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Biomaterials > Metals and Alloys > Flashcards

Metals and Alloys Flashcards

1
Q
  1. Define metal, metalloid and alloy: METAL
A

any of a class of chemical elements … generally characterized by ductility, luster, conductivity of heat and electricity

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2
Q
  1. Recognize the relevance of the relationship between structure and properties
A

see pic

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3
Q
  1. List the methods of forming and shaping metals
A

Casting Machining Cold Working Powder Metallurgy

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4
Q
  1. Describe metallic bonding
A
  • Primary/Strong bonding - Metallic Bonding
  • Positive ions + surrounded by ‘cloud’ of electrons
  • Electrons can move in the cloud
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5
Q
  1. List the consequences of metallic bonding (4)
A

High Conductivity(thermal and electrical) -movement of electrons

  • Opacity to light -electrons absorb electromagnetic and photon energy
  • Easy ability to form alloys
  • High plasticity
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6
Q
  1. Define crystallinity
A

shows a long-range regular arrangement of atoms

–Contrast this to an amorphous –glassy-material which has no such regularity. All metals are crystalline

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7
Q
  1. Define unit cell
A

smallest repeating unit in a crystal (consider 3 out of a possible 14)

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8
Q
  1. List the various types of crystalline imperfection
A

–point defects

–line defects

–[plane defects]

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9
Q
  1. Identify bcc, fcc and cph (or hcp) unit cells
A

see pic

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10
Q
  1. Describe the mechanism of plastic strain of metals in terms of movement of dislocations
A

Plastic strain (permanent) -slip of layers of atoms over each other. A metal is soft if the dislocations can be easily moved through the crystal structure while applying force to the material.

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11
Q
  1. Identify point, line and planar defects
A
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12
Q
  1. Draw a typical temperature-time curve for the cooling of a metal
A

see slides

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13
Q
  1. Draw and describe grain structures of the following types: equiaxed coarse grain, equiaxed fine grain and fibrous structure
A

fine grain leads to harder, stronger more dense.

not really sure what else i was supposed to take away from this

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14
Q
  1. Illustrate the structure of an interstitial solid solution, and quote an example of this
A

Steel C atoms in Fe crystal structure

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15
Q
  1. Describe the phenomena that occur in the solidification of an alloy where there is partial solid solubility
A

On cooling further under specific conditions, ‘precipitation’ of a second and different solid phase may occur

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16
Q
  1. Describe the effect of cold working, stress relief anneal, recrystallization and grain growth on the structure of a metal
A

fibrous grain

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17
Q
  1. List the dental applications of alloys
A

Metals are strong and tough. Polymers are not so strong and ceramics are too brittle. Metals in mouth must be biocompatible - resist corrosion and no release of metallic ions.

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18
Q
  1. Define metal, metalloid and alloy: METALLOID
A

exhibit both metallic and non-metallic behavior (Si, As, B)

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19
Q
  1. Define metal, metalloid and alloy: ALLOY
A

a mixture of metals - almost everything we use in dentistry is an alloy, we dony use metals

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20
Q
  1. List the methods of forming and shaping metals: CASTING
A

Pouring liquid metal into mold

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21
Q
  1. List the methods of forming and shaping metals: MACHINING
A

Cutting metal: drilling, turning, …

22
Q
  1. List the methods of forming and shaping metals: COLD WORKING
A

Deforming metal in solid state: forging, extruding

23
Q
  1. List the three principal factors that determine the hardness of an alloy
A

see slides

24
Q
  1. Describe the effect of chemical composition, mechanical history and thermal history on the hardness of an alloy
A

see slides

25
Q

List the four possibilities when a molten alloy is solidified

A

Solid Solution - Interstitial (1)

26
Q

List the four possibilities when a molten alloy is solidified

A

Complete Solid Insolubility (2)

27
Q

List the four possibilities when a molten alloy is solidified

A

Partial Solid Insolubility (3)

Once the initial solid solution is formed, on further cooling the alloy under specific conditions, precipitation of a second phase (same metals mixed in different quantities and with different crystal unit cell) occurs. The resulting alloy has grains of both phases. The alloy is stronger because the second phase pins the movement of the dislocations

28
Q

List the four possibilities when a molten alloy is solidified (4)

A

Intermetallic Compound formation

29
Q
  1. Identify point, line and planar defects: POINT
A

see pic

30
Q
  1. Identify point, line and planar defects: LINE
A

see pic

31
Q
  1. Identify point, line and planar defects: PLANAR
A

see pic

32
Q

Properties of metal

A

Usually strong (hard) and stiff

Tough - not brittle

Lustrous - shine

Dense

Good conductors of electricity

33
Q
A
34
Q

Point defects

A

instead of metal A atom in one position, metal B atom is there - substitiutional

element b smaller than metal a, put in a cavity in between metal A’s with ease - interstitial

vacancies - missing atom

35
Q

line defects

A

dislocation in a crystal - see pic

36
Q

plane defects

A

as you cool the metal, orientation of the crystals is different and have different orientations leading to discontinuity in the boundaries

37
Q

Distinguish between elastic and plastic properties - metals

ELASTIC

A

Elastic strain (recoverable) - stretch metal and interatomic bonds, after you remove force, returns to its structure

Elasticity of metals depends mainly on the resistance of the metallic bond to be stretched. The metallic bond acts as a spring

38
Q

Modulus of elasticity mainly depends on the _____ nature of each metal

A

chemical

39
Q

distinguish between elastic and plastic properties of metals

PLASTIC (slip of layers of atoms over each other)

A

Plasticity, i.e. permanent deformation of metals is due to the formation and movement of dislocations.

40
Q

The easier the dislocations move with no impediments in the crystal structure, the softer the metal is.

A

In order words, to strengthen a metal the movement of the dislocations should be made difficult.

41
Q

Metals are very tough because they can develop significant plasticity, i.e., metals can form and move dislocations. If dislocations are difficult to move,

A

the material will be more brittle, less tough. Ceramics are brittle because they can not form dislocations, they break bonds instead.

42
Q

Polymers have permanent deformation because they are viscoelastic, they have viscous component (disentanglementof molecules). Metals are not viscoelastic, ___

A

heir plasticity does not depend on the time you apply a load, but on the magnitude of the load.

43
Q

Pure metals are often too ___ and ___for dental use

A

soft and ductile

44
Q

Dental Significance of Metals

Point #1 - Pure, untreated metals are usually too ____

A

soft/weak - gold, alumin, titanium, iron

45
Q

Dental Significance of Metals

Point #2 -

The strength of an alloy mostly depends on: (3 things)

A

composition, mechanical history and thermal history

46
Q

Dental Significance of Metals

Point #3 The elasticity of a metal mostly depends on

A

the composition of the unalloyed metal

47
Q

Principles for selection of alloys

A
48
Q

Metallic Alloys used in dentistry (3)

A
49
Q

Applications of Alloys in Dentistry

A
50
Q
A

Biomaterials (6 decks)

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