Preparation And Properities Of Al₂O₃-ZrO₂-YAG Multi-Phase Composite Ceramic

Yttrium Aluminum Garnet (Y₃Al₅O₁₂, YAG) has high melting point, high hardnessand low creep rate. It is potential to be used as high temperature structure material.Tetragonal Zirconia Polycrystalline (TZP) has high bending strength and hightoughness, a-Al₂O₃ has high melting point. The multiphase ceramic compositeconsisting in a-Al₂O₃, tetragonal zirconia and YAG is promising.The essential conception and the technique preparation of multiphase ceramiccomposite are introduced in this thesis, especially making a summary ofAl₂O₃-ZrO₂-YAG composite investigation activities up to date. It is demonstrated thatprominent improvement on the research of Al₂O₃-ZrO₂-YAG composite ceramicfocuses on the Al₂O₃-ZrO₂-YAG eutectic and its properities. In this research,Al₂O₃-ZrO₂-YAG composite ceramic powder and Al₂O₃-ZrO₂+YAG mixed powderwere synthesized by co-precipitation and nano-in-situ method at low temperature.Such powders were sintered into Al₂O₃-ZrO₂-YAG multiphase composite ceramic byconventional powder metallurgy method.YAG was synthesized by Al-Y-O powders, which was also prepared byco-precipitation, after calcination at 1100℃for 5 hours. Meanwhile, the main phasein Al-Zr-Y-O powders calcinated at 1100℃was tetragonal zirconia, others wereamorphous phases. It is indicated that Al₂O₃ and YAG restrained the transformation ofZrO₂ from the tetragonal phase to monoclinic phase and ZrO₂ also inhibited thecrystalline growth of Al₂O₃ and YAG. Al₂O₃-ZrO₂-YAG composite powder has ball shape with the size of about 100nm.Its sintering activity is better than that of Al₂O₃-ZrO₂+YAG mixed powder. Under thesame condition, relative density and mechanical performance of the ceramic sinteredby Al₂O₃-ZrO₂-YAG composite powder are better than those of the ceramic preparedby Al₂O₃-ZrO₂+YAG mixed powder. This indicates that the blending at ion level insolution can lead to the perfect dispersion of relevant components in multiphaseceramic composite.The bending strength, Vickers hardness and fracture toughness ofAl₂O₃-ZrO₂-YAG multiphase ceramic composite sintered by composite powdersunder the condition of 1400℃×1h+1520℃×1.5h+1640℃×2h were 299.75MPa,17.95GPa and 12.2548MPa·m^1／2 respectively, while the relative density of which is96ï¼…,. The phase composition of such ceramic analyzed by XRD was a-Al₂O₃,tetragonal ZrO₂ and YAG. The SEM photographs showed that the growth of crystal was complete. The size of crystal is about 1～3μm. Some crystals grew abnormally.Transcrystalline fracture happened during ceramic fracture.