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6 Questions on Phase Transformations in Material Processing - Exam 3 | MATL 6300, Exams of Materials science

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 #3
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. Can you have a displacement of the Matano interface in a diffusion couple from the original weld
interface without a Kirkendall marker shift? Explain why or why not.
pf3
pf4
pf5

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Download 6 Questions on Phase Transformations in Material Processing - Exam 3 | 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. Can you have a displacement of the Matano interface in a diffusion couple from the original weld interface without a Kirkendall marker shift? Explain why or why not.

_________________________________________________________________

  1. An A-B diffusion couple has been analyzed at a composition XA = 0.65 where X (^) A is the atom

fraction. The interdiffusion coefficient ( D = X DB A + X DA B ) was determined to be 5.5x10- cm 2 /sec and ∂ X (^) A /x = 2.44 cm -1^. Experimentally it has been determined that the markers move

in a manner described by the following equation:

2 x (^) t = K

where K is a constant, x is the distance moved by the markers from the Matano interface, and t is the diffusion time. For XA = 0.65 and 50 hours diffusion time, x = 0.01 cm.

(a) What is the velocity of the markers in cm/sec? (b) Determine the numerical values of the intrinsic diffusion coefficients DA and DB. Note that the

velocity of the markers in terms of diffusion constants can be expressed by (^ A B )^ A

X

v D D X

_________________________________________________________________

  1. What degree of undercooling is required to insure homogeneous nucleation occurs in alloy ufailum? Properties of alloy ufailum are as follows: Tm = 600 oC, γs-l (interfacial energy between solid and liquid) = 200 erg/cm^2 , L (latent heat) = − 2x10^3 J/cm 3 , r* (critical nucleus size) =1.5x10 -7^ cm. Remember that 1 erg = 10-7^ J.

_________________________________________________________________

  1. The following is a schematic of the diffusion couple consisting of A and B which form a substitutional alloy. Assuming DA < DB, determine (a), (b), and (c). (a) Marker position after diffusion (b) Line of pores (Kirkendall porosity) after diffusion (c) Net flux of vacancies
  2. Draw two curves corresponding to homogeneous and heterogeneous nucleation on each plot.

Marker

A B

∆GLÆS

r

∆T

Nucleation rate (I)