The Effect of Li, He and Ca on Grain Boundary Cohesive Strength in Ni
- Bettis Atomic Power Laboratory
Boron is added to nickel-base superalloys such as Alloy X-750 in order to enhance high temperature strength and ductility so that the alloy may be more easily hot worked[1]. Boron additions also have been shown to ameliorate intergranular hydrogen embrittlement in nickel[2], and to improve the high temperature resistance of Alloy X-750 to aqueous stress corrosion cracking (SCC) in the absence of irradiation[3]. Recent quantum mechanical calculations demonstrate that boron strengthens grain boundaries in pure nickel[4], and may contribute to the observed benefits of boron on workability and fracture resistance of nickel alloys. Alloy X-750 exhibits greater susceptibility to intergranular stress corrosion cracking (IGSCC) when irradiated[5], and it has been proposed that the presence of grain boundary helium and/or lithium is responsible. Arguments have been advanced that helium embrittlement of the grain boundaries is primarily responsible for the greater observed susceptibility to IGSCC in irradiated X-750[1]. Alternatively, it has been proposed that lithium promotes IGSCC either by entering the water at the crack tip and lowering the local pH, or by inducing a restructuring of the grain boundary itself[1]. Direct embrittlement of grain boundaries by lithium also has been investigated by ion bombardment in Nimonic PE16, illustrating that under certain conditions lithium can produce degrees of embrittlement in nickel comparable to that produced by helium[6]. It is important to understand the relative roles of these species in grain boundary embrittlement in nickel alloys so that better predictive abilities and mitigation strategies can be developed. Toward that end, quantum mechanical calculations have been performed to investigate the influence of isolated lithium and helium atoms on the cohesive strength of an ideal grain boundary in pure nickel.
- Research Organization:
- Bettis Atomic Power Laboratory (BAPL), West Mifflin, PA
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC11-98PN38206
- OSTI ID:
- 756727
- Report Number(s):
- B-T-3301
- Journal Information:
- Scripta Metallurgica (submitted to), Journal Name: Scripta Metallurgica (submitted to)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALLOYS
ATOMS
BORON
BORON ADDITIONS
DUCTILITY
EMBRITTLEMENT
FLAPW
FRACTURES
GRAIN BOUNDARIES
HEAT RESISTING ALLOYS
HELIUM
HELIUM 6
HELIUM EMBRITTLEMENT
HYDROGEN EMBRITTLEMENT
LITHIUM
MITIGATION
NICKEL
NICKEL ALLOYS
NIMONIC PE16
STRESS CORROSION
ab initio calculation
embrittlement
grain boundaries
nickel alloys