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Study Guide for Exam 1 - Phase Transformations in Material Processing | MATL 6300, Exams of Materials science

Auburn University (AU)Materials science
Prof. Dong-Joo Kim

Material Type: Exam; Professor: Kim; Class: PHASE TRANSFORMATIONS IN MATERIAL PROCESSING; Subject: Materials Engineering; University: Auburn University - Main Campus; Term: Spring 2010;

Typology: Exams

2012/2013

Uploaded on 03/16/2013

dixiedigger88
dixiedigger88 🇺🇸

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MATL 5300/6300/6306 Spring 2010
Exam #1
Time Allowed 75 min
Name
PLEASE READ THE FOLLOWING BEFORE STARTING
• Please answer all questions in the space provided.
• No credit will be given for irrelevant answers, so please READ THE QUESTIONS with care!
• Credit is given for method as well as for solutions so it is essential that you CLEARLY show how
your answers were derived.
• Put labels and units properly.
1. A portion of the phase diagram for the system Iron – Iron Carbide is shown in the figure below.
Two compositions of alloys with C0,1 = 1 at. % Carbon (n) and C0,2 = 6 at. % Carbon B (o) are
held at a temperature of 1400 K in the γ single-phase field and homogenized. These alloys are
then instantaneously quenched to a temperature T = 1100 K and allowed to isothermally
transform. Consider the growth of precipitates from γ at the 1100 K transformation temperature
for each case. Answer the following questions:
5 10 15
600
20 25
Composition (atomic% Carbon)
800
1000
1200
1400
1600
Temperature (K)
α
α + Fe3C
γ
Liquid
γ + Fe3C
Fe3C
n o
α+
γ
γ + Liquid
pf3
pf4
pf5

Partial preview of the text

Download Study Guide for Exam 1 - Phase Transformations in Material Processing | MATL 6300 and more Exams Materials science in PDF only on Docsity!

MATL 5300/6300/6306 Spring 2010

Exam

Time Allowed 75 min

Name

PLEASE READ THE FOLLOWING BEFORE STARTING

  • Please answer all questions in the space provided.
  • No credit will be given for irrelevant answers, so please READ THE QUESTIONS with care!
  • Credit is given for method as well as for solutions so it is essential that you CLEARLY show how your answers were derived.
  • Put labels and units properly.
  1. A portion of the phase diagram for the system Iron – Iron Carbide is shown in the figure below.

Two compositions of alloys with C0,1 = 1 at. % Carbon (n) and C0,2 = 6 at. % Carbon B (o) are

held at a temperature of 1400 K in the γ single-phase field and homogenized. These alloys are then instantaneously quenched to a temperature T = 1100 K and allowed to isothermally transform. Consider the growth of precipitates from γ at the 1100 K transformation temperature for each case. Answer the following questions:

Composition (atomic% Carbon)

Temperature (K)

α + Fe 3 C

Liquid

γ + Fe 3 C

Fe 3 C

n o

γ + Liquid

_________________________________________________________________

(a) Draw the schematic composition profiles for both cases (n and o). Label axes and compositions properly, and determine carbon flux for both cases in the plot. Assume that carbon is moved by bulk diffusion and local equilibrium of the precipitate/matrix interface is obtained.

(b) Draw the schematic composition profiles for both cases (n and o) if the precipitation of a new phase from γ-matrix is not diffusion controlled but interface controlled, i.e. diffusion across the precipitate/matrix interface is very fast.

(c) Assuming the equilibrium condition at 1100 K is reached, fill out the types of equilibrium

_________________________________________________________________

(c) Estimate an approximate value for the flux of carbon through the sheet if the thickness is 2 mm (0.8 wt% C = 60 kgm -3^ at 1000 oC)

  1. Diffusion of solute A in solvent B occurs by substitutional diffusion. B is face centered cubic in structure with a lattice parameter of 3.0 x 10-8^ cm. Vibrating reed techniques are used to determine the mean successful jump frequency of A in B. This technique yields 10^10 successfully

_________________________________________________________________

jump per sec at 500 oC. A technician working for you makes a measurement of the diffusion of A in B at 500 oC. After 100 minutes he finds A has diffused into B a distance of 0.21 cm.

(a) Has your technician made a mistake? Prove why or why not. Be numerical in your explanation!!

(b) What assumptions have you made in your calculations above.