Effect of electrode potential on stress corrosion cracking and crack chemistry of a nickel-base superalloy

Book · Mon Dec 01 04:00:00 EST 1997

OSTI ID:548582

Lillard, J A; Kelly, R G; Gangloff, R P ^[1]

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1. Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering

The aqueous environment assisted cracking (EAC) resistance of a superalloy, Alloy 718 (Ni-19Fe-18Cr-5Nb-1Ti-0.6Al), was characterized by a rising displacement fracture mechanics methods. This precipitation-strengthened alloy was susceptible to room-temperature EAC in acidified sodium chloride at cathodic and anodic potentials. The threshold for stable crack growth in chloride (K{sub TH}) was as low as 47 MPa{radical}m, reduced from the laboratory air crack initiation toughness (K{sub ICi}) of 81--85 MPa{radical}m. The fracture morphology changed from ductile microvoids in air to a mixture of voids, transgranular facets, and intergranular facets in acidic chloride. Subcritical crack growth rates were on the order of 5 x 10{sup {minus}9} m/s for rising displacement at a stress intensity of 70 MPa{radical}m and were an order of magnitude slower for constant displacement conditions. The degree of reduction in K{sub TH} from K{sub ICi}, the amount and type of fracture surface features, and the crack growth rate depended on the applied electrode potential. Microstructure produced by sub- or super-{delta} solvus heat treatment affected these dependencies. Ion analysis indicated that alloy dissolution occurred at the crack tip even at cathodic polarizations.

• OSTI ID: 548582
• Report Number(s): CONF-970332--
• Country of Publication: United States
• Language: English

Related Subjects

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21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
36 MATERIALS SCIENCE
CORROSION RESISTANCE
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CRACKS
EXPERIMENTAL DATA
FRACTURE PROPERTIES
HEAT RESISTING ALLOYS
INCONEL 718
MICROSTRUCTURE
PRECIPITATION HARDENING
SODIUM CHLORIDES
STRESS CORROSION
WATER CHEMISTRY