Hydrogen transport in nickel base stainless alloys
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II.
INTRODUCTION
A number of studies have established that high-strength, single-phase nickel base alloys are susceptible to hydrogen embrittlement (HE) when exposed to H-generating aqueous environments. 1-7Those studies have established that the embrittlement is strongly dependent on the thermomechanical treatment (TMT) of the alloys. Two similar nominally single-phase nickel base alloys that exhibit such a dependence are HASTELLOY* Alloys C-276 with nominal *Registered trademark, Cabot Corporation
composition 55Ni 16Cr 16Mo 5Fe 4W 2Co, and G with nominal composition 45Ni 22Cr 6Mo 18Fe 2Co 2Nb 2Cu. In particular, the HE tendency of the cold worked form of Alloy C-276 increases markedly following low temperature (200 to 500 ~ thermal exposures. 1'2'3 Identical thermomechanical processing also causes an increase, but to a much lesser degree, in the HE of Alloy G . 2'3's'9 The thermomechanical processing that increases HE has also been shown to alter H absorption and motion in Alloys C-276 and G. ~~ That suggests that there may be a correlation between H transport and embrittlement tendency in the alloys; if that correlation could be determined, it might be possible to improve embrittlement resistance by controlling H transport. For example, control of H transport to alter the performance of carbon steels in H generating environments has recently been reported. ~4:5 Such efforts to control HE requires a thorough understanding of H transport in the alloys of interest. This paper presents the results of an H transport study for Alloys C-276 and G. Those two alloys were selected for the reasons stated previously, i.e., they are similar in composition and structure, yet they exhibit different degrees of HE tendency when H charged. To determine if H transport kinetics were related to the embrittlement tendencies of the alloys, the H transport parameters were measured, and a model for H transport was developed for each alloy. DAVID A MEZZANOTTE, formerly Graduate Assistant with the Department of Metallurgical Engineering and Materials Science, Umversity of Notre Dame, is now with E. I. DuPont, Savannah River Laboratory, Aiken, SC 29801 JAMES A KARGOL is Assistant Professor, Department of Metallurgical Engineering and Materials Science, University of Notre Dame, Notre Dame, IN 46556. NICHOLAS F. FIORE, formerly Professor and Chairman of the Department of Metallurgical Engineering and Materials Science, University of Notre Dame, is now Corporate Director of Technology, Cabot Corporation, Boston, MA 02110. Manuscript submitted August 11, 1981. METALLURGICAL TRANSACTIONS A
EXPERIMENTAL
A. Materials
Portions of commercial heats of Alloys C-276 and G were alternately cold rolled and solution-annealed in an inert atmosphere into 6, 16, and 40 /xm thick foils. Permeation experiments were performed on the alloys in each of four thermomechanical conditions. Since substitutional solid solution strengthening was the primary strengthening mechanism for these nominally single-phase alloys, a cold reduction of 60 pct was utilized t
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