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Materials > Chapter 12 > Flashcards

Chapter 12 Flashcards

1
Q

Age hardening

A

A special dispersion-strengthening heat treatment. By solution treatment, quenching,
and aging, a coherent precipitate forms that provides a substantial strengthening effect. (Also
known as precipitation hardening.)

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2
Q

Artificial aging

A

Reheating a solution-treated and quenched alloy to a temperature below the
solvus in order to provide the thermal energy required for a precipitate to form

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3
Q

Athermal transformation

A

When the amount of the transformation depends only on the temperature,
not on the time (same as martensitic transformation or displacive transformation).

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4
Q

Austenite

A

The name given to the FCC crystal structure of iron and iron-carbon alloys

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5
Q

Avrami relationship

A

Describes the fraction of a transformation that occurs as a function of
time. This describes most solid-state transformations that involve diffusion; thus martensitic transformations
are not described.

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6
Q

Bainite

A

A two-phase microconstituent, containing ferrite and cementite, that forms in steels that
are isothermally transformed at relatively low temperatures

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7
Q

Bake-hardenable steels

A

These are steels that can show an increase in their yield stress as a result
of precipitation hardening that can occur at fairly low temperatures (100°C), conditions that simulate
baking of paints on cars. This additional increase leads to better dent resistance

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8
Q

Cementite

A

The hard, brittle ceramic-like compound Fe3C that, when properly dispersed, provides
the strengthening in steels.

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9
Q

Coherent precipitate

A

A precipitate with a crystal structure and atomic arrangement that have
a continuous relationship with the matrix from which the precipitate is formed. The coherent precipitate
provides excellent disruption of the atomic arrangement in the matrix and provides excellent
strengthening.

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10
Q

Dihedral angle

A

The angle that defines the shape of a precipitate particle in the matrix. The dihedral
angle is determined by the relative surface energies of the grain boundary energy of the matrix
and the matrix-precipitate interfacial energy.

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11
Q

Displacive transformation

A

A phase transformation that occurs via small displacements of
atoms or ions and without diffusion. Same as athermal or martensitic transformation

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12
Q

Ferrite

A

The name given to the BCC crystal structure of iron that can occur as or . This is not
to be confused with ceramic ferrites, which are magnetic materials.

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13
Q

Guinier-Preston (GP) zones

A

Clusters of atoms that precipitate from the matrix in the early
stages of the age-hardening process. Although the GP zones are coherent with the matrix, they are
too small to provide optimum strengthening.

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14
Q

Interfacial energy

A

The energy associated with the boundary between two phases.

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15
Q

Isothermal transformation

A

When the amount of a transformation at a particular temperature
depends on the time permitted for the transformation.

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16
Q

Martensite

A

A metastable phase formed in steel and other materials by a diffusionless, athermal
transformation.

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17
Q

Martensitic transformation

A

A phase transformation that occurs without diffusion. Same as
athermal or displacive transformation. These occur in steels, Ni-Ti, and many ceramic materials.

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18
Q

Natural aging

A

When a coherent precipitate forms from a solution treated and quenched agehardenable
alloy at room temperature, providing optimum strengthening.

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19
Q

Nitinol

A

A nickel-titanum shape memory alloy.

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20
Q

Pearlite

A

A two-phase lamellar microconstituent, containing ferrite and cementite, that forms in
steels cooled in a normal fashion or isothermally transformed at relatively high temperatures

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21
Q

Precipitation hardening

A

See age hardening.

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22
Q

Shape-memory effect

A

The ability of certain materials to develop microstructures that, after
being deformed, can return the material to its initial shape when heated (e.g. Ni-Ti alloys).

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23
Q

Smart materials

A

Materials that can sense an external stimulus (e.g., stress, pressure, temperature
change, magnetic field, etc.) and initiate a response. Passively smart materials can sense external
stimuli; actively smart materials have sensing and actuation capabilities.

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24
Q

Solution treatment

A

The first step in the age-hardening heat treatment. The alloy is heated above
the solvus temperature to dissolve any second phase and to produce a homogeneous single-phase
structure.

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25
Q

Strain energy

A

The energy required to permit a precipitate to fit into the surrounding matrix during
nucleation and growth of the precipitate.

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26
Q

Superelastic behavior

A

Shape-memory alloys deformed above a critical temperature show a large
reversible elastic deformation as a result of a stress-induced martensitic transformation

27
Q

Supersaturated solid solution

A

The solid solution formed when a material is rapidly cooled
from a high-temperature single-phase region to a low-temperature two-phase region without the
second phase precipitating. Because the quenched phase contains more alloying element than the
solubility limit, it is supersaturated in that element.

28
Q

Tempering

A

A heat treatment used to reduce the hardness of martensite by permitting the martensite
to begin to decompose to the equilibrium phases. This leads to increased toughness

29
Q

Time-temperature-transformation (TTT) diagram

A

The TTT diagram describes the time
required at any temperature for a phase transformation to begin and end. The TTT diagram assumes
that the temperature is constant during the transformation.

30
Q

Widmanstätten structure

A

The precipitation of a second phase from the matrix when there is
a fixed crystallographic relationship between the precipitate and matrix crystal structures. Often
needle-like or plate-like structures form in the Widmanstätten structure.

31
Q

T / F - Strengthening Mechanisms - Cold Work/strain hardening

A

True

32
Q

T / F - Strengthening Mechanisms - Grain size control

A

True

33
Q

T / F - Strengthening Mechanisms - Alloying (solid solution strengthening)

A

True

34
Q

T / F - Strengthening Mechanisms - Dispersion strengthening

A

True

35
Q

You must ____ the solubility limit for Dispersion strengthening

A

Exceeding

36
Q

growth of the precipitates normally occurs by ___-___

diffusion and redistribution of atoms

A

long-range

37
Q

the overall rate, or _____, of the transformation process

depends on both nucleation and growth

A

kinetics

38
Q

Nucleation is favored by low T (large ________)

A

undercooling)

39
Q

Growth is favored by high T (______ driven)

A

diffusion

40
Q

The maximum transformation rate is the sum of the

_______ rate and the _______ rate.

A

nucleation, growth

41
Q

Converting to a “time” basis results in the “_______

A

C-curve

42
Q

Aluminum alloys are commonly _________ strengthened

A

dispersion

43
Q

The form and location of the dispersed phase depends

on the “___” taken

A

path

44
Q

Interfacial energy influences…

A

the shape of the dispersed phase

45
Q

Precipitation Hardening means…

A

Dispersed particles impede dislocation motion

46
Q

T / F Requirements for Age Hardening - The alloy system must display decreasing solid
solubility with decreasing temperature.

A

True

47
Q

T / F Requirements for Age Hardening - The alloy system must display increasing solid
solubility with decreasing temperature.

A

False

48
Q

T / F Requirements for Age Hardening - The alloy must be quenchable

A

True

49
Q

T / F Requirements for Age Hardening - The matrix should be relatively hard and brittle,
and the precipitate should
be hard and brittle.

A

False

50
Q

T / F Requirements for Age Hardening - The matrix should be relatively soft and ductile,
and the precipitate should
be hard and brittle

A

True

51
Q

T / F Requirements for Age Hardening - A coherent precipitate
must form.

A

True

52
Q

Manufacturing benefits of an age hardening alloy

A

Little or no distortion during aging – can machine to shape in the solutionized stated and then age harden!

53
Q

Use of an age hardened alloy at elevated temperature Must maintain a ….

A

low enough temperature to not result in aging

54
Q

Hypoeutectoid is __ 0.77%C |

A

<

55
Q

Hypereutectoid is ___ 0.77%C

A

>

56
Q

Heat treat martensite to form ______ martensite

A

tempered

57
Q

tempered martensite less _____than martensite

A

brittle

58
Q

tempering reduces internal ______caused by quenching

A

stresses

59
Q

_______ and ______are important in the transformation of oen solid to another

A

Nucleation, Growth

60
Q

Dispersion strengthening takes on many forms name 2

A

–Precipitation strengthening (Age hardening)

–Eutectoid strengthening

61
Q

Steel benefits from ___-________ structures

A

non-equilibrium

62
Q

Isothermal transformation diagrams allow us to understand the _________ times required

A

transformation

63
Q

Some transformations are ___________

A

diffusionless

64
Q

From an engineering perspective, Martensite is most useful as a precursor to ________ ________

A

tempered Martensite

Materials (8 decks)

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