Question  #34–You  would  be  given  a  chart  similar  to  that  below  and  asked  to   answer  the  questions  (similar  to  #1,  and  #2,  below.     Element   Crystal  structure     Atomic  radius   Fe         BCC           0.124  nm   Cr         BCC         0.125  nm   Al       FCC         0.125  nm   N       HCP         0.065  nm   1.  For  which  combination  of  metals  do  you  expect  substitutional  solid  solution   strengthening  to  occur?   a)  Fe  and  Cr   b)  Fe  and  Al   c)  Fe  and  N   d)  Cr  and  Al   e)  Cr  and  N   f)  Al  and  N     Answer:  a)   consider  the  4  requirements  for  substitutional  atoms:     Similar:  size–a)  b)  and  d)  would  be  correct  if  we  consider  only  size.   xl  structure–only  a)  is  correct.  We  can  eliminate  all  other  choices.   Similar  electronegativities–if  not  specified,  assume  that  they  are  similar  for  metals  given   Similar  valences.  You  would  be  given  a  periodic  table  to  determine  this.  Since  Fe  and  Cr  are   only    2    columns  apart  on  the  periodic  table,  this  is  similar  enough  for  our  purposes.     2.    For  which  combination  of  metals  do  you  expect  diffusion  to  be  the  fastest?   a)  N  in  Fe  at  700°C       b)    N  in  Fe  at  900°C     c)  Cr  in  Fe  at  700°C       d)    Cr  in  Fe  at  900°C   e)  Al  in  Fe  at  700°C       f)      Al  in  Fe  at  900°C             Answer:  b)   The  fastest  diffusion  is  interstitial  N  is  part  of  the  small  diffusing  element  list   (NOCH),  so  will  be  the  fastest  diffusing  species.  We  can  eliminate  all  but  a)  and  b)     Since  diffusion  is  faster  at  higher  temperature,  we  eliminate  a)   Materials Moments: Arthur C—Food Containers Lewis & Ray—Al Composites Background image: http://images.iop.org/objects/ntw/news/10/4/9/image1.jpg * Exam I Friday 21 February Covers Chapters 1 – 7 Review Questions posted on Canvas Strengthening Mechanisms Sections 7.8 – 7.13 Strengthening Metals Underlying Principle for Strengthening Metals Dislocations facilitate plastic deformation Inhibiting (binding, stopping, slowing) dislocation motion makes metals stronger Strengthening Metals: (Ways to restrict dislocation motion) Composition change:Solid-solution strengthening (Diffusion)Case hardeningAlloying Solid-solution strengthening (Diffusion)Alloying Carburizing furnace Image: http://heatingitup.files.wordpress.com/2011/12/carburizing-furnace.jpg * City Steel Heat Treating Co. f16_07_pg190 Case Hardening – Hard Case w/ tough core Low-C Steels (> 0.30% C): Carburizing, Nitriding, Carboni ...

1. Question
#34–You
would
be
given
a
chart
similar
to
that
below
and
asked
to
answer
the
questions
(similar
to
#1,
and
#2,
below.
Element
Crystal
structure
Atomic

2. radius
Fe
BCC
0.124
nm
Cr
BCC
0.125
nm
Al
FCC
0.125
nm
N

3. HCP
0.065
nm
1.
For
which
combination
of
metals
do
you
expect
substitutional
solid
solution
strengthening
to
occur?
a)
Fe
and
Cr
b)
Fe
and
Al
c)
Fe

4. and
N
d)
Cr
and
Al
e)
Cr
and
N
f)
Al
and
N
Answer:
a)
consider
the
4
requirements
for
substitutional
atoms:
Similar:
size–a)
b)
and
d)

5. would
be
correct
if
we
consider
only
size.
xl
structure–only
a)
is
correct.
We
can
eliminate
all
other
choices.
Similar
electronegativities–if
not
specified,
assume
that
they
are
similar
for
metals
given

6. Similar
valences.
You
would
be
given
a
periodic
table
to
determine
this.
Since
Fe
and
Cr
are
only
2
columns
apart
on
the
periodic
table,
this
is
similar
enough
for
our
purposes.

7. 2.
For
which
combination
of
metals
do
you
expect
diffusion
to
be
the
fastest?
a)
N
in
Fe
at
700°C
b)
N
in
Fe
at
900°C

8. c)
Cr
in
Fe
at
700°C
d)
Cr
in
Fe
at
900°C
e)
Al
in
Fe
at
700°C
f)
Al
in
Fe
at
900°C

9. Answer:
b)
The
fastest
diffusion
is
interstitial
N
is
part
of
the
small
diffusing
element
list
(NOCH),
so
will
be
the
fastest
diffusing
species.
We
can
eliminate
all
but
a)
and

10. b)
Since
diffusion
is
faster
at
higher
temperature,
we
eliminate
a)
Materials Moments:
Arthur C—Food Containers
Lewis & Ray—Al Composites
Background image:
http://images.iop.org/objects/ntw/news/10/4/9/image1.jpg
*
Exam I

11. Friday 21 February
Covers Chapters 1 – 7
Review Questions posted on Canvas
Strengthening Mechanisms
Sections 7.8 – 7.13
Strengthening Metals
Underlying Principle for Strengthening Metals
Dislocations facilitate plastic deformation
Inhibiting (binding, stopping, slowing) dislocation motion
makes metals stronger
Strengthening Metals:
(Ways to restrict dislocation motion)
Composition change:Solid-solution strengthening
(Diffusion)Case hardeningAlloying
Solid-solution strengthening (Diffusion)Alloying

12. Carburizing furnace
Image:
http://heatingitup.files.wordpress.com/2011/12/carburizing-
furnace.jpg
*
City Steel Heat Treating Co.
f16_07_pg190
Case Hardening – Hard Case w/ tough core
Low-C Steels
(> 0.30% C):
Carburizing,
Nitriding,
Carbonitriding
Carburized depth of 0.030” to 0.050”
in 4 hours @ 1700°F
f16_07_pg190.jpg
Alloying
http://tankiialloy.en.made-in-
china.com/offer/AqCnWidOrYcV/Sell-Copper-Nickel-Alloy-
Strip.html
Cu-Ni Alloy

13. Cu-Ni Alloy
*
f04_07_pg178
f04_07_pg178
Atoms diffuse to a location that reduces strain energy
Underlying principle:
f04_07_pg178.jpg
f16_07_pg190
f16_07_pg190
Fig. 7.17
Tensile strains
Solid-
Solution
Strengthening:
Smaller Substitutional Impurity

14. f16_07_pg190.jpg
f16_07_pg190
Solid-