Metals

Question 1

Density =

Answer 1

Mass/ Volume (kgm^-3)

Question 2

Why are metals so dense?

Answer 2

They have a closely packed atomic stucture

Question 3

What does the stiffness of a metal indicate?

Answer 3

It’s resistance to elastic deformation; indicated by the young modulus.

Question 4

Are metals, ceramics and polymers high or low YM?

Answer 4

Metals and ceramics tend to be high; whereas polymers tend to be low.

Question 5

What does the strength of a material indicate?

Answer 5

The resistance to plastic/ permanent deformation.

Indicated by the yield strength.

Question 6

The yield strength of metals, ceramics and polymers:

Answer 6

Ceramics have high yield strength; metals vary and polymers are low.

Question 7

What does the toughness of a material refer to?

Answer 7

The resistance to cracking/ fracture.

Indicated by the fracture energy.

Question 8

Would low toughness materials not be suitable for tension or compression?

Answer 8

Tension (maybe compression)

Question 9

What does the conductivity of a material refer to?

Answer 9

How easily heat can pass through a material

Question 10

Materials with higher conductivity tend to be…

Answer 10

Metals.

Question 11

Benefits of metals…

Answer 11

They tend to be low cost materials

Question 12

What is the mechanical behaviour of metals?

Answer 12

They are strong; do not deform easily and can take high loads.
When they do deform it is progressive.

Question 13

Elastic deformation of metals:

Answer 13

When a load is applied the atomic bonds will stretch; when removed they do not return (not permanent)

Question 14

Plastic deformation of metals:

Answer 14

When load is increased; atoms slip past each other and when the load is removed they remain in that position.

Question 15

Dislocations of atoms in a metal:

Answer 15

Atoms will not slip a layer at a time but singularly. This happens because it requires a lot of energy to slip a whole layer.

Question 16

What happens with dislocations and how it deforms?

Answer 16

For permanent deformation it requires a dislocation to move.

Question 17

Slip allows for…

Answer 17

Ductility and toughness

Question 18

Strengthening mechanisms for dislocations?

Answer 18

• Atoms in solution (alloys metal)
• Add another phase
• Other dislocations get tangled with each other
• Structure changes at grain boundary/ orientation.

Question 19

What does ferrous mean and what metals have ferrous?

Answer 19

Indicates the presences of iron
Iron (Fe)
Steel (Fe +C)

Question 20

Cast iron

Answer 20

High levels of carbon. Carbon phases lead to low strength and toughness in tension.

Question 21

What would be the problem with cast iron joints in a structure?

Answer 21

Lead to collapse as there would be a stress concentration

Question 22

What is steel?

Answer 22

Alloy of carbon and iron

Question 23

How is steel processed?

Answer 23

• Heating an iron ore with coke and limestone in a blast furnace.
• Liquid metal and slag is removed every few hours.
• Adding oxygen reduces carbon content

Question 24

Rolling metals =

Answer 24

This can squeeze out porosity and refine the microstructure

Question 25

Forging =

Answer 25

Pressing the metal into shape

Question 26

Extrusion =

Answer 26

Taking larger pieces of metal and thinning it out into a long rod.

Question 27

Phases in steel:

Answer 27

• Austetine
• Ferrite
• Cementite
• Pearlite
• Martensite

Question 28

Transformation from steel to pearlite:

Answer 28

Mixture of ferrite and cementite Fe3c; these grow alternating plates giving a strong structure and resistant to crack so tough.

Question 29

Transformation to martensite:

Answer 29

Cooling quickly means that ferrite and cementite cannot form properly so the structure becomes distorted as carbon wont fit into bcc structure in ferrite. This causes a hard and brittle metal that doesn’t allow dislocations to get through.

Question 30

Heat treatment of steel:

Answer 30

• Annealing; high temp
• slow cooling gives pearlite
• Quenching = fast cooling gives martensite
• Tempering = low temp allows carbides to form

Question 31

Wrought steel =

Answer 31

Shaped by deformation; carbon is kept for weldability and higher strength. High strength low alloy = reduction in grain size. Produces carbide and nitride also strengthens.

Question 32

Cast steel =

Answer 32

Casting steel directly into shape; cheaper and easier but poorer mechanical properties.
Phase changes cause martensite to be produced at surface.

Question 33

Stainless steel =

Answer 33

Produces protective oxide surface, used for aesthetic reason as long-life.

Question 34

Non-ferrous metals =

Answer 34

All the other metals; more expensive than iron based.

Question 35

Aluminium =

Answer 35

Lightweight; alloyed for strength, susceptible to degradation by heat.

Question 36

Titanium =

Answer 36

High strength; used in aerostructures

Ti-6Al-4V most common

Question 37

Copper =

Answer 37

Easy to form; oxidation gives colour. Not used for primary load.