ENGR 1210: FA 2014; HW 5
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Homework 5 on chapter 5; (Total points: 60)
Reading assignments: Chapter 5 from textbook, notes and slides
Student Name: _______________________________ MTSU ID: ____________________
Honor pledge: I _______________________________ acknowledge that I have neither received
nor given any unauthorized help/aid during this assignment.
Part 1 Key Engineering Terms: fill in the blanks ” 10 points
1. Diffusion: mass transport by ___________________________________ motion.
2. Interdiffusion: In an alloy atoms tend to ____________________________________.
3. Self-diffusion: In _______________________________ solids, atoms also migrate.
4. Vacancy diffusion: Atoms diffuse into ______________________________________.
5. Activation energy is the energy required to cause a particular
_______________________________________ to occur.
6. Carburization is a heat treatment for steels to harden the surface using a gaseous or solid
source of ___________________________________.
7. Concentration gradient is the rate of change of __________________________________
with distance in a nonuniform material.
8. The primary driving factor for diffusion is
______________________________________________.
9. Interstitial diffusion is diffusion of small atoms from one
_____________________________________ position to another in the crystal structure.
10. Nitriding is a process in which ______________________________________________
is diffused into the surface of a material, such as a steel, leading to increased hardness
and wear resistance.
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Part 2 Learning concepts/reflections/problems ” 40 points
1. (a) Compare interstitial and vacancy atomic mechanisms for diffusion.
(b) Cite two reasons why interstitial diffusion is normally more rapid than vacancy
diffusion. 10 points
2. Write the expression for Fick”s first law and Fick”s second law and define each term.
10 points
3. A steel sheet of 5 mm thick has nitrogen atmosphere on both sides at 1000 ºC and is
permitted to achieve steady state diffusion condition. Diffusion coefficient of Nitrogen at
1000 ºC is 1.85 X 10-9 m2
/s. diffusion Flux = 1.0 X 10-6 kg/m2
s. Surface concentration
of Nitrogen at high pressure surface is 2 kg/m3
. How far into steel from high pressure
side be the concentration 0.4 kg/m3
? Assume linear concentration profile.
10 points
4. Determine the carburizing time necessary to achieve a carbon concentration of 0.30 wt%
at a position 4 mm into an iron”carbon alloy that initially contains 0.10 wt% C. The
surface concentration is to be maintained at 0.90 wt% C, and the treatment is to be
conducted at 1100°C. Assume Pre-exponent term D0 = 2.3 X 10-5 m2
/s and activation
energy, Qd = 148,000 J/mol; R = 8.31 J/mol.K. Use table 5.1 for error function.
10 points
Part 3 Materials design ” 10 points
1. What are the factors affecting diffusion? Explain how in 1-2 sentences each.
10 points
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Bonus questions: 10 points
1. Give 2 examples of diffusion from real world applications. Explain the diffusing species
involved. 5 points
2. For a steel alloy it has been determined that a carburizing heat treatment of 10-h duration
will raise the carbon concentration to 0.45 wt% at a point 2.5 mm from the surface.
Estimate the time necessary to achieve the same concentration at a 5.0-mm position for
an identical steel and at the same carburizing temperature? 5 points
Note: Please use extra sheets wherever necessary to answer the questions. All HW must be
uploaded via D2L Dropbox system. Students are highly encouraged to refer textbook, notes
and slides.