This preview shows pages 1–2. Sign up to view the full content.
Homework #5  Solutions
Due:
10/06/08
1.)
The diffusion coefficient of Ni in an austenitic stainless steel is 10
22
m
2
/s at 500
o
C
and 10
15
m
2
/s at 1000
o
C.
From this information, calculate the activation energy
(in kJ/mol) for the diffusion of nickel in this alloy.
D
(m
2
/s)
T
(K)
10
22
773
10
15
1273
Using
D = D
o
exp

Q
d
RT
we set up two simultaneous equations with
Q
d
and
D
o
as unknowns.
Solving for
Q
d
and
eliminating
D
o
in terms of temperatures
T
1
and
T
2
and
D
1
and
D
2
we get
Q
d
=

R
ln D
1

ln D
2
1
T
1

1
T
2
=
 8.31J/molK [ ln 10
22
 ln10
15
]
[1/773 – 1/1273]
=
263,000 J/mol
=
263 kJ/mol
2.) For the diffusion data given below, answer the following questions;
a.)
Which process has the higher activation energy: i.) the diffusion of C in BCC Fe
or ii.) the diffusion of Fe in BCC Fe.
What is the graphical basis of your
argument?
b.) From the limited data here would you expect that the grain boundaries in a
polycrystal constitute overall a faster or a slower diffusive path?
Why?
c.) What is the activation energy for the diffusion of Cu in Cu?
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 02/10/2009 for the course MAT 33 taught by Professor Keith during the Spring '07 term at Lehigh University .
 Spring '07
 keith

Click to edit the document details