材料期刊网

It is possible to enhance the high temperature oxidation resistance and thus prolong the life time of non-oxide refractories by the application of oxide coating.In this work, silicon nitride bonded silicon carbide refractories were coated with alumina using the plasma spraying technique.X-ray diffraction showed γ-Al2O3 to be the dominent phase in the as-sprayed alumina coatings.The stresses developed in the coating layer during post-spray heat-treatment have been analysed.It was found that the coating was under a compressive stress below, but when heated above 1100℃, the γ-Al2O3 phase transformed into α-Al2O3 and this led to the formation of a destructive tensile stress(up to 1700 MPa) which caused cracks to form in and along the weak bond between the alumina coating and SiC grains.The coatings then delaminated and offered little protection to the refractory substrate from oxidation.Future research will be directed on the avoidance of metastable phase formation in the plasma sprayed coating and to increase the bond strength between coatings and SiC grains.