The processing and property measurement of Y-TZP/Al2O3 ceramic-ceramic composites was investigated. The wet chemical synthesis route was adopted for the preparation of 3Y-TZP matrix dispersed with Al2O3 in three different volume fractions. Characterization of the resultant powders was carried out and their densification behaviour was studied by sintering in air in the temperature range 1200–1600 °C. The role of alumina as grain-growth inhibitor for Y-TZP, and the mechanical response of these ultrafine-grain ceramic composites in terms of Klc characteristics, have been discussed.

Processing and properties of Y-TZP/Al2O3 composites

The elastic properties of Al2O3–ZrO2 composite were determined from ultrasonic velocity measurements, and were found to be dependent upon the amount of ZrO2 phase, the compacting pressure of the green ceramic and sintering time. The velocity in the Al2O3–ZrO2 composite increased to a maximum for about 3 wt% unstabilized ZrO2 dispersed in Al2O3. The velocity decreased monotonically thereafter. The increase in moduli, as shown by an increase in velocity, has been attributed to phase transformation of the unstabilized ZrO2 from tetragonal to a monoclinic phase, which presumably leads to a toughening and strengthening effect, and also due to the action of ZrO2 in stopping grain growth of Al2O3 during densification. The excessive shear strain, induced by the tetragonal→monoclinic transformation phase, with greater than 50 wt% ZrO2 content, caused microcracks to appear in the composite. This reduced the elastic moduli of the composite. It was found that the composition dependence of the elastic moduli lie outside the theoretical bound of Voigt and Reuss for the elastic moduli of two-phase materials, and that by increasing the compacting pressure, an improvement in the elastic moduli of the sintered composite occurred irrespective of ZrO2 content. The thermal expansion of the composites showed no appreciable change with addition of zirconia up to 5 wt% ZrO2. However, dimensional changes due to phase transformation particularly with high zirconia content have been established.

Ultrasonic through-transmission method of evaluating the modulus of elasticity of Al2O3–ZrO2 composite

Young's moduli of green and sintered unstabilized - ceramics have been determined by measuring compression and shear velocities through the material and, from separate measurements, the associated bulk density. Young's modulus and sintered density of - ceramics can be enhanced by increasing the compacting pressure when forming the green ceramics and with the addition of <5 wt% of unstabilized . For a particular green compacting pressure, the trend in the diametrical compressive fracture stress is similar to that of Young's modulus. The fracture stress also increases with a higher green compacting pressure at a constant wt% .

http://iopscience.iop.org/article/10.1088/0022-3727/30/6/017/pdf

The elastic moduli and diametrical compressive fracture stress of - ceramics

The present work deals with the characterization of 3.0 mol.% yttria stabilized zirconia (3Y-TZP) powders prepared as composite precursors containing up to 20.0 vol.% of alumina. Following the wet-chemistry route of co-precipitation, a homogeneous dispersion of component hydroxides was obtained. Effect of calcination treatment on t-phase and primary particle size evolution of zirconia was investigated by XRD technique. A marked difference with respect to inhibition of crystallization reaction of 3Y-TZP was observed in the presence of alumina. This is attributed to the increased diffusion lengths of the two developing phases. The powders could be retained in the ultrafine and quasi-amorphous state by a suitable choice of alumina content and calcination treatment.

Studies on crystallization behaviour of 3Y-TZP/Al2O3 composite powders

This article deals with a comprehensive study of the processing and mechanical properties of the ceramic material Al2O3 on Fused Filament Fabrication technology (FFF). It describes the basic input analyses of the material, such as TGA, FTIR, and MVR. These analyses enabled the design and testing of process parameters for the 3D printing of parts. The article also presents the post-processes, including the technological parameters required to finalize parts made from this material, i.e., chemical debinding in acetone at elevated temperatures + thermal debinding and sintering. The microhardness was measured on the processed samples, depending on the density of the inner filling. The resulting hardness had an almost linear relationship between the percentage of filler (20–40–60–80–100%) and the resulting microhardness (1382–2428 HV10). Flexural strength was also measured on the test specimens with different degrees of internal filling (80–90–100%). However, inner filling do not affect the flexural strength (316.12–327.84–331.61 MPa). The relative density of the final parts was measured on a ZEISS METROTOM 1500 CT machine and reached 99.54%.

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Alumina Manufactured by Fused Filament Fabrication: A Comprehensive Study of Mechanical Properties and Porosity

The incorporation of ZrO2 in Al2O3 matrix was performed by conventional mechanical mixing and co-precipitation methods. The densification behaviour on sintering up to 1800°C and the resulting microstructural features of these ceramics have been studied. In either case no appreciable densification was noticed up to 1600°C. The co-precipitated powder compacts containing 20% ZrO2 after sintering at 1700°C achieved the density of 4.14 gm.cm−3 and open porosity about 3.0%. Microstructural features showed a pronounced grain growth inhibition effect with increasing concentration of ZrO2. Vacuum hot-pressing was found to be beneficial from the point of view of densification and mechanical properties of these compacts.

Studies on Zirconia Dispersed Alumina Ceramics

Characteristics of powders play an important role in the densification and grain growth during the sintering process of oxide ceramics. During the process of grinding for reduction of particle size, factors like impurity, hydration etc have to be controlled by the comminution period, ratio of material to grinding media (balls) as well as the use of proper liquid medium.In this investigation characterization of powders prepared by comminution of technical grade commercial alumina has been made with respect to wet grinding media and ratio of weight of balls to material. Powders thus obtained were examined by chemical analysis (purity), BET (surface area), SEM (shape and size), particle size distribution by X-ray (Sedigraph) methods. The influence of powder properties on the sintering behaviour of compacts was studied at 1400° and 1500°C for two hours.It was observed that an increased amount of balls reduced the particle size to a limiting stage with characteristic size distribution; a corresponding increase...

Studies on Sintering of Technical Grade Alumina—Part I: Characterization of Ground Alumina Powders

Alumina bodies have been prepared from commercially available, technical grade alumina. Effects of processing parameters and additions like clay, pyrophyllite and magnesium carbonate on densification have been studied in the range of 1500°–1800°C with a view to the utilization of these compositions for electrical applications.The bodies have been evaluated for microstructures and electrical properties at room temperature for 20 MHz. It was observed that alumina bodies containing 91–93% Al2O3 densified to the extent of 3.4–3.5 gm.cm−3 with imperviousness at 1500° to 1600°C. Bodies containing pyrophyllite exhibited dissipation factor as low as 0.0002 along with dielectric constant (K), in the range 6–7, while bodies containing alumina over 97% had a dissipation factor as low as 0.0001 having K in the range 7–8 when densities of these bodies exceeded 3.6 gm.cm−3 and open porosity decreased below 1%.

Alumina Bodies for Electrical Applications

During sintering studies on zirconia with calcia in the range of 0.50 to 5.0 wt%, properties like crushing strength and thermal shock resistance were measured. Samples containing 15 to 90% cubic zirconia phase were subjected to crushing strength test at room temperature as well as high temperature up to 1200°C and thermal fatigue test from 1400°C to room temperature.The results show that mixtures containing up to 2 wt% of calcia (uncalcined or calcined up to 1000°C) developed up to 40% of cubic phase, and exhibited better mechanical strength as well as better thermal fatigue resistance.

P. Y. Dalvi

Papers

Studies on Zirconia Dispersed Alumina Ceramics

Studies on Sintering of Technical Grade Alumina—Part I: Characterization of Ground Alumina Powders

Alumina Bodies for Electrical Applications

Strength and Thermal Fatigue Properties of CaO-Partially Stabilized Zirconia (Ca-PSZ)