Metals & Alloys Flashcards
what are metals like at an ambient temp
hard and lustrous
closely packed crystalline
opaque
conduct heat and electricity
what si the except to the metal’s features at an ambient temp
Hg
what is an alloy
mix of two or more metals (binary alloy = 2)
what is the alloy system
all possible combinations of an alloy
what do metals show in a molten state
display mutual solubility
what si the common structure of metals
crystalline structure
many small crystals
what is metals form when cooling
impurities enable metal atoms to deposit
nucleate crystal growth
what are crystals called
grains
when do grains grow until
until all melt metal consumed
what is the area where crystals abut their neighbours
grain boundary
what are the types of nucelation
heterogenous
homogeneous
what is heterogenous nucelation
many sites
majority dental applications
what is homogenous nucelation
single site
metal is pure need 4 metal atoms to come together
requires specialised equipment
what does grain size influence
physical properties
what is grain size controlled by
manufacturer
-rapid solidification
- extra nucleation sites
(both small grain size)
what is the technique for casting dental gold alloy
lost wax technique
how does temp affect grain size
if similar to melt, slow cooling and large grain size
if diff melt, rapid cool and small grain size
how does he shape of the mould affect grain size
walls of mould initiate growth and therefore influence direction of crystal growth
what can be used to visualise grain boundaries
light reflecting microscope
who using light reflecting microscope what has to be done to see grain boundaries
polish metal surface see irregularities - scatter light
apply etch chem
when using an acid etching material what does it do
preferential attack of areas under high stress such as grain boundaries
are metals easy to shape
readily deformable, malleable and ductile metals/alloys
what can metals/alloys be shaped by
hammering rolling pressing drawing into a wire thro a die wrought/ cold working
how’s metal drawn into wire
grains elongated in direction of drawing
laminar structure
how is there a limit to working with cold metals
practical implications
work hardening
what is casting
molten –> investment mould
what is amalgamation
mix with mercury
plastic mass
hardening chemical reaction
crystallisation
what is ductility
the max degree of extension in response to an applied tensile force
what is malleability
the max degree of compression in response to an applied compressive force
what are elemental metals uses
not much practical uses
severe limitations of their props
extended uses when mixd with alloys
when alloys cool from molten they may….
remai soluble - solid solution
be complete;ly insole in eachther
be partially sol in each other
for intermettalic compounds in metals have affinity for each other
what are the three types of solid solution
ordered solid solution
random solid solution
interstitial solid solution
what is ordered solid solution
component metal atoms have sp sites in common lattice
atom radii similar
if radii diff = distortion
what is random solid solution
random sites in common crystal lattice
what is interstitial solid solution
atoms of one lie in the primary lattice sites of other
atomic radii dept
in solid solutions pure metals are…..
harder
stronger
higher elastic limits
what is the hardening effect
solution hardening
as atoms of differing radii from mechanical resistance to dislocations
what sit he insolubility of metals
rare
consequences - areas of pure metal a and/or b
risks of corrosion
what are the different phases of alloys
solid solution of metal b in metal a
solid solution of metal a in b
what bond does metals form in affinity
intermettalic compounds
what is precise chemical formulation
sp valence requirements satisfied few crystal imperfections means less potential forlsip plane movement hard brittle low ductility
what si the use of cooling curves
melt metals/alloy
record and plot temp versus time
what is Tm
melting point
what does the plateau indicate in melting point
temp constant during crystallition
what are phase diagrams
series of cooling curves for alloys of diff composition
phase diagram results
use to make struct and coring predictions
in phase diagrams for each composiiotn…..
determine t1 and t2
plot these ag percentage composition
what can be predicted between liquidus and solidus
solid and liquid composoitons
what does distance between solidus and liquids show
larger separation = greater coring
what happens when alloy components insoluble to each other
sp point where crystallisation occurs at sp temp
what is a eutectic alloy
behave like pure metal
narrow MP
application as solders
