Claims
- 1. A method of making a boron carbidealuminum composite, comprising:
- heating a particulate boron carbide in the presence of free carbon to 1800.degree.-2250.degree. C. wherein the resulting boron carbide exhibits a substantially reduced reaction rate with aluminum; and
- reacting said boron carbide with aluminum, wherein a boron carbide-aluminum composite is formed having a microstructure including principally boron carbide and aluminum metal homogeneously distributed throughout said composite.
- 2. The method of claim 1 wherein the heated boron carbide is characterized by a composition close to the carbon-rich end of the boron carbide's solid solution range.
- 3. The method of claim 1 wherein the free carbon present is graphite.
- 4. The method of claim 1 wherein said aluminum constitutes 1-40 % by volume of the composite.
- 5. An article of manufacture, comprising:
- a boron fiber coated with a boron carbide aluminum composite made by the method of claim 1.
- 6. The method of claim 1 wherein said aluminum metal phase is an alloy selected from the group consisting of Al-Cu, Al-Mg, Al-Si, Al-Mn-Mg and Al-Cu-Mg-Cr-Zn or mixtures thereof.
- 7. The method of claim 6 wherein said aluminum alloy constitutes 1-40% by volume of the composite.
- 8. The method of claim 1 wherein heating said boron carbide is conducted at about 2,100.degree. to 2,250.degree. C. for at least about 30 minutes.
- 9. A method of making a boron carbide-aluminum composite of selected ceramic and metal content and microstructure, having high fracture toughness, fracture strength and Young's modulus, and low density, comprising;
- dispersing a particulate boron carbide of less than 10 micrometers average particle size in water at a pH selected to maximize electrostatic repelling forces on boron carbide particle surfaces;
- consolidating said boron carbide into a porous compact;
- sintering said compact, whereby an open porous structure is retained;
- infiltrating said compact with aluminum; and
- heat treating said compact, whereby a voidless composite is formed having a plurality of microstructure phases.
- 10. The method of claim 9 wherein sintering is at about 1800.degree.-2250.degree. C. in the presence of graphite, whereby subsequent reaction rates of boron carbide with aluminum are substantially reduced and composites are formed having a microstructure that is principally boron carbide and aluminum.
- 11. The method of claim 10 wherein said graphite is a particulate dispersed with said boron carbide, or where the boron carbide sample is immersed in a graphite powder bath without prior powder mixing.
- 12. The method of claim 10 wherein said composite has microstructure comprising separate aluminum and ceramic phases each in an interconnected continuous form.
- 13. The method of claim 9 wherein consolidating said boron carbide is accomplished by slip casting.
- 14. The method of claim 9 wherein consolidating said boron carbide is accomplished by injection molding.
- 15. The method of claim 9 wherein consolidating said boron carbide is accomplished by isostatic pressing.
- 16. The method of claim 9 wherein consolidating said boron carbide is accomplished by pressure casting.
- 17. The method of claim 9 wherein infiltration is achieved by submerging said porous compact in liquid metal aluminum.
- 18. The method of claim 17 wherein said infiltration is conducted at 1150.degree.-1250.degree. C.
- 19. The method of claim 9 wherein said infiltrating aluminum is an aluminum alloy selected from the group consisting of Al-Cu, Al-Mg, Al-Si, Al-Mn-Mg, and Al-Cu-Mg-Cr-Zn or mixtures thereof, and said infiltration is conducted at a temperature and for a period of time whereby the contact angle of said alloy with said composite is less than 45.degree..
- 20. The method of claim 19 wherein said heat treating is accomplished at 170.degree.-400.degree. C.
- 21. The method of claim 9 wherein said boron carbide particulate is of 5 micrometers average particle size and the pH is greater than about 5, resulting in a boron carbide suspension of about 27% by volume boron carbide, and compact density of 50-52% by volume.
- 22. The method of claim 9 wherein said boron carbide particulate is about 1 micrometer average particle size and pH is about 6-11, resulting in a boron carbide suspension of about 45-50% by volume boron carbide, and compact density of 66-68% by volume.
- 23. A low-density boron carbide-aluminum composite produced by heating a particulate boron carbide in the presence of free carbon to 1800.degree.-2250.degree. C. such that the resulting boron carbide exhibits a substantially reduced reaction rate with aluminum and reacting said carbon-enriched boron carbide with aluminum, wherein a boron carbide-aluminum composite is formed having a microstructure including principally boron carbide and aluminum metal phases.
- 24. The composite of claim 23 wherein the enriched boron carbide is characterized by a composition close to the carbon-rich end of the boron carbide's solid solution range.
- 25. The composite of claim 23 wherein the free carbon present is graphite.
- 26. The composite of claim 23 wherein said aluminum phase constitutes 1-40 % by volume of the composite.
- 27. A low-density boron carbide-aluminum composite produced by:
- dispersing a particulate boron carbide of less than 10 micrometers average particle size in water at a pH selected to maximize electrostatic repelling forces on boron carbide particle surfaces;
- consolidating said boron carbide into a porous compact;
- sintering said compact, whereby an open porous structure is retained;
- infiltrating said compact with aluminum; and
- heat treating said compact, whereby a voidless composite is formed having a plurality of microstructure phases.
- 28. The composite of claim 27 wherein said sintering is at about 1800.degree.-2250.degree. C. in the presence of graphite, whereby subsequent reaction rates of boron carbide with aluminum are substantially reduced and composites are formed having a microstructure that is principally boron carbide and aluminum.
- 29. The composite of claim 28 wherein said graphite is a particulate dispersed with said boron carbide or where the boron carbide sample is immersed in a graphite powder bath without prior powder mixing.
- 30. The composite of claim 28 wherein said composite has a microstructure comprising separate aluminum and ceramic phases each in an interconnected, continuous form.
- 31. The composition of claim 28 wherein said aluminum phase constitutes 1-40 % by volume of the composite.
- 32. The composite of claim 27 wherein infiltration is achieved by submerging said porous compact in liquid metal aluminum.
- 33. The composite of claim 32 wherein said infiltration is conducted at 1150.degree.-1250.degree. C.
- 34. The composite of claim 27 wherein said infiltrating aluminum is an aluminum alloy selected from the group consisting of Al-Cu, Al-Mg, Al-Si, Al-Mn-Mg, and Al-Cu-Mg-Cr-Zn, or mixtures thereof, and said infiltration is conducted at a temperature and for a period of time whereby the contact angle of said alloy with said composite is less than 45.degree. C.
- 35. The composite of claim 34 wherein said heat treating is accomplished at 170.degree.-400.degree. C.
- 36. The composite of claim 27 wherein said boron carbide particulate is of 5 micrometers average particle size and the pH is greater than about 5, resulting in a boron carbide suspension of about 27% by weight boron carbide, and compact density of 50-50% by weight.
- 37. The composite of claim 27 wherein said boron carbide particulate is about 1 micrometer average particle size and pH is about 6-11, resulting in a boron carbide suspension of about 45-50% by weight boron carbide, and compact density of 66-68% by weight.
DESCRIPTION
The United States Government has rights to this invention pursuant to Contract No. AFOSR 83-0375, awarded by the Defense Advanced Research Project Agency (No. 45831) and the Air Force Office of Scientific Research (No. 83-0375).
US Referenced Citations (6)