Contributions of segregated phosphorus to the intergranular stress corrosion cracking of nickel

Conference · Wed Feb 01 04:00:00 EST 1984

OSTI ID:6269387

H, Jones R; Danielson, M J; Bruemmer, S M; Baer, D R; Thomas, M T

Phosphorus segregated to the grain boundaries of nickel has been observed to accelerate intergranular stress corrosion cracking (IGSCC) at passive and transpassive potentials in 1 N H/sub 2/SO/sub 4/ while sulfur had a negligible effect. Straining electrode tests of nickel with 0.26 monolayers of phosphorus or sulfur were conducted at potentials of +0.4 V to +2.0 V (SCE) and a strain rate of 2 x 10/sup -6/ s/sup -1/ while the crack growth rate-stress intensity relationships were measured with compact tension samples tested at +0.9 V (SCE). Crack tip chemistry estimates for a phosphorus enriched intergranular crack were made using a model by Turnbull. This analysis indicated that a potential drop of 40 mV would occur in a 2 mm long, 10 ..mu..m wide crack and that the solution at the crack tip would be saturated with nickel ions. Crack tip corrosion rate estimates were used in conjunction with a stress corrosion model by Parkins to indicate that the IGSCC rate was 10 to 180X faster than the calculated value. The discrepancy between the measured and calculated crack growth rates may reflect limitations in the crack tip corrosion rate or crack growth rate modeling or a mechanical contribution to the crack growth rate. Differences between intergranular corrosion and stress corrosion tests show that the application of a stress caused intergranular cracks to be aligned perpendicular to the stress direction while intergranular corrosion crevices were randomly oriented. Also, intergranular stress corrosion cracks occurred at potentials of +0.4 to 1.5 V (SCE) while intergranular corrosion only occurred at potential greater than +1.4 V (SCE).

• Research Organization: Pacific Northwest Lab., Richland, WA (USA)
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 6269387
• Report Number(s): PNL-SA-11270; CONF-8310205-12; ON: DE85003112
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
AQUEOUS SOLUTIONS
CHEMICAL REACTIONS
CORROSION
CRACK PROPAGATION
CRACKS
CRYSTAL STRUCTURE
CURRENT DENSITY
DISPERSIONS
ELEMENTS
FAILURES
FRACTURES
GRAIN BOUNDARIES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INTERGRANULAR CORROSION
METALS
MICROSTRUCTURE
MIXTURES
NICKEL
NONMETALS
PHOSPHORUS
SEGREGATION
SOLUTIONS
STRESS CORROSION
SULFUR
SULFURIC ACID
TRANSITION ELEMENTS