Metals and Alloys

Question 1

structure of materials at room temperature?

Answer 1

hard and lustrous, closely packed crystal structure, radiopaque, conduct heat/electricity

excpetion = Hg liquid at room temp

Question 2

what is an alloy?

Answer 2

2 metals = binary

3 metals = ternary

Question 3

crystal structure in metals?

Answer 3

crystaline, many small particles, form from molten

Question 4

what is an alloy system?

Answer 4

all possible combinations of an alloy

Question 5

what do alloys display in the molten state?

Answer 5

mutual solubility - alloys dissolve in each other

Question 6

what happens when metals cool?

Answer 6

impurities allow metal atoms to deposit upon them = nucleate crystal growth

Question 7

how to grains grow?

Answer 7

grains grown until all of the melt is a metal.

Question 8

what is a grain boundary?

Answer 8

where grains abut their neighbours

Question 9

heterogenous nucleation?

Answer 9

many sites of nucleation

majority

Question 10

homogenous nucleation?

Answer 10

one site
pure metal = 4 atoms
specialised equipment

Question 11

how does grain size affect physical properties?

Answer 11

rapid solidification

extra nucleation sites - e,g addition of iridium to gold

Question 12

if the temperature of the mould is similar to the melt whathappens?
diff to melt?

Answer 12

slow cooling = large grain

rapid cooling = small grain

Question 13

if the temp of the mould is sim shape of mould?

Answer 13

initiate growth and influence direction of crystal growth

Question 14

how to visualise grain boundaries?

Answer 14

light reflecting microscope
polished metal surfaces - irregularities scatter light
application of acid - attack areas under stress - grain boundaries

Question 15

how to shape metals and alloys?

Answer 15

cam be readily deformable, malleable, ductile =
hammering, rolling, pressing, drawn into a wire
can be wrought/cold working

Question 16

what is ductility?

Answer 16

max degree of extension in response to applied tensile force

Question 17

what is malleability?

Answer 17

max degree of compression in response to applied compressive force

Question 18

on cooling from molten components alloys may?

Answer 18

• 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

Question 19

what is an ordered solid solution?

Answer 19

metals atoms have specific states in a common lattice
one shown substantial - similar atomic radii
radii differ - distortions of lattice

Question 20

what is a random solid solution?

Answer 20

random sites in a common crystal lattice

Question 21

interstitial solid solution?

Answer 21

atoms of one lie within the primary lattice sites of the other, atomic radii dependent

Question 22

properties of pure metals?

Answer 22

harder, stronger, higher elastic limits

Question 23

what is the hardening effect?

Answer 23

atoms of diff radii form mechanical resistance to dislocations

Question 24

what happens to grains when drawn into a wire?

Answer 24

elongated in direction of drawing into a laminer structure

limit to how much remodelling can take place

Question 25

what is casting?

Answer 25

molten into an investment mould

Question 26

what is amalgamation?

Answer 26

mix with Hg, plastic mass, hardening, chem reaction, crystallisation

Question 27

insolubility of metals?

Answer 27

rare areas of each pure metal risks electrolytic corrosion

Question 28

partial solubility of metals?

Answer 28

alloy has diff phases solid solition of metal b in a solid solution of metal a in b

Question 29

what is metal affinity?

Answer 29

form intermetallic compounds precise chem formaulation specific valence requirements satisfied - few crystal imperfections = less potential for skip plane movement hard brittle, low ductility

Question 30

cooling curves?

Answer 30

melt metal/alloy | record and plot temp versus time

Question 31

what is tm?

Answer 31

melting point | where plateau's = crystallisation

Question 32

what is a phase diagram?

Answer 32

series of cooling curves for alloys of diff compositions | make structural/coring predictions

Question 33

for each metal composition calculate?

Answer 33

T1, T2, = temp of crystalisation of metal A, temp of crystalisation of metal B plot against % of compositions

Question 34

what can you predict between liquidus and solidus?

Answer 34

predict solid and liquid compositions

Question 35

the larger the seperation between liquidis and solidus the greater the what?

Answer 35

greater the coring

Question 36

the point where alloy components are insoluble in each other mean what?

Answer 36

the sepcific part where crystallisation occurs at specific temperatures

Question 37

what is a eutectic alloy?

Answer 37

behaves like a pure metal narrow melting range narrow melting point lower then component metals application as solders