Influence of density and heat treatment on creep behavior of SiAlON ceramics and their microstructural characterisation

Silicon nitride (Si3N4) based materials are used in high temperature applications due to their high strength, toughness and low density. The mechanical and chemical properties of Si3N4 can be tailored further with the addition of aluminum and oxygen into the structure, which are called SiAlON materials. Creep deformation determines the usage and life of the materials in high temperature applications. In order to increase the high temperature resistance, materials can be subjected to below eutectic temperature (BET) or above eutectic temperature (AET) heat treatments, according to the eutectic point of the glassy phase. In this study, the influence of different heat treatments (BET, BET+AET and oxidation) and density difference of as-received samples on the creep behavior of the β-SiAlON materials that have Er-Sm-Ca multi cation system and %10 SiC as secondary phase were investigated. Samples were subjected to four-point bending test in air atmosphere under 1350 – 1390°C temperatures and 100 MPa flexural stress for 72 hours. Microstructural characterizations of the samples were carried out by X-ray diffraction (XRD) and microscopy techniques (SEM and EDX) before and after creep tests. According to the creep test results, samples subjected to BET heat treatment show better creep performance than the high density as-received ones. Moreover, increase in creep resistance is identified in low density as-received samples.