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MEC207 > Metals 6 > Flashcards

Metals 6 Flashcards

1
Q

List the point defects

A

Substitutional impurity
Impurity interstitial
Vacancy
Self interstitial

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2
Q

On which scales can there be defects?

A

Macro
Micro
Atomic

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3
Q

How are vacancies produced?

A

Variation in solidification

Large atomic vibrations

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4
Q

What is the result of vacancies?

A

Variations in strain fields of lattice die to distortion of the lattice

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5
Q

Which material property is linked to vacancies and what else is it related to?

A

Creep

Long term exposure to elevated temperature

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6
Q

What is the basis of alloying?

A

Substitutional atoms

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7
Q

What is the result of increasing the % of substitutional atoms on tensile strength?

A

Initially the more added the bigger the increase

Adding too much has opposite effect

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8
Q

What are reasons for alloying besides mechanical properties?

A

Optimising corrosion resistance, magnetism etc

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9
Q

What is the effect of adding small amounts of C to Fe?

A

Creates steel
Changes crystal structure from BCC to BCT
Hardness increases due to distortion of the lattice

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10
Q

What do self interstitial atoms cause?

A

Distortion of atomic planes

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11
Q

What is the most important linear defect and what does it cause?

A

Dislocations

Lattice distortion

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12
Q

Why does plasticity occur?

A

Dislocations move on slip planes under the application of shear stress

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13
Q

What is yield stress?

A

Stress required for plastic deformation to occur

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14
Q

Why is plastic deformation permanent?

A

The atoms have slipped over one another

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15
Q

Which is the active slip plane?

A

One for which shear stress is greatest

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16
Q

Define slip plane and slip direction

A

Plane: plane of greatest packing density
Direction: closest-packed direction within a plane

17
Q

Define strength

A

Resistance to plastic deformation

18
Q

Define toughness

A

Resistance to crack propagation

19
Q

How are strength and toughness related?

A

Increasing one is usually at the expense of the other

20
Q

List the temperature dependencies of the crystal structures

A

FCC- 12 slip systems, 5 operate at all temperatures; ductile at all temperatures. No DBTT
BCC- 48 slip systems- highly temp dependent. DBTT
HCP- 12 slip systems- temp dependent. DBTT

21
Q

What is Von Mises Criterion?

A

For plastic deformation at least 5 independent slip systems must be operational

22
Q

What is FATT?

A

Fracture appearance transition temp
Brittle: shiny, crystalline
Ductile: dull, dimpled

23
Q

How to calculate resolved shear stress

A

τR = σcosφcosλ where σ is applied stress, φ is from normal force to slip plane and λ is force to slip direction

24
Q

What can act as an obstacle to dislocation motion?

A

Other dislocations
Grain boundaries
Precipitates
Cracks

25
Q

What can assist dislocation motion?

A

Elevated temp

Availability of slip systems

MEC207 (21 decks)

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