Materials: Topic 3, Metallic Materials

Question 1

The most characteristic property of metals

Answer 1

their high thermal and electrical conductivity

Question 2

What is a ferrous material?

Answer 2

Metals in which the major constituent is the element

iron

Question 3

What is the major alloying element to steel?

Answer 3

Carbon

Question 4

What is annealing?

Answer 4

Softens the steel by heating and allowing to cool
slowly in the furnace. Results in stress free, large grained
structure.

Question 5

What is normalising?

Answer 5

Faster cooling than annealing. Stress relief

without grain growth

Question 6

Why are scientists so fascinated by sponges?

Answer 6

Because they’re so absorbing!

Question 7

What is hardening and tempering?

Answer 7

This operation hardens the finished component to its required mechanical properties.

Question 8

Advantages of steel:

Answer 8

Cheap
High Strength/Stiffness
High Toughness
Excellent Formability
Easy to Join and Weld
Versatile
Recyclable

Question 9

Disadvantages of steel:

Answer 9

Very Dense

Poor Corrosion Resistance

Question 10

2 ways to protect against corrosion

Answer 10

Paint it

Coat it

Question 11

dun dun dun dun dun

Answer 11

https://www.youtube.com/watch?v=y6120QOlsfU

Question 12

The four steps of annealing:

Answer 12

• Recovery
– Dislocations untangle and annihilate
– Stress relief
• Recrystallisation
– New stress free grains nucleate at boundaries and dislocation entanglements
• Growth
– Grains grow and consume deformed grains
• RESULT: Softer material.

Question 13

The hardening and tempering process:

Answer 13

• Heated up and quenched
• Crystallographic transformation to body
centred tetragonal Martensite
• Very hard and brittle
• Tempering, low temperature heat
treatment maintains strength but
recovers some ductility

Question 14

Three surface hardening processes that only heat the surface:

Answer 14

– Flame hardening: a high temperature flame is directed at the component

– Induction hardening: an induction coil replaces the furnace but only heats the required area.

– Laser hardening: a laser beam is used to provide the heating of very small areas.

Question 15

Three surface hardening processes that modify the surface chemistry:

Answer 15

– Carburising: carbon is added to the surface of an otherwise low carbon steel allowing the surface to be
hardened.

– Nitrocarburising: adds a mixture of carbon and nitrogen to the surface.

– Nitriding: a thin nitride layer is deposited on the surface to increase its hardness.

Question 16

Define a non ferrous material:

Answer 16

A metal that does not contain iron, is not magnetic and is usually more resistant to corrosion than ferrous metals.

Question 17

What country produces the most magnesium currently?

Answer 17

China

Question 18

Place steel, aluminium, magnesium and titanium in order of density (most dense first).

Answer 18

1) Steel - 7.8 mg/m^3
2) Titanium - 4.5
3) Aluminium - 2.7
4) Magnesium - 1.8

Question 19

Place steel, aluminium, magnesium and titanium in order of price per tonne (most expensive first).

Answer 19

1) Titanium - £12,000/tonne
2) Magnesium - 1,000
3) Aluminium - 900
4) Steel - 350

Question 20

Uses and traits of aluminium and aluminium alloys

Answer 20

– Density: 2.7Mg/m^3 Melting point: 660°C
– Electrical conductivity in the order of 60% copper.
– High thermal conductivity.
– Resistant to corrosion.
– Non - magnetic.
– Available cast & wrought & can be made heat treatable.
– Main uses include aircraft forgings and skins, drinks cans, window frames, cooking pans, power lines and road wheels.

Question 21

Uses and traits of magnesium and magnesium alloys

Answer 21

– Density: 1.74Mg/m^3 , Melting point: 650°C
– Magnesium is the lightest metal in general use.
– Not strong enough to be used pure - alloyed with Mn, Al and Zn and grain refined with Zr.
– Very good machinability.
– Mg alloys are roughly as resistant to atmospheric attack as mild steel.
– Main uses include high performance racing wheels and crankcases.

Question 22

Uses and traits of titanium and titanium alloys

Answer 22

– Density: 4.5 Mg/m^3 , Melting point: 1670°C
– Heat treatment and alloying produces a wide range of properties.
– Low density and high strength combine to give Ti alloys the highest specific strengths of engineering alloys.
– Non - magnetic.
– Adequate strengths can be achieved up to 700°C.
– Very good corrosion resistance, especially in sea water.
– Main uses include gas turbine engines as compressor blades, bolts etc. for the chemical industry and replacement hip joints.

Question 23

Uses and traits of zinc

Answer 23

– Density: 7.1 Mg/m^3 , Melting point: 420°C
– Very good corrosion resistance.
– Used in galvanising coatings.
– Used extensively for die castings.
– Main uses include galvanising of out door structural components, & die castings for use in domestic appliances, optical instruments etc.

Question 24

Uses and traits of copper

Answer 24

– Density: 8.9 Mg/m^3 , Melting point: 1083°C
– High electrical and thermal conductivity.
– Good corrosion resistance.
– Produced in a range of qualities depending on the purity and oxygen content.
– Main uses are in electrical applications, heat exchangers, condenser plates and tubes etc.

Question 25

Uses and traits of brass

Answer 25

– Brass is an alloy of copper and zinc ( 0 to
50% Zn).
– Melting point of 60/40 brass: ~ 900°C
– Wide range of mechanical properties can be
produced.
– 70/30 a Brass has good ductility and
strength, it will withstand a large amount of
cold work without fracture - used for
cartridge cases .
– 60/40 a-b Brass is good for hot working and
casting. Cooling rate controls proportions of
a-b and hence properties.
– Brass is easy to machine.
– Corrosion resistance is good.

Question 26

Uses and traits of bronze

Answer 26

– An alloy of copper and tin ( 10 to 30%
Sn).
– Good corrosion resistance.
– Machinability can be a problem but is improved by addition of up to 2 % lead.
– Alloyed with other elements for specific applications.
• Coinage bronze: 3.5% Sn, 1.5% Zn.
• Phosphor bronze: solid solution strengthens and reduces the coefficient of friction.
• Bearing bronze: 10 - 20 % (Pb) added to
provide lubrication.

Question 27

Uses and traits of nickel based super alloys

Answer 27

– Density of Ni based super
alloys: 7.9 Mg/m^3
– Melting point: 1277°C
– Ni is alloyed with complex range of elements (Cr, Mo,
W, Ti, C, Fe) to give materials with very good high temperature properties.
– Machinability is extremely poor.
– Main uses include hot end of gas turbine engines.