Metal and alloys 1 and 2
No description yet. This curated deck is ready for daily study.
Card preview (24)
What metals and alloys are widely used in dentistry
• partial denture framework (CoCr, Type 4 gold) • crowns (stainless steel) • denture base (stainless steel) • orthodontic appliance (NiTi) • restorations (amalgam-unique)
What properties are we interested in looking at regarding metals and alloys
• strength • ductility • rigidity • hardness • elastic limit
What can affect properties of metals
defects (dislocations) on properties
What can affect structure
processing (e.g. quenching, cold working, annealing)
Disadvantage of metals
poor aesthetics
Define metal
aggregate of atoms in crystalline structure
Define alloy
combination of metal atoms in a crystalline structure
What information can we gain from a stress-strain curve (know what this looks like)
• Fracture strength • Elastic limit • Ultimate tensile strength • Ductility • malleability • ductility • rigidity
What is the elastic limit
maximum stress without plastic deformation
What is ductility
amount of plastic deformation prior to fracture
What is on the y and x axis of a stress strain curve
x = strain % y= stress (MPa)
What do mechanical properties depend on
• Choice of metal 2. crystalline structure
what does crystalline structure depend on
• history (method of production) - shaping - crucial for dental applications e.g. cold working, swaging
What are the factors which affect mechanical properties
• crystalline structure - grain size and grain imperfections
What are some crystal or lattice structures
• cubic • face-centred cubic • body centred cubic
What does the cooling curve of pure metal look like
• gradual decrease in temp • plateau • gradual decrease in temp
what is the plateu phase of the cooling curve of pure metal
melting point
what triggers the end of the plateu phase on the cooling curve of pure metal
retains temp until all metal changes from liquid to solid, then it cools down further
How does crystal growth occur
• atoms act as nuclei of crystallisation • crystals grow to form dendrites (3D branched lattice network) • crystals (or grains) grow until they impinge on other crystals • region where grains make contact is called grain boundary
what is the grain boundary
where grains (crystals) make contact
what is the grain structure where crystal growth of equal dimension in each direction
equi-axed grains
what is the grain structure where crystal growth is molten metal cooled quickly in cylindrical mould
radial
what is the grain structure where wire is pulled through die
fibrous
what are the different names for the different grain structures of crystal growth
• equi-axed • radial • fibrous