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A type of hexagonal boron nitride-magnesium aluminosilicate composite ceramics was fabricated by hot-pressed sintering under different pressures. The relationships between sintering pressure, microstructure, and mechanical properties were investigated. The results indicate that sintering pressure has a great influence not only on the mechanical properties of composite ceramics, but also on crystallization of magnesium aluminosilicate (MAS) and structural order of hexagonal boron nitride. Under the given sintering pressure of 30 MPa, the fracture toughness of composites was greatly improved 66 % (from 2.49 to 4.12 MPa m, with similar densities). It also exhibits the highest bend strength of 245 ± 23 MPa. The fracture behavior of composites and the mechanism of sintering pressure which affect the crystallization of mullite in MAS were also discussed. [ABSTRACT FROM AUTHOR]

The TaC0.7 composition was spark plasma sintered (SPS) at 1600°-1900°C using TaC and Ta as the starting powders. Densification process, phase evolution, microstructure development, and the mechanical properties of the composites were investigated. The results indicated that the TaC0.7 composition could be SPS to >95% of theoretical density in 5 min at 1600°C or above. The phase formation was associated with carbon diffusion from the starting particles TaC to Ta to form Ta2C and Ta6C5 as intermediate phases, and subsequently the equilibrium phases of TaC y and ζ-Ta4C3− x. The presence of lamellar ζ-Ta4C3− x regions enhanced the flexure strength (up to 972 MPa) and fracture toughness (up to 13.8 MPa·m1/2). [ABSTRACT FROM AUTHOR]

Abstract: Self-toughening α-SiAlON/6H-SiC composites containing both α-SiAlON and α-SiC elongated grains in the microstructures were previously fabricated by spark plasma sintering (SPS). In this study, the α-SiAlON/6H-SiC composites were heat treated at 1850°C for 3h. The effects of the heat treatment on the phase compositions, microstructures, and mechanical properties were investigated. The results showed M′ phases formed from crystallization of the intergranular glassy films. No polytype transformation for the SiC phase was observed. Both α-SiAlON and α-SiC grains grow anisotropic in the heat treatment, rather than converted into the brittle equiaxed morphologies. The flexural strength and fracture toughness of the post heat-treated composites were further increased and the 40wt% SiC composition reached 907MPa and 8.5MPam1/2, respectively. [Copyright &y& Elsevier]

Abstract: Highly densified Al2O3/LiTaO3 (ALT) ceramic composites were fabricated by hot-pressing in a nitrogen atmosphere. The addition of Al2O3 particles could significantly improve the densification of LiTaO3. Sintering mechanism of the LiTaO3 ceramic incorporated with Al2O3 particles is proposed. Dielectric constant of 5vol.% Al2O3/LiTaO3 (5ALT) composite ceramic was slightly increased in the range from 30kHz to 106 Hz, but the dielectric loss was lowered in the whole range from 103 Hz to 106 Hz. Piezoelectric constant (d 33) of the 5ALT ceramic composite is about 50% of that of LiTaO3 single crystal. [Copyright &y& Elsevier]

Abstract: The GdSmZr2O7 ceramic is prepared by pressureless-sintered method under different conditions as a possible solid electrolyte. The crystal structure, microstructure and electrical properties are characterized by the X-ray diffraction, field-emission scanning electron microscopy and ac impedance spectroscopy, respectively. The GdSmZr2O7 ceramic exhibits a single phase of the pyrochlore-type structure. The total conductivity of the GdSmZr2O7 ceramic obeys the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173K. The GdSmZr2O7 ceramic is an oxide-ion conductor in the oxygen partial pressure range of 1.0×10−4 to 1.0atm at all test temperature levels. According to the experimental results of the present work, the maximum value of the total conductivity for the GdSmZr2O7 ceramic is about 1.01×10−2 Scm−1 at 1173K. [Copyright &y& Elsevier]

Abstract: The sinterability of ZrC was enhanced by high-energy ball milling as well as introduction of graphite and SiC as sintering additives. Densification process and microstructure development were investigated for ZrC-based ceramics densified by pressureless sintering. As-received ZrC powder showed poor sinterability. After high-energy ball milling, ZrC powder can be sintered to 98.4% theoretical density at 2100°C. The obtained ceramic had fine microstructure and fewer entrapped pores. Introduction of 2wt.% graphite combined with high-energy ball milling lowered the densification temperature of ZrC. The relative density of obtained ceramic reached up to 95% at 1900°C. Introduced SiC inhibited ZrC grain growth during sintering and consequently avoided the entrapped pores within the grains. The relative density of ZrC–SiC reached up to 96.7% at 2100°C. ZrC–SiC composite formed an interesting intragranular structure and had high fracture strength at room temperature. [Copyright &y& Elsevier]

Abstract: A study was conducted of the effect of additions of samarium oxide on the thermal expansion and thermal conductivity of zirconium oxide for thermal barrier coatings. Sm x Zr1−x O2−x/2 (0.1≤ x ≤0.5) ceramic powders synthesized with a chemical-coprecipitation and calcination method were sintered at 1873K for 15h. Structures of the synthesized powders and sintered ceramics were identified by X-ray diffractometer. The morphologies of ceramic powders were observed by transmission electron microscope. The thermal expansion coefficients and thermal diffusion coefficients of Sm x Zr1−x O2−x/2 ceramics were studied with a high-temperature dilatometer and a laser flash diffusivity technique from room temperature to 1673K. The thermal conductivity was calculated from thermal diffusivity, density and specific heat of bulk ceramics. Sm0.1Zr0.9O1.95 ceramics consists of both monoclinic and tetragonal structures. However, Sm0.2Zr0.8O1.9 and Sm0.3Zr0.7O1.85 ceramics only exhibit a defect fluorite structure. Sm0.4Zr0.6O1.8 and Sm0.5Zr0.5O1.75 ceramics have a pyrochlore-type lattice. With the increase of Sm2O3 content, the linear thermal expansion of Sm x Zr1−x O2−x/2 ceramics increases except for Sm0.1Zr0.9O1.95. The thermal conductivities of Sm x Zr1−x O2−x/2 ceramics ranged from 1.41 at 873K to 1.86Wm−1 K−1 at room temperature in a test temperature range of room temperature to 1673K, and the results can be explained by phonon scattering mechanism. [Copyright &y& Elsevier]