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I. Nature of Materials

A. Atomic StructureB. Types of Bonding

C. Crystalline Structures

1. types

2. defectsD. Amorphous Materials

1. Implications on order

2. Solidification

II. Mechanical Properties

A. Types of Loads

B. Mechanical Testing

C. Effect of Temperature

D. Viscosity, Viscoelasticity

III. Physical Properties

A. DensityB. Thermal Expansion

C. Melting

D. Diffusion

IV. Dimensions & Surfaces

A. Dimensions vs. Tolerance

B. Types of Measurement

Instruments

C. Surface Texture (4 features)D. Surface Integrity

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V. Metals

A. Definition

B. Types of Alloys

C. Phase diagram

1. Three types of

information

2. ID phase transformationsD. Fe-C Alloys

1. Classification

2. General Properties

VI. Ceramics

A. Definition

B. Classification

C. Mechanical Properties

VII. Polymers

A. Definition

B. Synthesis

C. Structure

D. Response to heat

E. Types

VIII. Composites

A. Definition

B. Components

C. Classification

D. Types of Mechanical

Reinforcement

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Atomic Structure

Valence electrons determine all of thefollowing properties

1) Chemical

2) Electrical

3) Thermal

4) Optical

5) Mechanical

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Primary Bonding

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Ionic bond metal + nonmetal

donates acceptselectrons electrons

Dissimilar electronegativities

ex: MgO Mg 1s22s22p63s2 O 1s22s22p4

[Ne] 3s2

Mg2+ 1s22s22p6 O2- 1s22s22p6

[Ne] [Ne]

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Occurs between + and - ions.

Requires electron transfer. Large difference in electronegativity required.

Example: NaCl

Ionic Bonding

Na (metal)

unstable

Cl (nonmetal)

unstable

electron

+ -Coulombic

Attraction

Na (cation)

stable

Cl (anion)

stable

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C: has 4 valence e

-

,needs 4 more

H: has 1 valence e-,

needs 1 more

Electronegativitiesare comparable.

Covalent Bonding similar electronegativityshare electrons

bonds determined by valences&porbitals dominate bonding Example: CH4

shared electronsfrom carbon atom

shared electrons

from hydrogenatoms

H

H

H

H

C

CH 4

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Metallic Bonding Metallic Bond:

Delocalized as electron cloud

Results in good electrical and thermal conductivit

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Arises from interaction between dipoles

Permanent dipoles-molecule induced

Fluctuating dipoles (London forces)

-general case:

-ex: liquid HCl

-ex: polymer

Adapted from Fig. 2.14,

Callister & Rethwisch 3e.

SECONDARY BONDING

asymmetric electronclouds

+ - + -

secondarybonding

HH HH

H 2 H 2

secondarybonding

ex: liquid H2

H Cl H Clsecondarybonding

secondarybonding

+ - + -

secondary bonding

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Crystalline Structure

Manner in which atoms are located at regularand 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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Three Crystal Structures in Metals

Three types of crystal structure: (a) body-

centered cubic, (b) face-centered cubic, and

(c) hexagonal close-packed

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Crystal Structures for Common Metals

Room temperature crystal structures for some

of the common metals:

Body-centered cubic (BCC)

Chromium, Iron, Molybdenum, Tungsten

Face-centered cubic (FCC)

Aluminum, Copper, Gold, Lead, Silver, Nickel

Hexagonal close-packed (HCP) Magnesium, Titanium, Zinc

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Imperfections (Defects) in Crystals

Nearly all engineering materials possess defects

Defects are often introduced during

solidification

Imperfections can also be introduced purposely;

e.g., addition of alloying ingredient in metal

Types of defects: (1) point defects, (2) line

defects, (3) surface (interfacial) defects

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Point Defects

Imperfections in crystal structure involving either a

single atom or a small number of atoms

Point defects: (a) vacancy, (b) ion-pair vacancy (Schottky

Defect), (c) interstitial, (d) displaced ion (Frenkel Defect).

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Line Defects

Connected group of point defects that forms a

line in the lattice structure

Most important line defect is a dislocation,

which can take two forms:

Edge dislocation

Screw dislocation

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Edge Dislocation

Edge of an extra plane of atoms that exists in the lattice

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Screw Dislocation

Spiral within the lattice

structure wrapped

around an

imperfection line, like

a screw is wrapped

around its axis

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Interfacial or Surface Defects

Imperfections that extend in two directions

to form a boundary

Examples: External: the surface of a crystalline object is an

interruption in the lattice structure

Internal: grain boundaries are internal surface

interruptions

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Polycrystalline Nature of Metals

A block of metal may contain millions of

individual crystals, called grains

Such a structure is calledpolycrystalline

Each grain has its own unique lattice orientation

But collectively, the grains are randomly oriented in the

block

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G i d G i B d i i M t i l

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Mostengineering materials are polycrystal l ine.

Each "grain" is a single crystal.

If grains are randomly oriented, overall component properties

are not directional. Grain sizes typ. range from 1 nm to 2 cm

(i.e., from a few to millions of atomic layers).

Grains and Grain Boundaries in Materials

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Si l l l

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Single Crystals

-Properties vary withdirection: anisotropic.

-Example: the modulus

of elasticity (E) in BCC iron:

Data from Table 3.7,

Callister & Rethwisch 3e

Polycrystals

-Properties may/may not

vary with direction.

-If grains are randomly

oriented: i so t rop ic.(Epoly iron= 210 GPa)

-If grains are textured,

anisotropic.

200 mm Adapted from Fig.5.19(b), Callister &

Rethwisch 3e.

(Fig. 5.19).

Single vs. Polycrystals

E (diagonal) = 273 GPa

E (edge) = 125 GPa

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Crystalline vs. Amorphous materials

Difference in structure between: (a) crystallineand (b) noncrystalline materials

Crystal structure is regular, repeating;

amorphous materials are less tightly packedand randomly oriented

(a) (b)

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True Stress-Strain Curve

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True Stress-Strain Curve

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Strain Hardening in Stress-Strain Curve

Note that true stress increases continuously

in the plastic region until necking

In the engineering stress-strain curve, the

significance of this was lost because stress was

based on the original area value

It means that the metal is becoming stronger

as strain increases

This is the property called strain hardening

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T St St i i L L Pl t

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True Stress-Strain in Log-Log Plot

289/26/2014

K= strength coefficient;

and

n = strain hardening

exponent

Flow Curve

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Categories of Stress-Strain

Relationship: Perfectly Elastic

Behavior is defined

completely by modulus of

elasticity E Fractures rather than yielding

to plastic flow

Brittle materials: ceramics,

many cast irons, andthermosetting polymers

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Stress-Strain Relationships: Elastic

and Perfectly Plastic

Stiffness defined by E

Once Yreached, deforms

plastically at same stress level Flow curve: K= Y,n= 0

Metals behave like this when

heated to sufficiently high

temperatures (aboverecrystallization)

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Stress-Strain Relationships: Elastic

and Strain Hardening

Hooke's Law in elastic region,

yields at Y

Flow curve: K> Y, n> 0 Most ductile metals behave

this way when cold worked

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Testing of Brittle Materials

Hard brittle materials (e.g., ceramics) possess

elasticity but little or no plasticity

Conventional tensile test cannot be easily applied

Often tested by a bendingtest(also called

flexure test)

Specimen of rectangular cross-section is

positioned between two supports, and a load isapplied at its center

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Bending Test

Bending of a rectangular cross section results

in both tensile and compressive stresses in the

material: (left) initial loading; (right) highly

stressed and strained specimen

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Testing of Brittle Materials

Brittle materials do not flex

They deform elastically until fracture

Failure occurs because tensile strength of outer

fibers of specimen are exceeded

Failure type: cleavage- common with ceramics

and metals at low temperatures, in which

separation rather than slip occurs along certaincrystallographic planes

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Effect of Porosity

Despite various processing steps pores maystill exist in ceramic

Porosity (P) has a negative influence on elastic

properties and strength E = E0(1-1.9P+0.9P2)

sfs= s0exp(-nP)

10 vol% porosity will decrease flexuralstrength by 50% from measured value of

nonporous material.

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Hardness

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Hardness

Resistance to permanently indenting the surface.

Large hardness means:

-- resistance to plastic deformation or cracking in

compression.

-- better wear properties.

e.g.,10 mm sphere

apply known force measure size

of indent afterremoving load

dDSmaller indentsmean largerhardness.

increasing hardness

mostplastics

brassesAl alloys

easy to machinesteels file hard

cuttingtools

nitridedsteels diamond

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Effect of Temperature on Properties

General effect of

temperature onstrength and

ductility

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Hot Hardness

Hot HardnessAbility of a

material to retain

hardness at elevated

temperatures

Typical hardness as a

function of

temperature forseveral materials

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Eff t f H ti Aft H d i

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1 hour treatment at Tanneal...

decreases TSand increases %EL. Effects of cold work are reversed!

3 Annealing

stages to

discuss...

Adapted from Fig. 8.22, Callister & Rethwisch3e.

Effect of Heating After Hardening

ten

siles

treng

th(M

Pa

)

duc

tility(%EL

)tensile strength

ductility

600

300

400

500

60

50

40

30

20

annealing temperature (C)200100 300 400 500 600 700

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R

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Annihilation reduces dislocation density.

Recovery

Scenario 1

Results from

diffusion

Scenario 2

4. opposite dislocationsmeet and annihilate

Dislocationsannihilateand forma perfectatomic

plane.

extra half-planeof atoms

extra half-planeof atoms

atomsdiffuseto regions

of tension

2. grey atoms leave byvacancy diffusionallowing disl. to climb

tR

1. dislocation blocked;cant move to the right

Obstacle dislocation

3. Climbed disl. can now

move on new slip plane

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Recrystallization

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New grains are formed that:

-- have a small dislocation density

-- are small

-- consume cold-worked grains.

Adapted from

Fig. 8.21 (a),(b),

Callister &

Rethwisch 3e.

33% cold

worked

brass

New crystals

nucleate after

3 sec. at 580C.

0.6 mm 0.6 mm

Recrystallization

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F rther Recr stalli ation

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All cold-worked grains are consumed.

Adapted fromFig. 8.21 (c),(d),

Callister &

Rethwisch 3e.

After 4

seconds

After 8

seconds

0.6 mm0.6 mm

Further Recrystallization

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Grain Growth

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At longer times, larger grains consume smaller ones.

Why? Grain boundary area (and therefore energy)

is reduced.

After 8 s,

580C

After 15 min,

580C

0.6 mm 0.6 mm

Adapted from

Fig. 8.21 (d),(e),

Callister &

Rethwisch 3e.

Grain Growth

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TR



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R t lli ti T t T

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Recrystallization Temperature, TRTR= recrystallization temperature= point of highest rate of

property change

1. Tm => TR0.3-0.5 Tm(K)

2. Due to diffusionannealing timeTR= f(time) shorter

annealing time => higher TR

3. Higher %CW=> lower TR

strain hardening4. Pure metals lower TRdue to dislocation movements

Easier to move in pure metals => lower TR

Hot workabove TR

Cold workbelow TR

Smaller grains

stronger at low temperature

weaker at high temperature

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Recrystallization and Manufacturing

Recrystallization can be exploited in

manufacturing

Heating a metal to its recrystallization

temperature prior to deformation allows a

greater amount of straining

Lower forces and power are required to perform

the process Forming a metal at temperatures above its

recrystallization temperature is called hot working

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Tensile deformation of a polymer

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elasticappliedstress

viscoelastic

viscous

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Fundamental Concepts

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Fundamental Concepts Component pure metals and/or compounds of which

an alloy is composed

System- 1) specific body of material under consideration,2) series of alloys consisting of same components.

Solubility limitmaximum conc. of solute atoms thatmay dissolve in solvent to form solid solution

Phasehomogeneous portion of a system with uniformphysical and chemical characteristics.

EquilibriumSystem is stable over time.

Metastable - state of equilibrium never completely

achieved, small changes may occur, may persistindefinitely.

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S lid S l i

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Solid Solutions

Crystal structure is maintained Impurity atoms are randomly distributed

throughout host

For interstitial solid solutions, impurity atomsfill the voids or interstices among host atoms

Atomic diameter of interstitial atom

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Impurities in Metals

Conditions for substitutional solid solution (S.S.) 1. r (atomic radius) < 15%

2. Proximity in periodic table

i.e., similar electronegativities

3. Same crystal structure for pure metals 4. Valency

All else being equal, a metal will have a greater tendency to

dissolve a metal of higher valency than one of lower valency

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Solute element or compound present in minor concentration

Solvent element or compound present in greatest amount (host atoms)

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Criteria for Solid Solubility

CrystalStructure

electroneg r(nm)

Ni FCC 1.9 0.1246Cu FCC 1.8 0.1278

Both have the same crystal structure (FCC) and have similar

electronegativities and atomic radii suggesting high mutual

solubility.

Simple system (e.g., Ni-Cu solution)

Ni and Cu are totally soluble in one another for all proportions.

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PHASE DIAGRAMS

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Phase Diagrams

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Phase Diagrams

Indicate phases as a function of T, C, and P.

For this course:

- binary systems: just 2 components.- independent variables: T and C (P = 1 atm is almost always used).

Phase

Diagram

for Cu-Ni

system

Adapted from Fig. 10.3(a), Callister &

Rethwisch 3e.

2 phases:

L (liquid)

a (FCC solid solution)

3 different phase fields:L

L +a

a

wt% Ni

20 40 60 80 10001000

1100

1200

1300

1400

1500

1600

T(C)

L (liquid)

a

(FCC solid

solution)

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Isomorphous Binary Phase Diagram

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Cu-Ni

phase

diagram

Isomorphous Binary Phase Diagram

Phase diagram:

Cu-Ni system. System is:


Rethwisch 3e.

-- binaryi.e., 2 components:

Cu and Ni.

-- isomorphousi.e., complete

solubility of one

component in

another; aphase

field extends from0 to 100 wt% Ni.

wt% Ni

20

40

60

80

100

0

1000

1100

1200

1300

1400

1500

1600

T(C)

L (liquid)

a

(FCC solid

solution)

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Phase Diagrams

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wt% Ni20 40 60 80 1000

1000

1100

1200

1300

1400

1500

1600

T(C)

L (liquid)

a

(FCC solid

solution)

56

Phase Diagrams:Determination of phase(s) present

Rule 1: If we know T and Co, then we know:-- which phase(s) is (are) present.

Examples:

A(1100C, 60 wt% Ni):1 phase: a

B

(1250C, 35 wt% Ni):2 phases: L + a

B

(1250C,35)

A(1100C,60)Adapted from Fig. 10.3(a), Callister &

Rethwisch 3e.

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Phase Diagrams:

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wt% Ni

20

1200

1300

T(C)

L (liquid)

a

(solid)

30 40 50

Cu-Nisystem

Phase DiagramsDetermination of phase compositions

Rule 2: If we know T and C0, then we can determine:

-- the composition of each phase.

Examples:

TAA

35

C032

CL

At TA = 1320C:

Only Liquid (L) presentCL= C0 ( = 35 wt% Ni)

At TB

= 1250C:

Both aand L present

CL = Cliquidus ( = 32 wt% Ni)

Ca = Csolidus ( = 43 wt% Ni)

At TD = 1190C:

Only Solid (a) present

Ca= C0 ( = 35 wt% Ni)

Consider C0= 35 wt% Ni

D

TD

tie line

4

Ca3


Rethwisch 3e.

B

TB

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Phase Diagrams

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Rule 3: If we know T and C0, then can determine:

-- the weight fraction of each phase. Examples:

At TA : Only Liquid (L) present

WL = 1.00, Wa= 0At TD : Only Solid (a) present

WL = 0, Wa = 1.00

Phase Diagrams:Determination of phase weight fractions

wt% Ni

20

1200

1300

T(C)

L (liquid)

a

(solid)

3

0

4

0

5

0

Cu-Ni

system

TAA

35C0

32CL

BTB

D

TD

tie line

4Ca3

R

S

At TB : Both a and L present

73.032433543

= 0.27

WL

SR + S

Wa R

R + S

Consider C0= 35 wt% Ni


Rethwisch 3e.

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The Inverse Lever Rule

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Tie lineconnects the phases in equilibrium with each

otheralso sometimes called an isotherm

The Inverse Lever Rule

WL=

ML

ML+ M

=S

R + S=C

C0

C

CL

W

=R

R + S=C

0 C

L

C

CL

wt% Ni

20

1200

1300

T(C)

L (liquid)

a

(solid)

30 40 50

B

T

B

tie line

C0

CL Ca

SR

Adapted from Fig. 10.3(b),


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E Cooling of a C Ni Allo

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60

wt% Ni20

120 0

130 0

3 0 4 0 5 0110 0

L (liquid)

a

(solid)

T(C)

A

35C0

L: 35wt%Ni

Cu-Nisystem

Phase diagram:

Cu-Ni system.



Consider

microstuctural

changes that

accompany the

cooling of aC0= 35 wt% Ni alloy

Ex: Cooling of a Cu-Ni Alloy

4635

4332

a: 43 wt% Ni

L: 32 wt% Ni

Ba: 46 wt% NiL: 35 wt% Ni

C

EL: 24 wt% Ni

a: 36 wt% Ni

24 36D

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Mechanical Properties: Cu-Ni System

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Mechanical Properties:Cu-Ni System

Effect of solid solution strengthening on:

-- Tensile strength (TS) -- Ductility (%EL)

Adapted from Fig. 10.6(a),


Tens

ile

Streng

th(MPa

)

Composition, wt% NiCu Ni0 20 40 60 80 100

200

300

400

TS forpure Ni

TS for pure Cu

Elonga

tion

(%EL)

Composition, wt% NiCu Ni

0 20 40 60 80 10020

30

40

50

60

%ELforpure Ni

%ELfor pure Cu

Adapted from Fig. 10.6(b),


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Binary Eutectic Systems

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2 componentshas a special composition

with a min. melting T.



Binary-Eutectic Systems

3 single phase regions

(L, a, b)

Limited solubility:a: mostly Cu

b: mostly Ag

TE : No liquid below TE

: Composition at

temperature TE

CE

Ex.: Cu-Ag system

Cu-Agsystem

L (liquid)

a L+ a

L+b

b

a + b

C , wt% Ag20 40 60 80 1000

200

1200

T(C)

400

600

800

1000

CE

TE 8.0 71.9 91.2779C

Ag)wt%1.29(Ag)wt%.08(Ag)wt%9.71( b+aLcooling

heating

Eutectic reaction

L(CE) a(CaE) + b(CbE)

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EX: Pb Sn Eutectic System

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L+a

L+b

a + b

200

T(C)

18.3

C, wt% Sn

20 60 80 1000

300

100

L (liquid)

a

183C

61.9 97.8b

For a 40 wt% Sn-60 wt% Pb alloy at 150C, determine:

-- the phases presentPb-Snsystem

EX: Pb-Sn Eutectic System

Answer:a+ b-- the phase compositions

-- the relative amountof each phase

150

40C0

11Ca

99Cb

SR

Answer:Ca= 11 wt% SnCb= 99 wt% Sn

Wa

=Cb- C0

Cb- Ca

= 99 - 4099 - 11

= 5988

= 0.67

SR+S

=

Wb=C0 - Ca

Cb - Ca=

R

R+S

=

29

88 = 0.33=

40 - 11

99 - 11

Answer:



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64

Lamellar Eutectic Structure

Adapted from Figs. 10.14 & 10.15,


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Eutectic Eutectoid & Peritectic

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65

Eutectoidone solid phase transforms to two other solid phases

S2 S1+S3

a+ Fe3C (For Fe-C, 727C, 0.76 wt% C)

intermetallic compound - cementite

cool

heat

Eutectic, Eutectoid, & Peritectic

Eutectic- liquid transforms to two solid phases

L a+ b (For Pb-Sn, 183C, 61.9 wt% Sn)coolheat

cool

heat

Peritectic- liquid and one solid phase transform to a second solid

phase

S1 + L S2

+ L (For Fe-C, 1493C, 0.16 wt% C)

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Intermediate Compounds

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66

Intermediate Compounds

Mg2Pb

Note: intermetallic compound exists as a line on the diagram

stoichiometry is fixed.

Adapted fromFig. 10.20, Callister &

Rethwisch 3e.

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Classification of Metal Alloys

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Adapted from Fig. 10.28, Callister &

Rethwisch 3e

Classification of Metal AlloysMetal Alloys

Steels

Ferrous Nonferrous

Cast Irons

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Based on data provided in Tables 13.1(b), 13.2(b), 13.3, and 13.4, Callister & Rethwisch 3e.

Steels

Low Alloy High Alloy

low carbon

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Adapted from Fig. 10.28, Callister &

Rethwisch 3e



Classification of Metal AlloysMetal Alloys

Steels

Ferrous Nonferrous

Cast Irons

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Cast Irons

Ferrous alloyswith > 2.1 wt% C

more commonly 3 - 4.5 wt% C

Low meltingrelatively easy to cast

Generally brittle

Cementite decomposes to ferrite + graphite

Fe3C3 Fe (a) + C (graphite)

generally a slow process

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Fe C True Equilibrium Diagram

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Fe-C True Equilibrium Diagram

Graphite formation

promoted by

Si > 1 wt%

slow cooling



1600

1400

1200

1000

800

600

4000 1 2 3 4 90

L

+L

a+ Graphite

Liquid +

Graphite

(Fe) C, wt% C

0.6

5740C

T(C)

+ Graphite

100

1153C

Austenite4.2 wt% C

a +

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Nonferrous Alloys

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Based on discussion and data provided in Section 13.3, Callister & Rethwisch 3e & Fundamentals of Modern

Manufacturing 4thedition.

Nonferrous Alloys

NonFerrousAlloys

Al Alloys

-low r: 2.7 g/cm3Produced from bauxiteGood conductor, corrosion res.Wrought (1XXX), Cast (1XX.X)

Mg Alloys

-very low r: 1.7g/cm3

machinable-Produced from MgCl2

Refractory metals

-high melting Ts-Nb, Mo, W, TaNi Alloys

-Similar to steels-oxid./corr. resistant

Ti Alloys

-relativelylowr:4.5g/cm3

vs 7.9 for steel-reactiveathighTs-space applic.

Cu Alloys

Brass:Zn is subst. impurity

corrosion resistant)

Bronze: Sn, Al, Si, Ni aresubst. impurities

CXXXXX)

Cu-Be:precip. hardenedfor strength

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Noble metals

Au, Ag, Pt, Pd

Chemically inactive (in bulk)

Used for jewelry, decorative applications

Generally corrosion resistant and good

conductors

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Superalloys

Superior combinations of properties

Used in high temperature, corrosive

environments

Aircraft turbine components, nuclear reactors,

petrochemical equipment

Classified according to predominant metal in

alloy (Co, Ni, Fe)

Doped with refractory metals (Nb, Mo, W, Ta)

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Polymerization

As a chemical process, the synthesis ofpolymers can occur by either of two

methods:

1. Addition polymerization2. Step polymerization

Production of a given polymer is generallyassociated with one method or the other

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Addition Polymerization In this process, the double bonds between

carbon atoms in the ethylene monomers are

induced to open up so they can join with

other monomer molecules

The connections occur on both ends of the

expanding macromolecule, developing long

chains of repeating mers

It is initiated using a chemical catalyst to open

the carbon double bond in some of the

monomers9/26/2014 76ME/IE 380 - Abiade

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Addition Polymerization

Model of addition (chain) polymerization: (1)initiation, (2) rapid addition of monomers, and

(3) resulting long chain polymer molecule with

nmers at termination of reaction

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Step Polymerization

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p y

In this form of polymerization, two reacting

monomers are brought together to form anew molecule of the desired compound

As reaction continues, more reactantmolecules combine with the molecules first

synthesized to form polymers of length n= 2,then length n= 3, and so on

In addition, polymers of length n1and n2also

combine to form molecules of length n= n1+n2, so that two types of reactions areproceeding simultaneously

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Step Polymerization

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Step Polymerization

Model of step polymerization showing the

two types of reactions occurring: (left) n-merattaching a single monomer to form a

(n+1)-mer; and (right) n1-mer combining with

n2-mer to form a (n1+n2)-mer.

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l

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Some Examples

Polymers produced by additionpolymerization:

Polyethylene, polypropylene, polyvinylchloride,

polyisoprene

Polymers produced by step polymerization:

Nylon, polycarbonate, phenol formaldehyde

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l l S f l

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81

Molecular Structures for Polymers

secondarybonding

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Physical characteristics of polymers depends on MW, shape and structure of

molecular chains.

Structure of the chains may be controlled during synthesis.

Polymers usually consist of 2 or more of the molecular structures.

low packing Covalently linked Distinct mech/thermal propflexible

linear branched crosslinked network

Molecular Configurations for Polymers

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82

Molecular Configurations for Polymers

The regularity and symmetry of the side atom or group can

influence the properties

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head to tail head to head

Stereoregularity

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83

g y

Refers to situation in which atoms are linked in same

order but differ in spatial arrangment

isotacticall Rgroups on same side of

chain

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC C C

H

H

H

R

C C

H

H

H

R

C C

H

H

H

R R

H

H

H

CC

syndiotacticRgroups alternate

sides

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Stereoregularity (cont.)

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84

Stereoregularity (cont.)

atacticRgroups randomly positioned

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

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Conversion from one tactic structure to another is not possible by rotation of bonds.Bonds must be severed and reformed after rotation.

All configurations may be observed in a single polymer.

Copolymers

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85

Copolymers

two or more monomers

polymerized together randomA and B randomly

positioned along chain

alternatingA and B alternatein polymer chain

block large blocks of A unitsalternate with large blocks of Bunits

graftchains of B units grafted

onto A backbone

A B

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Crystallinity in Polymers

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86

y y y

Complex, molecules (vs. ions,

atoms)

Ordered atomic

arrangements involving

molecular chains

Crystal structures in terms ofunit cells

Example shown

polyethylene unit cell

Adapted from Fig.

4.10, Callister &

Rethwisch 3e.

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Polymer Crystallinity

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87

Polymer Crystallinity

Crystalline regions

thin platelets with chain folds at faces

Chain foldedstructure

10 nm

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Polymer Crystallinity (cont.)

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88

Polymer Crystallinity (cont.)

Polymers rarely 100% crystalline

Difficult for all regions of all chains tobecome aligned

Degree of crystallinity

expressed as % crystallinity.-- Some physical properties

depend on % crystallinity.

-- Heat treating causes

crystalline regions to grow

and % crystallinity to

increase.

Adapted from Fig. 14.11, Callister 6e.

crystallineregion

amorphous

region

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Th l B h i f P l

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Thermal Behavior of Polymers

The melting behavior of a polymer is determined

by its crystallinity

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Thermo (plastic,set) polymers

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Thermoplastic Soften & liquefy when heated

Harden when cooled

Soften/hardening is reversible

Secondary bonding diminishes astemperature increases

Normally soft

Most linear and some branched

structures

Synthesized by applying heat andpressure

Thermoset Permanently hardens during

formation

Network polymers

Bonds anchor chains to prohibit chainmovement during heat treatment

Extensive crosslinking exists (10

50%)

Polymer degradation only occurs at

excess temperatures

Generally harder and stronger.

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Response to mechanical forces at high temperature related to dominant

molecular structure

Strength vs. Temperature

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Amorphous TP is glass-like below Tg

100 % Crystalline polymer has no rubbery transition

Partially crystallized polymer has intermediate behavior

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Physical Properties of TP

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Physical Properties of TP

Lower densities than metals or ceramics Typical specific gravity for polymers are 1.2 (comparedto ceramics (~ 2.5) and metals (~ 7)

Much higher coefficient of thermal expansion

Roughly five times the value for metals and 10 timesthe value for ceramics

Much lower melting temperatures

Insulating electrical properties

Higher specific heats than metals andceramics

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Cross-Linking in TS Polymers

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Cross Linking in TS Polymers

Three categories:1. Temperature-activated systems

2. Catalyst-activated systems

3. Mixing-activated systems

Curing is accomplished at the fabrication

plants that make the parts rather than the

chemical plants that supply the startingmaterials to the fabricator

939/26/2014 ME/IE 380 - Abiade

Mechanical Properties of Polymers

Stress Strain Behavior

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94

Stress-Strain Behavior

Deformation strains for polymers > 1000%

brittle polymer

plastic

elastomerelastic moduli

less than for metals Adapted from Fig. 7.22,Callister & Rethwisch 3e.

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95

Composites

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Composite

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96

Composite

Combination of two or more individualmaterials

Design goal: obtain a more desirablecombination of properties (principle of

combined action)

e.g., low density and high strength

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Terminology/Classification

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97

Composite:

-- Multiphase material that is artificially

made.

Phase types:

-- Matrix - is continuous

-- Reinforcing/Dispersed - is discontinuous and

surrounded by matrix

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Interphase

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p

In some cases, a third ingredient must beadded to bond primary and secondary phases

Called an interphase, it is like an adhesive

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Interphases

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Interphases

Formation of an interphase consisting of asolution of primary and secondary phases attheir boundary

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Terminology/Classification

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100

Dispersed phase:

-- Purpose:MMC: increase sy, TS, fatigue and creep resist.

CMC: increase toughnessPMC: increase E, sy, TS, creep resist.

-- Types: particle/flakes, fiber, structural

Matrix phase:

-- Purposes are to:- transfer stress to dispersed phase- protect dispersed phase from

environment

-- Types: MMC, CMC, PMC

metal ceramic polymer

gy/

woven

fibers

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Classification of Composites

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101

Classification of Composites

Particulates

particle

Flakes

Particle-reinforced

Continuous

(aligned)

Aligned Randomly

oriented

Discontinuous

(short)

Fiber-reinforced

Laminates Sandwich

panels

Structural

Composites

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Fiber Orientation

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Fiber orientation in composite materials:

(a) one-dimensional, continuous fibers; (b)

planar, continuous fibers in the form of a

woven fabric; and (c) random, discontinuous

fibers

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Three Factors that Determine Properties

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1. Materials used as component phases in thecomposite

2. Geometric shapes of the constituents and

resulting structure of the composite system

3. How the phases interact with one another

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Example: Fiber Reinforced

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Polymer

Model of

fiber-reinforced

composite material

showing direction in

which elastic

modulus is being

estimated by therule of mixtures

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Variations in Strength and Stiffness

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Variations in Strength and Stiffness

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Classification: Fiber-Reinforced (iii)

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106

Critical fiber length for effective stiffening & strengthening:

Ex: For fiberglass, common fiber length > 15 mm needed

Particle-reinforced Fiber-reinforced Structural

c

fd

t

s2

lengthfiber

fiber diameter

shear strength of

fiber-matrix interface

fiber ultimate tensile strength

For longer fibers, stress transference from matrix is more efficientShort, thick fibers:

c

fd

t

s2

lengthfiber

Long, thin fibers:

Low fiber efficiency

c

fd

t

s2

lengthfiber

High fiber efficiency9/26/2014 ME/IE 380 - Abiade

Composite Benefits

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PMCs: Increased E/r

E(GPa)

Density, r[mg/m3]

0.1 0.3 1 3 10 300.010.1

1

10

102

103

metal/metal alloys

polymers

PMCs

ceramics

Adapted from T.G. Nieh, "Creep rupture of a

silicon-carbide reinforced aluminum

composite", Metall. Trans. AVol. 15(1), pp.

139-146, 1984.

MMCs:

Increasedcreep

resistance10

-8

10-6

10-4

6061 Al

6061 Alw/SiC

hi k

ess (s-1)

CMCs: Increased toughness

fiber-reinf

un-reinf

particle-reinf

Force

Bend displacement

Documents

Part 1-Review (1)