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(1)

Chapter 3. Structural &

Manufacturing Properties of Metals

Sung-Hoon Ahn

School of Mechanical and Aerospace Engineering

Seoul National University

(2)

Introduction

(3)

© Prof. Ahn, Sung-Hoon

Gas turbine

(4)

Periodic table ( )

Metalloids(준금속) : the elements that are difficult to classify exclusively as metals or nonmetals and have properties between those of elements in the two classes

Amphoteric elements(양쪽성 원소) : the elements which have reactivity of a substance with both acids and bases, acting as an acid in the presence of a base and as a base in the presence of an acid.

Amphoteric elements

(5)

© Prof. Ahn, Sung-Hoon

Atomic bonds

 Primary atomic bonds

 Ionic: attraction of positive & negative ions

 Covalent: sharing of electrons

 Metallic: free electron

 Secondary atomic bonds

 van der Waals

 Hydrogen bond

(6)

Primary bonds

(7)

© Prof. Ahn, Sung-Hoon

Secondary bonds

(8)

Potential Energy Curves

0

Energy

Internuclear distance

Attractive energy Repulsive

energy

Equilibrium

length bond

Net energy

(9)

© Prof. Ahn, Sung-Hoon

Energy

Internuclear distance Net energy

A

B

(10)

Crystal Structure of Metals

Crystal – crystalline structure lattice

 3 basic patterns of

atomic arrangement in most metals

 BCC (body-centered cubic)

 FCC (face-centered cubic)

 HCP (hexagonal close-

packed)

(11)

© Prof. Ahn, Sung-Hoon

Crystal Structure of Metals (cont.)

(12)

Crystal Structure of Metals (cont.)

(13)

© Prof. Ahn, Sung-Hoon

Crystal Structure of Metals (cont.)

(14)

Atomic Packing Factor

Body-centered cubic

Face-centered cubic

Hexagonal close-packed

(15)

© Prof. Ahn, Sung-Hoon

Deformation of Crystal

elastic deformation plastic deformation

 slip

 slip band

 twinning

(16)

Strength of single crystal

 Theoretical shear strength  Theoretical tensile strength

10 2γ energy Surface

sin 2 Work

2

2 sin 2

max

2 max

0 max

max

max max

E a

E

x dx a

E

a x E x x

 

 

 

 

 

 

 

 

(17)

© Prof. Ahn, Sung-Hoon

Strength of single crystal (cont.)

(18)

Imperfections

 Point defects

 Vacancy

 Interstitial atom

 Impurity atom

 Linear defects

 Dislocations

 Planar imperfections

 Grain boundary

 Phase boundary

 Volume (bulk) imperfections

 Voids

 Inclusions

 Phases

 Cracks

(19)

© Prof. Ahn, Sung-Hoon

Imperfections (cont.)

(20)

Grains & Grain boundaries

 Hall-Petch equation

 ASTM : American Society for

Testing and Materials

(21)

© Prof. Ahn, Sung-Hoon

Plastic Deformation-Polycrystalline Metal

 Anisotropy ( )  Preferred orientation

( )

 Tension-slip directions align with the loading direction

 Compression-slip perpendicular to the loading direction

 Mechanical fibering

 Alignment of impurities, inclusions, and voids

 Weaken grain boundaries-

week/less ductile in vertical

direction

(22)

Recovery, Recrystallization and Grain growth

(23)

© Prof. Ahn, Sung-Hoon

Failure ( ) and Fracture ( )

 Buckling

 Out-of plane deformation

 Fracture

 Ductile fracture

• Shear

 Brittle fracture

• Tensile

(24)

Ductile Fracture

 Fibrous pattern with dimples

(25)

© Prof. Ahn, Sung-Hoon

Ductile Fracture (2)

 Effect of inclusions

 Transition temp.

 Strain aging

(26)

Brittle Facture

 Cleavage plane – max. tensile stress

(27)

© Prof. Ahn, Sung-Hoon

Brittle Facture (2)

 Fatigue fracture

 beach marks, striations

(28)

Size Effect

 Smaller, stronger

 Whisker

 CNT

SiC whisker

(0.5 micro meter dia.) Multiwall CNT (20 nano meter dia.)

(29)

© Prof. Ahn, Sung-Hoon

Physical Properties

 Density

 Melting point

 Specific heat

 Thermal

conductivity

 CTE

(30)

Ferrous Alloys

 Carbon steel

 More carbon, higher hardenability, strength, hardness, wear resistance, lower ductility, weldability, toughness

 Low-carbon steel (<0.3%)

 Medium-carbon steel (0.3~0.6%)

 High-carbon steel (>0.6%)

 Alloy steel

(31)

© Prof. Ahn, Sung-Hoon

Ferrous Alloys (2)

 Stainless steel

 Chromium oxide film

(32)

Ferrous Alloys (3)

 Tool and die steel

 High Speed Steel (HSS)

(33)

© Prof. Ahn, Sung-Hoon

Aluminum and Aluminum Alloys

 High strength-to-weight ratio, corrosion resistance, high

thermal and electrical conductivity

(34)

Aluminum and Aluminum Alloys (2)

(35)

© Prof. Ahn, Sung-Hoon

Magnesium and Magnesium Alloys

 Lightest engineering metal, good vibration-damping

characteristics

(36)

Copper and Copper Alloys

 Best conductors of electricity and heat

(37)

© Prof. Ahn, Sung-Hoon

Copper and Copper Alloys

 Best conductors of electricity and heat

(38)

Nickel and Nickel Alloys

 High strength, toughness, corrosion resistance

(39)

© Prof. Ahn, Sung-Hoon

Superalloys

 Heat resistance, high temperature

(40)

Titanium and Titanium Alloys

 High strength-to-weight ratio, corrosion resistance

(41)

© Prof. Ahn, Sung-Hoon

High/Low Melting Temperature

 Refractory metals

 Molybdenum

 Niobium

 Tungsten

 Tantalum

 Low melting point metals

 Lead

 Zinc

 Tin

(42)

p282

(43)

© Prof. Ahn, Sung-Hoon

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© Prof. Ahn, Sung-Hoon

(46)
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© Prof. Ahn, Sung-Hoon

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© Prof. Ahn, Sung-Hoon

(50)
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© Prof. Ahn, Sung-Hoon

(52)
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© Prof. Ahn, Sung-Hoon

(54)

Young’s Modulus 1~1.2TPa

 Shear Modulus of CNT: 0.41~1TPa

 Strength of CNT: 10~63GPa

(55)

© Prof. Ahn, Sung-Hoon

(56)
(57)

© Prof. Ahn, Sung-Hoon

(58)

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