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Dense, highly textured Zr B2 and Zr B2- Mo Si2 ceramics were fabricated via a strong magnetic field alignment method followed by spark plasma sintering. Unlike with the previous studies, which only focused on the alignment of single-phase particles, both Zr B2 and Mo Si2, which exhibited a magnetic anisotropy, have been aligned in this study. The alignment of Mo Si2 in the same direction of Zr B2 enhanced the degree of orientation of Zr B2, decreased the grain size, but increased the aspect ratio of the platelet Zr B2 grains. The microstructure and anisotropic mechanical properties as well as the oxidation resistance in different directions were discussed. [ABSTRACT FROM AUTHOR]

Abstract: Four-point flexure creep deformation of ZrB2–30vol% SiC ceramics in argon atmosphere under a static load of 19MPa for 0–100h at 1500 and 1600°C was investigated. The strain rate at 1600°C was 3.7 times higher than that at 1500°C. Microstructural evolution during creep consisted of nucleation and growth of triple-point cavitations which were always associated with SiC particles. Due to the low stress, only isolated cavitations were nucleated, and no microcracks were formed. For up to 100h at 1500 and 1600°C, the grains maintained their size and shape. The cavitations in both size and number showed no obvious difference from 26 to 100h at 1500°C, whereas that showed a significant increase from 26 to 100h at 1600°C. Present study suggested that ZrB2–30vol% SiC exhibited relatively good microstructural stability and creep resistance at 1500°C in argon atmosphere. [Copyright &y& Elsevier]

ZrB2-20vol% SiC composites added with 3vol% Yb2O3 were hot-pressed at 1900°C, and then heat-treated at 2000°C in argon. The effect of heat treatment on phase composition, microstructure, and mechanical properties of the composites was investigated. Results showed that the high temperature heat treatment led to the depletion of Yb-containing phases by decomposition or evaporation, the formation of some pores at multiple-grain junctions, significant microstructural coarsening with the increase of ZrB2 grain size from ∼1.9μm to ∼4.8μm, and the change of fracture mode from mixed inter/transgranular to fully transgranular. In addition, Vickers' hardness, fracture toughness and flexural strength were severely degraded after heat treatment. [ABSTRACT FROM AUTHOR]

The relationships between microstructures and mechanical properties especially strength and toughness of high-entropy carbide based ceramics are reported in this article. Dense (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C (HEC) and its composite containing 20 vol.% SiC (HEC-20SiC) were prepared by spark plasma sintering. The addition of SiC phase enhanced the densification process, resulting in the promotion of the formation of the single-phase high-entropy carbide during sintering. The high-entropy carbide phase demonstrated a fast grain coarsening but SiC particles remarkably inhibited this phenomena. Dense HEC and HEC-20SiC ceramics sintered at 1900 °C exhibits four-point bending strength of 332 ± 24 MPa and 554 ± 73 MPa, and fracture toughness of 4.51 ± 0.61 MPa·m1/2 and 5.24 ± 0.41 MPa·m1/2, respectively. The main toughening mechanism is considered to be crack deflection by the SiC particles. [ABSTRACT FROM AUTHOR]

Single-phase titanium-zirconium oxycarbonitride ceramics, prototypically Ti 1/2 Zr 1/2 (C 1/3 N 1/3 O 1/3), was obtained by spark plasma sintering of the corresponding Ti and Zr- oxide, carbide and nitride. It was revealed that a single-phase Ti 1/2 Zr 1/2 (C 1/3 N 1/3 O 1/3) solid solution with rock-salt structure formed at 2000°C, below which the secondary phase of ZrO 2 was evident. The as-sintered ceramics was chemically homogeneous from nanoscale to microscale and the carbon, nitrogen, and oxygen contents in Ti 1/2 Zr 1/2 (C 1/3 N 1/3 O 1/3) ceramics were determined to be 5.39wt%, 5.44wt% and 6.00wt%, corresponding to an empirical formula of Ti 0.51 Zr 0.49 (C 0.37 N 0.32 O 0.31). The product possesses a relative density of 95.2% and Vickers hardness of 21.6 ± 2.4 GPa. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Gas burst has been commonly observed during reactive sintering, especially when combustion was initialized therein. In this study, a model system (Zr + 2B = ZrB 2) was chosen to investigate this phenomenon by a combination of thermo-analysis, mass spectrum investigation and electron microscopy studies. Results showed the combustion lead to a formation of various gaseous byproducts such as CO, CO 2 , N 2 , BO, BO 2 and B 2 O 3 etc. Especially for BO(g), its generation consumed boron in the raw materials, resulting in the residual Zr-containing phase that accelerated the formation of interlocked ZrB 2 grains in the sintered ceramics, which show relatively high strength (516 ± 42 MPa). Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Chemical reactivity of hot-pressed Si 3 N 4 –ZrB 2 ceramics at 1500–1700 °C under N 2 and Ar atmosphere is investigated by X-ray diffraction, thermodynamic calculation, and phase diagram. Results show that there are chemical reactions in Si 3 N 4 –ZrB 2 ceramics. The chemical reactions accelerate the decomposition and phase transformation of Si 3 N 4 . The reaction products include ZrN, BN, ZrSi 2 , SiC or Si, which strongly depend on the atmosphere or temperature. The source of N 2 for ZrN and BN products is both atmosphere and decomposition of Si 3 N 4 at 1600 °C or above, whereas that is only atmosphere at 1500 °C. There is no reaction in Si 3 N 4 –ZrB 2 ceramics at 1500 °C under Ar. The MgO–Lu 2 O 3 sintering adds lead to the significant increase of relative density of Si 3 N 4 –ZrB 2 from 48% to 94% at 1500 °C in Ar. Therefore, it is possible that dense Si 3 N 4 –ZrB 2 ceramics with no reaction could be achieved at 1500 °C or below in Ar. [ABSTRACT FROM AUTHOR]

A pressureless sintering process using different amounts of boron carbide (B 4 C) as sintering aid was investigated for the densification of zirconium diboride (ZrB 2 ). The sintering mechanism was converted from solid state sintering to liquid phase sintering as sintering temperature increased from 2150 to 2250 °C. B 4 C addition improved densification by removing the oxide impurities during solid state sintering. Besides, it could restrain the growth of ZrB 2 grains. At 2250 °C, ZrB 2 and B 4 C formed liquid phase which was well wetting ZrB 2 grains during liquid phase sintering process. The different roles of B 4 C on the microstructure development, mechanical properties and oxidation resistance of the sintered ZrB 2 -based ceramics were investigated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fine grained ZrB2–SiC–hBN composite were reactively densified from coarse precursors. [•] Employ the SHS ignited in ZrN–Si–B4C systems to improve microstructure homogeneity. [•] Strength reliability and strain tolerance of obtained ceramics were much improved. [ABSTRACT FROM AUTHOR]

Abstract: AlB2 is used as a sintering additive to densify ZrB2 ceramics. The AlB2 phase plays a positive role in the densification process of ZrB2 ceramics by removing the oxygen impurity and liquid phase sintering. With 5vol% AlB2 addition, both mechanical properties and oxidation resistance can be improved compared with monolithic ZrB2 ceramics. [Copyright &y& Elsevier]

ZrB2–SiC–BN composites were fabricated from a powder mixture of ZrH2, Si3N4 and B4C via reactive hot pressing (RHP) and reactive spark plasma sintering (R-SPS). The phase composition, density, microstructure and mechanical properties of the final products were studied and compared. The sample fabricated by the R-SPS process showed higher density, flexural strength and fracture toughness and had a more homogeneous microstructure compared to the one fabricated by the RHP process. [Copyright &y& Elsevier]

Abstract: ZrB2 powders with different particle size or different morphologies have been synthesized by boro/carbothermal reduction (BCTR) method using ZrO2, B4C and graphite or carbon black as starting materials in this work. Results revealed that the carbon black with fine particles decreased the synthesis temperature and resulted in a finer ZrB2 powder compared with graphite in vacuum. However, the synthesis temperature was almost the same for both the carbon black and graphite cases if the reaction took place in argon atmosphere. Furthermore, vacuum atmosphere led to the formation of rod-like ZrB2 powder, whereas argon atmosphere resulted in quasi-spherical ZrB2 powder. Thermodynamic calculation was conducted and possible mechanisms were discussed for understanding the above phenomena. [Copyright &y& Elsevier]