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51318-10700-Environmentally Assisted Cracking of High Strength Nickel Based Alloys Under Cathodic Protection

Environmentally assisted cracking of high strength nickle based alloys was investigated in 3.5wt% NaCl under cathodic protection.

Product Number: 51318-10700-SG
Author: Ramopal Thodla
Publication Date: 2018
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Environmentally assisted cracking of high strength nickle based alloys under was investigated in 3.5wt% NaCl under cathodic protection. Rising displacement tests were performed on C22HS and MP98T were performed at a slow K-rate of 0.005 Nmm*-3/2/s. The result suggests that there is no significant environmental effect for MP98T. However C22HS exhibited a decrease in the initiation toughness. Tests performed under K control under a range of conditions on 718 and K-500. In general, the crack growth rate (CGR) measured under constant K were lower than those obtained under rising displacement tests under similar conditions. The CGR in both 718 decreased with decreasing potential. The CGR was also observed to depend strongly on the loading mode. There m was a strong effect of increasing K, with with increasing K tests resulting in substantially higher CGR’s than at constant under similar conditions. The above results suggest that the rate limiting step for crack propagation may be the generation of hydrogen at the tip end. A crack strain rate based model was applied to rationalize the data though more work is needed to establish the various parameters associated with the model.

Key Words: Environmentally Assisted Cracking, High Strength Nickle Based Alloys, Cathodic Polarization, 718, C22HS, dK/da effect

Environmentally assisted cracking of high strength nickle based alloys under was investigated in 3.5wt% NaCl under cathodic protection. Rising displacement tests were performed on C22HS and MP98T were performed at a slow K-rate of 0.005 Nmm*-3/2/s. The result suggests that there is no significant environmental effect for MP98T. However C22HS exhibited a decrease in the initiation toughness. Tests performed under K control under a range of conditions on 718 and K-500. In general, the crack growth rate (CGR) measured under constant K were lower than those obtained under rising displacement tests under similar conditions. The CGR in both 718 decreased with decreasing potential. The CGR was also observed to depend strongly on the loading mode. There m was a strong effect of increasing K, with with increasing K tests resulting in substantially higher CGR’s than at constant under similar conditions. The above results suggest that the rate limiting step for crack propagation may be the generation of hydrogen at the tip end. A crack strain rate based model was applied to rationalize the data though more work is needed to establish the various parameters associated with the model.

Key Words: Environmentally Assisted Cracking, High Strength Nickle Based Alloys, Cathodic Polarization, 718, C22HS, dK/da effect

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