Environmentally induced fracture of nickel alloys: a comparison of hydrogen and mercury embrittlement with respect to temperature

Thesis/Dissertation · Tue Jan 01 00:00:00 EST 1985

OSTI ID:5821568

King, R K

Previous studies have compared electrolytic hydrogen embrittlement (HE) and liquid metal embrittlement (LME) by mercury for numerous nickel alloys. All alloys tested exhibited embrittlement to some degree with HE and LME having similar fractographies. This study examines the effect of temperature on He and LME of Monel 400 over the range -30 and 80/sup 0/C. Slow strain rate tensile tests were conducted at two strain rates, 1.6 x 10/sup -5/s/sup -1/ and 1.6 x 10/sup -3/s/sup -1/, and two grain sizes, 35 ..mu..m and 250 ..mu..m. Behavior of Monel 400 is compared with previously studied nickel alloys. Results showed that intergranular, tranogranular, and microvoid-coalescence fractures can be obtained in both hydrogen and mercury. Fracture mode is governed by strain at fracture. Embrittlement ceases below -20/sup 0/ in both environment, believed due to lack of mobility of adsorbed hydrogen and lack of wetting by mercury. LME is more severe than HE because hydrogen blunts cracks by promoting plasticity. HE ceases at about 80/sup 0/C because excess plasticity promotes crack blunting and inhibits initiation. LME fractures remain brittle to 80/sup 0/C. An incubation period is normally needed for adsorption of the embrittler or for penetration of the crack through the plane stress surface zone. Otherwise ductile failures in mercury often exhibit longitudinal splitting, believed to be due to the combination of high normal stress, low shear stress, and a clean surface. The existence of a temperature window for LME can be explained on the basis of strain activated localized wetting. Results of this study are consistent with a decohesion mechanism producing intergranular fracture; competing with an enhanced dislocation nucleation mechanism producing transgranular fracture. Monel 400 exhibited the range of features observed for other nickel base alloys at appropriate conditions of temperature, strain rate, and grain size.

• Research Organization: Oklahoma State Univ., Stillwater (USA)
• OSTI ID: 5821568
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MONEL 400
EMBRITTLEMENT
FRACTURE PROPERTIES
COMPARATIVE EVALUATIONS
GRAIN SIZE
LOW TEMPERATURE
MEDIUM TEMPERATURE
NICKEL BASE ALLOYS
STRAIN RATE
TEMPERATURE EFFECTS
TENSILE PROPERTIES
ALLOYS
COPPER ALLOYS
CRYSTAL STRUCTURE
IRON ALLOYS
MANGANESE ALLOYS
MECHANICAL PROPERTIES
MICROSTRUCTURE
NICKEL ALLOYS
SIZE
360103* - Metals & Alloys- Mechanical Properties
360105 - Metals & Alloys- Corrosion & Erosion