The present invention relates generally to the preparation of silicon carbide whisker-reinforced alumina ceramic articles, and more particularly to a method of preparing such articles in preselected configurations by pressureless, liquid-phase sintering selected compositions of the whiskers and alumina particulates and then hot isostatically pressing the sintered composites to provide a configured article of near theoretical density.
Reinforced ceramic composites are receiving increasing interest in applications requiring properties such as high chemical, wear and erosion resistance and good structural integrity at high temperatures such as present in heat engines and the like. Such reinforced ceramics are presently being considered as suitable structural materials for the fabrication of turbocharger rotors, cylinders, bearings, and other components of heat engines which will enable the heat engines to run more efficiently at higher temperatures than heretofore possible with similar components formed of metal. Particularly useful reinforced ceramic material have been provided by reinforcing various refractory oxides such as alumina (Al.sub.2 O.sub.3) with silicon carbide (SiC) whiskers which function to substantially increase the fracture toughness of the ceramic and thereby effectively inhibit deleterious crack formation and crack growth due to material fatigue. Such SiC whisker-reinforced ceramics are described and claimed in assignee's allowed co-pending U.S. patent application Ser. No. 578,407 filed Feb. 9, 1984 entitled "Silicon Carbide Whisker-Reinforced Composites and Method for Making Same". In this copending patent application the ceramic composites which exhibit increased fracture toughness and resistance to cracking are prepared by forming a mixture of particulate ceramic material such as Al.sub.2 O.sub.3, 3Al.sub.2 O.sub.3. 2SiO.sub.2, or boron carbide (B.sub.4 C) and about 5 to 60 vol. % of SiC whiskers. These whiskers have a monocrystalline structure and are of a size of about 0.6 micrometers in diameter and a length in the range of about 10 to 80 micrometers. This whisker-ceramic particulate mixture is then hot-pressed at a pressure in the range of about 28 to 70 MPa and at a temperature in the range of about 1600.degree. to 1900.degree. C. for a duration of about 0.75 to 2.5 hours to provide a whisker-reinforced composite with a density greater than about 99% of the theoretical density of the ceramic matrix material. Inasmuch as the whiskers, ceramic materials and the blending procedures as well as the physical and chemical properties described in assignee's aforementioned co-pending patent application are essentially similar to those utilized and achieved in the present invention, assignee's co-pending application is incorporated herein by reference.
While the SiC whisker-reinforced ceramic composite provided by the practice of the method described in assignee's aforementioned application provided articles of significantly increased strength and fracture toughness over conventional ceramics, the fabrication process was limited to the formation of articles with relatively simple shapes. The hot pressing of the whisker-ceramic particulate mixture in die sets inhibited the fabrication of articles with relatively complex shapes such as turbocharger rotors, cylinders, bearings, and the like and required extensive machining and other finishing processes which considerably increased the expense of fabricating structural components of complex shapes. However, the demand for fracture resistant and toughened structural ceramic articles of shaped configurations enhanced the desirability of a fabrication technique wherein products of relatively complex geometries such as mentioned above can be economically fabricated.