Metals and Alloys Flashcards
structure of materials at room temperature?
hard and lustrous, closely packed crystal structure, radiopaque, conduct heat/electricity
excpetion = Hg liquid at room temp
what is an alloy?
2 metals = binary
3 metals = ternary
crystal structure in metals?
crystaline, many small particles, form from molten
what is an alloy system?
all possible combinations of an alloy
what do alloys display in the molten state?
mutual solubility - alloys dissolve in each other
what happens when metals cool?
impurities allow metal atoms to deposit upon them = nucleate crystal growth
how to grains grow?
grains grown until all of the melt is a metal.
what is a grain boundary?
where grains abut their neighbours
heterogenous nucleation?
many sites of nucleation
majority
homogenous nucleation?
one site
pure metal = 4 atoms
specialised equipment
how does grain size affect physical properties?
rapid solidification
extra nucleation sites - e,g addition of iridium to gold
if the temperature of the mould is similar to the melt whathappens?
diff to melt?
slow cooling = large grain
rapid cooling = small grain
if the temp of the mould is sim shape of mould?
initiate growth and influence direction of crystal growth
how to visualise grain boundaries?
light reflecting microscope
polished metal surfaces - irregularities scatter light
application of acid - attack areas under stress - grain boundaries
how to shape metals and alloys?
cam be readily deformable, malleable, ductile =
hammering, rolling, pressing, drawn into a wire
can be wrought/cold working
what is ductility?
max degree of extension in response to applied tensile force
what is malleability?
max degree of compression in response to applied compressive force
on cooling from molten components alloys may?
- remain soluble in each other - solid solution
- be completely insoluble in each other
- be p/soluble in each other
- form intermettalic compounds if metals have affinity for each other
what is an ordered solid solution?
metals atoms have specific states in a common lattice
one shown substantial - similar atomic radii
radii differ - distortions of lattice
what is a random solid solution?
random sites in a common crystal lattice
interstitial solid solution?
atoms of one lie within the primary lattice sites of the other, atomic radii dependent
properties of pure metals?
harder, stronger, higher elastic limits
what is the hardening effect?
atoms of diff radii form mechanical resistance to dislocations
what happens to grains when drawn into a wire?
elongated in direction of drawing into a laminer structure
limit to how much remodelling can take place
what is casting?
molten into an investment mould
what is amalgamation?
mix with Hg, plastic mass, hardening, chem reaction, crystallisation
insolubility of metals?
rare
areas of each pure metal
risks electrolytic corrosion
partial solubility of metals?
alloy has diff phases
solid solition of metal b in a
solid solution of metal a in b
what is metal affinity?
form intermetallic compounds
precise chem formaulation
specific valence requirements satisfied - few crystal imperfections = less potential for skip plane movement
hard brittle, low ductility
cooling curves?
melt metal/alloy
record and plot temp versus time
what is tm?
melting point
where plateau’s = crystallisation
what is a phase diagram?
series of cooling curves for alloys of diff compositions
make structural/coring predictions
for each metal composition calculate?
T1, T2, = temp of crystalisation of metal A, temp of crystalisation of metal B
plot against % of compositions
what can you predict between liquidus and solidus?
predict solid and liquid compositions
the larger the seperation between liquidis and solidus the greater the what?
greater the coring
the point where alloy components are insoluble in each other mean what?
the sepcific part where crystallisation occurs at specific temperatures
what is a eutectic alloy?
behaves like a pure metal
narrow melting range
narrow melting point lower then component metals
application as solders
