Metals and Alloys Flashcards
what is an alloy?
mixture of 2 or more metals
in molten state metals display ? solubility
mutual
what are the two classifications of metals?
noble metals - highly resistant to oxidation and corrosion e.g. gold, platinum
base metals e.g. cobalt, copper, nickel
describe the structure of metals when solid?
regular crystalline structure
as metal cools solidification starts at specific sites called ?. ? in metal molten mass enable metal atoms to deposit on them.
nuclei
impurities
what happens during crystal growth when metal cools?
nuclei grow in 3 dimensional directions forming branched structures called dendrites
when metals cool, when does crystal growth stop?
when crystals touch each other
what is a grain boundary?
when crystals touch each other
what affect does decreasing the grain size have on the concentration of grain boundaries?
smaller grain size
higher concentration of grain boundaries
mechanical properties of metals are enhanced by what grain size?
smaller
how can manufacturer control the grain size? 3
rapid cooling - smaller grains
slow cooling - larger grains
temperature and shape of mould
what is amalgamation?
metal mixed with mercury (Hg)
define ductility
the maximum degree of extension in response to an applied tensile force
define malleability
the maximum degree of compression in response to an applied compressive force
on cooling from molten components metals may remain soluble in each other - solid solutions
what are the 3 types of solid solution?
ordered solid solution
random solid solution
interstitial solid solution
what is an ordered solid solution
component metal atoms have specific sites in the lattice
what is a random solid solution?
metal atoms occupy random sites in common crystal lattice
what is a interstitial solid solution?
atoms of one lie within the primary lattice sites of another
name 3 properties of pure metals
harder
stronger
higher elastic limits
on cooling molten component metals may be insoluble in each other (this is rare). this means they are susceptible to what?
electrolytic corrosion
on cooling molten component of metals may be partially soluble in each other. the metals have two different phases, what are they?
phase 1: solid solution of metal B in metal A
phase 2: solid solution of metal A in metal B
on cooling molten component of metals may be partially soluble in each other. solubility is ? dependant. when temperature decreases from melting point to room temperature solubility ?
temperature
decreases
on cooling molten component of metals may form intermettalic compounds if the metals have affinity for each other. what are the properties of this type of alloy? 4
less potential for slip plane movement as few crystal imperfections
hard
brittle
low ductility
is this temperature time graph for pure metals or alloys?
pure metals
what does the plateau region indicate?
temperature constant during crystallisation
Metal A has the highest melting point. at T1 crystallisation is rich in A or B?
A
metal A has the highest melting point. at T2 crystallisation is rich in A or B?
B
what happens between T1 and T2?
crystallisation over a range of temperatures. crystallisation starts at T1 and is complete at T2
what is coring?
alloy is cooled too fast. the exterior portion solidifies whilst the inner portion remains hot and soft. the exterior has a different composition to the interior reducing the alloys quality and performance.
coring affects what?
corrosion resistance
what is the upper line called?
liquidus line
what is the lower line called?
solidus line
understand this
nice one
when alloy components are insoluble in each other crystallisation occurs when?
at a specific temperature
what is a eutectic alloy?
melting point lower than component metals
in this region what states are A and B?
A is solid
B is solid
in this region what states are A and B?
A is solid
B is liquid
in this region what states are A and B?
A is liquid B is solid
where is the eutectic point (eutectic alloy)
