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Evaluation of a Diffusion/Trapping Model for Hydrogen Ingress in High-Strength Alloys.
Annual rept. 15 Sep 93-14 Sep 94,
SRI INTERNATIONAL MENLO PARK CA
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The ingress of hydrogen in various high-strength alloys was investigated with a view to characterizing their susceptibility to hydrogen embrittlement HE. A potentiostatic pulse technique was applied to two precipitation-hardened iron-base alloys AerMet 100 and alloy A-286, two Cu-containing alloys Be-Cu and alloy K-500, and a superferritic stainless steel UNS 544660 in 1 molL acetic acid-1 molL sodium acetate. The data were analyzed using a diffusiontrapping model to obtain the irreversible trapping constant k and hydrogen entry flux for each alloy. Irreversible trapping was negligible in overaged AerMet 100 but pronounced in the aged alloy. The order of the k values for AerMet 100 and two steels 4340 and 1 18Ni previously studied inversely parallels their threshold stress intensities for stress corrosion cracking. Likewise, the k values of alloy A-286, 18Ni steel, and also alloy 718 from earlier work are consistent with test data for their relative resistance to HE. The results for AerMet 100 and alloy A-286 extend the previously reported correlation between k and HE resistance. Unaged Be-Cu is intrinsically more susceptible to HE than unaged alloy K- 500. The type of heat treatment has a marked effect on the rapping behavior of alloy K-500. The intrinsic susceptibility of the annealed and aged alloy is twice that or the direct-aged alloy. The propensity of the S44660 alloy to undergo HE at cathodic protection potentials can be attributed to the absence of an oxide and hence the relatively unrestricted entry of H.
APPROVED FOR PUBLIC RELEASE