Influence Of Zirconia Fibers On Thermal Shock Resistance Of Alumina Ceramic

Alumina ceramics are low cost and widely used, but with high brittleness, low fracture toughness and poor thermal shock resistance, their service lives are short and application fields are limited. Zirconia fiber is a kind of advanced inorganic fiber with high elastic modulus and strength, excellent capabilities of endurance to high temperature, corrosion and oxidation resistance. And there are good physical and chemical compatibility as well as similar coefficient of thermal expansion. In this paper, zirconia fibers were added to alumina. We expect to improve their thermal shock resistance by means of raising flexural strength, fracture toughness and controlling porosity. This is good to extending their fields and lives of application, as well as reducing resource waste.Zirconia fibers and alumina powder were used as raw material, PVA as binder. With blending, drying, prilling and dry pressing, the composites were made by sintering at the temperatures of1560℃、1590℃、1620℃and1650℃. Performances were tested, thermal shock resistance and its mechanism were studied.Influence of sintering temperature, fiber content and length on porosity, relative density, flexural strength, fracture toughness and thermal shock resistance of composites were studied. The results showed that flexural strength, fracture toughness raised firstly and then decreased by increasing fiber content. When sintering temperature was1650℃and fiber content was15wt%, flexural strength and fracture toughness of composites were the highest. The porosity decreased with increasing sintering temperature and raised with increasing fiber content. The relative density decreased firstly and then increased with increasing fiber content. When fiber content was15wt%, the relative density was the lowest.The effects of blending time on mechanical properties and thermal shock resistance of composites were observed. The results showed that mechanical properties and thermal shock resistance were increased firstly and then decreased with raising blending time. When blending time was3h, the flexural strength and fracture toughness of composites were62%and28%higher than that of monolithic alumina ceramics respectively.The residual strength of composites after water-coolling decreased with raising temperature difference. When fiber content was20wt%, the thermal shock resistance was best and the△Tc is about500℃, higher than200℃of monolithic alumina ceramics. When temperature difference is1400℃, air-coolling time increased firstly and then decreased with raising fiber content. When fiber content was15wt%, the thermal shock time of samples was30, higher than10of monolithic alumina ceramics; the thermal shock time of crucible was16, higher than3of alumina crucibles.The composites thermal shock resistance and its mechanism were studied. Zirconia fibers with higher elastic modulus and strength raised composites flexural strength. Crack deflection, fiber bridging, debonding and extraction consumed lots of energy. By these means, the thermal shock resistance was enhanced. Adding fibers increased porosity, so cracks would deflect, bifurcate and pin when run into pores, leading to cracks shortening, increasing and forming of net structure, so as to raise fracture energy and thermal shock resistance.