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Eutectic superalloys by edge-defined, film-fed growthThe feasibility of producing directionally solidified eutectic alloy composites by edge-defined, film-fed growth (EFG) was carried out. The three eutectic alloys which were investigated were gamma + delta, gamma/gamma prime + delta, and a Co-base TaC alloy containing Cr and Ni. Investigations into the compatibility and wettability of these metals with various carbides, borides, nitrides, and oxides disclosed that compounds with the largest (negative) heats of formation were most stable but poorest wetting. Nitrides and carbides had suitable stability and low contact angles but capillary rise was observed only with carbides. Oxides would not give capillary rise but would probably fulfill the other wetting requirements of EFG. Tantalum carbide was selected for most of the experimental portion of the program based on its exhibiting spontaneous capillary rise and satisfactory slow rate of degradation in the liquid metals. Samples of all three alloys were grown by EFG with the major experimental effort restricted to gamma + delta and gamma/gamma prime + delta alloys. In the standard, uncooled EFG apparatus, the thermal gradient was inferred from the growth speed and was 150 to 200 C/cm. This value may be compared to typical gradients of less than 100 C/cm normally achieved in a standard Bridgman-type apparatus. When a stream of helium was directed against the side of the bar during growth, the gradient was found to improve to about 250 C/cm. In comparison, a theoretical gradient of 700 C/cm should be possible under ideal conditions, without the use of chills. Methods for optimizing the gradient in EFG are discussed, and should allow attainment of close to the theoretical for a particular configuration.
Document ID
19750009404
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Hurley, G. F.
(Tyco Labs., Inc. Waltham, MA, United States)
Date Acquired
September 3, 2013
Publication Date
January 1, 1975
Subject Category
Metallic Materials
Report/Patent Number
C-325
NASA-CR-134756
Accession Number
75N17476
Funding Number(s)
CONTRACT_GRANT: NAS3-16790
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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