Microstructures
by
George
Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA,
1966
Copyright©2005 by George Langford
Non Ferrous Alloys - Lesson 3 -
Twelfth specimen
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Here is an aluminum bronze, shown at 100X.
It was a valve stem, used in a steam atmosphere. The copper -
aluminum phase diagram is shown again at left to help you.
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This failure is quite similar in appearance to
dezincification. It is also called de-alloying.
It is completely analogous to dezincification.
What structural composition does the alloy have ?
That is, to what part of the phase diagram does the microstructure
correspond ?
Pause and cogitate, then take a look
at the answer.
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This was probably difficult for
you to answer, but the alloy seems to be all alpha. There are no
second phases present in the unaffected matrix at far right. The
"stripes" at the left may be the result of remnants of coring in the
wrought microstructure which affected the degree of de-alloying.
The dendrite cores would be least susceptible.
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