversible

• Plastic Deformation - irreversible

Tensile Properties

Hooke’s Law

• used for Elastic Deformation

• linear properties between stress and strain

• Proportional Limit

• Yielding

• Ultimate Tensile Strength (UTS)

• Fracture Stree

Elastic Behavior (4)

Proportional Limit

point wherein departure from linearity of stress-strain curve starts

Yielding

phenomena wherein it starts to transition from elastic to plastic

Ultimate Tensile Strength (UTS)

before necking

maximum stress a material can withstand while being stretched or pulled before it breaks

Fracture Stress

stress at the point of breaking of fracture

Ductility (%EL)

• degree of plastic deformation that have been sustained at fracture

• expressed as %elongation

Resilience

• capacity to absorb energy when it is plastically deformed, and to have its energy recovered upon unloading

• strain energy per unit volume required to stress a material from an unloaded state

Toughness

• energy to break a unit volume of a material

• approximately by the area under stress-strain

Hardness

• a property that described the resistance to permanently indenting to the surface or localized plastic deformation

• higher hardness means resistance to plastic deformation

• Rockwell

• Brinell

• Knoop

Hardness Tests

Mohs Scale of Hardness

• most are solid at normal temperature

• relatively high density

• some are very good conductors of heat and electricity

• magnetic properties

Macroscopic Physical Properties of Metals (4)