Materials

Question 1

Alloying Definition

Answer 1

Solid mixture of different metals or other materials (forms when one material dissolved in other liquid material)

Question 2

Type 1 Alloy: Small and Big Atoms

Answer 2

Interstitial Alloy: small sized atoms put in gaps of crystal lattice

Question 3

Type 2 Alloy: Big Atoms only

Answer 3

Substitutional Alloy: Atoms of added element takes place of pure metal atoms in crystal lattice

Question 4

Ferrous metals mainly composed of…

Answer 4

Mainly Iron

Question 5

Non-ferrous metals mainly composed of…

Answer 5

All metals EXCEPT iron

Question 6

Benefits of recycling metals

Answer 6

Resource and energy conservation, cost reduction

Question 7

Limitations of recycling materials

Answer 7

Mixing different grades of metals can reduce overall quality of recycled materials

Question 8

Strength Definition

Answer 8

Resistance to stress or under a load (force it can resist before DEFORMING OR FRACTURING)

Question 9

Toughness Definition

Answer 9

Ability to absorb energy before FRACTURE (doesn’t include deformation –> something that deforms easily but doesn’t break is tough)

Question 10

Hardness Definition

Answer 10

Resistance to surface abrasions/deformations (e.g. scratches, dents)

Question 11

Stiffness Definition

Answer 11

Ability to resist elastic deformation

Question 12

Quenching definition

Answer 12

Rapid cooling process alters specific properties of materials by manipulating cooling rate.

Question 13

Quenching process

Answer 13

• Material heated above recrystallisation temp. and below melting point
• Grain restructures, becomes smaller
• Rapid cooling using media (e.g. water, oil)

Question 14

Quenching results

Answer 14

Increased hardness, reduced ductility, increased brittleness

Question 15

Tempering definition

Answer 15

Heat treatment process for iron-based alloys

Question 16

Tempering process

Answer 16

Usually done after hardening forming processes (i.e. drawing)
- Material heated above upper critical temp.
- Quenched
- Reheated to lower temps. than before (cooling rate slower than quenching)

Question 17

Tempering results

Answer 17

Increased ductility, reduces brittleness, removes excess hardness, increased toughness, relieves internal stresses

Question 18

Annealing definition

Answer 18

Uses heat to reduce hardness and increase ductility and toughness.

Question 19

Annealing process

Answer 19

• Material heated beyond recrystallisation temp.
• Slowly cooling down encouraging new grain formation, relieving internal stresses and making crystal flow more refined

Question 20

Annealing results

Answer 20

Creates softer steel than tempering, used on materials that don’t ned to endure substantial stresses, reverses work hardening from forming processes (e.g. drawing)

Question 21

What heat-treatment processes are most commonly used together and why?

Answer 21

Quenching and Tempering
- Tempering quicker than annealing and tempered steel is harder and stronger than annealed steel

Question 22

Yield Point meaning

Answer 22

Point of permanent deformation

Question 23

Elastic region/deformation meaning

Answer 23

Material is put under stress but can still return to it’s original shape

Question 24

Plastic region/deformation meaning

Answer 24

Material is permanently deformed

Question 25

FCC Crystal Structure meaning

Answer 25

Face centred cubic: atoms at each corner and centre of ALL cube faces

Question 26

FCC Crystal Metal examples

Answer 26

Copper, Aluminium, Silver, Gold

Question 27

FCC Crystal Structure properties

Answer 27

- Low hardness - Low yield strength - Good ductility

Question 28

BCC Crystal Structure meaning

Answer 28

Body centred cubic: atoms located in all 8 corners of cube and single atom in centre

Question 29

BCC Crystal Structure metal examples

Answer 29

chromium, iron, tungsten

Question 30

BCC Crystal structure properties

Answer 30

- High yield strength - High hardness - Limited ability to form

Question 31

HCP Crystal Structure meaning

Answer 31

Hexagonal close packed: top and bottom face has atoms at each point and one in middle. Mid plane has three atoms seperate by one face each.

Question 32

HCP crystal structure examples

Answer 32

Cadmium, titanium, zinc, magnesium

Question 33

HCP crystal structure properties

Answer 33

- Brittle - Low yield strength - Inability to form

Question 34

How do grains form

Answer 34

When metal cools crystals form and eventually run into each other and cannot grow further, causing grains

Question 35

What are grain boundaries

Answer 35

Regions where atoms do not join with neighbouring atoms in a neat/stable way. Regions of high internal stress and atoms do not move easily at these boundaries.

Question 36

Small grains properties

Answer 36

More grains boundaries More obstacles for dislocations Stronger metal More hardening during deformation

Question 37

Large grains properties

Answer 37

Fewer grain boundaries Dislocations move more easily Softer and more ductile metal

Question 38

Work hardening process

Answer 38

Crystal lattices in metals are mainly nest but have imperfections called dislocations - Allows for metals to bend and stretch without breaking because atoms can move into these empty gaps When metal permanently deformed, dislocation FORCED to move More deformation = more dislocations = more entanglement causing them to block each other

Question 39

Work hardening result

Answer 39

Metal becomes stronger and resists further deformation, more brittle and less ductile, stronger internal structure, more tangled dislocations