Metals & Alloys

Lower EL, UTS and hardness Increased ductility New smaller equiaxed grains

Deformed grains are replaced by a new set of undeformed grains that nucleate and grow until the original grains have been entirely consumed. Occurs when the metal/alloy is heated.

Spoils the benefits of cold working

Depends on the amount of cold work The greater the amount of cold work, the lower the recrystallisation temperature

Causes grain growth Large grains replace smaller grains during the process creating poorer mechanical properties

Heating the metal/alloy so that greater thermal vibrations allows migration of atoms (i.e. rearrangement of atoms)

Improved mechanical properties - EL, UTS, hardness Corrosion resistance Lower melting point than the individual metal

Steel - burs, instruments Amalgam - restorative material Gold alloy - inlays, crowns, bridges, partial dentures, wires Nickel chromium - crowns, bridges, wires

a) one phase - solid solution b) two phases - no common lattice

Substitutional (random or ordered) Interstitial

Atoms of one metal replace the other metal in the crystal lattice/grain Can be either random (size, valency, crystal structure etc) or ordered (regular lattice arrangement)

Atoms markedly different in size Smaller atoms located in spaces in lattice/grain structure of a larger atom

Temperature range One temperature

Liquidus - line representing the temperatures which different alloy compositions begin to crystallise Solidus - line representing the temperatures which different alloy compositions have completely crystallised

+ generates many small grains which prevent dislocation movement, improving its mechanical properties - Causes coring - every layer has a different composition (ratio of material A:material B)

+ allows metal atoms to diffuse through lattice + ensures grain composition is homogenous - this results in large grains

Stress relief annealing (used to combat cons of cold working) Homogenising annealing (used to combat cons of coring)

a) Rolling movement along slip plane, little energy required to reach the grain boundary. b) Defect falls into the larger space in between the large and small atoms, more energy/force is required for the defect to overcome the different sized atoms, and ‘climb’ out of the space, to move along the lattice to the grain boundary.

Alloys (solid solutions) require more energy to move defects along the lattice and therefore are more fracture resistant than metals.

An aggregate of atoms in a crystalline structure

Crystalline structure Grain size Grain imperfections

High elastic limit Increased UTS & hardness Overall stronger material Decreased ductility

Superior mechanical properties when compared to other materials. However they have poorer aesthetics.

The strengthening of a metal by plastic deformation. Processes include rolling, drawing, pressing, spinning, extruding and heading. Done on a metal at low temperature (below recrystallisation temp) Causes slip. Increases hardness and tensile strength. Decreases ductility.