Effect of glass additives on the strength and toughness of polycrystallinealumina

The effect of stress at grain boundaries on the mechanical properties of al umina ceramics was investigated. Residual stresses at grain-boundaries resu lted from a mismatch in thermal expansion coefficient (TEC) between the alu mina matrix and the glass-phase segregated at grain-boundaries. The BaO Al2 O3-SiO, (BAS) system and the Li2O Al2O3-SiO2 (LAS) system glasses were chos en to have a higher and a lower TEC than that of alumina, respectively, res ulting in microscopic tensile and compressive stresses at grain-boundaries for Al2O3/BAS and Al2O3/LAS composites, respectively. The experimental resu lts showed that the Al2O3/BAS composite fractured intergranularly with a fr acture toughness higher than that of monolithic alumina. On the other hand, the Al2O3/LAS composite experienced transgranular fracture and high bendin g strength despite its low toughness. Both composites could be sintered to full density at 1500 degreesC for 2 h due to the presence of a liquid phase . It was concluded that strengthening and toughening of alumina ceramics co uld be tailored by designing their grain-boundary microstresses. (C) 2001 E lsevier Science Ltd. All rights reserved.