MPEM_ppt_ch03(단국대)

Manufacturing Processes Manufacturing Processes ggfor Engineering Materials for Engineering Materials

(5(5thth Edition in SI Units)Edition in SI Units)(5(5thth Edition in SI Units)Edition in SI Units)

Chapter 3: Structure and ManufacturingChapter 3: Structure and ManufacturingProperties of MetalsProperties of Metals

Chapter 3: Structure and Manufacturing Properties of MetalsChapter 3: Structure and Manufacturing Properties of MetalsManufacturing Processes for Engineering Materials Manufacturing Processes for Engineering Materials

The Crystal Structure of Metals(금속의결정구조)• When metals solidify the atoms arrange themselves in orderly

configurations called crystals(결정).

A t f t i th t l i ll d t lli• Arrangement of atoms in the crystal is called crystalline structure(결정구조).

• Smallest group of atoms showing the characteristic lattice• Smallest group of atoms showing the characteristic lattice structure(격자구조)of a particular metal is known as a unit cell(단위포).( )

• Crystal structures modified by adding atoms of another metal or metals is known as alloying(합금).


The Crystal Structure of MetalsThe Crystal Structure of Metals

• 3 basic patterns of atomic arrangement in metal:

Body-centered cubic Face-centered cubic Hexagonal close packed


(체심입방형, bcc) (면심입방형, fcc) (조밀육방형, hcp)

Deformation and Strength단결정의변형과강of Single Crystals (단결정의변형과강도)

• Crystal undergoes elastic deformation then plastic (permanent) deformation.

2 b i h i d i l ti d f ti• 2 basic mechanisms during plastic deformation:

a. Slip(슬립) one plane of atoms slip over an adjacent plane under shear stressunder shear stress

b. Twinning(쌍정) portion of the crystal forms a mirror image of itself across the plane of twinningof itself across the plane of twinning


Deformation and Strengthof Single Crystals

xπ2• Shear stress at a displacement x isbxπττ 2sinmax=

2• For small values of ,bx /

bxπττ 2

max=

• From Hooke’s law, ⎟⎠⎞

⎜⎝⎛==

axGGγτ

• Hence,a

Gbπ

τ2max =

• Assume b approx a, πτ

2maxG

=


Slip systems (슬립계)Slip systems (슬립계)

• Direction of slip is known as a slip system(슬립계).

• Different number of potential slip systems:

bcc crystals 48 possible slip systems, high slip

fcc crystals 12 slip systems, moderate slip

hcp crystal 3 slip systems, low slip


Ideal tensile strength of metals 속의이 적인장강(금속의이론적인장강도)

• When the tensile stress reaches the atomic bonds, it is known as the ideal tensile strength.

F th h h• From the graph, we have

aEπλσ

2max =πλσmax=Work

• Combining these equations,

aπ2 π

aEγσ =max

• Substitute appropriate values,

10maxE

≈σ


Imperfections (결함)Imperfections (결함)

• Discrepancy in actual strength is explained in terms of imperfections(결함) in the crystal structure.

I f ti d d f t t i d• Imperfections and defects categorized as:

a) Point defects(점결함)

b) Di l ib) Dislocations(전위)

c) Grain boundaries(결정립계)

d) kd) Cracks(균열)


Strain hardening (변형경화, work 가공경화hardening, 가공경화)

• Increase in the shear stress and overall strength of the metal gis known as strain or work hardening(변형경화, 가공경화).

• This also increases the metal’s strength.

• Degree of strain hardening is indicated by strain‐hardening exponent n.


Grains and Grain Boundaries 결정립과결정립계(결정립과결정립계)

• Number and size of the grains developed in metal depend on the rate of nucleation(핵생성).

V i t d i lidifi ti f lt t l• Various stages during solidification of molten metal:


Grains and Grain BoundariesGrains and Grain Boundaries

• Surfaces that separate the individual grains are called grain boundaries(결정립계).

E h i i t f i l t l• Each grain consists of single crystal or polycrystalline aggregate.

• Single grain is anisotropic(이방성) and• Single grain is anisotropic(이방성) and polycrystalline metal is isotropic(등방성).


Grain size(결정립도)Grain size(결정립도)

• Grain size(결정립도) influences the mechanical properties of metals.

L i l t th d h d hi h• Large grain low strength and hardness, high ductility

• The yield strength Y is related to grain size by as Hall Petch• The yield strength, Y, is related to grain size by as Hall‐Petch equation.

2/1−+= kdYYYi = basic yield stressk t t+= kdYY i k = constantd = grain diameter


Grain sizeGrain size

• Grain size is measured by counting the number of grains in a given area.

• Grain‐size number, n, is related to the number of grains, N.

12 −= nN


Influence of grain boundaries 결정립계의영향(결정립계의영향)

• Grain boundaries influence strength, ductility of metals and strain hardening.

Pl ti d f ti t k l th h i b d• Plastic deformation takes place through grain‐boundary sliding(결정립계의미끄러짐).

• Creep mechanism(크리프현상) results from grain boundary• Creep mechanism(크리프현상) results from grain‐boundary sliding.

• At a low‐melting‐point metals• At a low melting point, metals, strong metal can crack under very low stresses known as grain‐boundary embrittlement

(결정립계취화).


Plastic Deformation of Polycrystalline 다결정금속의소성변형Metals (다결정금속의소성변형)

• During plastic deformation, mass continuity in grain boundaries is maintained.

Th i ld b l t d i di ti d• The grains would become elongated in one direction and contract in the other.

• Two types of anisotropy(이방성) in metals:• Two types of anisotropy(이방성) in metals:

1. Preferred orientation(선택적방향성)

2 Mechanical fibering(기계적섬유화)2. Mechanical fibering(기계적섬유화)


Recovery, Recrystallization,회복 재결정 결정립성장and Grain Growth (회복, 재결정, 결정립성장)

• The temperature range and the time required depend on• The temperature range and the time required depend on the material.

• 3 events take place during the heating:3 events take place during the heating:

Recovery(회복)

‐ number of mobile‐ number of mobile dislocations reduced

Recrystallization(재결정)Recrystallization(재결정)

‐ new grains form

Grain growth(결정립성장)Grain growth(결정립성장)

‐ grains grow bigger


Cold, Warm, and Hot Working (냉간, 간 열간가온간, 열간가공)

• When plastic deformation above recrystallization temperature, it is called hot working(열간가공), vice versa it is known as cold working(냉간가공)known as cold working(냉간가공).


Failure and Fracture (파손과파괴)Failure and Fracture (파손과파괴)

• 2 types of failure:

1. Fracture(파괴)

2. Buckling(좌굴)

• 2 categories of fracture is ductile and brittle.


Ductile fracture (연성파괴)Ductile fracture (연성파괴)

• Ductile fracture(연성파괴) is where plastic deformation which precedes failure of the part.

It t k l l l hi h th h t i• It takes place along planes on which the shear stress is a maximum.

• The surface shows a fibrous pattern with dimples• The surface shows a fibrous pattern with dimples.

• In a tension‐test specimen, fracture begins at the centre of the necked regionthe necked region.


Ductile fractureDuctile fracture

Effects of inclusions (개재물의영향)

• Influence on ductile fracture and formability of materials.

• Consist of impurities of various kinds and second‐phase particles.

T f h ff id f i• Two factors that affect void formation:

1. Strength of the bond between inclusion and matrix

d f h l2. Hardness of the inclusion


Ductile fractureDuctile fracture

Transition temperature (천이온도)

• Metals undergo a sharp change in ductility to toughness th h t iti t tthrough transition temperature.

• Abrupt changes in shape and surface notches occur.


Ductile fractureDuctile fractureStrain aging (변형시효)Strain aging (변형시효)

• Strain aging is where carbon atoms in steels segregate to dislocations and increase resistance to dislocation movement.

• Increase strength and reduce ductility.


Brittle fracture (취성파괴)Brittle fracture (취성파괴)

• Brittle fracture(취성파괴)occurs with little plastic deformation before separation of the material.

I t i b ittl f t t k l l l• In tension, brittle fracture takes place along a cleavage plane(벽개면).

Defects(결함)

• Scratches flaws or internal cracks• Scratches, flaws or internal cracks.

1lengthCrack

1∝σ


Brittle fractureBrittle fracture

• Cracks subjected to stresses in 3 modes of direction:

Mode I tensile stress perpendicular to the crack.

Modes II and III shear stresses in 2 directions.

Fatigue fracture (피로파괴)

• Minute external / internal cracks d l d f h ldevelop at defects in the material.

• Fracture surface in fatigue is term by b h kbeach marks.


Brittle fractureBrittle fractureFatigue fractureg

• Fatigue life is influenced by method of preparation of its surfaces.

• Fatigue strength improved by:

1. Compressive residual stresses on surfaces

2. Heat treatment

3. Fine surface finish

4. Selecting appropriate materials free from significant g pp p ginclusions, voids, and impurities


Brittle fractureBrittle fracture

Stress‐corrosion cracking (응력부식균열)

• Ductile metal can fail by stress‐corrosion cracking.

• Susceptibility of metals depends on:

a) the material

b) the presence and magnitude of tensile residual stresses

c) the environment


Physical Properties (물리적성질)Physical Properties (물리적성질)

• Properties of particular interest in manufacturing are:

Density(밀도)

melting point(융점)

specific heat(비열)

thermal conductivity and expansion(열전도도, 열팽창)

electrical and magnetic properties(전기‐자기적성질)

resistance to oxidation and corrosion(내부식성)


DensityDensity

• Density depends on weight, radius and packing of the atoms.


Melting pointMelting point

• Depends on the energy required to separate its atoms.

• Re‐crystallization temperature is related to its melting point ti h li d h t t tioperations such as annealing(풀림처리) and heat treating.

• Higher melting point, more difficult the operation.

M l i i l l d h f i l• Melting points are also related to the rate of material removal and tool wear.


Specific heatSpecific heat

• Specific heat is the energy required to raise the temperature of a unit mass of a material by one degree.

Hi h t t ill ff t th d t lit b• High temperature will affect the product quality by

a) affecting surface finish and dimensional accuracy

b) i l d dib) causing tool and die wear

c) resulting in metallurgical changes in the material


Thermal conductivityThermal conductivity

• Thermal conductivity indicates the rate at which heat flows within and through the material.

• Alloying elements with difference in thermal conductivities will have effect on thermal conductivity of alloyswill have effect on thermal conductivity of alloys.


Thermal expansionThermal expansion

• Coefficient of thermal expansion is inversely proportional to the melting point of the material.

Th l t lt f i d• Thermal stresses(열응력) results from expansion and contraction of components.

• Thermal stresses may also be caused by anisotropy of• Thermal stresses may also be caused by anisotropy of thermal expansion(이방성열팽창) of the material.

• Thermal fatigue(열피로) results from thermal cycling• Thermal fatigue(열피로) results from thermal cycling.

• Thermal shock(열충격) is the development of cracks after a single thermal cycle.single thermal cycle.


Electrical and magnetic propertiesElectrical and magnetic properties

• Electrical conductivity(전기전도도) is a measure of how well the material conducts electric current.

El t i l i ti it i th i f d ti it d• Electrical resistivity(비저항) is the inverse of conductivity, and materials with high resistivity (절연체, insulators).

• Superconductivity(초전도성) is where zero electrical resistivity• Superconductivity(초전도성) is where zero electrical resistivity occurs below a critical temperature.

• Piezoelectric effect(압전효과) is a reversible interaction• Piezoelectric effect(압전효과) is a reversible interaction between an elastic strain and an electric field used in making transducers.


Resistance to corrosionResistance to corrosion

• Corrosion is the deterioration of metals and ceramics while degradation(열화) is a term used in plastics.

C i ti f l li d h• Corrosion can occur over an entire surface or localized such as in pitting(피팅).

• Stress corrosion cracking(응력부식균열) is the effect of a• Stress‐corrosion cracking(응력부식균열) is the effect of a corrosive environment.


General Properties and Applications of Ferrous Alloys• Ferrous alloys(철합금) are useful metals in terms of

mechanical, physical and chemical properties.

All t i i th i b t l• Alloys contain iron as their base metal.

• Carbon steels are least expensive of all metals while stainless steels is costlystainless steels is costly.


Carbon and alloy steels (탄소강과합 강합금강)

• Composition and processing are controlled in a manner that is suitable for different applications.

l l dd d l f• Several elements are added to steels for

Hardenability

St thStrength

Hardness

ToughnessToughness

Wear resistance

WorkabilityWorkability

Weldability

Machinability


y

Carbon and alloy steelsCarbon and alloy steels

Carbon steels

• Classified as low, medium and high:

1. Low‐carbon steel or mild steel(저탄소강, 연강), < 0.3%C, bolts, nuts and sheet plates.

2 M di b l 0 3% 0 6%C hi2. Medium‐carbon steel(중탄소강), 0.3% ~ 0.6%C, machinery, automotive and agricultural equipment.

3 High carbon steel(고탄소강) > 0 60% C springs cutlery cable3. High‐carbon steel(고탄소강), > 0.60% C, springs, cutlery, cable.



Alloy steels(합금강)

• Steels containing significant amounts of alloying elements.

• Structural‐grade alloy(구조용합금강) steels used for construction industries due to high strength.

O h ll l d f i h h d• Other alloy steels are used for its strength, hardness, resistance to creep and fatigue, and toughness.

• It may heat treated to obtain the desired properties• It may heat treated to obtain the desired properties.



High‐strength low‐alloy steels(고강도저합금강)

• Improved strength‐to‐weight ratio.

• Used in automobile bodies to reduce weight and in agricultural equipment.

S l• Some examples are:

1. Dual‐phase steels

ll d l2. Microalloyed steels

3. Nano‐alloyed steels


Stainless steels (스테인리스강)Stainless steels (스테인리스강)

• Characterized by their corrosion resistance, high strength and ductility, and high chromium content.

St i l fil f h i id t t th t l• Stainless as a film of chromium oxide protects the metal from corrosion.


Stainless steelsStainless steels

• Five types of stainless steels:

1. Austenitic steels(오스테나이트계)

2. Ferritic steels(페라이트계)

3. Martensitic steels(마르텐사이트계)

4. Precipitation‐hardening (PH) steels(석출경화계)

5. Duplex‐structure steels(이중구조계)


Tool and die steels (공구및금형강)Tool and die steels (공구및금형강)

• Designed for high strength, impact toughness, and wear resistance at a range of temperatures.


General Properties and Applications 비철금속of Nonferrous Metals(비철금속) and Alloys

• More expensive than ferrous metals, nonferrous metals and alloys.

E l f li ti• Examples of applications are:

a) aluminium for aircraft bodies

b) ib) copper wire

c) titanium for jet‐engine turbine blades

d) l f kd) tantalum for rocket engines


Aluminium and aluminium alloysAluminium and aluminium alloys

• Factors for selecting are:

1. High strength to weight ratio

2. Resistance to corrosion

3. High thermal and electrical conductivity

4. Ease of machinability

5. Non‐magnetic


Magnesium and magnesium alloysMagnesium and magnesium alloys

• Magnesium (Mg) is the lightest metal.

• Alloys are used in structural and non‐structural applications.

• Typical uses of magnesium alloys are aircraft and missile components.

Al h d ib i d i h i i• Also has good vibration‐damping characteristics.


Copper and copper alloysCopper and copper alloys

• Copper alloys have electrical and mechanical properties, corrosion resistance, thermal conductivity and wear resistanceresistance.

• Applications are electronic components, springs and heat exchangersexchangers.

• Brass(황동) is an alloy of copper and zinc.

• Bronze(청동) is an alloy of copper and tin• Bronze(청동) is an alloy of copper and tin.


Nickel and nickel alloysNickel and nickel alloys

• Nickel (Ni) has strength, toughness, and corrosion resistance to metals.

U d i t i l t l d i k l b ll• Used in stainless steels and nickel‐base alloys.

• Alloys are used for high temperature applications, such as jet engine components and rocketsjet‐engine components and rockets.


Superalloys (초합금)Superalloys (초합금)

• Superalloys are high‐temperature alloys use in jet engines, gas turbines and reciprocating engines.


Titanium and titanium alloysTitanium and titanium alloys

• Titanium (Ti) is expensive has high strength to weight ratio• Titanium (Ti) is expensive, has high strength‐to‐weight ratio and corrosion resistance.

• Used as components for aircrafts jet‐engines racing‐carsUsed as components for aircrafts, jet engines, racing cars and marine crafts.


Refractory metals (내열금속)Refractory metals (내열금속)

• Refractory metals have a high melting point and retain their strength at elevated temperatures.

• Applications are electronics, nuclear power and chemical industriesindustries.

• Molybdenum columbium tungsten and tantalum are• Molybdenum, columbium, tungsten, and tantalum are referred to as refractory metal.


Other nonferrous metalsOther nonferrous metals

1. Beryllium

2. Zirconium

3. Low‐melting‐point metals: ‐ LeadZinc‐ Zinc

‐ Tin

4 Precious metals:4. Precious metals: ‐ Gold ‐ Silver‐ Platinum


Special metals and alloysSpecial metals and alloys

1. Shape‐memory alloys(형상기억합금)

2. Amorphous alloys(비정질합금)

3. Nanomaterials(나노재료)

4. Metal foams(금속발포재)


MPEM_ppt_ch03(단국대)

Documents

Transcript of MPEM_ppt_ch03(단국대)