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Title:Hydrogen embrittlement of selected nickel and iron-base superalloys
Author(s):Hicks, Peter David
Doctoral Committee Chair(s):Altstetter, Carl J.
Department / Program:Engineering, Metallurgy
Engineering, Materials Science
Discipline:Engineering, Metallurgy
Engineering, Materials Science
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Metallurgy
Engineering, Materials Science
Abstract:Two nickel base superalloys (IN718 and IN625) and one iron base superalloy (A286) were chosen as candidate alloys for this hydrogen embrittlement (HE) study. The HE susceptibility of these alloys, in both annealed (ann) and aged conditions to: a mild gaseous hydrogen (H) environment, dynamic H charging, and H precharging, was evaluated in constant extension rate tests (CERT) and subcritical crack growth (SCG) studies.
CERT testing showed that all three alloys were not embrittled in a 101 kPa H$\sb2$ gas environment (25$\sp\circ$C and 50$\sp\circ$C), but that they all showed a tendency for brittle cracking under severe dynamic cathodic charging (up to 500 A/m$\sp2$). Embrittlement by H precharging up to 50 weight parts per million (wt ppm) decreased in the following order: IN718 (aged) (reduction of area decreased by 76% for a dissolved H concentration of 50 wt ppm), A286 (aged), IN625 (ann), IN718 (ann) and A286 (relative immunity to precharged H) respectively.
SCG tests showed a typical three stage SCG behavior for IN718 (aged) and IN625 (ann) for intermediate hydrogen concentrations. For all alloys, the threshold stress intensity (K$\sb{\rm th}$) decreases. For all alloys, the threshold stress intensity (K$\sb{\rm th}$) decreases with increasing H concentration, but this effect saturates at = 40 wt ppm H for IN625 (ann) and IN718 (aged). For IN718 (aged) and IN625 (ann), increasing the temperature in the range of 0$\sp\circ$C to 50$\sp\circ$C tends to decrease K$\sb{\rm th}$ as well.
Hydrogen enhanced localization of plasticity and void pressurization due to H are used to explain the observed HE of these alloys. The effect of H on the stacking fault energy, dislocation dynamics, trapping sites, microstructure and cracking ahead of the main crack front are discussed with reference to the above alloys and their HE.
Issue Date:1990
Rights Information:Copyright 1990 Hicks, Peter David
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9114264
OCLC Identifier:(UMI)AAI9114264

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