Hot corrosion of the B2 nickel aluminides. Final report
The hot corrosion behavior of the B2 nickel aluminides was studied to determine the inherent hot corrosion resistance of the beta nickel aluminides and to develop a mechanism for the hot corrosion of the beta nickel aluminides. The effects of the prior processing of the material, small additions of zirconium, stoichiometry of the materials, and preoxidation of the samples were also examined. Additions of 2, 5, and 15 w/o chromium were used to determine the effect of chromium on the hot corrosion of the beta nickel aluminides and the minimum amount of chromium necessary for good hot corrosion resistance. The results indicate that the beta nickel aluminides have inferior inherent hot corrosion resistance despite their excellent oxidation resistance. Prior processing and zirconium additions had no discernible effect on the hot corrosion resistance of the alloys. Preoxidation extended the incubation period of the alloys only a few hours and was not considered to be an effective means of stopping hot corrosion. Stoichiometry was a major factor in determining the hot corrosion resistance of the alloys with the higher aluminum alloys having a definitely superior hot corrosion resistance. The addition of chromium to the alloys stopped the hot corrosion attack in the alloys tested. From a variety of experimental results, a complex hot corrosion mechanism was proposed. During the early stages of the hot corrosion of these alloys the corrosion is dominated by a local sulphidation/oxidation form of attack. During the intermediate stages of the hot corrosion, the aluminum depletion at the surface leads to a change in the oxidation mechanism from a protective external alumina layer to a mixed nickel-aluminum spinel and nickel oxide that can occur both externally and internally. The material undergoes extensive cracking during the later portions of the hot corrosion.
- Research Organization:
- Case Western Reserve Univ., Cleveland, OH (United States)
- OSTI ID:
- 6272335
- Report Number(s):
- N-93-25128; NASA-CR--191082; E--7621; NAS--1.26:191082; CNN: NCC3-94; RTOP 505-63-40
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360105* -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CORROSION RESISTANCE
CRACKING
DECOMPOSITION
MINERALS
NICKEL ALLOYS
NICKEL COMPOUNDS
NICKEL OXIDES
OXIDATION
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PYROLYSIS
SPINELS
SURFACES
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
ZIRCONIUM ADDITIONS
ZIRCONIUM ALLOYS