Chemical vapor deposition of thoriated tungsten protective cups Page: 9 of 45
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A manufacturing process was developed for chemically vapor co-depositing, in
production quantities, a tungsten 2 percent thoria alloy into a protective cup configuration
from gaseous phases. Tungsten hexafluoride and thorium acetylacetonate were used as the
active plating species, hydrogen as the metal reductant, and carbon dioxide as the thorium
The cups were deposited on expendable male, molybdenum mandrels that were
machined precisely to the required inside dimensions of a finished cup. Since the plated
tungsten bonds intimately onto the molybdenum mandrel, the inside surface of the cup conforms
exactly to the outside dimensions of the mandrel. The mandrels were removed by chem-milling.
In the as-fabricated condition, the cups were extremely frangible as evidenced by the
columnar and poorly defined grain structure. A stress relieving heat treatment at approximately
20000C recrystallized the grains into an equiaxed fine grain structure that was resistant to
grain growth after heating to 22000C for 5 hours. It appeared that the thoria was present as a
super fine dispersion within the grains of tungsten as manifest by the resistance of the material
to grain growth and property degradation at elevated temperatures. The stress relieving heat
treatment reduced the hardness from approximately 800 KHN to 350 KHN, resulting in a
readily machinable material. Preliminary strength measurements of this material indicate an
ultimate tensile strength of approximately 135,000 psi at room temperature, and 8100 psi at
At the conclusion of this program, PDS 30103 was written to define the process for
controlling the quality of CVD (chemical vapor deposited) thoriated tungsten protective cups.
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Blay, J.S. Chemical vapor deposition of thoriated tungsten protective cups, report, January 1, 1968; Pittsburgh, Pennsylvania. (https://digital.library.unt.edu/ark:/67531/metadc1026564/m1/9/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.