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Self-Lubricating Composites of Porous Nickel and Nickel-Chromium Alloy Impregnated with Barium Fluoride-Calcium Fluoride Eutectic
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
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Self-lubricating composites were prepared by vacuum-impregnating porous nickel or Inconel X-750 nickel-chromium alloy with a barium fluoride - calcium fluoride eutectic composition. Density measurements and photomicrographs of the resulting composite structures demonstrated that this process completely filled the voids of the porous metals with the fluoride eutectic. The compressive yield strength of the nickel composites was quite low about 30 000 psi therefore, in order to avoid severe plastic deformation during the friction and wear experiments, it was necessary to employ moderate contact stresses. However, alloy composites were comparatively resistant to plastic deformation the compressive yield strength was 78 000 pounds per square inch or about 75 percent of the strength of the age-hardened alloy in the dense, wrought form. The air at moderate contact stresses, the friction and wear properties of nickel composites were only slightly inferior to those of the alloy composites. Oxidation of nickel composites becomes serious at 12000 F, however, and limits the usefulness of this material in air to a maximum temperature of about 11000 F. The corresponding temperature limitation of the alloy composites in air was about 1350 F. In a hydrogen atmosphere, the alloy composites performed satisfactorily to 15000 F and may be suitable to somewhat higher temperatures. The frictional properties of the composites were significantly improved by the application of a thin, sintered coating of the eutectic fluoride to the bearing surfaces of the composites.
APPROVED FOR PUBLIC RELEASE