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EEAC001

Materials Science and Engineering

Chapter 1: Introduction

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Research in Computational Materials Group:

Simulation of impact resistance of carbon nanotube materials

Temperature distribution in a simulation of heat transfer in a carbon nanotube material

Generation of crystal defects and melting in a metal target irradiated by a short laser pulse

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From atoms to microstructure: Interatomic bonding, structure of crystals, crystal defects, non-crystalline materials.

Mass transfer and atomic mixing: Diffusion, kinetics of phase transformations.

Mechanical properties, elastic and plastic deformation, dislocations and strengthening mechanisms, materials failure.

Phase diagrams: Maps of equilibrium phases.

Polymer structures, properties and applications of polymers.

Electrical, thermal, magnetic, and optical properties of materials.

Topics:

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• Historical PerspectiveStone → Bronze → Iron → Advanced materials

• What is Materials Science and Engineering ?Processing → Structure → Properties → Performance

• Classification of MaterialsMetals, Ceramics, Polymers, Semiconductors

• Advanced MaterialsElectronic materials, superconductors, etc.

• Modern Material's Needs, Material of FutureBiodegradable materials, Nanomaterials, “Smart” materials

Chapter 1: Introduction

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• Beginning of the Material Science - People began to make tools from stone – Start of the Stone Age about two million years ago. Natural materials: stone, wood, clay, skins, etc.

• The Stone Age ended about 5000 years ago with introduction of Bronze in the Far East. Bronze is an alloy (a metal made up of more than one element), copper + < 25% of tin + other elements.Bronze: can be hammered or cast into a variety of shapes, can be made harder by alloying, corrode only slowly after a surface oxide film forms.

• The Iron Age began about 3000 years ago and continues today. Use of iron and steel, a stronger and cheaper material changed drastically daily life of a common person.

• Age of Advanced materials: throughout the Iron Age many new types of materials have been introduced (ceramic, semiconductors, polymers, composites…). Understanding of the relationship among structure, properties, processing, and performance of materials.Intelligent design of new materials.

Historical Perspective

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A better understanding of structure-composition-properties relations has lead to a remarkable progress in properties of materials. Example is the dramatic progress in the strength to density ratio of materials, that resulted in a wide variety of new products, from dental materials to tennis racquets.

Figure from: M. A. White, Properties of Materials (Oxford University Press, 1999)

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Material science is the investigation of the relationship among processing, structure, properties, and performance of materials.

What is Materials Science and Engineering ?

Processing

PropertiesStructureObservational

MaterialsOptimization Loop

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• Subatomic level (Chapter 2)Electronic structure of individual atoms that defines interaction among atoms (interatomic bonding).

• Atomic level (Chapters 2 & 3)Arrangement of atoms in materials (for the same atoms can have different properties, e.g. two forms of carbon: graphite and diamond)

• Microscopic structure (Ch. 4)Arrangement of small grains of material that can be identified by microscopy.

• Macroscopic structureStructural elements that may be viewed with the naked eye.

Structure

Monarch butterfly~ 0.1 m

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Length-scales

Angstrom = 1Å = 1/10,000,000,000 meter = 10-10 m

Nanometer = 10 nm = 1/1,000,000,000 meter = 10-9 m

Micrometer = 1µm = 1/1,000,000 meter = 10-6 m

Millimeter = 1mm = 1/1,000 meter = 10-3 m

Interatomic distance ~ a few ÅA human hair is ~ 50 µmElongated bumps that make up the data track on a CD are ~ 0.5 µm wide, minimum 0.83 µm long, and 125 nm high

MSE 2090: Introduction to Materials Science Chapter 1, Introduction 10

Prog

ress

in a

tom

ic-le

vel u

nder

stan

ding

DNA~2 nm wide

Things Natural Things ManmadeThe Scale of Things (DOE)

10 nm

Cell membrane

ATP synthaseSchematic, central core

Cat~ 0.3 m

Dust mite300 μm

Monarch butterfly~ 0.1 m

MEMS (MicroElectroMechanical Systems) Devices10 -100 μm wide

Red blood cellsPollen grain

Fly ash~ 10-20 μm

Bee~ 15 mm

Atoms of siliconspacing ~tenths of nm

Head of a pin1-2 mm

Magnetic domains garnet film

11 μm wide stripes

Quantum corral of 48 iron atoms on copper surfacepositioned one at a time with an STM tip

Corral diameter 14 nm

Prog

ress

in m

inia

turiz

atio

n

Indium arsenidequantum dot

Quantum dot array --germanium dots on silicon

Microelectronics

Objects fashioned frommetals, ceramics, glasses, polymers ...

Human hair~ 50 μm wide

Biomotor using ATP

The

Mic

row

orld

0.1 nm

1 nanometer (nm)

0.01 μm10 nm

0.1 μm100 nm

1 micrometer (μm)

0.01 mm10 μm

0.1 mm100 μm

1 millimeter (mm)

0.01 m1 cm10 mm

0.1 m100 mm

1 meter (m)100 m

10-1 m

10-2 m

10-3 m

10-4 m

10-5 m

10-6 m

10-7 m

10-8 m

10-9 m

10-10 m

Visib

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~ 2-5 μm

meter m 100 1 mcentimeter cm 10-2 0.01 mmillimeter mm 10-3 0.001 mmicrometer μm 10-6 0.000001 mnanometer nm 10-9 0.000000001 m

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Length and Time Scales in Materials Modelingby Greg Odegard, NASA

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Length and Time Scales in Materials Modeling

Mes

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pic

10-9

10-8

10-7

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, met

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Mo Li, JHU, Atomistic model of a nanocrystalline

Dislocation Dynamics Nature, 12 February, 1998

Farid Abraham, IBMMD of crack propagation

Nan

osco

pic

Leonid Zhigilei, UVAPhase transformation on

diamond surfaces

Elizabeth Holm, Sandia

Intergranular fracture

Monte Carlo Potts model

P ti d d i t t

Structure, Processing, & Propertiesex: hardness vs microstructure of steelProperties depend on microstructure

ex: microstructure vs cooling rate of steelProcessing changes microstructure(d)

N)

00

600

(d)1040 steel

0.4 wt. % C steelBAINITE

ss (B

HN

300

400

50030m

(c)

4m

(b)(a)

PEARLITE

MARTENSITE

SPHEROIDITE

Har

dnes

100

200

300 4m

30m30m

MARTENSITE

H

Cooling Rate (ºC/s)

1000.01 0.1 1 10 100 1000

Chapter 1 -

Data obtained from Figs. 10.30(a) and 10.32 with 0.4 wt% C composition, and from Fig. 11.14 and associated discussion, Callister 7e. Micrographs adapted from (a) Fig. 10.19; (b) Fig. 9.30;(c) Fig. 10.33; and (d) Fig. 10.21, Callister 7e.

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Read this chapter for a general orientation to the MSE field.

An important unifying concept in materials science and engineering is that there is a direct relationship between a material’s processing,

i t t ti d fmicrostructure, properties and performance

Chapter 1 - 14

Materials have historically definedMaterials have historically defined the level of societal development and development of materials with new capabilities have allowed pmajor technological advances– Stone Age– Bronze Ageg– Iron Age

Now? Silicon AgeSilicon AgeComposites Age Biomaterials Age

Requirements•mechanical strength•good lubricitybi tibilit

Chapter 1 -

•biocompatibility

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Hip Implant

Key problems to overcome– fixation agent to hold acetabular cup Ball– cup liner material

generation of wear particles could cause bone cell death

– femoral stem fixing agent (“glue”), hydroxyapatite Acetabular

Cup and Liner

Femoral IN THIS EXAMPLE METALS, CERAMICS AND POLYMERS ARE USED IN COMBINATION

StemARE USED IN COMBINATION TO ACHIEVE FUNCTIONALITY REQUIRING A WIDE RANGE OF PROPERTIES

Chapter 1 - 16

COMPARISONS OF CLASSES OF MATERIALSELASTIC MODULUS (GPa)ELASTIC MODULUS (GPa)

IT IS CRITICAL TO HAVE A GENERAL FEELING FOR THE BASIC BEHAVIORS OF THEBEHAVIORS OF THE DIFFERENT CLASSES OF MATERIALS

Chapter 1 - 17

COMPARISONS OF CLASSES OF MATERIALSTENSILE STRENGTH (MPa)TENSILE STRENGTH (MPa)

Chapter 1 - 18

COMPARISONS OF CLASSES OF MATERIALSFRACTURE TOUGHNESSFRACTURE TOUGHNESS

Chapter 1 - 19

COMPARISONS OF CLASSES OF MATERIALSELECTRICAL CONDUCTIVITYELECTRICAL CONDUCTIVITY

~ 1026 range

Chapter 1 - 20

Bohr Model

The Bohr model assumes electrons move in circular orbits of radius “r” about the nucleus and the electrons have discrete energy statesdiscrete energy states

Electrons have zero energy when they are free and hence the energy of an electron is negative when it is bound to

tan atom.The energy required to remove the electron from the atom is

given by the equation:

E = - 13.6 Z2 eV Z = atomic numbern = principal quantum

n2 n = principal quantumnumber

For hydrogen Z = 1 and n = 1 so the single electron

Chapter 1 -

For hydrogen, Z = 1 and n = 1, so the single electron would require 13.6 eV to be removed

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Bohr Model of an Atom

Since electrons have discrete allowed energy levels, the transition of an electron to a different energy level requires

i h h b i f ( l “ ”) heither the absorption of energy (moves to a larger “n”) or the emission of energy (moves to a lower “n”)

The value of emitted energy when an electron moves to a lowerThe value of emitted energy when an electron moves to a lower principal quantum number shell is also a discrete value that is characteristic of the element and the shell-to-shell transitiontransition

Analyses of the energies of electrons emitted from an excited atom would allow identification of the element from which the electron was emitted; this is the basis for the surface analytical technique Auger Electron Spectroscopy

Chapter 1 -

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Quantum Mechanical Model of Atom

Atoms are more complex than the Bohr model, with electrons having often non-circular orbitals about the nucleusthe nucleus

Identification of the electronic structure requires four (n, l, m, s) quantum numbers:( , , , ) q– n, the principal quantum number is the major

determining factor of the energy and must be a positive integer 1, 2, 3, 4, … (sometimes also

The orbital describing the distribution of p l t l ti tidentified as K, L, M, N, …

– l, determines the ways in which the orbital angular momentum is quantized and varies from 0 for the “s” subshell; 1 for the “p” subshell; 2 for the “d”

electrons relative to the nucleus has a dumbbell shape. Up to 2 electrons can i lt ls subshell; 1 for the p subshell; 2 for the d

subshell, etc. Electrons in the “s” subshell have zero angular momentum and thus have a spherically symmetric orbit. Higher subshell

simultaneously occupy the shown orbital. Identical orbitals lie along the x and y axes.

Chapter 1 -

electrons have angular momentums and their orbitals are extended in certain directions.

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Ionization energies

The following is a list of the first ionization energies for selected elements which would create a +1 ionselected elements, which would create a +1 ion

ARRANGED IN APPROXIMATE LOCATION AS IN PERIODIC TABLE

H 13.6 eV HeLi 5.4 eV C F 24.6 e VNa 5.2 eV 11.2 eV 17.4 eV

NNeCs 3.9 eV 21.6 eV

Chapter 1 - 24

Electronic Structure

• Electrons have wavelike and particulate propertiesproperties. – This means that electrons are in orbitals defined

by a probability.– Each orbital at discrete energy level determined

by quantum numbers.

Quantum # Designationn = principal (energy level-shell) K, L, M, N, O (1, 2, 3, etc.)l = subsidiary (orbitals) s, p, d, f (0, 1, 2, 3,…, n-1)ml = magnetic 1, 3, 5, 7 (-l to +l)m = spin ½ -½

Chapter 1 -

ms = spin ½, -½

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Electron Energy States

• have discrete energy states• tend to occupy lowest available energy state.

Electrons...

4p4d

N-shell n = 4

py gy

3d

4s

3s3p M-shell n = 3Energy

2s2p L-shell n = 2

Chapter 1 -

1s K-shell n = 126

Specifying Total Electronic Structure

Pauli Exclusion Principle– No two electrons in a given atom can have the same set of

quantum numbers, thus only 1 electron is allowed in each quantum state

Electrons occupy the lowest available quantum states

Now consider the case of Fe, which has 26 electrons(next slide)(next slide)

Chapter 1 - 27

Electronic Configurations

ex: Fe - atomic # = 26 1s2 2s2 2p6 3s2 3p6 3d6 4s2

valence electrons

3d

4p4d

N-shell n = 4

3 M h ll 3

3d

4s

2

3s3p M-shell n = 3Energy

1s

2s2p

K shell n = 1

L-shell n = 2

Chapter 1 -

1s K-shell n = 1

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RELATIVE ENERGIES OF ELECTRONS IN SHELLS AND SUBSHELLS

Chapter 1 - 29

SURVEY OF ELEMENTSMost elements: Electron configuration not stable.

Electron configurationAtomic #Element1s 11Hydrogen

(stable)1s 11Hydrogen1s 22Helium1s 22s 13Lithium1s 22s 24Beryllium1 22 22 15B

...

1s 22s 22p 15Boron1s 22s 22p 26Carbon

...1s 22s 22p 6 (stable)10Neon

...

1s 22s 22p 63s 111Sodium1s 22s 22p 63s 212Magnesium1s 22s 22p 63s 23p 113Aluminum

...1s 22s 22p 63s 23p 6 (stable)... 1s 22s 22p 63s 23p 63d 10 4s 24p 6 (stable)

18...36

Argon...Krypton

Chapter 1 -

Why? Valence (outer) shell usually not filled completely so are not at lowest energy.

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Electron Configurations

Valence electrons are those in unfilled shells

Filled shells more stable

Valence electrons are most available for bonding andValence electrons are most available for bonding and control the chemical, electrical, thermal and optical properties

example: C (atomic number = 6)

1s2 2s2 2p2

valence electrons

Chapter 1 -

valence electrons

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The Periodic TableColumns: Similar Valence Structures so similar propertiesColumns: Similar Valence Structures so similar properties

p 1e

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ert g

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Ne

Ar

F

ClS

Li Be

H

Na Mg

Se

Te

Po At

I

Br

Ar

Kr

Xe

Rn

ClSg

BaCs

CaK Sc

SrRb Y

Electropositive elements: Electronegative elements:

Po At RnBaCs

RaFr

Chapter 1 -

Readily give up electronsto become + ions.

Readily acquire electronsto become - ions.

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Electronegativity

Ranges from 0.7 to 4.0,

Large and small values = very reactive elements

Smaller electronegativity Larger electronegativity

Chapter 1 -

CHAPTER 2 CONTINUED NEXT LECTURE 33

Capacity to accept electrons to form negative ions

Broad Classification of Materials

Metals: metallic bonding– strong, high modulus, ductile, medium to high Tmp– high thermal and electrical conductivityg y– crystalline, opaque, reflective

Polymers/plastics: covalent and van der Waals bonding– soft, ductile, low strength, low modulus, low density– thermal and electrical insulators– optically translucent or transparent.

Ceramics: ionic and covalent bonding– metallic+non-metallic element compounds (oxides, carbides, etc.)– brittle, crystalline or amorphous, high Tmp– strong, high modulus– electrically and thermally insulating

Chapter 1 - 34

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Types of Materials

Let us classify materials according to the way the atoms are bound together (Chapter 2).

Metals: valence electrons are detached from atoms, and spread in an 'electron sea' that "glues" the ions together. Strong, ductile, conduct electricity and heat well, are shiny if polished.

Semiconductors: the bonding is covalent (electrons are shared between atoms). Their electrical properties depend strongly on minute proportions of contaminants. Examples: Si, Ge, GaAs.

Ceramics: atoms behave like either positive or negative ions, and are bound by Coulomb forces. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and carbides). Hard, brittle, insulators. Examples: glass, porcelain.

Polymers: are bound by covalent forces and also by weak van der Waals forces, and usually based on C and H. They decompose at moderate temperatures (100 – 400 C), and are lightweight. Examples: plastics rubber.

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Properties are the way the material responds to the environment and external forces.

Mechanical properties – response to mechanical forces, strength, etc.

Electrical and magnetic properties - response electrical and magnetic fields, conductivity, etc.

Thermal properties are related to transmission of heat and heat capacity.

Optical properties include to absorption, transmission and scattering of light.

Chemical stability in contact with the environment -corrosion resistance.

Properties

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Different materials exhibit different crystal structures(Chapter 3) and resultant properties

(a) (b)force

Material Selection

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Different materials exhibit different microstructures(Chapter 4) and resultant properties

Material Selection

Superplastic deformation involves low-stress sliding along grain boundaries, a complex process of which material scientists have limited knowledge and that is a subject of current investigations.

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Material selection: Properties/performance and cost

metalsceramics

polymerssemiconductors

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Composition, Bonding, Crystal Structure and Microstructure DEFINE Materials Properties

Composition

Bonding Crystal Structure

ThermomechanicalProcessing

Microstructure

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Design of materials having specific desired characteristics directly from our knowledge of atomic structure.

• Miniaturization: “Nanostructured" materials, with microstructure that has length scales between 1 and 100 nanometers with unusual properties. Electronic components, materials for quantum computing.

• Smart materials: airplane wings that adjust to the air flow conditions, buildings that stabilize themselves in earthquakes…

• Environment-friendly materials: biodegradable or photodegradable plastics, advances in nuclear waste processing, etc.

• Learning from Nature: shells and biological hard tissue can be as strong as the most advanced laboratory-produced ceramics, mollusces produce biocompatible adhesives that we do not know how to reproduce…

• Materials for lightweight batteries with high storage densities, for turbine blades that can operate at 2500°C, room-temperature superconductors? chemical sensors (artificial nose) of extremely high sensitivity, cotton shirts that never require ironing…

Future of materials science