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Flashcards in Metals Deck (37):
1

Density =

Mass/ Volume (kgm^-3)

2

Why are metals so dense?

They have a closely packed atomic stucture

3

What does the stiffness of a metal indicate?

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

4

Are metals, ceramics and polymers high or low YM?

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

5

What does the strength of a material indicate?

The resistance to plastic/ permanent deformation.
Indicated by the yield strength.

6

The yield strength of metals, ceramics and polymers:

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

7

What does the toughness of a material refer to?

The resistance to cracking/ fracture.
Indicated by the fracture energy.

8

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

Tension (maybe compression)

9

What does the conductivity of a material refer to?

How easily heat can pass through a material

10

Materials with higher conductivity tend to be...

Metals.

11

Benefits of metals...

They tend to be low cost materials

12

What is the mechanical behaviour of metals?

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

13

Elastic deformation of metals:

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

14

Plastic deformation of metals:

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

15

Dislocations of atoms in a metal:

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.

16

What happens with dislocations and how it deforms?

For permanent deformation it requires a dislocation to move.

17

Slip allows for...

Ductility and toughness

18

Strengthening mechanisms for dislocations?

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

19

What does ferrous mean and what metals have ferrous?

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

20

Cast iron

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

21

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

Lead to collapse as there would be a stress concentration

22

What is steel?

Alloy of carbon and iron

23

How is steel processed?

-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

24

Rolling metals =

This can squeeze out porosity and refine the microstructure

25

Forging =

Pressing the metal into shape

26

Extrusion =

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

27

Phases in steel:

-Austetine
-Ferrite
-Cementite
-Pearlite
-Martensite

28

Transformation from steel to pearlite:

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

29

Transformation to martensite:

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.

30

Heat treatment of steel:

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

31

Wrought steel =

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.

32

Cast steel =

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

33

Stainless steel =

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

34

Non-ferrous metals =

All the other metals; more expensive than iron based.

35

Aluminium =

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

36

Titanium =

High strength; used in aerostructures
Ti-6Al-4V most common

37

Copper =

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