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This paper presents the experimental investigation of the effect of Nb2O5 content on the phase composition, microstructure, and physical and mechanical performance of the zirconia-toughened alumina (ZTA) ceramics, aimed to optimize the additional amount of Nb2O5, refine the ceramic grains, and improve the densification, hardness and fracture toughness. ZTA ceramics with various Nb2O5 contents were prepared using the spark plasma sintering method. The addition of trace amounts of Nb2O5 did not produce a new Nb-rich phase; the Nb atoms were dissolved in the ZrO2 grains. The addition of trace amounts of Nb2O5 led to grain refinement and an increase in density, but the addition of excessive Nb2O5 resulted in grain growth and a decrease in relative density. Furthermore, the addition of Nb2O5 promoted uniformity of the microstructure. The sample with 0.25 wt.% Nb2O5 had the maximum Vickers hardness and indentation fracture toughness, which were 1228.40 HV and 9.17 MPa √m, respectively. Mechanical properties of the composite mainly depended on the grain size, which was influenced to some extent by the relative density. [ABSTRACT FROM AUTHOR]

Zirconia toughened alumina (ZTA) ceramics are commonly used in various industries. Adding suitable additives is an effective way to improve the performance of ZTA ceramics. However, the common reinforcement in ZTA, chromia (Cr2O3), tends to volatilize at high temperature in the presence of oxygen, limiting ceramic densification. Consequently, additional amounts of Cr2O3 are typically limited to below 1 wt%. In this study, spark plasma sintering was utilized to inhibit the volatilization of Cr2O3. Dense ZTA ceramics with high Cr2O3 content (from 1 to 10 wt%) were prepared at 1350 °C. The impact of the solid solution on the structure and properties of the ceramics was investigated. The findings demonstrate that the high Cr2O3 solution can regulate the grain size in the matrix, leading to an enhancement in both hardness and fracture toughness. The optimum performance of the sample was obtained with a 5 wt% dosage of Cr2O3, where the maximum values of Vickers hardness and fracture toughness were 20.66 GPa and 6.37 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

Gasping the controlling mechanism of multi-core-rim structure, like the ratio of multi-cores and the rim thickness, is a key to develop Ti(C, N)-based cermets with high performances. In this work, three types of cermets with the same nominal composition were fabricated by doping self-made (Ti, W, Ta) (C, N) pre-solid solution powders with different compositions, (Ti, 61.3 W, 8.6Ta) (C, N), (Ti, 53.3 W, 7.5Ta) (C, N) and (Ti, 47.1 W, 6.6Ta) (C, N). Effect of the composition of (Ti, W, Ta) (C, N) pre-solid solutions on the multi-core-rim microstructure and mechanical properties of cermets was investigated. Results showed that the decrease of W and Ta contents in the pre-solid solutions leads to an increase of white cores with thinner rims and a decrease of black cores with thicker rims. Thermodynamic calculations indicated that the decrease of W and Ta contents strengthens the thermal stability of the pre-solid solutions. With the decrease of the thermal stability difference between black core Ti(C, N) and white core (Ti, W, Ta) (C, N), more rimless black particles are reserved via Ostwald ripening process. The rim thickness and core size were statistically analyzed, which indicates that the cermet doping medium-solid-solution (Ti, 53.3 W, 7.5Ta) (C, N) exhibits smallest ceramic grains with thinnest rims. An optimal comprehensive mechanical performance was obtained in the cermet doping (Ti, 53.3 W, 7.5Ta) (C, N). It implies that an appropriate pre-solid solution of W and Ta in (Ti, W, Ta) (C, N) promises fine multi-core-rim structure and thus sound mechanical properties of Ti(C, N)-based cermets can be obtained under the same condition of alloy composition and processing parameters. [ABSTRACT FROM AUTHOR]

Acicular mullite-reinforced porous self-bonded ceramics were fabricated using mullite powders as principal raw materials, alumina and silicon dioxide powders as starting synthetic source of self-bonded mullite phase, and 2 wt% AlF3·3H2O as an accelerant. The influences of self-bonded mullite weight percent on the phase composition, microstructures, mechanical performance and thermal conductivities of acicular mullite-reinforced porous self-bonded samples were investigated. As self-bonded mullite weight percent varied between 0 and 50 wt%, linear shrinkage, bulk density and thermal conductivities of fired porous self-bonded mullite samples reduced, whereas their porosity increased. Addition of appropriate amounts of self-bonded mullite decreased the mean pore size and window size in porous sample, and enhanced the mechanical strength. When self-bonded mullite weight percent reached 50 wt%, the compressive and flexural strength of acicular mullite-reinforced porous self-bonded ceramics was, respectively, kept as 19.9 MPa and 8.8 MPa, with a porosity of 74.7%, a diminutive mean pore size of 159 μm and a window size of 44 μm. Moreover, the linear shrinkage and thermal conductivity of the materials at 50 °C were only 7.4% and 0.23 W m K−1, respectively. [ABSTRACT FROM AUTHOR]

Magnesium potassium phosphate ceramics are chemically bonded ceramics employed as biomaterials, in nuclear waste encapsulation and for concrete repair. The microstructure dictates material performance and depends on the raw mix composition. Synchrotron X-ray computed microtomography was employed to describe the 3D microstructure and its time evolution during hardening and gain insights into the reaction mechanisms. Any excess water with respect to the stoichiometry of the reaction brought about an increase in porosity, but, notably, a reduction in the average pore size. Crystals filled the water 'pockets' in the ceramic volume by growing larger, although less densely packed, increasing the complexity of the pore shape. Platelet over elongated crystal habit was favoured. Such a change in shape is likely related to a change in reaction mechanism, as crystallization from a gel-like amorphous precursor is hindered and progressively substituted by a through-solution mechanism. It is proposed that the time evolution of the microstructure is dictated by the balance between crystallization from amorphous precursor, prevailing in relatively 'dense' systems (with stoichiometric water or in low excess), and water segregation, prevailing at higher water contents. The former mechanism was shown to produce an increase in porosity with time, because of the density mismatch between the amorphous and the crystalline phase. [ABSTRACT FROM AUTHOR]

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2AlO·2.8SiO·1.2TiO· xLaO ( x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different LaO concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the 'regions' (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the 'regions' is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of LaO, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C. [ABSTRACT FROM AUTHOR]

Vitrified bonded SiC composite ceramics were prepared using a simple powder blending, forming, and sintering process. The effect of SiC particle size on the mechanical and dielectric properties of vitrified bonded SiC composite ceramics was investigated. Vitrified bonds wet and coat SiC particles during sintering and form continuous bonding networks upon cooling. The vitrified bonds render the ceramics high flexural strength and act as impedance mismatching modification layer between SiC particles and air. With varying SiC particle size, the microstructure, and properties of the vitrified bonded SiC composite ceramics change accordingly and at 7 μm, it reaches optimal microstructure, a highest flexural strength of 67.85 MPa and highest reflection loss. However, the dielectric loss of composite ceramics decreases as the SiC particle size increases. [ABSTRACT FROM AUTHOR]