Influence of Additive SiO₂ on Thermal Shock Resistance of Plasma-sprayed Al₂O₃ Coating

The influence of additive SiO₂ with different content on the thermal shock resistance of plasma-sprayed Al₂O₃ coating was investigated.The experimental results have shown that the thermal shock lifetime of the plasma-sprayed coating and the lifetime of plasma-sprayed coating before coating failure were increased obviously when adding 3%AiO₂ into the plasma-sprayed Al₂O₃ coating.The reasons are that the suitable content of SiO₂ in the coating makes the gas holes and microcracks in the coating increase remarkably and the size of the gas holes be uniform and most of them be within 1~2μm in diameter and microcracks well-distribute in the coating films.This pattern of gas hole and microcrack can release internal stress in the coating and decrease the coating elastic moduel, so the thermal shock resistance of Al₂O₃+3% SiO₂ coating is increased remarkably.But a surfeit of SiO₂ is subject to cause stress concentration and to produce coarsing crack, because of obvious difference between the thermal expansion coefficient of Al₂O₃ and that of SiO₂.And, the thermal shock resistance is on the decrease when the gas hole rate increases largely.