Influence of compositional modifications on the corrosion of iron aluminides of molten nitrate salts

Technical Report · Tue Jan 01 04:00:00 EST 1991

DOI:https://doi.org/10.2172/5195667· OSTI ID:5195667

Tortorelli, P F; Bishop, P S

The corrosion of iron-aluminum alloys by molten nitrate salt as a function of aluminum, chromium, and other minor elements has been studied as part of an alloy design effort aimed at the development of a strong, ductile, corrosion-resistant FeAl type of aluminide. Short- term weight change data were used to examine the compositional dependence of the corrosion processes that occurred upon exposure of iron aluminides to highly oxidizing nitrate salts of 650{degrees}C. Corrosion resistance was found to increase with increasing aluminum concentrations of the alloy up to approximately 30 at. % Al. Chromium additions to the aluminide were not detrimental and may have improved the corrosion behavior for certain aluminum concentrations. No effects of minor alloying additions (C, B, Ti, and Zr) could be determined. The best overall corrosion resistance as measured by weight change results were obtained for an Fe-35.8 at. % Al aluminide containing some chromium. Based on linear weight loss kinetics, the weight change measurements for the most resistant compositions predict corrosion rates of 300 {mu}m/year or less at 650{degrees}C. These rates are substantially better than typical nickel-based alloys and stainless steels. From a consideration of the weight changes; the microstructural, thermodynamic, and X-ray diffraction data; and the salt analyses, corrosion of iron aluminides by the molten nitrate salt appears to be controlled by oxidation of base metal components and a slow release of material from an aluminum-rich product layer into the salt. The rate of release was substantially lower than that previously found for iron and iron-based alloys. This would imply that corrosion of iron aluminides could be minimized by maximizing the surface coverage of this aluminum-rich layer either by alloying or by an appropriate preoxidation treatment.

• Research Organization: Oak Ridge National Lab., TN (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5195667
• Report Number(s): ORNL/TM-11598; ON: DE92015648
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ALKALI METAL COMPOUNDS
ALLOYS
ALUMINIUM ALLOYS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
COHERENT SCATTERING
CORROSION
CORROSION RESISTANCE
CORROSIVE EFFECTS
CRYSTAL STRUCTURE
DIFFRACTION
INTERMETALLIC COMPOUNDS
IRON ALLOYS
IRON BASE ALLOYS
MICROSTRUCTURE
MOLTEN SALTS
NITRATES
NITROGEN COMPOUNDS
OXIDATION
OXYGEN COMPOUNDS
POTASSIUM COMPOUNDS
POTASSIUM NITRATES
SALTS
SCATTERING
SODIUM COMPOUNDS
SODIUM NITRATES
X-RAY DIFFRACTION