1
Louisiana State University
Mechanical Engineering Department
ME 2733- Materials of Engineering; Spring 2003 (Section 2)
Midterm Exam Part II
March 25, 2003
Name:_________________________
Problem 1
. Consider a copper sample with the energy for vacancy formation
Q
v
=0.9eV/atom. Knowing that at 400
o
C the equilibrium concentration of vacancies is
1.46x10
22
vacancies/m
3
what is the vacancy concentration at 900
o
C?
The Boltzmann’s constant is k=8.62x10
-5
eV/atom K.

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2
Name:_________________________
Problem 2
.
Consider a 5 mm thick steel plate through which a steady state diffusion of carbon takes
place. The concentrations of carbon at the two faces are maintained constant at 0.62
Kg/m
3
and 0.17 Kg/m
3
. Knowing that the pre-exponential coefficient D
0
=6.2x10
-7
m
2
/s
and the activation energy for diffusion is Q
d
= 80,000J/mol compute the temperature at
which we have a diffusion flux of 5.8x10
-10
Kg/m
2
s.