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AEM 338 Engineered
Materials Testing
Introduction to Materials Technology
Sergio Sgro
Eastern Kentucky University
Lecture Objectives
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State reasons for studying materials
List and describe common terms related to the study of materials
Describe and define terms and conditions associated with atomic
structure and atomic theory
Recognize and describe how the periodic table of elements is
used and the structure of the table
List and describe how the various bonding forces act to hold
atoms together
Define the various structures of materials in crystal lattice
formation
Describe the solidification process
List and recognize various organizations and their purposes.
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1.1 Introduction
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Materials Technology
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Specifications, properties, selection, and testing of
engineering materials
Engineering Materials
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Primarily used in construction of various
structures, machines, etc.
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1.2 Atomic theory
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Why study engineering materials
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To understand the characteristics of materials and
their structures
Categories (ways to classify)
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Chemical composition
Material’s natural state
Manufacturing/refining to bring to useful state
Atomic structure
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1.2 Atomic theory
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Classification into one of the following:
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Elements
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Compounds
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mixtures
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1.2 Atomic theory
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By studying elements, scientists discovered
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Repetitive patterns
Allowed them to predict nature and properties of
elements not discovered until much later
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1.2 Atomic Theory
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1.2 Atomic theory
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An atom consists of
Valence Electron
Unfilled shell of
electrons
Proton (+)
-
+
+
-
+
+
+
+
-
-
2
32
-
+
-
8
18
Electron (-)
neutrons
1/2000 the weight of either
a proton or neutron
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1.2 Atomic theory
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The number of PROTONS in the nucleus
determines what element the atom
represents
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1.2 Atomic theory
Atoms are held together in molecules by
various types of bonds
1.
2.
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Primary bonds - generally associated with
formation of molecules
Secondary bonds - generally associated with
attraction between molecules
Primary bonds are much stronger than
secondary bonds
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1.2 Atomic theory
PRIMARY BONDS
Characterized by strong atom-to-atom
attractions that involve exchange of valence
electrons
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Following forms:
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Ionic
Covalent
Metallic
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1.2 Atomic theory: Ionic Bonding
Atoms of one element give up their outer
electron(s), which are in turn attracted to
atoms of some other element to
increase electron count in the outermost
shell to eight
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1.2 Atomic theory: Covalent Bonding
Electrons are shared (as opposed to
transferred) between atoms in their
outermost shells to achieve a stable set of
eight
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1.2 Atomic theory: Metallic Bonding
Sharing of outer shell electrons by all atoms
to form a general electron cloud that
permeates the entire block
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1.2 Atomic theory: Secondary Bonds
Whereas primary bonds involve atom-to-atom
attractive forces, secondary bonds involve
attraction forces between molecules
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No transfer or sharing of electrons in secondary
bonding
Bonds are weaker than primary bonds
Three forms:
1.
2.
3.
Dipole forces
London forces
Hydrogen bonding
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1.2 Atomic theory: Dipole Forces
Arise in a molecule comprised of two atoms
with equal and opposite electrical charges
Each molecule therefore forms a dipole that
attracts other molecules
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1.2 Atomic theory: London Forces
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Attractive force between nonpolar molecules,
i.e., atoms in molecule do not form dipoles
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However, due to rapid motion of electrons in
orbit, temporary dipoles form when more
electrons are on one side
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1.2 Atomic theory: Hydrogen Bonding
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Occurs in molecules containing hydrogen atoms
covalently bonded to another atom (e.g., H2O)
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Since electrons to complete shell of hydrogen atom
are aligned on one side of nucleus, opposite side
has a net positive charge that attracts electrons in
other molecules
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1.2 Atomic theory:
Macroscopic Structures of Matter
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Atoms and molecules are the building blocks of
more macroscopic structure of matter
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When materials solidify from the molten state, they
tend to close ranks and pack tightly, arranging
themselves into one of two structures:
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Crystalline
Noncrystalline
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1.4 Crystalline structures
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Crystalline structures
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Simple, body-centered cubic (bcc), face-centered
cubic (fcc), close-packed hexagonal
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1.2 Atomic theory: Crystalline Structure
Structure in which atoms are located at regular
and recurring positions in three dimensions
 Unit cell - basic geometric grouping of atoms
that is repeated
 The pattern may be replicated millions of
times within a given crystal
 Characteristic structure of virtually all metals,
as well as many ceramics and some
polymers
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Progression of crystal structures
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Illustration of the BCC
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Metal lattices
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Some metals undergo a change in structure
at different temperatures
IRON
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BCC at room temperature
Changes to FCC 1674 F (912 C)
Back to BCC above 2550 F (1400 C)
Referred to as ALLOTROPIC or polymorphs
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Supercooling process
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Metals in liquid state (VERY HOT)
As heat decreases
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Primary and secondary forces develop in distinct
patterns characteristic for that material (lattices) –
this is called the FREEZING POINT
Lattice formation creates heat, grows until
stopped by another lattice or container
Where lattice structures collide, it is a grain
boundary
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GRAIN BOUNDARY: Bounding surfaces between
crystals
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1.5 Specification of material
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What and why?
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Clear and accurate descriptions of technical
requirements of materials, products, or services.
They may state requirements for quality, use of
material and methods to produce a desired
product, system, application, or finish
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1.6 standards
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What are they?
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A consortium or group of people defining common
definitions and procedures
Only work when people adopt and use them
properly
ASTM standards
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American Society for Testing Materials (ASTM)
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REVIEW
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Questions?
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