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Exploratory Development and Evaluation of Low Cost Boron Aluminum Composites.

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Final technical rept. Mar 74-Aug 75,

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One inch wide monolayer boron-aluminum cast tape was successfully fabricated by passing collimated nitrided boron through molten aluminum. This process appears economically quite attractive in that cost projections for fabricating 20,000 lbs of tape per year are approximately 20 per pound exclusive of the cost of fiber and 76 per lb including the cost of fiber. Although cast nitrided boron-aluminum tape composites still has technical problems in providing adequate transverse strength simultaneously with good longitudinal strength retention, the cast tape process still appears to have merit for consideration with other less reactive fibers or for producing lower strength boron-aluminum at considerably lower cost than diffusion bonded material. Although the cost of production quantities of boron-aluminum green tape for diffusion bonding will probably be comparable to that for cast tape, the latter has a distinct cost advantage in terms of low pressure vacuum bag only secondary fabrication with attendant lower pressure, cycle time, and tooling cost. The nitrided boron is produced by first oxidizing the fiber surface, then converting the oxide to a nitride. Because boron nitride does not bond readily to aluminum, there is a delicate balance required to obtain sufficient fiber-matrix reaction to provide a reasonable bond, but not so much as to significantly degrade the fiber properties. The nitrided boron was found to exhibit 30 higher strength than unnitrided boron and retain its strength better when subjected to high temperature exposure. This resistance to several thermal environments allows the cost boron-aluminum tape to be fabricated into structures at 1220 F using vacuum bag pressure only.

Subject Categories:

  • Laminates and Composite Materials
  • Fabrication Metallurgy

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