Thermal shock and oxidation resistances of SiC composite ceramic sheath for immersion heater

The immersion heater sheath of SiC composite ceramic with multi-layer structure was partly immersed into molten aluminum to investigate the thermal shock and oxidation resistance properties of the sheath with different parts. The microstructure and phase composition of the SiC composites were characterized by scanning electron microscope and X-ray diffraction. The failure reason and failure position for the immersion heater sheath were determined. The results show that the residual bending strength of inner sheath material keeps higher than 270 MPa after the long-term oxidation experiment; which could not lead to the failure of the whole sheath. The outer sheath material is affected by thermal shock together with long-term oxidation. The porosity of the outer sheath materials is obvious increased and the residual bending strength is significantly reduced in the region between the molten surface and 100mm beneath the molten surface, which would be the main reason for the failure of the whole immersion heater sheath.