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dental material science 2 > metals and alloys > Flashcards

metals and alloys Flashcards

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1
Q

give some dental uses of metals and alloys?

A 
partial denture framework (CoCr)
crowns (stainless steel)
denture base (stainless steel)
orthodontist appliance (NiTi)
restorations (amalgam)
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2
Q

an aggregate of atoms in a crystalline structure is a?

A

metal

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3
Q

a combination of metal atoms in a crystalline structure is an?

A

alloy

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4
Q

crystal growth of equal dimension in each direction is known as?

A

equi-axed grains

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5
Q

regions of a crystal where grains make contact are known as?

A

grain boundaries

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6
Q

a single crystal with atoms orientated in a given direction is a?

A

grain

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7
Q

why are small fine grains advantageous ?

A 
high elastic limit
increased UTS (ultimate tensile strength) and hardness
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8
Q

why are small fine grains not advantageous?

A

decreased ductility

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9
Q

does fast cooling give small fine grains or large course grains?

A

small fine grains

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10
Q

does slow cooling give small fine grains or large course grains?

A

large course

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11
Q

imperfections/defects in the crystal lattice are known as?

A

dislocations

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12
Q

which technique allows dislocations to be collected at the grain boundary?

A

cold work

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13
Q

how does cold work result in stronger/harder material?

A

results in dislocations being collected at the grain boundary

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14
Q

what techniques does cold working involve?

A

benign and rolling a metal at low temperature

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15
Q

what effect does cold working have on elastic limit (EL), ultimate tensile strength (UTS) and hardness?

A

increase all

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16
Q

what effect does cold working have on the ductility of a metal?

A

reduced ductility

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17
Q

cold working increases residual stress causing distortion of the metal over time, how is this relieved?

A

annealing process

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18
Q

briefly describe what the annealing process involves?

A

heating a metal/alloy so that greater thermal vibrations allow migration of atoms

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19
Q

name the 3 stages of annealing?

A

recovery
recrystallisation
grain growth

20
Q

describe the purpose of the recovery stage of annealing?

A

eliminates residual stress caused from cold working allowing atoms to rearrange within grains

21
Q

what happens during the recrystallisation stage of the annealing process?

A
  • cold work material is subject to a temp above recrystallisation temp
  • this causes new smaller grains, lowers EL, UTS and hardness while increasing ductility
  • spoils the benefits of cold work allowing more cold work
22
Q

what happens during the grain growth stage of the annealing process?

A

excessive temp rise causes large grains to replace smaller ones

23
Q

a combination of 2 or more metals or metals within a metalloid is known as?

A

an alloy

24
Q

list the advantages of an alloy compared to a metal?

A

improved mechanical properties (EL, UTS and hardness)
more corrosion resistant
lower melting pt than individual metal

25
Q

give some dental uses of alloys?

A

steel burs and instruments
amalgam
gold alloy crowns/bridges

26
Q

what is a phase in relation to an alloy?

A

a physically distinct homogenous structure

27
Q

a homogenous mixture at an atomic state is known as a ?

A

solution

28
Q

how many phases does a solid solution have?

A

1

29
Q

name the 3 types of solid solution?

A

random substitutional solid solution
ordered substitutional solid solution
interstitial solid solution

30
Q

smaller atoms located in lattice/grain stricture of larger atoms describes which type of solid solution?

A

interstitial

31
Q

which crystallises at a single temperature, an alloy or a pure metal?

A

pure metal

32
Q

which crystallises over a temperature range, an alloy or a pure metal?

A

alloy

33
Q

the line representing the temperature by which an alloys composition begins to crystallise is known as?

A

liquidus

34
Q

the line representing temp by which an alloys composition has completely crystallised is known as ?

A

solidus

35
Q

which type of alloy cooling, slow or fast, results in a desirable homogenous grain composition but undesirable large grains ?

A

slow cooling

36
Q

do we cool alloys slowly or rapidly?

A

rapidly

37
Q

does rapid cooling of an alloy result in a homogenous grain structure?

A

no

38
Q

a defect in an alloy caused by cooling too quickly is known as?

A

coring

39
Q

how can coring of an alloy be reversed?

A

homogenous annealing

40
Q

which requires little energy/force, dislocation of metal lattice or dislocation of alloy?

A

metal lattice

41
Q

describe dislocation of a defect in an alloy?

A

defect climbs over each atom and settles in-between metal atoms until it reaches grain boundary, this requires a lot of energy

42
Q

a mix of metals having melting pt lower than any of its components is known as?

A

eutectic alloy

43
Q

what are the ideal properties for a partial denture alloy?

A

rigid
strong
hard
ductile

44
Q

for the denture base, do you want high or low youngs modulus and why?

A

high to maintain shape in use

45
Q

for the denture clasps, do you want high or low youngs modulus and why?

A

low to allow flexure over tooth

dental material science 2 (8 decks)

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