Chapter 4 (imperfections) Flashcards

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1
Q

what is solidification

A

the result of casting of molten material

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2
Q

steps of solidification:

A
  1. Nuclei form
  2. Nuclei grow
  3. grain structure is achieved (not considered a step)
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3
Q

what do we call grains that are of equal length

A

equiaxed

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4
Q

what do we call grains that have been elongated

A

columnar

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5
Q

List the types of point defects

A
  1. Vacancy
  2. interstitial
  3. substitutional
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6
Q

how can we increase the number of vacancies

A

increase temp

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7
Q

solvent:

A

host element

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8
Q

solute:

A

minor element

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9
Q

list the conditions for solid subsitution, and what is this law called?

A
  1. difference in atomic radius must be less than 15%
  2. similar electronegativities
  3. same crystal structure
  4. Valency
    this law is called the W. Hume-Rothery rule
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10
Q

plastic deformation is produced by what type of defect

A

line defects, more specifically dislocations

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11
Q

where would impure atoms go?

A

interstitial spaces

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12
Q

Linear Defect:

A

1D misalignment

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13
Q

Edge Dislocation

A

extra half plane is inserted (b vector is perpendicular to dislocation line)

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14
Q

screw dislocation

A

spiral planar ramp is inserted (b vector is parallel to dislocation line)

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15
Q

3 properties of grain boundaries

A
  1. high mobility
  2. high diffusivity
  3. high chemical reactivity
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16
Q

how are grain boundaries produced

A

by the solidification process

17
Q

how can we explain the causing of equiaxed grains

A

there a greater delta T near the wall during formation

18
Q

what kind of defect is a grain boundary

A

Area defect

19
Q

which factors can cause vacancies?

A

solidification process, heating, neutrons, working

20
Q

what is substitutional solid solution

A

when a host atom is replaced by another atom which can be either larger or smaller. note: DO NOT CONFUSE WITH SUBSTITUTIONAL DIFFUSION!!!

21
Q

what is an insterstitial solid solution

A

same as substitutional except it goes between atoms and is typically smaller

22
Q

what do these (S.S.S) cause?

A

distortions to the lattice

23
Q

will a metal have a greater tendency to dissolve another metal of lower or higher valency?

A

higher

24
Q

if you have both a screw and edge dislocation, what is this referred to as?

A

mixed dislocation

25
Q

put in order of reactivity/energy: surface, bulk, boundary

A

surface>boundary>bulk

26
Q

give a few examples of bulk defects

A

cracks, holes

27
Q

list 4 methods to observe grain boundaries in metals/ceramics

A
  1. section and grind the sample
  2. polish it with diamond paste
  3. etch it chemically
  4. microscope
28
Q

briefly describe the intercept method to determine the size of grain boundaries

A

draw random equal length lines through the photomicrograph. count the number of grains crossed per line and get the average. grain size=(line length/avg grains crossed)/(magnification)