Alloys

Question 1

alloys

Answer 1

combination or mixture of two or more metals
OR
a metal with a metalloid (Si, C)

Question 2

advantages of using an alloy over a metal

Answer 2

improved properties
higher elastic liit, fracture strength, hardness, corrosion resistamce, lower melting point
than individual metals

Question 3

advantages of using an alloy over a metal

Answer 3

improved properties
higher elastic liit, fracture strength, hardness, corrosion resistamce, lower melting point
than individual metals

Question 4

dental uses of alloys

Answer 4

steel [burs, insturments]
gold alloy [crown, bridge]
cobalt chrome [RPD]
amalgam [restorative]
nickell titanium [wires]

Question 5

phase definition

Answer 5

physically distinct homogenous structure, can have more than one component

Question 6

solution definition

Answer 6

homogenous mixture at an atomic scale

Question 7

phases of grains

Answer 7

1. metal A only =
2. metal A and B in a lattice
3. metal A and B in homogenous mixture, one phase

Question 8

states upon crystallisation

Answer 8

1. insoluble, 2 phases
2. from intermetallic compound
3. soluble and form solid solution
   - substitution = atoms of one metal replace other
   - interstitial = atoms markedly different in sie, smaller atoms in spaces in lattice of larger atom

Question 9

difference in metal and alloy in crystallisation temps

Answer 9

metals - crystallise at one temperature
alloys - crystallises over temperature range

Question 10

cooling and composition

Answer 10

must cool slowly, allows atoms to diffuse through lattice, ensure homegous grains
BUT RESULTS IN LARGE GRAINS = BAD MECHANICAL PROP, SO NO SLOW COOLING WANTED

Question 11

rapid cooling of alloys

Answer 11

results in coring, concentration gradient is formed
coring helps improve mechanical properties by reducing dislocation movement and resulting in small grains = BETTER MECH PROP

Question 12

desired speed of cooling alloys

Answer 12

rapid

Question 13

homogenous anneal

Answer 13

gently vibrate and heat atoms, helps diffuse and reduce coring but not altering grains tructure, allows more homogenous proportion of metal through depth

Question 14

dislocation in alloys

Answer 14

defect has to fall into space between large and small atoms and climb along to grain boundary
requires great deal of energy
more stress to move dislocations in solid solution, more fracture resistant and stronger than metals

Question 15

eutectic alloys

Answer 15

when alloy melts at temperature higher than that of its individual metals [stronger together]
physically distinct grains, soluble in liwuid
cools at single temperature - not range like normal alloys

Question 16

metal vs alloys

Answer 16

alloys has better mechprop than metal [fracture strength, rigidity, elastic limit, surface hardnesa] due to solutionm order and precipitation hardening
BUT
cored structure must be removed by annealing

Question 17

coring may;

Answer 17

reduce corrosion resistance of solid alloy form