showed a severe drop in strength after a quench from only 200°C. Rhodes and co-workers [43] reported an increase in Weibull modulus to 22.5 for alumina containing 25 vol% SiC whiskers, compared to Weibull modulus of only 4.6 for the baseline alumina with no whiskers. High modulus means low scatter in strength data and generally high reliability. For example, the baseline alumina strength test bars showed large variation in strength, ranging from 300 to 650 MPa, while the alumina with 25% SiC whiskers varied only from about 580 to 700 MPa.

As was the case with silicon nitride and alumina-TiC, the first major industrial application of alumina-SiCw composites was for cutting tool inserts. The increased toughness allowed these cutting tools to survive better than monolithic alumina, and the excellent high-temperature strength and chemical corrosion resistance allowed longer life and higher rate of cutting than cemented carbide tools. An interesting example is the use of alumina-SiCw inserts for turning and threading an aircraft landing gear lever arm made of hardened (56-58 HRC) 300 M alloy steel. The turning operation was reduced from 12.5 to 1.5 h and the threading operation was reduced from 75 to 10 min [10].

Alumina-SiCw composites have also been used successfully in other industrial applications including wire drawing dies, extrusion dies, tooling for making aluminum cans, valve seats, seals, and plungers for chemical pumps.

SiC whiskers have been added as reinforcement to other ceramic materials. Buljan and co-workers [33] prepared by hot pressing silicon nitride matrix samples that contained 30 vol % SiC whiskers. They reported strength/toughness of 970 MPa/6.4 MPa ■ m1/2 at room temperature, 820 MPa/7.5 MPa ■ m1/2 at 1000°C, and 590 MPa/7.7 MPa ■ m1/2 at 1200°C. These values are not significantly different from those that can be achieved with self-reinforced silicon nitride at substantially lower cost.

Other researchers have explored the use of SiC whiskers to increase the low-temperature toughness and the temperature capability of molybdenum dis-ilicide (MoSi2). MoSi2 is brittle and has low toughness (~ 5.3 MPa ■ m1/2) at temperatures up to about 1000°C. Around 1000°C, MoSi2 goes through a brittle/ductile transition. At 1200°C MoSi2 has a yield strength of 139 MPa that drops to 19 MPa at 1400°C and 8 MPa at 1500°C. Addition of 20 vol% SiC whiskers increases the room temperature toughness to 6.8 MPa ■ m1/2,1200°C yield strength to 386 MPa, the 1400°C yield strength to 125 MPa, and the 1500°C yield strength to 70 MPa [36, 44]. The MoSi2-SiCw composite has potential to increase the life and durability of industrial heating elements and also critical parts in glass melting furnaces.

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