metals and alloys

• partial denture framework = CoCr, type IV gold • crowns = stainless steel • denture base =stainless steel • orthodontic appliance = NiTi • restorations = amalgam

• as it undergoes a setting reaction and the rest don’t

• shows alloys are versatile - able to take on complex shapes

• strength • rigidity • elastic limit • ductility • hardness

• their aesthetics

• aggregate of atoms in crystalline structure - building blocks of alloys

• combination of metal atoms in a crystalline structure

• shows that when you increases stress you increase strain = change shape • shows the fracture stress, elastic limit and UTS of the material • also shows the malleability and ductility of material

• ultimate tensile strength

• amount of plastic deformation prior to fracture - measure of extent material can be shaped

• if apply compressive stress

• history = method of production, structure depends on how you produce it • shaping = crucial for dental application (cold working, swaging)

• crystalline structure = lattice of atoms - grain size and grain imperfections = grain is a single crystal

• a single crystal with atoms orientated in given directions (dendrites)

• cubic = simple cubic and relate structures • face-centered cubic = cubic close packed and related structure • body-centred cubic = body centred cubic and relate structures • metals have atoms positioned at regularly arranged sites

• alloys start molten in a container and are then allowed to cool down • reaches a plateau where it goes from liquid to solid state and maintains temperature until all molten metal is now solid then it cools down again

• atoms at these sites act as nuclei of crystallisation • crystals then grow to form dendrites = atoms cool around the nuclei • crystals (or grains) grow until they impinge on other crystals and then stop growing • dendrites grow until they impact on another

• grain boundary

• how it is processed - can be in all different sizes = sizes can also affect properties

• equi-axed grains

• radial = molten metal cooled quickly in cylindrical mould - fibrous = wire pulled through die = cold worked metal/alloy

• fast cooling • more nuclei of crystallisation and lots of grains are produced • mechanical properties are enhanced = best you can get

• few nuclei - large coarse grains = weaker

• help crystallisation process • impurities or additives act as foci for crystal growth • using these is another way in controlling grain size