Metals and Alloys

Question 1

Types of metal cubic structures

Answer 1

Cubic - corners have atoms

Face centred cubic - corners and faces have atoms

Body centred cubic- corners have atoms and connected one atom in the centre of the cube

Question 2

Definition of a Metal

Answer 2

an aggregate of atoms in a crystalline structure

Question 3

Definition of an alloy

Answer 3

combination of metal atoms in a crystalline structure (metals are the building blocks of these)

Question 4

Describe the parts of the cooling curve

Answer 4

upper descending curve- molten metal
Flat line - liquid > solid
Lower descending curve - Cooling

Question 5

What are metal nuclei

Answer 5

aggregates of metal atoms in little spheres that form during cooling

Question 6

What do nuclei turn into and then what do they turn into after that

Answer 6

Dendrites

Grains

Question 7

What is the area where grains touch called

Answer 7

Grain boundary

Question 8

Name the three types of grains and what defines them

Answer 8

Equi-axed grains- grains of equal size (gradual cooling)

Radial grains- formed from rapid cooling (quenching)

Fibrous- formed when grains undergo cold working

Question 9

How to alter grains

Answer 9

Quenching (rapid cooling)
Slow cooling (large nuclei, coarse grains)
Nucleating agents - act as a foci for crystal growth

Question 10

What are the pros and cons of small grains

Answer 10

pros - high elastic limit, increased ultimate tensile strength and hardness

cons- decreased ductility

Question 11

What is slip (clue dislocation of columns)

Answer 11

• defect in metal grain
• force applied
• defect moves along an axis parallel to that force
• reaches grain boundary
• crystal structure changes with no defect

Question 12

Describe Cold working

Answer 12

• done at temperatures below recrystallisation (altering existing grains)
• causes slip
• Increases = elastic limit, UTS and hardness
• Decreases = ductility, corrosion resistance, impact resistance

Question 13

Residual stress (as a result of cold working)

Answer 13

• Cold working helps some properties but results in imperfection in the lattice
• results in undesirable distortion
• relieved by annealing

Question 14

What terms are used to describe the metallic components of alloy grains

Answer 14

Phase- physically distinct homogenous structure
- One phase = grains of metal A only
- Two phase = Individual grains of A + B in lattice network
Solution- homogenous mixture at atomic level
- Solid solution = One phase but Metal A + B in homogenous mixture

Question 15

What is Liquidus

Answer 15

temperature the alloy begins to crystallise at

Question 16

What is solidus

Answer 16

temperature where it solidifies (completely crystallised)

Question 17

What is the difference between metals and alloys in terms of crystallisation

Answer 17

metals crystallise at one temperature

alloys crystallise over a temperature range

Question 18

What is Coring and how is it rectified

Answer 18

• It happens when an alloy is cooled rapidly
• results in a concentration being formed from the centre of an alloy to the periphery
• rectified by using a homogenising anneal

Question 19

Why is slip more difficult in alloys than metals

Answer 19

• because the metal atoms have to climb over and through atoms of different sizes instead of ones the same size as it
• the slip plane in alloys is much less easier to roll over than in metals

Question 20

What is a Eutectic Alloy and what makes it unusual

Answer 20

An alloy that melts at a temperature higher than that of its individual metals

i.e together stronger

Therefore it breaks the rule of alloys having a temperature melting range, it instead has one melting temperature