AEM 338 Engineered Materials Testing Introduction to Materials Technology Sergio Sgro Eastern...

AEM 338 Engineered Materials Testing

Introduction to Materials TechnologyIntroduction to Materials Technology

Sergio SgroEastern Kentucky University

Eastern Kentucky UniversityINT 238INT 238

Lecture Objectives

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.


1.1 Introduction

Materials Technology Specifications, properties, selection, and testing of

engineering materials

Engineering Materials Primarily used in construction of various

structures, machines, etc.


1.2 Atomic theory

Why study engineering materials To understand the characteristics of materials and

their structures Categories (ways to classify)

Chemical composition Material’s natural state Manufacturing/refining to bring to useful state Atomic structure


1.2 Atomic theory Classification into one of the following:

Elements

Compounds

mixtures


1.2 Atomic theory

By studying elements, scientists discovered Repetitive patterns Allowed them to predict nature and properties of

elements not discovered until much later


1.2 Atomic Theory


1.2 Atomic theory An atom consists of

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++ 2 8

18 32

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Valence ElectronValence Electron

Proton (+)Proton (+)

Electron (Electron (--))neutronsneutrons

Unfilled shell of electrons

1/2000 the weight of either a proton or neutron

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+

++

++ 2 8

18 32

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Valence ElectronValence Electron

Proton (+)Proton (+)

Electron (Electron (--))neutronsneutrons

Unfilled shell of electrons

1/2000 the weight of either a proton or neutron


1.2 Atomic theory

The number of PROTONS in the nucleus determines what element the atom represents


1.2 Atomic theory

Atoms are held together in molecules by various types of bonds1. Primary bonds - generally associated with

formation of molecules

2. Secondary bonds - generally associated with attraction between molecules

Primary bonds are much stronger than secondary bonds


1.2 Atomic theory

PRIMARY BONDS

Characterized by strong atom‑to‑atom attractions that involve exchange of valence electrons

Following forms: Ionic Covalent Metallic


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


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


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


1.2 Atomic theory: Secondary BondsWhereas primary bonds involve atom‑to‑atom

attractive forces, secondary bonds involve attraction forces between molecules No transfer or sharing of electrons in secondary

bonding Bonds are weaker than primary bonds Three forms:

1. Dipole forces

2. London forces

3. Hydrogen bonding


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


1.2 Atomic theory: London Forces Attractive force between nonpolar molecules,

i.e., atoms in molecule do not form dipoles However, due to rapid motion of electrons in

orbit, temporary dipoles form when more electrons are on one side


1.2 Atomic theory: Hydrogen Bonding Occurs in molecules containing hydrogen atoms

covalently bonded to another atom (e.g., H2O)

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


1.2 Atomic theory: Macroscopic Structures of

Matter Atoms and molecules are the building blocks of

more macroscopic structure of matter

When materials solidify from the molten state, they tend to close ranks and pack tightly, arranging themselves into one of two structures: Crystalline Noncrystalline


1.4 Crystalline structures

Crystalline structures Simple, body-centered cubic (bcc), face-centered

cubic (fcc), close-packed hexagonal


1.2 Atomic theory: Crystalline StructureStructure 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


Progression of crystal structures Illustration of the BCC


Metal lattices

Some metals undergo a change in structure at different temperatures

IRON 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


Supercooling process

Metals in liquid state (VERY HOTVERY HOT) As heat decreases

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 GRAIN BOUNDARY: Bounding surfaces between

crystals


1.5 Specification of material

What and why? 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


1.6 standards

What are they? A consortium or group of people defining common

definitions and procedures Only work when people adopt and use them

properly ASTM standards

American Society for Testing Materials (ASTM)


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AEM 338 Engineered Materials Testing Introduction to Materials Technology Sergio Sgro Eastern...

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