Metals

Question 1

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

Answer 1

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

Question 2

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

Answer 2

1779 - Iron bridge, coalbrookdale

Question 3

What was the first major bridge built with wrought steel?

Answer 3

Forth Railbridge, scotland, 1890

Question 4

What kind of bonding is present in metals?

Answer 4

Metallic bonds

Question 5

What are the properties of metallic bonds

Answer 5

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

Question 6

What kind of metals are most engineering metals?

Answer 6

Alloys

Question 7

What do FCC, HCP, BCC dstand for

Answer 7

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

Question 8

What metals have an FCC structure?

Answer 8

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

Question 9

What metals have a BCC structure?

Answer 9

Chromium, Iron (alpha), Molbdenum

Question 10

What metalls have an HCP structure?

Answer 10

Cobalt, magnesium

Question 11

What type of imperfections are found in the chrystal structure?

Answer 11

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

Question 12

What is the definition of a grain boundary?

Answer 12

The interface between adjacent chrystalline regions that have different orientation

Question 13

What is the definition of a dislocation?

Answer 13

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

Question 14

What is the difference between interstital and substitutional atoms?

Answer 14

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

Question 15

What failure are grain boundaries resposible for?

Answer 15

Intergranular fracture

Question 16

What failure are dislocations responsible for?

Answer 16

Plastic deformation

Question 17

Why do dislocations cause failures?

Answer 17

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

Question 18

How do dislocations move through the structure?

Answer 18

• 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

Question 19

What causes dislocations to occur?

Answer 19

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

Question 20

What is the effect of shear stress on dislocation?

Answer 20

Moves allong in the direction of the imposed stress

Question 21

How do we hinder the movement of dislocations?

Answer 21

Creating obstacles to dislocation motion

Question 22

What is the definition of an alloy?

Answer 22

Metal mixed with other elements

Question 23

What are the properties of an alloy determined by?

Answer 23

The composition of the microstructure and the distribution of the phases

Question 24

How much carbon and manganese is in steel?

Answer 24

<2% carbon and 1% manganese

Question 25

Hoe many differrent grades of steel are there?

Answer 25

3,500

Question 26

What are the benefits of steels?

Answer 26

They are stronger and lighter, more fit for purpouse Modern cars are stronger and 25% lighter

Question 27

What is the benefite of a grain boundary?

Answer 27

act as a barrier to dislocation motion Increases yield stress

Question 28

How do we increase the yield stress?

Answer 28

Reduce the grain size

Question 29

What is the Hall-Petch equation?

Answer 29

sigma_y = sigma_o +k/sqrt(d) sigma_y = yield stress sigma_o, k = material constants d = grain size

Question 30

What does the Hall-Petch equation show?

Answer 30

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

Question 31

What is work hardening?

Answer 31

- 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

Question 32

What conclusion does work-hardening allow us to draw?

Answer 32

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

Question 33

What is solid solution strengthening?

Answer 33

Solute atoms have an associated strain field | These interact with the strain field around dislocations and inhibit motion

Question 34

What is precipitation strengthening/hardening?

Answer 34

- 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

Question 35

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

Answer 35

By using the longest line from the point to the 'boundary'