Effect of Sintering Temperature on Flexural Properties of Alumina Fiber‐Reinforced, Alumina‐Based Ceramics Prepared by Tape Casting Technique

Purpose: The purpose of this study was to investigate the effect of sintering temperature on flexural properties of an alumina fiber-reinforced, alumina-based ceramic (alumina-fiber/alumina composite) prepared by a tape casting technique. Materials and Methods: The alumina-based ceramic used a matrix consisting of 60 wt% Al2O3 powder and 40 wt% SiO2-B2O3 glass powder with the following composition in terms of wt%: 33 SiO2, 32 B2O3, 20 CaO, and 15 MgO. Prepreg sheets of alumina-fiber/alumina composite in which uniaxial aligned alumina fibers were infiltrated with the alumina-based matrix were fabricated continuously using a tape casting technique employing a doctor blade system. Four sintering temperatures were investigated: 900°C, 1000°C, 1100°C, and 1200°C, all for 4 hours under atmospheric pressure in a furnace. The surface of the alumina-fiber/alumina composite after sintering was observed with a field-emission scanning electron microscope (FE-SEM). A three-point bending test was carried out to measure the flexural strength and modulus of alumina-fiber/alumina composite specimens. In addition, sintered alumina fiber was characterized by X-ray diffraction (XRD). Results: FE-SEM observation showed that alumina-fiber/alumina composite was confirmed to be densely sintered for all sintering temperatures. Three-point bending measurement revealed that alumina-fiber/alumina composite produced at sintering temperatures of 1100°C and 1200°C exhibit flexural strengths lower than those of alumina-fiber/alumina composite produced at sintering temperatures of 900°C and 1000°C; alumina-fiber/alumina composite produced at sintering temperatures of 1100°C and 1200°C exhibit flexural moduli lower than that of alumina-fiber/alumina composite produced at a sintering temperature of 1000°C. Additional XRD pattern of alumina fiber indicated that with increasing sintering temperature, the crystallographic structure of γ-alumina transformed to mullite. Conclusions: There were significant differences in the flexural properties between the alumina-fiber/alumina composite sintered at the four temperatures. This indicates that the choice of optimum sintering temperature is an important factor for successful dental applications of alumina-fiber/alumina composite developed by the tape casting system.