Tensile properties and structure of several superalloys after long-term exposure to LiF and vacuum at 1,173 K
- National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
The use of the solid-to-liquid phase transformation of LiF to store thermal energy is under consideration for a space-based solar dynamic system. Although advantageous in terms of its energy density, the melting point of this salt (1,121 K) is beyond the commonly accepted upper-use temperature of 1,100 K for chromium-bearing superalloys in vacuum. However, one commercially available nickel-base superalloy (Hastelloy B-2) is chromium free; unfortunately, because of its high molybdenum content, this alloy can form phases that cause high-temperature embrittlement. To test the suitability of Hastelloy B-2, it has been exposed to molten LiF, its vapor and vacuum at 1,173 K for 2,500, 5,000, and 10{sup 4} h. For control, the chromium-containing cobalt-base Haynes alloy 188 and nickel-base Haynes alloy 230 were also exposed to LiF and vacuum at 1,173 K for 5,000 h. Neither LiF nor vacuum exposures had any significant effect on Hastelloy B-2 in terms of microstructural surface damage or weight change. Measurement of the post exposure tensile properties of Hastelloy B-2, nevertheless, revealed low tensile ductility at 1,050 K. Such embrittlement and low strength at elevated temperatures appear to preclude the use of Hastelloy B-2 as a containment material for LiF. Little evidence of significant attack by LiF was seen in either of the chromium-containing superalloys; however, considerable weight loss and near-surface microstructural damage occurred in both alloys exposed to vacuum. Although measurement of the post exposure room-temperature tensile properties of Haynes alloys 188 and 230 revealed no significant loss of strength or ductility, the severe degree of microstructural damage found in unshielded alloys exposed to vacuum indicates that chromium-bearing superalloys might also be unsuitable for prolonged containment of LiF in space above 1,100 K.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 201024
- Journal Information:
- Journal of Materials Engineering and Performance, Vol. 4, Issue 6; Other Information: PBD: Dec 1995
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
14 SOLAR ENERGY
HASTELLOY B
MICROSTRUCTURE
TENSILE PROPERTIES
CORROSION RESISTANCE
HAYNES 188 ALLOY
HAYNES ALLOYS
SOLAR ENERGY
HEAT STORAGE
MOLTEN SALTS
COMPATIBILITY
THERMAL ENERGY STORAGE EQUIPMENT
PHASE TRANSFORMATIONS
EMBRITTLEMENT
DUCTILITY
SURFACES
DAMAGE
WEIGHT MEASUREMENT