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Processing and properties of AIN matrix composite ceramics containing dispersed hard materials

: Burkardt, S.; Riedel, R.; Müller, G.

Journal of the European Ceramic Society 17 (1997), S.3-12
ISSN: 0955-2219
Fraunhofer ISC ()
AIN matrix composite ceramics; ceramic matrix composites; ceramics

The fabrication of AIN-(Y2O3) matrix ceramics reinforced with dispersed TiN or TiB2 particles is described and the resulting specimens are characterized by their mechanical properties and thermal conductivity. The microstructures of the TiN-reinforced specimens sintered at 1700 deg C without isothermal hold show homogeneously distributed TiN particles (ca. 1 mu m in the fine-grained (1-2 mu m)AIN matrix. In contrast, the coarse TiB2 grains (2-3 mu m) of the specimens sintered at 1750 deg C for 60 min are distributed inhomogeneously in the AIN matrix. Furthermore, the surface of the TiB2 grains reacted to TiN and BN during densification in 0 x 1 MPa N2. The mechanical properties of the AIN-(0x 5 wtPer cent Y2O3)/5 wtPer cent TiN composites sintered at 1700 deg C without holding time were determined to be 12x5 GPa, 390MPa and 3x6 MPa m(exp 1/2) for the Vickers hardness HV, the four-point bending strength roB and the fracture toughness KIc, rspectively. The AIN-(4 wtPer cent Y2O3)/25 wtPe r cent TiN specimen sintered at 1900 deg C for 60 min gave 10 x 7 GPa for the Vickers hardness and 270 MPa for the four-point bending bending strength. The fracture toughness was determined to be 8 x 3 MPa m(exp 1/2). In addition, the thermalconductivity of the AIN-TiN composites was of the order of 65 and 105 W m(exp-1) K(exp-1) for composites sintered at 1700 deg C without isothermal hold and at 1900 deg C for 60 min, respectively. The AIN-(2 wtPer cent Y2O3)/10 wtPer cent TiB2-containing specimen sintered at 1750 deg C for 60 min has HV of 9 x 5 GPa,roB of 220MPa and Kic of 3 x 7 MPa m(exp 1/2). The influence of fracture mode and intrinsic stresses on the mechanical properties is illustrated and discusse. Finally, the processing of AIN-(4 wtPer cent Y2O3) ceramics without reinforcing particles coated with the TiN-particle rinforced AIN is reported. These Layered materials exhibit a high thermal conductivity of 150 W m(exp-1) K(exp-1) inside the body and enhanced hardness, fracture s trength and frature toughness at the surface.