Microstructure design of liquid phase sintered silicon carbide in function of the powders characteristics

Different LPS-SiC were produced by pressureless sintering in argon atmosphere, starting from different powders: either alfa-SiC or Beta-SiC or mixtures of alfa and beta-SiC, using the same sintering aid system (Y2O3+Al2O3). The green densities and the densities after various sintering tests (Temperature range from 1850 to 1900° and holding time 1-2 hours) were related to the powder characteristics and to the processing conditions. The microstructure of materials from alfa-SiC powder is generally equiaxed and fine (grain size from 0.5 to 3.5 μm), while the use of beta-SiC powder favours the development of elongated grains (up to 7 μm) with a mean aspect ratio of about 4. It is possible to tailor morphology and grain size with a proper selection of powder mixtures alfa/beta-SiC. Mechanical properties were evaluated on selected samples.