T4 Flashcards
How does cold working (strain hardening) a material affect it’s properties
- increases tensile strength
- reduced ductility
- achieved by mech. deformation which causes dislocation density to increase. This makes dislocations closer so harder to deform more.
ALUMINIUM
What is annealing?
Very slow furnace cooling
What is normalizing?
Air cooling
What is quenching?
Liquid cooling
What is tempering?
Reheating, holding and cooling
4 main non equilibrium phases of steel:
- coarse pearlite: made with annealing
- fine pearlite: made by normalising (fine structure, less time to diffuse)
- bainite: comes from austenite. Has 2 phases ferrite/cementite but finer structure
- martensite: quenched (very fine, hard and strong but brittle)
What does tempering do?
Heats a material up to restore some ductility
How is a polymer formed?
A monomer with double carbon bonds reacts with others to form a chain of monomers with single bonds.
3 main polymer chains:
Linear: single chain, flexible, spaghetti, VDW bonding between chains.
Branched: side chains attached to main, bulkier, resistant to chain slippage, stiffer
Cross linked: adjacent linear chains are joined by covalent bonds, made in synthesis/non reversible reaction, made with additive atoms that bond to chains
Can you grind and reuse polypropylene
Yeah it’s a thermoplastic so will soften when reheated so can be remoulded
Explain why the tendency of a polymer to crystallise decreases with increasing molecular weight
Longer chains are harder for all regions along adjacent chains to align and produce an ordered atomic array
What’s a visco elastic polymer?
One that exhibits both viscous and elastic properties. When loaded there’s an increased elastic strain, loaded more strain increases due to viscous movement of polymer chains, when load removed elastic recovery of strain
How is fine pearlite made?
Normalising (air cooling), fast cooling leads to finer structure as there is less time for atoms to diffuse. Greater strength but less ductile than coarse.
How is coarse pearlite made?
With full annealing (slow furnace cooling). Has time to grow.
How is bainite formed?
Via transformation of austenite. Consists of ferrite and cementite but is even more fine (forms as needles or plates). Forms at lower temperatures than pearlite.
