Nanocrysrtalline Powders in the A12O3-ZrO2-CeO2-Y2O3 system for high-performance ceramics
X-ray diffraction, BET measurements, scanning electron and optical microscopy were used to analyze the properties variation of hydrothermal nanocrystalline powder with a composition 90 wt% Al<inf>2</inf>O<inf>3</inf>-10 wt%ZrO<inf>2</inf> (CeO<inf>2</inf>, Y<inf>2</inf>O<inf>3</inf>) after thermal treatment in the temperature range 400–1300 °C. The composition of the ZrO<inf>2</inf>-based solid solution was (mol %) 90ZrO<inf>2</inf>-8CeO<inf>2</inf>-2Y<inf>2</inf>O<inf>3</inf>. It was found that α-Al<inf>2</inf>O<inf>3</inf> is formed at 850 °C. Phase transformation F-ZrO<inf>2</inf>⇆T-ZrO<inf>2</inf> occurred at 1000 °C. Produced powder was sintered at 1300 °C. The present investigation demonstrates that heat treatment of composite nanocrystalline powders gives rise to complex processes. Understanding of such processes makes it possible to optimize conditions for fabrication of advanced ceramics with tailored properties.
Microstructural design of ZrO2–Y2O3–CeO2–Al2O3 materials
It is shown that microstructural design of ZrO2–Y2O3–CeO2–Al2O3 ceramics is based on interrelated processes in the synthesis of starting powders and their formation and sintering. Hydrothermal nanocrystalline powders are examined to establish the formation of self-reinforced and multilayer composites with high strength and bioinert implants of femoral heads resistant to ageing processes in the human body. The results serve as a scientific basis for microstructure design of fine-grained ZrO2-based composites in the ZrO2–Y2O3–CeO2–Al2O3 system with high strength and other properties.
Fracture behaviour of an Al2O3-ZrO2 multi-layered ceramic with residual stresses due to phase transformations
The fracture behaviour of a ceramic multi-layer designed with thin internal compressive layers and obtained by slip casting is studied. It consists of nine alternated Al 2 O 3 -5vol%tZrO 2 and Al 2 O 3 -30vol%mZrO 2 layers of530 μm and 100 μm thickness, respectively. Mechanical characterization includes evaluation of Vickers Hardness, Young's modulus and fracture strength under four-point bending. In addition, the residual stress magnitude and distribution in the laminate is determined both analytically, from calculations using the differential strain between layers and the elastic properties, and experimentally, using indentation techniques. The experimental findings in terms of mechanical strength and fractography show a subcritical growth of the natural flaws in the laminate before catastrophic failure occurs, owing to the relevant role of the thin Al 2 O 3 -30vol%mZrO 2 layers with compressive stresses inherent to the zirconia phase transformation. These layers are also responsible for the increase in toughness to levels of at least three times that of the reference Al 2 O 3 -5vol%tZrO 2 monolith.