Accession Number:

AD0831448

Title:

THE FABRICATION OF IRIDIUM AND IRIDIUM-ALLOY COATINGS ON GRAPHITE BY PLASMA-ARC DEPOSITION AND GAS-PRESSURE BONDING.

Personal Author(s):

Corporate Author:

BATTELLE MEMORIAL INST COLUMBUS OH COLUMBUS LABS

Report Date:

1968-02-01

Abstract:

Experimental work was conducted to develop high-density well-bonded coatings of iridium on graphite using the plasma arc deposition-gas pressure bonding technique. This effort involved determination of both the optimum plasma-arc spray and gas-pressure densification parameters as well as destructive and nondestructive characterization of the resultant coatings. Several grades of isotropic, high-thermal-expansion graphites were evaluated as possible substrate materials however, only AXF and L-56 grades appeared to be compatible for use with this process. It was found that the behavior of coatings produced by this process was strongly dependent on the impurity content of both the coating and the substrate at low oxygen partial pressures however, as the oxygen level of the environment increased, this effect diminished. Alloy coatings of iridium-rhenium and iridium-hafnia were produced by codeposition of individual powders followed by a homogenizing heat treatment where necessary. Densification of the rhenium-containing alloy was not achieved using the same parameters employed for the densification of pure iridium. Twenty-two oxidation specimens were prepared for testing as well as scaled-down shapes as demonstration pieces. The emittance of iridium was measured in vacuum, static air, and moving air. The emittance of hafnia-doped iridium was also measured at elevated temperatures. It was found that the addition of hafnia increased the emittance of the coating to approximately that of hafnia itself. Author

Descriptive Note:

Summary rept. (Final), 10 Apr 66-30 Nov 67,

Pages:

0144

Descriptors:

Identifiers:

Subject Categories:

Contract Number:

AF 33(615)-3706

File Size:

0.00MB

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