Microstructure and mechanical properties of LPS-SiC based materials with oxide additives

Full text of publication follows: This paper dealt with the microstructure and the strength property of monolithic SiC and SiCf/SiC composite materials by the addition of oxide particles. SiC based materials were fabricated by a hot pressing process through a liquid phase sintering (LPS), using a commercial SiC powder with an average size of about 0.3 μm. The sintering additive was a Al2O3-Y2O3 mixture with a constant composition ratio of Al2O3 and Y2O3 particles (Al2O3/Y2O3: 1.5). Two-dimensional Tyranno SA fibers were utilized as a reinforcing material for LPS-SiCf/SiC composite. A complex mixture with SiC, Al2O3, and Y2O3 particles was impregnated into the fabric structure, using a gas pressure casting. The compact preform for the fabrication of LPS-SiC based materials was sintered at the temperature of 1820 deg. C. The characterization of all materials was investigated by means of SEM with EDS, XRD and three point bending test. Especially, The mechanical property of LPS-SiC materials were examined at the elevated temperatures of 1000 deg. C and 1200 deg. C in the argon atmosphere. LPS-SiC materials represented a good density of about 3.1 Mg/m3, accompanying the creation of secondary phases like YAG in the morphology. LPS-SiC materials showed an average flexural strength of about 750 MPa at the room temperature. The flexural strength of LPS-SiC materials greatly decreased with the increase of test temperature. LPS-SiC materials retained a poor strength of about 300 MPa at the temperature of 1200 deg. C. LPS-SiCf/SiC composites exhibited a density of about 2.7 Mg/m3, due to some amount of matrix pores in the intra-fiber bundle microstructure. LPS-SiCf/SiC composites had an average flexural strength of about 300 MPa. Based on the mechanical property - microstructure correlation, process optimization methodology is also discussed.(authors)