Materials: Topic 3, Metallic Materials Flashcards
The most characteristic property of metals
their high thermal and electrical conductivity
What is a ferrous material?
Metals in which the major constituent is the element
iron
What is the major alloying element to steel?
Carbon
What is annealing?
Softens the steel by heating and allowing to cool
slowly in the furnace. Results in stress free, large grained
structure.
What is normalising?
Faster cooling than annealing. Stress relief
without grain growth
Why are scientists so fascinated by sponges?
Because they’re so absorbing!
What is hardening and tempering?
This operation hardens the finished component to its required mechanical properties.
Advantages of steel:
Cheap High Strength/Stiffness High Toughness Excellent Formability Easy to Join and Weld Versatile Recyclable
Disadvantages of steel:
Very Dense
Poor Corrosion Resistance
2 ways to protect against corrosion
Paint it
Coat it
dun dun dun dun dun
https://www.youtube.com/watch?v=y6120QOlsfU
The four steps of annealing:
• 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.
The hardening and tempering process:
• 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
Three surface hardening processes that only heat the surface:
– 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.
Three surface hardening processes that modify the surface chemistry:
– 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.
Define a non ferrous material:
A metal that does not contain iron, is not magnetic and is usually more resistant to corrosion than ferrous metals.
What country produces the most magnesium currently?
China
Place steel, aluminium, magnesium and titanium in order of density (most dense first).
1) Steel - 7.8 mg/m^3
2) Titanium - 4.5
3) Aluminium - 2.7
4) Magnesium - 1.8
Place steel, aluminium, magnesium and titanium in order of price per tonne (most expensive first).
1) Titanium - £12,000/tonne
2) Magnesium - 1,000
3) Aluminium - 900
4) Steel - 350
Uses and traits of aluminium and aluminium alloys
– 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.
Uses and traits of magnesium and magnesium alloys
– 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.
Uses and traits of titanium and titanium alloys
– 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.
Uses and traits of zinc
– 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.
Uses and traits of copper
– 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.
