The effects of compaction methods on the sintering density, microstructures, and mechanical properties were investigated in α-alumina ceramics. α-Alumina powders were granulated with a 10% aqueous solution of polyvinyl alcohol (PVA). Uniaxially pressed (UAP) and cold isostatic-pressed (CIP) samples were prepared by pressing uniaxially at a pressure of 1 ton for 1 min, and isostatically at 200 MPa for 15 min, respectively. Subsequently, both types of samples were sintered at 1,200℃, 1,300℃, 1,400℃, 1,450℃, 1,500℃, 1,550℃, and 1,600℃ at a rate of 5℃/min for 2 h. The CIP samples were better than the UAP samples for all properties measured, such as the sintering density, Vicker’s hardness, and toughness. The CIP sample sintered at 1,400℃ showed the maximum Vicker’s hardness and toughness; this may be attributed to the competing effects of a decrease in porosity and the growth of grains with increasing sintering temperature.

3YSZ + (x) Al₂O₃ composites (x = 20, 40, 60, 80 wt%) were fabricated and the influences of particle sizes of Al₂O₃ on their microstructures and mechanical properties were investigated with XRD, SEM, vickers hardness and fracture toughness. Al₂O₃-3YSZ composites containing Al₂O₃ powder of a 0.3 μm and an 1.0 μm, which are here in after named as Al2O3(0.3 μm)-3YSZ and Al₂O₃ (1.0 μm)-3YSZ, respectively, were made by mixing raw materials, uni-axial pressing and sintering at 1,400℃, 1,500℃, and 1,600℃. Al₂O₃ (0.3 μm)-3YSZ composites show the higher density and the better mechanical properties than Al₂O₃ (1.0 μm)-3YSZ composites. The Vickers hardness of the Al₂O₃ (0.3 μm)-3YSZ composites show a peak value of 1,997 Hv at the content of 60 wt% Al₂O₃, which is a slightly higher value in comparison with 1,938 Hv of the Al2O3(1.0 μm)-3YSZ composite. However, the fracture toughness of Al₂O₃-3YSZ composites monotonically increases with decreasing the content of Al₂O₃ without any peak values. Al₂O₃ (0.3 μm)-3YSZ and Al₂O₃ (1.0 μm)-3YSZ composites sintered at 1,600℃ have a maximum value of a 6.9 MPa·m1/2 and a 6.2 MPa·m1/2, respectively at the composition of containing 20 wt% Al2O3. It should be noticed that the mechanical properties and the sintering density of the Al₂O₃-3YSZ composites can be enhanced by using more fine Al₂O₃ powder due to their denser microstructure and smaller grain size.

Composite ceramics of alumina-TZP(3Y) have good mechanical and electrical properties. So, They have been used as high strength refractory materials and thick film substrates, etc. In this study, Composite ceramics of alumina-TZP(3Y) were fabricated by uniaxial pressing and sintering at 1,400, 1,500, and 1,600℃, and their microstructures and mechanical properties were investigated. As the TZP(3Y) content in composite ceramics increases from 20 wt.% to 80 wt.%, the fracture toughness increases monotonically, which seems to be related to the higher relative density and/or toughening mechanism by means of stabilized tetragonal zirconia phase at room temperature. In contrast to the fracture toughness, Vickers hardness of the composite ceramics shows maximum value (1,938 Hv) at a 40 wt.% of TZP(3Y). The result of Vickers hardness is likely to be due to more dense sintered microstructure of composite ceramics than pure alumina and reinforcement of composite ceramics with TZP(3Y), considering that Vickers hardness of pure Al2O3 is greater than that of TZP(3Y). It is also shown that the ZrO2 particles are 1°Cated between Al2O3 grains and suppress grain growth each other.

Glass ceramic has a high mechanical strength and low sintering temperature. So, it can beused as a thick film substrate or a high strength insulator. A series of glass ceramic samples based onMgO-Al2O3-SiO2-ZrO2 (MASZ) were prepared by melting at 1,600℃, roll-quenching and heat treatment atvarious temperatures from 900℃ to 1,400℃. Dependent on the heat treatment temperature used, glassceramics with different crystal phases were obtained. Their nucleation behavior, microstructure andmechanical properties were investigated with differential thermal analysis (DTA), X-ray diffraction (XRD),scanning electron microscopy (SEM), and Vicker`s hardness testing machine. With increasing the heattreatment temperature of MASZ samples, their hardness and toughness initially increase and then reachthe maximum points at 1,300℃, and begin to decrease at above this temperature, which is likely to bedue to the softening of glass ceramics. As the content of ZrO2 in MAS glass ceramics increases from 7.0wt.% to 13 wt.%, Vicker`s hardness and fracture toughness increase from 853 Kg/mm2 to 878 Kg/mm2and 1.6 MPa??m1/2 to 2.4 MPa??m1/2 respectively, which seems to be related with the nucleation of elongatedphases like fiber.