Metals and Alloys Flashcards
characteristics of metals?
hard lustrous closely packed crystalline structures opaque conductors of heat and electricity
define alloy?
mixture of 2 of more metals
2 metal alloy?
binary alloy
3 metal alloy?
ternary alloy
what do the metals in an alloy display in the molten state?
mutual solubility
Define nucleation
nucleation is the formation of crystals in a metal during cooling from molten to solid
define homogenous nucleation
single site of nucleation as the metal is pure and has no foreign particles
what does homogenous nucleation require during manufacturing?
specialised equipment
define heterogenous nucleation
multiple site nucleation as there are foreign particles present on which the crystals can form
what type of nucleation are the majority of dental materials manufactured by?
heterogeneous nucleation
What are crystals termed as?
grains
When do grains/crystals stop growing?
when all the molten metal is used up
what is the term for the interface between 2 grains in a polycrystalline material?
grain boundary
what does grain size influence and how is it controlled?
the physical properties of the mould; controlled by manufacturer
give 2 factors influencing grain size
temperature and shape of the mould
what are grain boundaries under?
high local stress
how are grain boundaries visualised?
light reflecting microscope, polished metal surface, ETCHING
give 3 ways of shaping readily deformable, malleable and ductile metals and alloys
hammering, rolling, pressing
give 2 others ways to shape metals and alloys
casting, amalgamation
define amalgamation
mixing with Hg
define ductility
maximum degree of EXPANSION in response to an applied TENSILE force
define malleability
maximum degree of COMPRESSION in response to an applied COMPRESSIVE force
upon cooling from molten what are the possible levels of solubility the metals in an alloy might display?
- remain soluble in each other to form a solid solution
- be completely insoluble in each other
- be partially soluble in each other
- form intermettalic compounds if the metals have a high affinity for one another
what are the 3 types of solid solution in an alloy?
- ordered solid solution
- random solid solution
- interstitial solid solution
define ‘ordered solid solution’
component metal atoms have specific sites in a common lattice
define ‘random solid solution’
component metal atoms have random sites in a common crystal lattice
define what is meant by ‘interstitial solid solution’
atoms of one metal lie within the primary lattice of the other
define the hardening effect of solid solutions in alloys
as atoms of differing radii form mechanical resistance to dislocations, the solution hardens
give 3 risks of insolubility of metals in an alloy
electrolytic corrosion
areas of pure metal A
areas of pure metal B
(no mixing in some areas)
give 2 risks of partial solubility of metals in an alloy
solid solution of metal B in metal A
solid solution of metal A in metal B
Give the value of Tm in cooling curves graphs
melting point (time melted)
what is formed when metals have a high affinity for each other?
intrmettalic compounds are formed with precise chemical formulation
what does the plateau (Tm) indicate in a cooling curve graph?
indicates the temperature constant during crystallisation
When metals in an alloy have different melting points, what does this mean for crystallisation?
crystallisation occurs over a range of temperatures
what results from heating an alloy too fast?
cored structure
describe cored structure
metal on outside is cooled and solid; metal on inside is hot and molten
what are phase diagrams useful for?
to make predictions on structure and coring
what do phase diagrams show?
the phases of states (liquid/solid) in the metals of an alloy
