Metals Flashcards

1
Q

metals - density

A

metals are generally most dense

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2
Q

stiffness

A

the resistance to elastic deformation measured in pascals

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3
Q

metals - stiffness

A

have a high modulus

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4
Q

strength

A

the resistance to permanent deformation measured in pa

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5
Q

metals -strength

A

strong but not the strongest

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6
Q

toughness

A

resistance to cracking, fracture

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7
Q

metals - toughness

A

are the toughest

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8
Q

metals -thermal conductivity/electrical conductivity

A

can have much higher conductivity, but not always

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9
Q

metals - cost

A

metals have a v large range of prices

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10
Q

the strengthening mechanisms

A

1 atoms in solution, different sizes deflect and create distortions (alloy)
2 dispersion strengthening, adding enough of another element to make a second phase
3 work hardening
4 reduce grain size,more boundaries present , more deflections

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11
Q

casting

A

pouring a melt into a mould

low cost but can lead to defects

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12
Q

rolling

A
properties are better if material is deformed - stronger
squeezes out pores 
refines microstructure 
work hardening 
good for producing long bits, eg rails
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13
Q

forging

A

hot softened metal pushed/ flattened into shape

produces good microstructure high strength

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14
Q

extrusions

A

can produce complex materials
steel needs high temp so not practical method
common for aluminium or polymers

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15
Q

austenite (gamma)

A

high temp phase
fcc structure
(can be present in stainless steels and non magnetic metals)

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16
Q

Ferrite (alpha)

A

high purity- a lot of carbon
v small region in phase diagram
bcc structure
present in most steels not as a single phase

17
Q

cementite (fe3C)

A

a ceramic like material, intermetallic
line compund, fixed composition
effects all mechanical properties

18
Q

pearlite

A

not a single phase
two phase region of ferrite and cementite
has practical implication on how fraction travel in materials

19
Q

martensite

A

not on phase diagram
isn an equi phase
produced by fast cooling
hard and brittle

20
Q

Extraction - Blast furnace

A

iron ore+coke+limestone
hot air blown in bellow
coke acts as a heat source, reducing agent accepting electrons from other reactions.
liquid metal and waste (slag) tapped of periodically
5% C - poor strength, not useful

21
Q

Steel making - Basic oxygen

A
molten iron poured into converter
oxygen blow 
oxidation of impurities, gives more heat (can melt some scrap)
~300 tonne, 30-40 min cycle 
large scale
22
Q

Steel making - electric arc furnace

A

iron and scrap steel
electrodes supply power
will melt 100 tonnes in 90 mins

23
Q

secondary steel making

A

small composition adjustments

creates certain alloys

24
Q

casting

A

requires a melt
tipping/injecting melt into a mould
low cost BUT can lead to defects

25
Q

rolling

A
properties better if deformed - work hardening 
-squeezes out pores 
-refines microstructure 
-work hardening 
good for long products, eg rails
26
Q

forging

A

dies can be flat, open die forging
shaped and closed die forming
often done with hot softened metal
produces good microstructure

27
Q

extrusion

A

produces complex cross sections in one long direction
not good for steel, need high temp
commonly used for polymers and aluminium

28
Q

Pearlite - phases

A
ferritie and Fe3C 
alternating plates, lamellae
plates are boundaries, stronger 
slow cooling 
final product can be controlled
29
Q

martensite - phases

A

quick cooling
no time for ferritie and Fe3C to form carbon doesnt fit in bbc ferrite
structure is distorted- v hard brittle material

30
Q

wrought steels

A
steels shaped by deformation 
carbon is low= weld-ability
high strength low alloy (hsla)
-grain size reduction 
-second phase 
strongest and toughest of regular steels
31
Q

cast steels

A

not used structurally
casting is easier and cheaper
martensite at the surface, v brittle difficult to machine

32
Q

stainless steel

A

has protective surface oxide
expensive -used for aesthetics/long-life structures
strong
good in certain application, not structural tho

33
Q

non ferrous structural metals

A

all metals not based on fe
mostly more expensive
have attractive properties

34
Q

aluminium

A
lightweight
usually alloyed for strengthening
food strength to weight ratio 
susceptible to degradation from heat 
used in, 
transport 
-panelling 
-internal fitting 
-cladding -bridges 
-roofs
35
Q

titanium

A

more expensive than aluminium
high strength to weight ratio
used for -cladding
-aircraft

36
Q

copper

A
not primary load support 
use din -roofing 
-flashing and cladding 
easy to form difficult to weld 
oxidation gives a green surface colour