Crack growth rate (CGR) behavior of UNS N07718 was investigated as a function of K-rate in two different environments under cathodic potentials, a mild environment containing 3.5wt% NaCl and a more aggressive environment containing 0.5M H2SO4. The CGR in 3.5wt% NaCl at -1050mV SCE exhibited a plateau CGR that was a strong function of K-rate. CGR measurements in sulfuric acid exhibited K dependence. The CGR exhibited a weak dependence on K-rate in sulfuric acid. In the sulfuric acid environment stable cracking was sustained at constant displacement, which was not readily observed in the 3.5wt% NaCl at -1050mV SCE.

A test was performed to understand the fatigue crack growth rate behavior under gentle cycling at two different values of Kmax in 3.5wt% NaCl/pH = 8.2 at -1050 mV SCE. The measured fatigue crack growth rate increased as the frequency was decreased from 1 mHz to 0.01 mHz. The measured CGR at 1mHz with 86400s hold periods at a Kmax of 55MPa√m and 66MPa√m was significantly lower than the CGR values measured in the rising displacement tests at the same K values. This suggested that crack tip strain rate may play a critical role in sustaining static crack growth.

Subject
Cathodic polarization, Strain rate, Crack growth, Materials, Materials performance, Crack initiation, Sodium chloride, Fatigue crack growth rate, Stress cracking, Lead, Constants, Crack length, Fatigue
Keywords:
Crack growth rate, K-rate, Cathodic Polarization, Low cycle fatigue, Static Crack Growth
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2017
Association for Materials Protection and Performance (AMPP)
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