| Summary: | The author hereby grants to the United States Navy, Wyman
Gordon, and M.I.T. permission to reproduce and distribute
copies of this thesis document in Whole or in part. === Alloy 625, the nickel based superalloy commonly called
Inconel* 625, was investigated for its susceptibility to
stress corrosion cracking in sea water using the slow strain
rate tensile test method. Four microstructures of the alloy
commonly found in end products were investigated.
Bimetallic couplings with other metals were simulated with a
potentiostat at plus and minus one volt with respect to a
saturated standard calomel electrode (SCE). Baseline tests
were conducted in air and sea water without applied
potential. The response of the alloy to cathodic protection
of minus three volts SCE was also investigated on the two
most commonly used microstructures, as cast" and
"forged/annealed". The different microstructures developed
were characterized with a scanning electron microscope
(SEM). The gage lengths, fracture surfaces, and sections of
test specimens were also examined with a SEM. The data from
the slow strain rate tensile tests were compared with data
from standard tensile tests performed on the same processed
material.
The results from this investigation indicate that Alloy 625
is not susceptible to stress corrosion cracking in the
normal sea water service environment where temperatures are
close to ambient. However, the results indicated that Alloy
625 is susceptible to the hydrogen embrittlement form of
stress corrosion cracking when subjected to potentials that
produce hydrogen evolution. This embrittlement leads to
intergranular cracking.
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