Accession Number : ADA194301

Title :   Evaluation of a Diffusion/Trapping Model for Hydrogen Ingress in High-Strength Alloys.

Descriptive Note : Final technical rept. 15 Mar 86-15 Mar 88,

Corporate Author : SRI INTERNATIONAL MENLO PARK CA

Personal Author(s) : Pound, Bruce G

PDF Url : ADA194301

Report Date : 15 Apr 1988

Pagination or Media Count : 77

Abstract : A diffusion/trapping model for hydrogen ingress was applied to three high-strength alloys, AISI 4340 Steel, Monel K500, and MP35N. The model was used with a potentiostatic double-pulse (PDP) technique, and current transient data were obtained in various electrolytes ranging in pH from 2.9 to 9.0. In all cases, the anodic charge can be analyzed as a function of charging time using an interface control model, in which the rate of hydrogen ingress is determined by the flux across the alloy interface and not by hydrogen diffusion in the alloy. The apparent rate constant for hydrogen trapping (k sub a) and the hydrogen ingress flux for each alloy were obtained using this model. The irreversible trapping constants for Monel K500 and MP35N were also evaluated from ka, but the densities of irreversible traps were three orders of magnitude smaller than the concentration of sulfur and phosphorus impurities, which were assumed to be the primary irreversible traps. The low values of the trap density are probably primarily due to sulfur and phosphorus segregated as clusters at grain boundaries. The two nickel-containing alloys, Monel K500 and MP35N, exhibited a lower flux of hydrogen across the alloy surface and a lower irreversible trapping constant than 4340 steel. The difference in both the nature of the principal irreversible traps, which were determined from the trapping constants, and the interfacial flux can be expected to contribute substantially to the difference in susceptibility of the steel and the two nickel-based alloys to hydrogen embrittlement. Keywords: Hydrogen embrittlement, High strength alloys.

Descriptors :   *ALLOYS, *DIFFUSION, *HIGH STRENGTH ALLOYS, *HYDROGEN, INTERFACES, RATES, TRANSIENTS, STEEL, NICKEL ALLOYS, HYDROGEN EMBRITTLEMENT

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE