NASA Scientific and Technical Aerospace Reports

Prior studies of Alloy 600 and Alloy X-750 have shown the existence of a maximum in stress corrosion cracking (SCC)
susceptibility in high temperature water (e.g., at 360 degrees C), when testing is conducted over a range of dissolved (i.e.,
aqueous) hydrogen (H(sub 2)) concentrations. It has also been shown that this maximum in SCC susceptibility tends to occur
in proximity to the nickel/nickel oxide (Ni/NiO) phase transition, suggesting that oxide phase stability may affect primary
water SCC (PWSCC) resistance. Previous studies have estimated the Ni/NiO transition using thermodynamic calculations
based on free energies of formation for NiO and H(sub 2)O. The present study reports experimental measurements of the
Ni/NiO transition performed using a contact electric resistance (CER) instrument.
NTIS
Nickel Alloys; Hydrogen
20040068249 Lockheed Martin Corp., Syracuse, NY, USA
Microstructural and Microchemical Characterization of Dual Step Aged Alloy X-750 and its Relationship to
Environmentally Assisted Cracking
Young, G. A.; Lewis, N.; Hanson, M.; Matuszyk, W.; Wiersma, B.; May 2001; 16 pp.; In English
Report No.(s): DE2004-821679; LM-01K034; No Copyright; Avail: Department of Energy Information Bridge
When exposed to deaerated high purity water, Alloy X-750 is susceptible to both high temperature (& 249 degrees
C) intergranular stress corrosion cracking (IGSCC) and intergranular low temperature (& 149 degrees C) fracture (LTF).
However, the microstructural and microchemical factors that govern environmentally assisted cracking (EAC) susceptibility
are poorly understood. The present study seeks to characterize the grain boundary microstructure and microchemistry in order
to gain a better mechanistic understanding of stress corrosion crack initiation, crack growth rate, and low temperature fracture.
Light microscopy, scanning electron microscopy, transmission electron microscopy, orientation imaging microscopy, scanning
Auger microscopy, and thermal desorption spectroscopy were performed on selected heats of Alloy X-750 AH.
NTIS
Alloys; Crack Propagation
20040068264 Lockheed Martin Corp., Syracuse, NY, USA
Atomistic Modeling Study of Alloying Element, Impurity Element, and Transmutation Products on the Cohesion of a
Nickel E5(l-brace)001(r-brace) Twist Grain Boundary
Young, G. A.; Najafabadi, R.; Strohmayer, W.; Baldey, D. G.; Hamm, B.; Jun. 2003; In English
Report No.(s): DE2004-821509; LM-03K047; No Copyright; Avail: National Technical Information Service (NTIS)
Atomistic modeling methods were employed to investigate the effects of impurity elements on the metallurgy, irradiation
embrittlement, and environmentally assisted cracking of nickel-base alloys exposed to nuclear environments. Calculations
were performed via ab initio atomistic modeling methods to ensure the accuracy and reliability of the results. A Griffith-type
fracture criterion was used to quantitatively assess the effect of elements or element pairs on the grain boundary cohesive
strength. In order of most embrittling to most strengthening, the elements are ranked as: He, Li, S, H, C, Zr, P, Fe, Mn, Nb,
Cr, and B. Helium is strongly embrittling (-2.04 eV/atom lowering of the Griffith energy), phosphorus has little effect on the
grain boundary (0.1 eV/atom), and boron offers appreciable strengthening (1.03 eV/atom increase in the Griffith energy).
NTIS
Nickel Alloys; Transmutation; Grain Boundaries
20040068268 Lockheed Martin Corp., Syracuse, NY, USA
Measurement of the Nickel/Nickel Oxide Transition in Ni-Cr-Fe Alloys and Updated Data and Correlations to Quantify
the Effect of Aqueous Hydrogen on Primary Water SCC
Attanasio, S. A.; Morton, D. S.; Jun. 2003; 18 pp.; In English
Report No.(s): DE2004-821507; LM-03K049; No Copyright; Avail: Department of Energy Information Bridge
Alloys 600 and X-750 have been shown to exhibit a maximum in primary water stress corrosion cracking (PWSCC)
susceptibility, when testing is conducted over a range of aqueous hydrogen (H(sub 2)) levels. Contact electric resistance (CER)
and corrosion coupon testing using nickel specimens has shown that the maximum in SCC susceptibility occurs in proximity
to the nickel-nickel oxide (Ni/NiO) phase transition. The measured location of the Ni/NiO transition has been shown to vary
with temperature, from 25 scc/kg H(sub 2) at 360 C to 4 scc/kg H(sub 2) at 288 C. New CER measurements show that the
Ni/NiO transition is located at 2 scc/kg H(sub 2) at 260 C. An updated correlation of the phase transition is provided.
NTIS
Nickel Alloys; Hydrogen
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