Test 2. Chapter 10 Flashcards

1
Q

nucleation

A
  • nuclei (seeds ) act as template to grow crystals
  • for nucleus to form rate of addition of atoms to nucleus must be faster than rate of loss
  • once nucleated, grow until reach equilibrium
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2
Q

driving force to nucleate increases as we increase temperature T

  • ___________(eutectic, eutectoid) More common
  • _________(peritectic)
A
  • supercooling (eutectic, eutectoid)

- superheating (peritectic

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3
Q

small supercooling –>

A

few nuclei-large crystals

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4
Q

large supercooling –>

A

rapid nucleation-many nuclei small crystals

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5
Q

what are two solidification processes?

A

homogeneous nucleation, heterogeneous nucleation

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6
Q

homogeneous nucleation

A
  • nuclei form in the bulk of liquid metal

- requires supercooling (typically 80-300C max)

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7
Q

heterogeneous nucleation

A
  • much easier since stable “nucleus” is already present
    could be wall of mold or impurities in the liquid phase
    -allow solidification with only .1-10C supercooling
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8
Q

by convention rate of transformation

A

r=1/t

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9
Q

reaction rate is a result of ___________ and _________ of crystal

A

nucleation and growth of crystal

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10
Q

Martensite:

A

y(FCC) to Martensite (BCT)

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11
Q

y to M transformation?

A
  • is very rapid

- % tranfs. depends on T only

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12
Q

M=_____________ is body centered tetragonal (BCT)

A

martensite

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13
Q

tempering martensite

A
  • reduces brittleness of martensite
  • reduces internal stress cause by quenching
  • produces extremely small Fe3C PARTICLES surrounded by alpha
  • decreases TS, YS but increases %RA
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