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ME 230: Control Of Properties Of Materials > Strengthening > Flashcards

Strengthening Flashcards

1
Q

What is yield strength

A

The ability to resist plastic deformation

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2
Q

What is plastic deformation

A

Permanent deformation
Governed by dislocation movemnet

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3
Q

Why does materials tend to break via dislocation slip

A

Easier to break a set of bonds and reform with neighbours then breaking all bonds and shifting over and thus plastic deformation tends to happen via dislocation slip

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4
Q

How is the strength of a material increased?

A

By adding obstacles (other defects) to interact and thus block dislocation movement

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5
Q

Ductility in relation to dislocations

A

Ductility is the capability to plastically defrom
Governed by how much dislocations are allowed to move freely

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6
Q

Why does strength and ductility need to be balanced

A

They are contradictory and thus as strength increases, duality decreases
Want to balance for optimal results

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7
Q

What is an alloy

A

A metal with other elements added- this can be as a solute or precipitate

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8
Q

What is strain hardening/work hardening

A

Introducing dislocations and increasing their density within a materials crystal structure by deforming it at cold temperatures (bellow recrystallization temperature)

Dislocations multiply and tangle, hindering movement
Increases strength since it dislocations block other dislocations, more resistant to plastic deformation

Strnegthing material by deforming it

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9
Q

What is grain boundary strengthening

A

Strengthening by reducing grain size
This increases the size of GB and thus strength as GB impede dislocation movement - harder to cross

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10
Q

What is solid solution strengthing

A

Strengthen by alloying, adding solutes which block movement through created strain field as dislocations are attracted to it, this means dislocations need more energy to break bond between solute and surroundings and drag it or energy needed to separate from the solute
Also energy needed to go through the particle

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11
Q

What is particle strengthing

A

Strengthening from the addition of a 2nd phase (alloying)

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12
Q

(T/F) Particle Strengthening can be manipulated and controlled via heat treatment

A

T

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13
Q

What happens to the energy imposed on a material to deform it

A

Most is lost as heat
Only about 10% remains in sample and is stored by increasing the defect population

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14
Q

Effects of cold working

A

Increased dislocation density
Change in grain geometry to a finer geometry
YS goes up with more cold work
Tensile strength also goes up
Elongation to failure (ductility) decreases

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15
Q

What is the relationship between strain hardening, cold working and work hardening

A

Synonyms for the same thing
They are the same

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16
Q

What is the goal of quenching and termpering

A

To produce a tougher steel or iron

17
Q

What are the three main phases of quench and tempering of steel

A
  1. Austenitizing or Normalizing
  2. Quenching
  3. Tempering
18
Q

What is Austenitizing

A

The first stage of strengthening steel
The steel is heated up to high temperatures above the recrystallization tempreture
Here austenite is formed

Relieves stress, thus highest ductility and almost lowest strength

19
Q

What Is austenite

A

The FCC structure form of Iron/steel
Can be gamma-Fe

20
Q

What is quenching

A

Typical second step in strengthening steel
Forming of martensite

Rapid cooling increases dislocation density very fast, strongest point

21
Q

What is tempering

A

Typically final step in strengthening steel
Tempers the martensite - manipulates it to get desired properties

Brings material properties to a comfortable middle point of strength and ductlity

22
Q

In the quenching process, when is the material the strongest and when is it the most ductility

A

Most ductile when austenitizing and least ductile after quenching

23
Q

What is age hardening

A

Precipitation hardening
Also known as aging or age hardening
Uses aging process to increase strength
Typically done on alumium

24
Q

Steps to age hardening

A
  1. Solution heat treatment or solutionizing: Heated past recrystallizing temp, turns system into complete solid solution, relieves stress
  2. Quenching - results in a super saturated solid solution at the end of this as the solubility decreases rapidly with the drop in temperature, creating precipitates
  3. Precipitation Heat treatment: control the precipitation of the beta phases (the aging stage)
25
Q

What are beta phases

A

Phases that exist but are not the main phase in a microstructure which exists since it is the most favourable to occur

Occurs / is the secondary phase when there are multiple phases at a given temperature in a phase diagram

26
Q

Does precipitation hardening or cold working involving aging

A

Precipitation hardening

27
Q

What are the results of the ageing process

A

Strength for al goes up and then down around 1 h - strengths to a point but when aged for too long, diffusion takes over and undoes the extra dislocation added

Curve always goes up to a max point (In terms of strength) and then goes down sharply

28
Q

What is the natural aging curve

A

A curve representing the YS and a function of gaining time of a material when aging at room temperature or operational temperature

29
Q

(T/F) Some alloys can be age hardened and some can not

A

T

30
Q

What are heat treatable alloys and which are not

A

Treatable:
AA2xxx (Al-Cu)
AA6xxx (Al-Mg-Si)
AA7xxx (Al-Zn)
2xxx
3xxx
7xxx
Cast Al

Not:
AA1xxx (commercially pure)
AA3xxx (Al-Mg)
AA4xxx (Al-Si)
AA5xxx (Al-Mg)

31
Q

What is hardeniablity

A

How easy (practical) it is to form martensite (be quenched to a temperable state)

32
Q

(T/F) Hardenablity applies to all materials

A

F
It’s only for steel/iron obv - it has to do with the formation of martensite

33
Q

Poor hardenablility alloys

A

SAE 1010
1040

34
Q

Good hardenablity alloys

A

SAE 4140
4340

35
Q

What is the goal of heat treatment

A

To control the properties of a material, in particular strength, without changing the chemical composition

ME 230: Control Of Properties Of Materials (7 decks)

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