Effect of Addition of Previously-Synthesized Ce-TZP/Al2O3 Submicrometric Powder on the Properties of Al2O3-Based Ceramics

Abstract

This work investigated the effect of a composite of tetragonal zirconia with alumina-reinforced Ceria (ATZ) previously synthesized, on the properties of alumina-based ceramics (Al 2 O 3 ). Monolithic alumina powder and Al 2 O 3 powder mixtures containing 5, 10, 15 and 20 wt.% of Ce-TZP/Al 2 O 3 were processed by high energy milling, compacted and then sintered at 1600 °C -2 h. Sintered pure alumina and composites were characterized by relative density, scanning electron microscopy, X-ray diffraction and surface roughness. Then, the elastic modulus, the Vickers hardness, the fracture toughness and the 4-point flexural strength were evaluated. The results indicated an increase in relative density as a function of the addition of ATZ, with values between 94.3 ± 0.8% and 98.9 ± 0.7%. The observed microstructure after sintering showed tetragonal ZrO 2 grains with average sizes of 0.6 μm well dispersed in the Al 2 O 3 matrix, which presents average grain sizes of around 1.5 μm. The crystalline phases identified in the composites were ZrO 2 -tetragonal and Al 2 O 3 hexagonal. The addition of the composite (ATZ) in the alumina matrix generates a gradual reduction in the elastic modulus (398 ± 15 GPa ~366 ± 34 GPa) and in the hardness (20.5 ± 1 GPa ~17.3 ± 0.7 GPa) of the sintered ceramics. On the other hand, the addition of this same composite (ATZ) in the alumina matrix considerably increases the materials fracture toughness, reaching values of approximately 6.7 ± 0.9 MPa.m 1/2 . The same trend was observed in the flexural strength results which ranged from 258 MPa (5wt.% Ce-TZP/Al 2 O 3 ) to 316 MPa (20wt.% Ce,Y-TZP/Al 2 O 3 ). The Ce-TZP reinforcement acts as a toughening agent of the Al 2 O 3 matrix due to the coupled mechanisms of toughening by zirconia phase transformation, residual stresses due to the difference in thermal expansion of the crystalline phases and differences in microstructural morphologies.