Claims
- 1. A ceramic comprising: 10 to 99 percent of a matrix consisting essentially of ZrO.sub.2, 1 to 90 percent of substantially strontium aluminate platelet grains having an aspect ratio greater than 2, wherein said zirconia is partially stabilized by a stabilizing agent and said ceramic has a sintered density greater than 95% of its theoretical density.
- 2. The ceramic of claim 1, wherein the molar ratio SrO/Al.sub.2 O.sub.3 is between 0.02 and 0.20.
- 3. The ceramic of claim 1, wherein the matrix has a grain size that is equiaxed and less than 5 microns.
- 4. The ceramic of claim 3, wherein the matrix is a mixture of zirconia and alumina.
- 5. The ceramic of claim 1, wherein the ZrO.sub.2 matrix is at least partially stabilized to the tetragonal configuration by the inclusion of CeO.sub.2.
- 6. The ceramic of claim 1, wherein the ZrO.sub.2 matrix is at least partially stabilized to the cubic configuration by the inclusion of CeO.sub.2.
- 7. The ceramic of claim 1, wherein the zirconia matrix comprises mixtures of polytypes comprising cubic and/or tetragonal and/or monoclinic polytypes of zirconia matrix.
- 8. The ceramic of claim 1 wherein said zirconia matrix is stabilized with a compound selected from the group consisting of CeO.sub.2, Y.sub.2 O.sub.3, Er.sub.3 O, La.sub.2 O.sub.3, Yb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, MgO, and CaO.
- 9. The ceramic of claim 8, wherein the ZrO.sub.2 matrix contains Y.sub.2 O.sub.3.
- 10. The ceramic of claim 1, wherein the strontium aluminate platelets are substantially made up of 6Al.sub.2 O.sub.3.SrO.
- 11. The ceramic of claim 1, wherein the aspect ratio of the strontium aluminate is greater than 5.
- 12. The ceramic of claim 1, wherein the strontium aluminate platelets have an average width of approximately 5 microns and a thickness of approximately 0.5 microns.
- 13. The ceramic of claim 1, wherein the fracture toughness, as measured by a double cantilever beam technique, is greater than 10 MPa.m.sup.1/2 at room temperature.
- 14. The ceramic of claim 13, having a room temperature four-point bend strength greater than 500 megapascals.
- 15. The ceramic of claim 14, wherein the Vicker's diamond pyramid hardness is greater than 10.0 gigapascals when measured at a load greater than 50 newtons.
- 16. The ceramic of claim 1, wherein the SrO/Al.sub.2 O.sub.3 molar ratio is between 0.01 and 0.30.
- 17. A method of preparing the ceramic of claim 1, comprising: (1) mixing a source of alumina, zirconia, and strontia in appropriate quantities to satisfy the compositional requirements of the ceramic of claim 1, (2) forming a shape, and (3) sintering at a temperature greater than about 1200.degree. C. for 30-150 minutes in order to allow in situ formation of strontium aluminate platelets.
- 18. The process of claim 17, wherein the source of SrO is SrZrO.sub.3.
- 19. The process of claim 17, wherein the source of SrO is Sr(NO.sub.3).sub.2.
- 20. The process of claim 17, wherein the source of SrO is SrCO.sub.3.
- 21. The process of claim 17, wherein the sintering temperature is between 1300.degree. C. and 1700.degree. C.
- 22. The process of claim 17, wherein densification occurs by way of pressureless sintering.
- 23. The process of claim 20, wherein pressure is applied to aid in the densification of the ceramic.
- 24. The ceramic of claim 1, wherein the loading of strontium-aluminate platelets constitutes 15-60 volume percent of the ceramic.
- 25. The ceramic of claim 1 wherein said matrix contains SrO.
- 26. The ceramic of claim 4 wherein Al.sub.2 O.sub.3 is present in substantial quantities.
- 27. A ceramic comprising:
- 10 to 99 percent of a matrix comprising ZrO.sub.2, 1 to 90 percent of substantially plate-like strontium aluminate grains having an aspect ratio greater than 2, said ceramic having a sintered density greater than 95% of the theoretical density of the ceramic and wherein said zirconia is partially stabilized by a stabilizing agent.
STATEMENT OF GOVERNMENT INTEREST
This invention was made with Government support under contract No. F49620-87-C-0077 awarded by the Defense Applied Research Project Administration (DARPA). The Government has certain rights in this invention.
US Referenced Citations (7)
Non-Patent Literature Citations (2)
Entry |
J. Mater, Sci., (17), 225-263, (1982). |
Tsukuma et al., "Mechanical Property and Microstructure of TZP and TZP/Al.sub.2 O.sub.3 Composites," Mat Res. Soc. Symp. PROC., vol. 78, pp. 123-135, (1987). |