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Lecture Problem 10'38

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On the basis of the photomicrograph for the lead-tin alloy shown in Figure 10.15 ... Can use a photomicrograph of an alloy to estimate its composition simply by ... – PowerPoint PPT presentation

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Title: Lecture Problem 10'38


1
Lecture Problem 10.38
  • Noel Godinez

2
Problem Statement
  • On the basis of the photomicrograph for the
    lead-tin alloy shown in Figure 10.15 and the
    Pb-Sn phase diagram (Figure 10.7), estimate the
    composition of the alloy, and then compare this
    estimate with the composition given in the figure
    legend of Figure 10.15.

3
Assumptions
  • The area fraction of each phase and
    microconstituent in the photomicrograph is equal
    to its volume fraction.
  • The densities of the a and ß phases as well as
    the eutectic structure are 11.2, 7.3, and 8.7
    g/cm3, respectively.
  • This photomicrograph represents the equilibrium
    microstructure at 180C.

4
Theory
  • Mass fraction and volume fraction conversion

5
Theory
  • Mass balance to obtain mass fractions of Pb and
    Sn

6
Solution
  • Estimating from the photomicrograph, the area
    fraction of primary a is approximately 1/5 of the
    total area. The remaining 4/5 is the area
    fraction of the eutectic.

7
Solution
  • From the phase diagram (Figure 10.7), we obtain
    the compositions of a and the eutectic.

8
Solution
  • Using the found values for the mass fractions and
    the compositions

9
Conclusion
  • Can use a photomicrograph of an alloy to estimate
    its composition simply by eyeballing it and
    making a couple of calculations!
  • Can use image processing to get more precise
    results.
  • Answer to this problem depends heavily on the
    assumptions made.
  • How good is the assumption that the area
    fractions are equal to the volume fractions?
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