Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BDS2 - DMS > Metals and Alloys 2 > Flashcards

Metals and Alloys 2 Flashcards

1
Q

What is an alloy?

A

A combination (or mixture) of two or more metals OR metals with a mettalloid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a metalloid?

A

Something that a metal can be replaced with e.g. Si, C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are 3 advantages of alloys over metals?

A

They have improved properties:

  • Mechanical (EL, UTS, hardness)
  • Corrosion resistance

AND

  • Lower melting point than an individual metal
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is STEEL used for in dentistry? (2 points)

A

Burs, instruments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is AMALGAM used for in dentistry?

A

Filling material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is GOLD ALLOY used for in dentistry? (5 points)

A
  • Inlays
  • Crowns
  • Bridges
  • Partial dentures
  • Wires
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is NICKEL CHROMIUM used for in dentistry? ( 3 points)

A
  • Crowns
  • Bridges
  • Wires
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the definition for ‘phase’?

A
  • Physically distinct homogeneous structure (can have more than one component)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the definition for a solution?

A
  • Homogeneous mixture at an atomic scale (lattice arrangement with 2 or more metals that coexist in the same lattice structure)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How many phases are there for grains composed of one metal only?

A

1 phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How many phases are these for grains composed of individual grains of metal A and B situated in a lattice network?

A
  • Two phases as the 2 metals don’t coexist in the same grain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How many phases are there for grains composed of Metal A and B in a homogeneous mixture?

A
  • One phase (homogeneous as the 2 metals are coexisting in the same lattice structure)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is a solid solution?

A

2 or more types of atoms or molecules that share a crystal lattice

  • The grains are of varying size and shape
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Are metals usually soluble or insoluble when molten?

A

Usually soluble

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

On crystallisation of alloys, what are the 3 possible options that can occur?

A
  1. Metals are insoluble with each other so there is no common lattice - 2 phases
  2. The metals form an intermetallic compound with specific chemical formulation
  3. The metals are soluble in each other and form a solid solution i.e. form a common lattice (there are 3 types of solid solution)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a ‘substitutional’ solid solution?

A
  • Atoms of one metal replace the other metal in the crystal lattice/grain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a ‘random’ substitutional solid solution?

A
  • Metals are similar in: size, valency, crystal structure

- They are randomly positioned

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is an ‘ordered’ substitutional solid solution?

A
  • Metal atoms in regular lattice arrangement

- Forms an ordered solid solution where you can predict the position of the different types of metals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is an ‘interstitial’ solid solution?

A
  • Atoms markedly different in size

- Smaller atoms are located in spaces in lattice/grain structure of larger atoms

20
Q

What does the plateau on the cooling curve if a pure metal indicate?

A
  • Where the crystallisation begins and the metal is becoming a solid (happens at one temperature)
21
Q

What is the cooling curve like for an alloy?

A
  • Temp TL is the temp at which crystallisation of the alloy begins
  • Crystallisation continues and the temp drops
  • TS is when the crystallisation process is complete
  • This is different from the cooling curve of a pure metal as the process of crystallisation doesn’t happen over a single temp
22
Q

For an alloy, are the cooling curves the same or different for alloys with different compositions of metals?

A

Different

23
Q

What is the lower line of a phase diagram called?

A

The solidus

24
Q

What is the liquidous on a phase diagram?

A

Line representing the temperatures at which different alloy compositions begin to crystallise

25
Q

What is the solidus in a phase diagram?

A

The line representing the temperatures which different alloy compositions have completely crystallised

26
Q

What does slow cooling of molten alloys allow? (3 point s)

A
  • Allows metal atoms to diffuse through the lattice
  • ENSURES grain composition is homogenous

BUT

  • This results in large grains (which is not desirable as it causes poor mechanical properties)
27
Q

What is the tie line on a phase diagram?

A

Horizontal line from liquidous to solidus

  • This is roughly when the first grain is going to form which is going to be a composition of 85% A and 15% B
28
Q

What does rapid cooling of alloys produce?

A

Coring

29
Q

Rapid cooling of a molten alloy causes CORING. What is this?

A

The composition of metals varies throughout the grain

30
Q

What are the conditions required for coring? (2 points)

A
  • Fast cooling of liquid state

- Liquidous and solidus must be separated and determines extent of the coring

31
Q

Is a phase diagram has a liquidous and a solidus that are quite far apart will you get a lot of or little coring?

A

A lot of coring

32
Q

What may coring reduce of the solid form of an alloy?

A

May reduce the corrosion resistance

33
Q

What does fast cooling of alloys cause? (2 points)

A
  • Generates many small grains which impede dislocation movement, improving its MECHANICAL PROPERTIES
  • BUT causes coring, which is undesirable
34
Q

What is homogenising annealing of alloys?

A
  • Once the solid, cored alloy is formed:
  • REHEAT to allow atoms to diffuse and so cause grain composition to become homogenous
  • NOTE: keep below recrystallisation temperature, otherwise grains are altered
35
Q

What is solution hardening? (2 points)

A
  • Alloys forming a SOLID SOLUTION and consisting of metals of different atomic size have a distorted grain structure
  • Which IMPEDES dislocation movement and so improves mechanical properties
36
Q

What is the dislocation movement like in a metal lattice and how much energy is needed for this? (2 points)

A
  • Defects ‘roll’ over the atoms in the lattice plane

- Little energy/force is needed for defect to move along the slip plane

37
Q

What is the dislocation movement like for a solid solution and how much energy is required for this? (3 points)

A
  • Defect does not ‘roll’ over the lattice plane. Instead it falls into the larger space existing between the large and small atom
  • More energy/force is needed for the defect to overcome the different sized atoms, and move along lattice to the grain boundary
  • Hence, it requires greater stress to move dislocations in a solid solution - making alloys inherently more fracture resistant (i.e. stronger) than metals
38
Q

What is order hardening?

A
  • Alloys forming an ORDERED SOLID SOLUTION (atoms distributed at specific lattice sites) have a DISTORTED grain structure
  • This IMPEDES dislocation movement and so improves mechanical properties
39
Q

What is an Eutectic alloy?

A

2 metals that are not soluble in one another

40
Q

What are the properties of Eutectic alloys? (4 points)

A
  • Metals are soluble in liquid state
  • Metals INSOLUBLE in solid state (2 phases)
  • i.e. each metal forms physically distinct grains
  • CONTRAST this with Au-Pt alloy
41
Q

What is the melting point of a eutectic alloy like?

A
  • Les than the MP of metal A&B that are combined to make the alloy
42
Q

What is eutectic composition?

A
  • Where liquidous and solidus coincide (i.e. where crystallisation process occurs at a single temperature)
  • Where grains of individual metals are formed simultaneously
43
Q

what are 3 properties of eutectic alloys?

A
  • Lowest melting point
  • Hard but brittle
  • Poor corrosion resistance
44
Q

What happens with alloys that are non-eutectic composition ? (3 points)

A
  • Excess metal crystallises first
  • Then liquid reaches eutectic composition
  • And BOTH metals crystallise (forming separate grains)
45
Q

What does the solubility limit line in a partially soluble alloy phase diagram indicate?

A
  • Indicates that a range of compositions of Ag and Cu (corresponding to the horizontal section of the solidus) ARE NOT POSSIBLE
  • Hence molten alloy composition z:
  • DOES NOT cool rapidly to produce a 50:50 grain comprising Ag and Cu
  • Instead grains of alpha and beta are formed
46
Q

In partially soluble alloys on annealing, a supersaturated alloy will undergo what?

A
  • Precipitation hardening
47
Q

Alloys have better mechanical properties than metals, give 3 examples of these and say what it is due to?

A
  • Fracture strength, rigidity, elastic limit surface hardness
  • This is due to solution, order and precipitation hardening

BUT
- CORED structure must be removed by annealing

BDS2 - DMS (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions