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PresRes 3 > Metals > Flashcards

Metals Flashcards

1
Q

What qualities do metals have?

A
  1. elecrtopositive element
  2. luster
  3. good thermal and electrical conductors
  4. high fracture toughness
  5. stronger, more ductile, denser than non-metals
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2
Q

Alloy

A
  1. mixture of 2 or more metals

2. sometimes mixed with non-metals

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3
Q

Classification of Metals

A
  1. elemental vs. alloy (alloys most common in dentistry)
  2. cast vs. wrought
  3. noble vs. non-noble
  4. application
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4
Q

What are the major crystal systems of metals used in dentistry?

A
  1. face centered cubic
  2. body centered cubic
  3. hexagonal close-paced
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5
Q

Noble Metals in Dentistry

A
  1. Palladium
  2. Ruthenium (used as a grain refiner)
  3. Osmium
  4. Gold
  5. Rhodium
  6. Iridium (used as a grain refiner)
  7. Platinum

**Gold, palladium, and platinum are the three MAJOR

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6
Q

Base Metals

A
  1. NOT noble
  2. ex: titanium, cobalt, silver, zinc, gallium, tin, aluminum
  3. in pure form, greater tendency to corrode in the mouth compared to noble metals
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7
Q

High Noble Alloys

A
  1. gold content greater or equal to 40 wt%

2. noble metal is the remainder

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8
Q

Titanium and Titanium Alloys

A

titanium greater or equal to 85 wt%

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9
Q

Noble Alloys

A

noble metal content greater or equal to 25 wt%

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10
Q

Predominantly Base Alloys

A

noble metal content less than 25 wt%

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11
Q

Should “precious” be used to describe noble?

A

NO!!

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12
Q

ADA Type I Alloy

A
  1. soft
  2. < 140 MPa tensile strength
  3. 18% elongation
  4. low sustainable stress, no occlusion
  5. used for inlays
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13
Q

ADA Type II Alloy

A
  1. medium
  2. 140-200 MPa tensile strength
  3. 18% elongation
  4. moderate sustainable stress, light occlusion
  5. used for onlays and inlays
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14
Q

ADA Type III Alloy

A
  1. hard
  2. 201-340 MPa
  3. 12% elongation
  4. high sustainable stress, full occlusion
  5. used for crowns, short-span fixed partial dentures
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15
Q

ADA Type IV Alloy

A
  1. extra-hard
  2. > 340 MPa tensile yield strength
  3. 12% elongation
  4. very high sustainable stress
  5. thin veneer crowns, long-span fixed partial dnetures, removable partial dentures
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16
Q

Homogeneous Nucleation: Pure Metal

A
  1. no impurities/clean container
  2. solid forms from liquid, sometimes requires “super-cooling”
  3. have a melting POINT
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17
Q

Review Phase Diagrams

A

DO IT!!

18
Q

Heterogeneous Nucleation: Pure Metal

A
  1. walls of container or impurity or impurity particles catalyze nucleation
  2. have a melting POINT
19
Q

Alloys

A
  1. exhibit a melting range

2. some very specific alloy compositions have a melting point

20
Q

Rapid vs. slow cooling of metals

A
  1. rapid cooling=more nuclei=smaller grains

2. slow cooling=fewer nuclei=larger grains

21
Q

Grain Refiners

A
  1. method to reduce grain size
  2. add <1 wt% of Iridium (Ir), ruthenium (Ru), or rhenium (Re) to noble casting alloys
  3. finer grain size=increased yield strength, composition uniformity, corrosion resistance
22
Q

Dendritic Metal Structure

A
  1. dendrites: formed through thermal supercooling

2. dendrites growth is along specific crystallographic directions

23
Q

Solid Solutions

A
  1. incorporation of “foreign” atoms (solute) into crystal structures of matrix atoms (solvent)
  2. may be a wide range of composition
24
Q

Substitutional solid solution

A

one atom is replaced with another atom

25
Q

Interstitial solid solution

A

atoms are fit in amongst the other atoms

26
Q

Disordered vs. ordered solid solutions of metals

A

disordered=stronger

27
Q

What does the solubility of a solid solution of metals depend on?

A
  1. size
    * *solubility decreases as size differences increases
  2. crystal structure
    * *greater solubility if same crystal (ex: FCC)
  3. Valence
    * *greater solubility if same (ex: both +2)
  4. chemical reactivity
28
Q

Intermetallic Compounds

A

differ from solid solutions in that they exist as fixed atomic ratios

29
Q

Point Defects

A
  1. substitution or interstitial atoms: depends upon size of atoms
  2. vacancies: vacant lattice site
  3. self-interstitial: matrix atom in an interstitial site
30
Q

Dislocations

A
  1. crystals are rarely ideal
  2. sometimes atoms are missing or extra half-planes of atoms are formed
  3. ex: line imperfections in crystalline solids
  4. hinder dislocation movement=increase strength
31
Q

Mechanisms for strengthening metals

A
  1. solid solution strengthening
  2. strain or work hardening
  3. precipitation hardening
  4. transformation strengthening
32
Q

Solid solution strengthening of metals

A
  1. interstitial solute atoms have a greater effect in modifying material behavior
  2. greater effect if solute atoms are ordered
  3. important factors
    * *size of solute atom
    * *relative nodulus of the two types of atoms
    * *electronic, chemical, and configurational interaction
33
Q

Solid solution strengthening of metals: __strength and hardness, __ductile than either pure metal

A
  1. higher strength and hardness

2. less ductile than either pure metal

34
Q

Solid solution strengthening of metals: melt __highest melting point of pure metals

A

melt below highest melting point of the pure metals

35
Q

Solid solution strengthening of metals: __corrosion resistance than multi-phase alloys

A

higher corrosion resistance than multi-phase alloys

36
Q

Strain hardening/cold working: strength/hardness __, ductility __

A

strength and hardness increase, ductility decreases

  1. plastic deformation=more difficult to deform/shape more
  2. increase in number and interaction between dislocations
  3. must re-heat to regain workability
37
Q

Manufacturing orthodontic wires

A
  1. cast as ingot
  2. series of mechanical reduction (grains become flattened, elongated)
  3. series of wire-drawing steps

**heat tx’s are done during the stages to eliminate work hardening

38
Q

Annealing

A
  1. heat tx used to soften metals and refine their grains

2. recrystallization=new grains nucleate above a certain temperature

39
Q

Steps in annealing

A
  1. original microstructure
  2. cold-worked
  3. new grains nucleate at recrystallization temperature
  4. grain growth above recrystallization temp
  5. annealing complete (equiaxed structure)
  6. further grain growth if heated longer
40
Q

Precipitation hardening of metals

A
  1. solute atoms not dissolved, but form separate second phase particles dispersed in matrix
  2. dislocations impeded by precipitates
    * *have to bow between and around (if precipitate is stronger than matrix)
41
Q

Transformation strengthening of metals

A
  1. change in morphology of lattice structure (occurs upon heating or cooling)
  2. ex: FCC to BCC

PresRes 3 (6 decks)

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