In-situ characterization of SiC-AlN multiphase ceramics

AlN and SiC can react and form a solid solution at temperatures above 1800 degrees C, a result that may be beneficial for sintering silicon carbide ce ramics. The pressureless sintered AlN-SiC multiphase ceramics have reached high density at a temperature of 2100 degrees C for 1 hr in Ar. Analytical scanning transmission electron microscopy was then used to determine the gr ain boundary, fracture surface, and the local compositions. Because AlN has a higher solid vaporization pressure than SiC, the vaporization rate of th e AlN solid would far exceed that of SiC at a sintering temperature. The va porizing AlN was deposited on the surface of SiC powder; SiC grains then el ongated in a random arrangement. The form of elongated rod crystals of 4H S iC is 5 to 8 mu m in length and 1 mu m in width. It resulted in the sample fracture section producing pulling-out and a strong tearing-open effect. Th e bending strength and the fracture toughness of the material obtained are 420 MPa and 4.40 MPa x m(1/2), respectively. (C) 1999 Kluwer Academic Publi shers.