chapter 11: metal alloys applications and processing

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Chapter 11 - 1

ISSUES TO ADDRESS...• How are metal alloys classified and how are they used?

• What are some of the common fabrication techniques?

• How do properties vary throughout a piece of materialthat has been quenched, for example?

• How can properties be modified by post heat treatment?

Chapter 11: Metal Alloys

Applications and Processing



Chapter 11 - 2

Adapted from Fig. 9.24,Callister 7e .(Fig. 9.24 adapted from Binary AlloyPhase Diagrams , 2nd ed.,Vol. 1, T.B. Massalski (Ed.-in-Chief),

ASM International, Materials Park, OH,1990.)

Adapted fromFig. 11.1,Callister 7e .

Taxonomy of MetalsMetal Alloys

Steels

Ferrous Nonferrous

Cast IronsCu Al Mg Ti

<1.4wt%C 3-4.5wt%C

Steels<1.4wt%C

Cast Irons3-4.5wt%C

Fe3C

cementite

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γ

austenite

γ +L

γ +Fe3Cα

ferriteα+Fe3C

α + γ

L+Fe3C

δ

(Fe) C o , wt% C

Eutectic:

Eutectoid:0.76

4.30

727°C

1148°C

T (°C) microstructure:

ferrite, graphitecementite



Chapter 11 - 3Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 7e .

SteelsLow Alloy High Alloy

low carbon

<0.25wt%C

Med carbon

0.25-0.6wt%C

high carbon

0.6-1.4wt%C

Uses autostruc.sheet

bridgestowerspress.vessels

crankshaftsboltshammersblades

pistonsgearswearapplic.

wearapplic.

drillssawsdies

high Tapplic.turbinesfurnacesV. corros.resistant

Example 1010 4310 1040 4340 1095 4190 304

Additions noneCr,V

Ni, Mo

noneCr, Ni

Mo

noneCr, V,

Mo, W

Cr, Ni, Mo

plain HSLA plainheat

treatableplain tool

austeniticstainless

Name

Hardenability 0 + + ++ ++ +++ 0

TS - 0 + ++ + ++ 0EL + + 0 - - -- ++

increasing strength, cost, decreasing ductility



Chapter 11 - 4

Refinement of Steel from OreIron Ore

CokeLimestone

3CO+Fe2O3 →2Fe+3CO2

C+O2 →CO2

CO2 +C→ 2CO

CaCO3 → CaO+CO2

CaO + SiO2 + Al2O3 → slag

purification

reduction of iron ore to metal

heat generation

Molten iron

BLAST FURNACE

slag

air

layers of cokeand iron ore

gasrefractory

vessel



Chapter 11 - 5

Ferrous Alloys

Iron containing – Steels - cast irons

Nomenclature AISI & SAE

10xx Plain Carbon Steels

11xx Plain Carbon Steels (resulfurized for machinability)

15xx Mn (10 ~ 20%)

40xx Mo (0.20 ~ 0.30%)43xx Ni (1.65 - 2.00%), Cr (0.4 - 0.90%), Mo (0.2 - 0.3%)

44xx Mo (0.5%)

where xx is wt% C x 100

example: 1060 steel – plain carbon steel with 0.60 wt% C

Stainless Steel -- >11% Cr



Chapter 11 - 6

Cast Iron

• Ferrous alloys with > 2.1 wt% C

– more commonly 3 - 4.5 wt%C

• low melting (also brittle) so easiest to cast

• Cementite decomposes to ferrite + graphiteFe3C 3 Fe (α) + C (graphite)

– generally a slow process



Chapter 11 - 7

Fe-C True Equilibrium Diagram

Graphite formationpromoted by

• Si > 1 wt%

• slow cooling

Adapted from Fig.11.2,Callister 7e . (Fig. 11.2adapted from Binary AlloyPhase Diagrams , 2nd ed.,Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International,Materials Park, OH, 1990.)

1600

1400

1200

1000

800

600

4000 1 2 3 4 90

L

γ +L

α + Graphite

Liquid +Graphite

(Fe) C o , wt% C

0 . 6

5740°C

T (°C)

γ + Graphite

100

1153°Cγ Austenite 4.2 wt% C

α + γ



Chapter 11 - 8

Types of Cast Iron

Gray iron

• graphite flakes

• weak & brittle under tension• stronger under compression

• excellent vibrational dampening

• wear resistant

Ductile iron

• add Mg or Ce• graphite in nodules not flakes

• matrix often pearlite - betterductility

Adapted from Fig. 11.3(a) & (b), Callister 7e .



Chapter 11 - 9

Types of Cast Iron

White iron

• <1wt% Si so harder but brittle

• more cementite

Malleable iron

• heat treat at 800-900ºC

• graphite in rosettes• more ductile

Adapted from Fig. 11.3(c) & (d), Callister 7e .



Chapter 11 -10

Production of Cast Iron

Adapted from Fig.11.5,Callister 7e .



Chapter 11 -11

Limitations of Ferrous Alloys

1) Relatively high density2) Relatively low conductivity

3) Poor corrosion resistance



Chapter 11 -12Based on discussion and data provided in Section 11.3, Callister 7e .

Nonferrous Alloys

NonFerrousAlloys

• Al Alloys-lower ρ: 2.7g/cm3

-Cu, Mg, Si, Mn, Zn additions

-solid sol. or precip.strengthened (struct.aircraft parts& packaging)

• Mg Alloys-very low ρ: 1.7g/cm3

-ignites easily-aircraft, missiles

• Refractory metals-high melting T -Nb, Mo, W, Ta• Noble metals

-Ag, Au, Pt-oxid./corr. resistant

• Ti Alloys

-lower ρ: 4.5g/cm3

vs 7.9 for steel-reactive at high T -space applic.

• Cu AlloysBrass: Zn is subst. impurity(costume jewelry, coins,

corrosion resistant)Bronze : Sn, Al, Si, Ni aresubst. impurity(bushings, landinggear)

Cu-Be:precip. hardenedfor strength



Chapter 11 -13

Metal Fabrication

• How do we fabricate metals?

– Blacksmith - hammer (forged)

– Molding - cast

• Forming Operations

– Rough stock formed to final shape

Hot working vs. Cold working

• T high enough for • well below T m recrystallization • work hardening

• Larger deformations • smaller deformations



Chapter 11 -14

FORMING

rollAo

Ad roll

• Rolling (Hot or Cold Rolling)(I-beams, rails, sheet & plate)

Ao Ad

force

die

blank

force

• Forging (Hammering; Stamping)(wrenches, crankshafts)

often at

elev. T

Adapted fromFig. 11.8,Callister 7e .

Metal Fabrication Methods - I

ram billet

container

containerforce

die holder

die

Ao

Ad extrusion

• Extrusion(rods, tubing)

ductile metals, e.g. Cu, Al (hot)

tensileforce

Ao

Ad die

die

• Drawing(rods, wire, tubing)

die must be well lubricated & clean

CASTING JOINING



Chapter 11 -15

FORMING CASTING JOINING

Metal Fabrication Methods - II

• Casting- mold is filled with metal

– metal melted in furnace, perhaps alloyingelements added. Then cast in a mold

– most common, cheapest method

– gives good production of shapes

– weaker products, internal defects

– good option for brittle materials



Chapter 11 -16

• Sand Casting(large parts, e.g.,

auto engine blocks)


• trying to hold something that is hot

• what will withstand >1600ºC?

• cheap - easy to mold => sand!!!• pack sand around form (pattern) of

desired shape

Sand Sand

molten metal




Chapter 11 -17

plasterdie formedaround waxprototype


auto engine blocks)

• Investment Casting

(low volume, complex shapese.g., jewelry, turbine blades)


Investment Casting

• pattern is made from paraffin.

• mold made by encasing inplaster of paris

• melt the wax & the hollow moldis left

• pour in metal

wax


Sand Sand

molten metal



Chapter 11 -18

plasterdie formedaround waxprototype


auto engine blocks)

• Investment Casting

(low volume, complex shapese.g., jewelry, turbine blades)


wax

• Die Casting(high volume, low T alloys)

• Continuous Casting

(simple slab shapes)

molten

solidified


Sand Sand

molten metal



Chapter 11 -19

CASTING JOINING

Metal Fabrication Methods - III

• Powder Metallurgy(materials w/low ductility)

pressure

heat

point contactat low T

densificationby diffusion athigher T

areacontact

densify

• Welding(when one large part is

impractical)

• Heat affected zone:(region in which the

microstructure has beenchanged).

Adapted from Fig.11.9, Callister 7e .(Fig. 11.9 from Iron

CastingsHandbook , C.F.Walton and T.J.Opar (Ed.), 1981.)

piece 1 piece 2

fused base metal

filler metal (melted)base metal (melted)

unaffectedunaffectedheat affected zone

FORMING



Chapter 11 -20

Annealing: Heat to T anneal, then cool slowly.

Based on discussion in Section 11.7, Callister 7e .

Thermal Processing of Metals

Types ofAnnealing

• Process Anneal:

Negate effect ofcold working by(recovery/

recrystallization)

• Stress Relief: Reduce

stress caused by:-plastic deformation-nonuniform cooling-phase transform.

• Normalize (steels):Deform steel with largegrains, then normalizeto make grains small.

• Full Anneal (steels):

Make soft steels forgood forming by heatingto get γ , then cool in

furnace to get coarse P .

• Spheroidize (steels):

Make very soft steels forgood machining. Heat justbelow T E & hold for

15-25 h.



Chapter 11 -21

a) Annealing

b) Quenching

Heat Treatments

c)

c) TemperedMartensite

Adapted from Fig. 10.22, Callister 7e .

time (s)10 10

310

510

-1

400

600

800

T (°C)

Austenite (stable)

200

P

B

T E

0 %

1 0 0 % 5 0 %

A

A

M + AM + A

0%

50%

90%

a)b)



Chapter 11 -22

Hardenability--Steels• Ability to form martensite• Jominy end quench test to measure hardenability.

• Hardness versus distance from the quenched end.

Adapted from Fig. 11.11,

Callister 7e . (Fig. 11.11adapted from A.G. Guy,Essentials of MaterialsScience , McGraw-Hill BookCompany, New York,1978.)

Adapted from Fig. 11.12,Callister 7e .

24°C water

specimen(heated to γ

phase field)

flat ground

Rockwell C

hardness tests

H a r d n e s s , H R C

Distance from quenched end



Chapter 11 -23

• The cooling rate varies with position.

Adapted from Fig. 11.13, Callister 7e .

(Fig. 11.13 adapted from H. Boyer (Ed.)Atlas of Isothermal Transformation andCooling Transformation Diagrams ,American Society for Metals, 1977, p.376.)

Why Hardness Changes W/Position

distance from quenched end (in) H a r d n e

s s ,

H R C

20

40

60

0 1 2 3

600

400

200A → M

A →

P

0.1 1 10 100 1000

T (°C)

M (start)

Time (s)

0

0%

100%

M (finish) M a r t e n s i t e

M a r t e n s i t e + P e a r l i t e

F i n e P e a r l i t e

P e a r l i t e



Chapter 11 -24

Hardenability vs Alloy Composition

• Jominy end quenchresults, C = 0.4 wt% C

• "Alloy Steels"(4140, 4340, 5140, 8640)--contain Ni, Cr, Mo

(0.2 to 2wt%)--these elements shiftthe "nose".

--martensite is easierto form.

Adapted from Fig. 11.14, Callister 7e .(Fig. 11.14 adapted from figure furnishedcourtesy Republic Steel Corporation.)

Cooling rate (°C/s)

H a r d n e s s ,

H R C

20

40

60

100 20 30 40 50Distance from quenched end (mm)

210100 3

4140

8640

5140

1 0 4 0

50

80

100

%M 4340

T(°C)

10-1

10 103

1050

200

400

600

800

Time (s)

M (start)

M (90%)

shift fromA to B due

to alloying

BA

T E



Chapter 11 -25

• Effect of quenching medium:

Mediumair

oilwater

Severity of Quenchlow

moderatehigh

Hardnesslow

moderatehigh

• Effect of geometry:When surface-to-volume ratio increases:

--cooling rate increases--hardness increases

Position

centersurface

Cooling rate

lowhigh

Hardness

lowhigh

Quenching Medium & Geometry



Chapter 11 -26

0 10 20 30 40 50wt% Cu

Lα+Lα

α+θθ

θ+L

300

400

500

600

700

(Al)

T (°C)

composition rangeneeded for precipitation hardening

CuAl2

A

Adapted from Fig. 11.24, Callister 7e . (Fig. 11.24 adapted fromJ.L. Murray, International Metals Review 30, p.5, 1985.)

Precipitation Hardening• Particles impede dislocations.

• Ex: Al-Cu system• Procedure:

Adapted from Fig.11.22, Callister 7e .

--Pt B: quench to room temp.

--Pt C: reheat to nucleate

small θ crystals within

α crystals.• Other precipitation

systems:• Cu-Be

• Cu-Sn• Mg-Al

Temp.

Time

--Pt A: solution heat treat

(get α solid solution)

Pt A (sol’n heat treat)

B

Pt B

C

Pt C (precipitate θ)



Chapter 11 -27

• 2014 Al Alloy:

• TS peaks withprecipitation time.

• Increasing T acceleratesprocess.

Adapted from Fig. 11.27 (a) and (b), Callister 7e . (Fig. 11.27 adapted from Metals Handbook:

Properties and Selection: Nonferrous Alloys and Pure Metals , Vol. 2, 9th ed., H. Baker (ManagingEd.), American Society for Metals, 1979. p. 41.)

Precipitate Effect on TS , %EL

precipitation heat treat time t e n s i l e s t r e n g t h ( M P a

)

200

300

400

1001min 1h 1day 1mo 1yr

204°C

n o n -

e q u i l .

s o l i d s

o l u t i o

n

m

a n y

s m a l l

p r e

c i p i t a t e

s

“ a g e d

”

f e w

e r l a r g e

p r e c i p i t a t

e s

“ o v e

r a g e d

”

149°C

• %EL reaches minimumwith precipitation time.

% E L

( 2 i n s a m p l e )

10

20

30

01min 1h 1day 1mo 1yr

204°C 149°C

precipitation heat treat time



Chapter 11 -28

Metal Alloy Crystal Stucture

Alloys

• substitutional alloys

– can be ordered or disordered

– disordered solid solution

– ordered - periodic substitution

example: CuAu FCC

CuAu



Chapter 11 -29

• Interstitial alloys (compounds)

– one metal much larger than the other

– smaller metal goes in ordered way intointerstitial “holes” in the structure of largermetal

– Ex: Cementite – Fe3C




Chapter 11 -30


• Consider FCC structure --- what types of

holes are there?

Octahedron - octahedral site = O H Tetrahedron - tetrahedral site = T D



Chapter 11 -31


• Interstitials such as H, N, B, C

• FCC has 4 atoms per unit cell

metal atoms

21

21

21

21

T D sites

4

3 4

1

,4

3 4

1

,

43

41

,43

41

,

8 T D sites

O H sites

2

1

21

21

21

21

4 O H sites



Chapter 11 -32

• Steels: increase TS , Hardness (and cost) by adding--C (low alloy steels)

--Cr, V, Ni, Mo, W (high alloy steels)--ductility usually decreases w/additions.

• Non-ferrous:

--Cu, Al, Ti, Mg, Refractory, and noble metals.

• Fabrication techniques:--forming, casting, joining.

• Hardenability

--increases with alloy content.

• Precipitation hardening--effective means to increase strength in

Al, Cu, and Mg alloys.

Summary

chapter 11: metal alloys applications and processing

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Transcript of chapter 11: metal alloys applications and processing