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Materials > Metals > Flashcards

Metals Flashcards

1
Q

What are the most used metals, and how much of them were used in 2018?

A

Steel: 1,808 million metric tonnes
Alumium: 21.9 million metric tonnes
copper: 14.9 million metric tonnes
gold: 2,600 metric tonnes

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2
Q

When was the first usage of cast iron during the structural revolution?

A

1779 - Iron bridge, coalbrookdale

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3
Q

What was the first major bridge built with wrought steel?

A

Forth Railbridge, scotland, 1890

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4
Q

What kind of bonding is present in metals?

A

Metallic bonds

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5
Q

What are the properties of metallic bonds

A

Free to move electrons make them malleable and good conductors, usually have high melting and boiling points

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6
Q

What kind of metals are most engineering metals?

A

Alloys

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7
Q

What do FCC, HCP, BCC dstand for

A

FCC: Face centered cubic
HCP: hexagonal close packed
BCC: body centered cubic

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8
Q

What metals have an FCC structure?

A

Aluminium, copper, gold. lead, nickel, platinum, silver

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9
Q

What metals have a BCC structure?

A

Chromium, Iron (alpha), Molbdenum

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10
Q

What metalls have an HCP structure?

A

Cobalt, magnesium

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11
Q

What type of imperfections are found in the chrystal structure?

A
  • Substitutional Atoms (solutes)
  • Interstital atoms (solutes)
  • Dislocations
  • Vacancies
  • Grain boundaries
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12
Q

What is the definition of a grain boundary?

A

The interface between adjacent chrystalline regions that have different orientation

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13
Q

What is the definition of a dislocation?

A

An irregularity within a crystal strucutre that contains an abrupt change in the arrangmement of atoms

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14
Q

What is the difference between interstital and substitutional atoms?

A

interstital allow for the same number of metal atoms and is nessled into the microstructure,
Substiutional replace one of the metal atoms in the chrystal

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15
Q

What failure are grain boundaries resposible for?

A

Intergranular fracture

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16
Q

What failure are dislocations responsible for?

A

Plastic deformation

17
Q

Why do dislocations cause failures?

A

Because the stress required to deform a crystal is mich less than the stress calculated from considering a defect-free structure

18
Q

How do dislocations move through the structure?

A
  • The row of bonds will break and reattatch itself to a diffferent row of bonds
  • Much easier for 1 row to bend rather than an entire plane
19
Q

What causes dislocations to occur?

A

When a plane of atoms is present that distorts the lattice structure

20
Q

What is the effect of shear stress on dislocation?

A

Moves allong in the direction of the imposed stress

21
Q

How do we hinder the movement of dislocations?

A

Creating obstacles to dislocation motion

22
Q

What is the definition of an alloy?

A

Metal mixed with other elements

23
Q

What are the properties of an alloy determined by?

A

The composition of the microstructure and the distribution of the phases

24
Q

How much carbon and manganese is in steel?

A

<2% carbon and 1% manganese

25
Q

Hoe many differrent grades of steel are there?

A

3,500

26
Q

What are the benefits of steels?

A

They are stronger and lighter, more fit for purpouse

Modern cars are stronger and 25% lighter

27
Q

What is the benefite of a grain boundary?

A

act as a barrier to dislocation motion

Increases yield stress

28
Q

How do we increase the yield stress?

A

Reduce the grain size

29
Q

What is the Hall-Petch equation?

A

sigma_y = sigma_o +k/sqrt(d)

sigma_y = yield stress
sigma_o, k = material constants
d = grain size

30
Q

What does the Hall-Petch equation show?

A

That we can achieve theoretical max strength of materials by decreasing the grain size

31
Q

What is work hardening?

A
  • Dislocations have an associated strain field
  • This strain field makes a barrier to dislocation motion
  • plastic deformation gives increases dislocation density leading to increased interactions and higher strength
  • Dislocations increase in density during plastic flow, and tange and pile up
32
Q

What conclusion does work-hardening allow us to draw?

A

THere is an ever increasing shear stress required for deformation, this increases the yield stress

33
Q

What is solid solution strengthening?

A

Solute atoms have an associated strain field

These interact with the strain field around dislocations and inhibit motion

34
Q

What is precipitation strengthening/hardening?

A
  • Fine distribution of second phase particles
  • have an associated straing field that interacts with that of dislocations
  • makes it harder for the dislocation move
  • effectively pin and lock dislocations
35
Q

When using the lever rule how do you find the phase you are interested in?

A

By using the longest line from the point to the ‘boundary’

Materials (13 decks)

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