materials info

what determines the equilibrium state

free energy

• by changing the entropy or enthalpy you can change the free energy

what dies the solidus-liquidus mark do

marks the boundary between 2 phase regions

formation of a crystal

CNT

key assumptions of the CNT theory

• crystal nucleus is spherical

• interface is sharp

classical nucleation theory (CNT)

crysal structures through slow and fast nucleation

more grain boundaries = higher yield dtrength

CNT on surface

how does a crystal form

• random collisions of clusters f atoms that posses a crystalline structure and density

• if the clusters surpass the critical size they will grow out to form the crystal

grain boundary of precipitates

• precipitates form grain boundairies

• this is because grain boundaries are relatively unstable regions of the microstucture (dangling bonds)

what does casting involve

• taking metals from the liquid region of the phase diagram and into the solid phase

• this is therefore cooling the molten phase, which makes it easier to change shape

what are the 5 casting types

requires post cast forging, rolling (semi finished)

• ingot casting

• continuous casting

casting directly to the final shape

• sand casting

• investment casting

• die casting

what is ingot casting typically used for

• primarily for producing smaller batches of specialized steels/alloys

• cast iron/ graphite mold

pros and cons of continuous casting

how to minimize/ prevent creep

minimise the number of grain boundaries

why does density decrease on melting

• we are breaking bonds

• the atoms are now free flowing and not confined to their lattice sites