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Magnesium matrix composites are essential lightweight metal matrix composites, following aluminum matrix composites, with outstanding application prospects in automotive, aerospace lightweight and biomedical materials because of their high specific strength, low density and specific stiffness, good casting performance and rich resources. However, the inherent low plasticity and poor fatigue resistance of magnesium hamper its further application to a certain extent. Many researchers have tried many strengthening methods to improve the properties of magnesium alloys, while the relationship between wear resistance and plasticity still needs to be further improved. The nanoparticles added exhibit a good strengthening effect, especially the ceramic nanoparticles. Nanoparticle-reinforced magnesium matrix composites not only exhibit a high impact toughness, but also maintain the high strength and wear resistance of ceramic materials, effectively balancing the restriction between the strength and toughness. Therefore, this work aims to provide a review of the state of the art of research on the matrix, reinforcement, design, properties and potential applications of nano-reinforced phase-reinforced magnesium matrix composites (especially ceramic nanoparticle-reinforced ones). The conventional and potential matrices for the fabrication of magnesium matrix composites are introduced. The classification and influence of ceramic reinforcements are assessed, and the factors influencing interface bonding strength between reinforcements and matrix, regulation and design, performance and application are analyzed. Finally, the scope of future research in this field is discussed. [ABSTRACT FROM AUTHOR]

In this study, amorphous + nanocrystalline Ti-BN mixed powders were obtained through first-step mechanical alloying; subsequently, almost completely amorphous SiBCN-Ti mixed powders were achieved in the second-step milling. The SiBCN-Ti bulk ceramics were consolidated through hot pressing sintering at 1900 °C/60 MPa/30 min, and the microstructural evolution and mechanical properties of the as-sintered composite ceramics were investigated using SEM, XRD, and TEM techniques. The as-sintered SiBCN-Ti bulk ceramics consisted of substantial nanosized BN(C), SiC, and Ti(C, N) with a small amount of Si2N2O and TiB2. The crystallized BN(C) enwrapped both SiC and Ti(C, N), thus effectively inhibiting the rapid growth of SiC and Ti(C, N). The sizes of SiC were ~70 nm, while the sizes of Ti(C, N) were below 30 nm, and the sizes of Si2N2O were over 100 nm. The SiBCN-20 wt.% Ti bulk ceramics obtained the highest flexural strength of 394.0 ± 19.0 MPa; however, the SiBCN-30 wt.% Ti bulk ceramics exhibited the optimized fracture toughness of 3.95 ± 0.21 GPa·cm1/2, Vickers hardness of 4.7 ± 0.27 GPa, Young's modulus of 184.2 ± 8.2 GPa, and a bulk density of 2.85 g/cm3. The addition of metal Ti into a SiBCN ceramic matrix seems to be an effective strategy for microstructure optimization and the tuning of mechanical properties, thus providing design ideas for further research regarding this family of ceramic materials. [ABSTRACT FROM AUTHOR]

• We investigate the structural stability problem for shell models in extrusion-based ceramics 3D printing and explore the factors that cause instability or collapse during fabrication. • We introduce a lightweight structural analysis solver for the given shell model based on moment equilibrium instead of volumetric mesh-like finite element methods. The structural analysis considers the gravity and adhesion force during printing and provides the real-time visualization of stability distribution. • We propose a structural optimization algorithm based on local shell thickening that enhances the stability during fabrication and does not affect the object's exterior appearance, expanding the feasible shape space of shell structures fabricated by extrusion-based ceramics 3D printing. The algorithm works directly on the printing file and produces the new G-code commands. [Display omitted] Additive manufacturing of ceramics gains increasing attention in recent years, as ceramic material like clay processes distinctive merits, including hardness, thermal and chemical stability, etc. The customer-level extrusion-based ceramics 3D printer is getting easily achievable. However, due to its semi-liquid and highly viscoelastic properties, the clay material causes new challenges to the computational aspects. It does not dry instantly and may collapse during the accumulated force from new layers breaks the moment equilibrium, especially when adjacent layers have less overlap region. We tackle this unique problem, focusing on shell-like models in extrusion-based ceramics printing in this paper. We propose a structural analysis algorithm that considers the moment equilibrium for each layer along the fabrication process. We also present a computational framework to enhance the structural stability by local thickening of the shell models without affecting the appearance. We demonstrate the printing process and physical results to validate our method. [ABSTRACT FROM AUTHOR]

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 crystallization behavior of amorphous Si2BC3N monoliths by heating at 1000°C-1400°C and 5 GPa was investigated with the special attention to the nucleation mechanisms of β-SiC and BN(C) phases. Nanoscale puckered structures arising in particle bridging areas were found and its evolution behavior well reflected the nucleation process of nanocrystallites. The temperature-dependent crystallization of amorphous Si2BC3N monoliths at 5 GPa passes through four stages: The material remains amorphous below 1100°C. It undergoes partial phase segregation (1100°C-1200°C), followed by initiation of nucleation (1200°C-1250°C), and then nucleation and growth of β-SiC and turbostratic BN(C) crystallites (>1250°C). The first principles calculation indicates the nucleation precedence of BN(C) phase over β-SiC. BN(C) nucleates preferentially at bridges between ceramic particles causing SiC to concentrate in particle interiors thus forming capsule-like structures. [ABSTRACT FROM AUTHOR]

Porous Si3 N4- Si2 N2 O- BN ceramic was fabricated at 1750°C using Si3 N4, BN, and ( NH4)2 HPO4 as starting materials. During the sintering process, oxygen from the decomposed products of ( NH4)2 HPO4 would bond Si and N in the liquid phase to form Si2 N2 O. The microstructure and properties of the porous ceramics were investigated. With the ( NH4)2 HPO4 content varied from 10 to 50 vol.%, porosity of the porous Si3 N4- Si2 N2 O- BN ceramic increased from 43.5% to 51%. The microstructure, mechanical, and dielectric properties was well controlled by adjusting ( NH4)2 HPO4 contents. The present technique offers a more simple way of synthesizing porous Si3 N4- Si2 N2 O- BN ceramics. [ABSTRACT FROM AUTHOR]

To understand the differences in material removal behavior during grinding for different ceramics, scratching of Al 2 O 3 , AlN, Si 3 N 4 and ZrO 2 (3Y-TZP) ceramics by a cube-corner diamond indenter was investigated in this paper. Scratching characteristics, including material deformation, scratching force, coefficient of friction (COF) and scratching damage of different ceramics were compared and analyzed. Elastic recovery rate model and stress field model were built to analyze the mechanism of material deformation and scratching damage during scratching on different ceramics. The results demonstrated that material deformation behaviors vary significantly, and depend on mechanical properties of the ceramics. Ceramics with higher hardness exhibit shallower penetration depth of scratching, while higher fracture toughness results in shorter maximum surface damage distance. Elastic recovery rate model can predict the extent of material deformation. The ceramic with the highest elastic recovery rate is Al 2 O 3 , followed by Si 3 N 4 , ZrO 2 , and finally AlN. Elastic recovery rate decreases with increase in force. In stress field model, AlN exhibits the highest maximum principal stress, followed by Al 2 O 3 and Si 3 N 4 , with ZrO 2 displaying the lowest stress. These distribution patterns are consistent with the results of scratching damage pattern. [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]

For the engineering applications of freeze-cast porous ceramics, the demand targets are often multiple and competing, which is a challenging problem to seek a Nash equilibrium in the high-dimensional design space. An accurate and robust quantification of process-structure-property correlations would provide an effective path to find the set of Pareto optimal materials for one specific need. In this work, using porous Si 3 N 4 -Si 2 N 2 O ceramics as the model materials, a hybrid model for the quantitative design of the microstructure and mechanical properties is developed from four physics-based process-microstructure models with sintering, solidification, phase transformation and grain growth kinetic theories, and the subsequent data-driven structure-property model utilizing a machine learning method, artificial neural network (ANN). The SHapely Additive exPlanations (SHAP) analysis is further introduced to interpret the ANN model and mathematically identify the contribution of each microstructure feature descriptor toward target mechanical property outputs. These results present a systematic understanding of the process-structure-property relationships through the hybrid model, guiding the optimal design of the freeze-cast porous ceramics with required microstructures and mechanical properties. [Display omitted] [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: Gadolinium zirconate (Gd2Zr2O7) prepared by solid state reaction exhibited a defect fluorite-type structure. Reactions between Gd2Zr2O7 ceramic and vanadium pentoxide (V2O5), sodium sulfate (Na2SO4), and V2O5 +Na2SO4 mixture were investigated from 700 to 1000°C in air using an X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). V2O5 reacts with Gd2Zr2O7 to form gadolinium vanadate (GdVO4) and monoclinic zirconia (m-ZrO2) at 900 and 1000°C in air. However, no chemical reaction product between Na2SO4 and Gd2Zr2O7 is found at 900 and 1000°C in air. V2O5 reacts with equal molar Na2SO4 to form sodium vanadate (NaVO3) at 610°C. In the temperature range of 700–1000°C, Na2SO4 +V2O5 mixture reacts with Gd2Zr2O7 in air to form the final reaction products of GdVO4 and m-ZrO2. [Copyright &y& Elsevier]

Abstract: Yb- and Y-doped α-SiAlON ceramics were effectively bonded by spark plasma sintering in less than 20min without using any interlayer materials at 1650–1700°C. The microstructures and mechanical properties of the joints were investigated by means of SEM, STEM, EDX, and three-point bending tests. The results showed that α-SiAlON joint formation was accompanied by fundamental rare earth diffusion. The intergranular liquids in the α-SiAlON ceramics at the bonding temperatures provided the diffusion paths for the species. α-SiAlON grain growth across the joining interfaces modified the joint microstructures to secure high bonding strength. [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: Structural evolution and thermophysical properties of (Sm x Gd1−x )2Zr2O7 (0≤ x ≤1.0) were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-temperature dilatometer and laser flash diffusivity measurements from room temperature to 1400°C. Pure Gd2Zr2O7 ceramics exhibit a defective fluorite-type structure, however, (Sm x Gd1−x )2Zr2O7 (0.1≤ x ≤1.0) ceramics are with a pyrochlore-type structure. The linear thermal expansion coefficients of (Sm x Gd1−x )2Zr2O7 ceramics increase with increasing test temperature. The thermal diffusivities of (Sm x Gd1−x )2Zr2O7 ceramics range from 0.390 to 0.770mm2 s−1, while the thermal conductivities of (Sm x Gd1−x )2Zr2O7 ceramics are located within the range of 1.20 to 1.99Wm−1 K−1 from room temperature to 1400°C. [Copyright &y& Elsevier]

Ball milling was used on synthesized Cr 2 AlC powders, and dense Cr 2 AlC bulk ceramics with almost pure phase were fabricated by hot pressing these ball milled Cr 2 AlC powders at 1300 °C for 2 h under 30 MPa. The phase compositions and the microstructures of powders and bulk ceramics were characterized. The mechanical properties and dislocation analysis of bulk ceramics were also investigated. Our results indicated that the grain size of powders became uniform and smaller after ball milling, which was also inherited in the bulk ceramics. Moreover, the mechanical properties of hot pressed Cr 2 AlC ceramics, including flexural strength, fracture toughness, and Vickers hardness, significantly increased by using ball milled powders treated at speed 200 rpm. The organization of hexagonal dislocation networks during hot pressing and reduction of grain size both had a positive effect on improving mechanical properties. [ABSTRACT FROM AUTHOR]

Studying the tribological behavior between diamond materials and ceramics is crucial for understanding the grinding mechanism of diamond wheels on ceramics. To comprehend the tribological characteristics between diamond materials and various ceramics, this paper presents a comparative study of the tribological behaviors of Al 2 O 3 , AlN, Si 3 N 4 , and ZrO 2 ceramics sliding against polycrystalline diamond (PCD) balls. The dependence of the coefficient of friction (COF), wear characteristics as well as the surface morphology of different ceramics and SiC-bonded PCD balls on load, sliding stage were examined. The effect of nanofluids on the COF and wear of different ceramics was also investigated. The results showed that the tribological characteristics of ceramic materials are strongly dependent on mechanical properties. Al 2 O 3 and AlN ceramics with lower fracture toughness exhibit a significantly higher COF and wear volume than that of Si 3 N 4 and ZrO 2 ceramics. Al 2 O 3 presents the highest COF (0.38) and wear volume, and Si 3 N 4 owns the lowest COF (0.08) and wear volume under the load of 9.8 N. By examining the wear grooves of different ceramics, it is found that Al 2 O 3 and AlN ceramics own larger debris than that of Si 3 N 4 and ZrO 2 , which also causes more smearing on the ceramic and adhesion of wear debris to the SiC-bonded PCD ball for Al 2 O 3 and AlN. Under lubricants, the COFs and the adhesion of wear debris are effectively reduced, and the wear rate of the ceramic is increased. There is little difference between deionized (DI) water and nanofluids on the effect of lubricants on COF for Al 2 O 3 and AlN. However, for ceramics with higher fracture toughness, the nanofluids can reduce the COFs of Si 3 N 4 and ZrO 2 in comparison with DI water. • The tribological behavior of ceramics is influenced by the mechanical properties. • Compared to ZrO 2 and Si 3 N 4 , Al 2 O 3 and AlN exhibit higher COF and wear volume. • Al 2 O 3 and AlN have larger debris, leading to significant adhesion to the PCD balls. • The nanofluids are effective in reducing the COF of Si 3 N 4 and ZrO 2. [ABSTRACT FROM AUTHOR]

Abstract Morphotropic phase boundaries (MPB) consisting of rhombohedral, nonpolar orthorhombic and orthorhombic bridging phases were formed within the range of 0.1 ≤ x ≤ 0.2 in Bi 1- x Nd x Fe 0.97 Ti 0.03 O 3 ceramics. The intricate phase coexistence was verified by X-ray diffraction refinements, new modes at ~305 cm−1 in Raman spectra and microstructure analyses. Impedance tests confirmed the MPB ranges via resistance fluctuations and revealed additional arcs from phase boundaries. Ferroelectric and magnetic properties were synchronously improved at MPB resulting in the apparent magnetodielectric effect with a permittivity change rate of ~1.5% at 10000 Oe. Additionally, magnetic domains were reversed at low voltages. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The mechanical properties, thermal shock resistance, and ablation resistance of nano ZrB 2 modified Si 2 BC 3 N ceramics were investigated. The results show that ZrB 2 stimulated microstructure evolution obviously. Therefore, the maximum strength and fracture toughness reach 559.6 MPa and 6.77 MPa·m1/2, which are improved by 61.0% and 29.4%, respectively. Furthermore, the residual strengths of 10 wt% ZrB 2 containing composites tested at 1000 ℃ retain 363.6 MPa, which is much higher than 97.7 MPa of pristine Si 2 BC 3 N ceramics. Besides, the ablation resistance of ZrB 2 modified Si 2 BC 3 N ceramics at 3000 ℃ is enhanced remarkably and the linear and mass ablation rates of ZrB 2 -10 are only 0.009 mm/s and 1.91 mg/s, respectively. The ablation in the ultra-high temperature zone is totally dominated by the ZrB 2 component, and the thermochemical erosion is determined by the oxidation resistance of ZrB 2 in the thermal affected zone. [ABSTRACT FROM AUTHOR]

Abstract Effects of raw h -BN particle size from 0.5 μm to 11 μm on the phase compositions, texture degree, bending strength, fracture toughness and thermal conductivity of hot-press sintered h -BN-MAS composite ceramics were investigated. Larger h -BN grain can facilitate the nanocrystallization of MAS phase due to the inhibiting crystallization effect of h -BN on α-cordierite. Texture degree of h -BN-MAS composite ceramics increased significantly with increasing raw h -BN particle size, and the 11.0μmBN-MAS composite ceramic shows typical textured structure. The h -BN-MAS composite ceramics show anisotropy in mechanical properties and thermal conductivity, and the anisotropy increased significantly with increasing raw h -BN particle size. The 0.5μmBN-MAS sample shows excellent mechanical properties, and the 10μmBN-MAS sample shows strong anisotropy in thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract Morphotropic phase boundaries (MPB) consisting of rhombohedral and orthorhombic phases formed within the range of 0.1 ≤ x ≤ 0.15 in Bi 1- x Er x Fe 0.97 Ti 0.03 O 3 ceramics. Orthorhombic phase transition was verified by the appearance of a new mode at 310 cm−1 in Raman spectra. Bridging phases as intermedia phases of MPB were rare in Bi 1- x Er x Fe 0.97 Ti 0.03 O 3. Polarization and permittivity improved at MPB. Moreover, impedance spectroscopy revealed additional arcs with a distinct small polaron conduction mechanism. Er3+ ions enhanced magnetic properties and induced a permittivity change at Neel temperature. The magnetodielectric effect resulted in a permittivity change rate of ~1% at 10000 Oe. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

α-cordierite glass-ceramic coating was prepared on the porous BN/Si 2 N 2 O ceramic by the glass-ceramic method at 1050 °C for 1–4 h. The effect of the holding time on the phase composition, microstructure, mechanical, water resistance and dielectric properties of the glass-ceramic coating was investigated. The resulting coating was mainly composed of α-cordierite and glass, and the α-cordierite content increased with increasing holding time. The coating/substrate interface was continuous without defects, and the glass liquid of the coating can infiltrated into the surface pores of the substrate. Additionally, the density and mechanical properties of coatings increased as the holding time increased. The obtained coated samples fabricated at 1050 °C for 2–4 h possessed a low water absorption (2.1–5%) and little open porosity (2.7–3.2%), demonstrating good water resistance. Furthermore, the coated samples prepared at 1050 °C for 3 or 4 h exhibited both low dielectric constant (4.1–4.3) and loss tangent (0.005–0.009) in the frequency range of 20–36 GHz. [ABSTRACT FROM AUTHOR]

In the present study, ablation behavior and properties of BN-MAS (magnesium aluminum silicate) composites impinged with an oxyacetylene flame at temperatures up to 3100 °C were investigated. As ablation time ranged from 5 to 30 s, the mass and linear ablation rates increased from 0.0027 g/s and 0.001 mm/s to 0.0254 g/s and 0.087 mm/s, respectively. A SiO 2 -rich protective oxide layer formed during the ablation process, which contributed to the oxidation resistance of the composites. Ablation products mainly consisted of magnesium-aluminum borosilicate glass, mullite, spinel and indialite. The thermal oxidation of h -BN during flame ablation and scouring of MAS by high-speed gas flow were the main ablation mechanisms. [ABSTRACT FROM AUTHOR]

Densification behavior, mechanical and thermal properties of ZrC 1 − x ceramics with various C/Zr ratios of 0.6–1.0 have been investigated by two-step reactive hot pressing of ZrC and ZrH 2 powders at 30 MPa and 1500–2100 °C. The two-step reactive hot pressed ZrC 1 − x ceramic has a higher relative density (> 95.3%) than that (91.9%) of stoichiometric ZrC sintered at 2100 °C. A cubic Zr 2 C-type ordered phase forms in the ZrC 1 − x sample obtained at a ZrC/ZrH 2 molar ratio of 0.6 at a relatively low temperature of 1100 °C. The decrease in C/Zr ratio is beneficial to densification of ZrC 1 − x ceramic, however, excess grain growth occurs after sintering above densification temperature. The elastic modulus and Vickers hardness decrease with decreasing the C/Zr ratio. With decreasing the C/Zr ratio, both thermal conductivity and specific heat decrease due to the enhanced scattering of conducting phonons and electrons by carbon vacancies. [ABSTRACT FROM AUTHOR]

MWCNTs modified Si 2 BC 3 N ceramics were prepared through SPS sintering mechanically alloyed amorphous Si 2 BC 3 N powder and MWCNTs at 1900 °C in N 2 atmosphere. The phase evolutions, microstructures and mechanical properties of the prepared ceramic were characterized by XRD, SEM and TEM (SAED and HRTEM), as well as the properties testing. The results show that the Si 2 BC 3 N ceramics are mainly composed of β-SiC, α-SiC and BN(C) phases. The introduction of MWCNTs can stimulate the formation of β-SiC in comparison with the pure Si 2 BC 3 N ceramics. Meanwhile, the particle sizes of BN(C) and SiC are reduced with the introduction of MWCNTs. Furthermore, the MWCNTs are mainly embedded in the Si 2 BC 3 N matrixes, contributing to enhanced bonding. Judging from the interfacial characteristic, the strengthening and toughening mechanisms of MWCNTs in Si 2 BC 3 N ceramics can be classified as “crack bridging”, “pull-out” and “crack deflection”. Based on these effects, the 1 vol% MWCNTs incorporated Si 2 BC 3 N ceramics have much higher flexural strength and fracture toughness of 462.1 MPa and 5.54 MPa·m 1/2 , respectively. [ABSTRACT FROM AUTHOR]

The high temperature oxidation behavior of three SiBCN monoliths: carbon-lean SiBCN with substantial Si metal, carbon-moderate SiBCN and carbon-rich SiBCN with excessive carbon, was investigated at 1500 °C for times up to15 h. Scale growth for carbon-lean and −moderate monoliths at 1500 °C cannot be described by a linear or parabolic rate law, while the carbon-rich monoliths oxidize according to a approximately linear weight loss equation. The microstructures of the oxide scale compose of three distinct layers. The passivating layer of carbon and boron containing amorphous SiO 2 and increased oxidation resistance of BN(C) both benefit the oxidation resistance. [ABSTRACT FROM AUTHOR]

The CoFe 2 O 4 (CFO)/Bi 3.15 Nd 0.85 Ti 3 O 12 (BNdT) composite ceramics with coherent-lattice interfaces were prepared to keep good ferroelectricity. The coherent-lattice interfaces exhibit (020) BNdT //(130) CFO orientation, as a result of a very small lattice mismatch. Raman spectra indicate symmetry breaking of CFO phase with the forbidden A 1g mode (~ 684 cm − 1 ) leading to new modes around 727 and 734 cm − 1 , suggesting that coherent interfaces have superlattice-like characteristics. The electric breakdown field increases to 400 kV/cm for the 30 mol% CFO ceramic comparing with 250 kV/cm for the pure BNdT. Partly enhanced ferroelectric polarization, as measured by hysteresis loops, is observed likely helped by this superlattice-like bonding. [ABSTRACT FROM AUTHOR]

Si-B-C-N ceramic monoliths with LaB 6 additive were prepared by mechanical alloying followed by spark plasma sintering. The microstructures and mechanical properties were investigated compared to LaB 6 -free Si-B-C-N counterparts. After sintered at 1900 °C/50 MPa, the La/Si-B-C-N monoliths provide well-developed BN(C) flakes (≤100 nm in thickness) and improved fracture toughness, while the BN(C) ones show no lamellar microstructures in Si-B-C-N systems. The solid-solution of La in BN(C) grains promotes ordered arrangement of BN(C) along the (0002) plane causing in situ growth of BN(C) thus leading to an increase in toughness by 40% (from 5.6 to 7.8 MPa m −1/2 ). [ABSTRACT FROM AUTHOR]

The exponentially increasing dielectric loss with rising temperature is the biggest obstacle hindering the application of hexagonal boron nitride (h -BN) ceramics as radome materials. Herein, a novel strategy is proposed to reduce high-temperature dielectric loss of h -BN ceramics by orienting grains. The relationship between electrical conductivity and temperature of h -BN ceramics shows that conductance loss of intrinsic defect ions thermal-excited above 667 °C is main cause of dielectric loss. And ab initio molecular dynamics calculations indicate that thermal-excited defect ions show much higher self-diffusion coefficient along a/b -axis of layered h -BN than that along c -axis. Therefore, by orienting h -BN grains, high-temperature dielectric loss of bulk ceramics will be minimized due to the suppressed defect ions transport perpendicular to orientation direction. As validation, resulting h -BN ceramics with oriented grains shows low dielectric loss tangent of 6.1 × 10−3 at 1000 °C, which is 45.5% lower than that of typical h -BN ceramics with random grains. [Display omitted] [ABSTRACT FROM AUTHOR]

Thermal conductive insulating ceramic materials are urgently needed in the packaging applications for modern electronic devices owing to their multi-functionality. The electrically insulating Al 2 O 3 ceramics with large thickness and high compactness is designed on SiC p /Al baseplate via plasma electrolytic oxidation (PEO) technique, which provides a new idea for the package structure of the IGBT power module. However, porous characteristics of PEO inorganic ceramics hinder effective electrical insulation and heat conduction in practical applications. Herein, the bipolar pulsed (B P) and unipolar pulsed (U P) PEO are tailored to obtain the ceramics respectively. In contrast, the B P mode enables the ceramic layer significantly thickened and densified due to the soft sparking discharge. Combined with outstanding electrical resistivity over 1012 Ω·cm, high breakdown voltage of 716 ± 38 V, high dielectric strength of 15.9 ± 0.8 V/μm, the B P ceramic layer exhibits superior performance in electrical insulation. Moreover, the B P shows excellent thermal cycling stability (>200 cycles), quite good thermal stability, and dielectric stability in the temperature range of 25 °C to 300 °C to realize high-temperature electrical insulation. This work paves a novel way to design and optimize power electronic module package materials and structures. • A ceramic layer is designed on SiC p /Al baseplate by PEO for IGBT power module package. • The bipolar pulsed PEO enables the ceramic layer significantly thickened and densified due to the soft sparking discharge. • The compact ceramic layer endows SiC p /Al baseplate outstanding electrical insulating protection. • The compact ceramic layer shows excellent thermal cycling stability, thermal conduction, and corrosion resistance. [ABSTRACT FROM AUTHOR]

A novel composite ceramics with excellent mechanical properties was fabricated by means of low temperature hot-pressing using hexagonal boron nitride ( h -BN) and magnesium aluminum silicate (MAS) as raw materials. The influences of starting MAS content on the microstructural evolution and mechanical properties of the composites were investigated. The results indicate that the effective enhancement of relative density of composites has been achieved, which shows that MAS is an effective liquid-phase sintering aid during the hot-pressing. MAS also can improve the structural ordering of h- BN flakes. On the other hand, h- BN exhibits significant inhibiting effect on the crystallization of α-Cordierite. Furthermore, h -BN flakes with layered structure can play a role in strengthening the MAS matrix. So h -BN and MAS are considered to be co-enhanced by each other, resulting in better sintering ability and the mechanical properties of composite ceramics are better than that of both h -BN and MAS. Composite ceramics incorporated with 50 wt% MAS exhibits the highest bending strength and fracture toughness of 213±25 MPa and 2.49±0.35 MPa m 1/2 , respectively. [ABSTRACT FROM AUTHOR]

BN/Si 3 N 4 composite ceramics with different BN content were prepared by water-based gel casting process with raw and Y–Al-oxides-coated BN powder, separately. A Y–Al oxides layer with the thickness ranging from dozens to hundreds of nanometers, serving as sintering additives, was coated on the surface of BN particles with the method of precipitation of inorganic salts. As a result, the fluidity of BN/Si 3 N 4 slurry with Y–Al-oxides-coated BN powder was much improved compared to that with raw BN. SEM examination showed the Y–Al-oxides-coated BN particles were homogeneously distributed within the Si 3 N 4 grain boundaries, and BN aggregation was barely detected. The BN/Si 3 N 4 composite ceramic prepared by Y–Al-oxides-coated BN powder showed a better sintering behavior than those prepared by raw BN due to the formation of fine and homogeneous microstructure in it. Compared to the BN/Si 3 N 4 ceramic with 15 vol% raw BN, the density and flexural strength of the ceramic with the same content of surface-coated BN were significantly improved to 8.5% and 67.2%, respectively. [ABSTRACT FROM AUTHOR]

Crack-healing ability and strength recovery of different ZrO 2 (Y 2 O 3 )–Al 2 O 3 –SiC (TZ3Y20A–SiC) ceramics have been investigated by tailoring heat treatment temperature, heat treatment time, SiC content and crack size. Heat treatment in air enhances distinctly the flexural strength of TZ3Y20A–SiC ceramics. A complete crack-healing of TZ3Y20A–10 vol%SiC ceramic can be realized by optional heat treatments at 1073 K for 30 h, 1273 K for 10 h or 1373 K for 5 h, respectively. With increasing the content of nanosize SiC particles from 10 to 20 vol%, the crack-healing process of TZ3Y20A–SiC ceramics speeds up at identical temperature levels. The pre-existing cracks with a width up to 0.45 μm are healed completely under the optimum heat treatment conditions, and the flexural strengths of crack-healed TZ3Y20A–SiC ceramics are completely recovered to the value of smooth specimens. Crack closure and rebonding of crack wall due to the formation of SiO 2 glassy phase by oxidation reaction between SiC and the oxidizing atmosphere are dominant healing mechanisms in TZ3Y20A–SiC ceramics. [ABSTRACT FROM AUTHOR]

Abstract: The hexagonal boron nitride (h-BN) grain shows typical lamellar structures, so textured materials can be achieved by arranging h-BN grains along the same direction. In this work, textured h-BN composite ceramics with the c-axis orientation arranged along pressure direction were manufactured by hot-press sintering using mullite as the sintering additive. The results show that sintering pressure is an important factor that affects not only the density and the textured degrees of composite ceramics, but also the mechanical properties. Based on the textured microstructure features, the composite ceramics show the obviously anisotropically characterized mechanical properties, such as elastic modulus, flexural strength and fracture toughness, together with various fracture mechanisms. [Copyright &y& Elsevier]

Crack healing behavior of hot-pressed TZ3Y20A-SiC ceramics has been investigated by high-temperature oxidation. Semi-elliptical surface cracks with a length of 100μm have been set on the tensile side of each specimen using a Vickers hardness indenter. Based on flexural strength and observations of crack appearance, the effect of crack healing is finally judged. Cracks on ZrO2(Y2O3)–Al2O3 (TZ3Y20A) ceramics cannot be healed by heat treatment. However, for TZ3Y20A-SiC ceramics, complete crack-healing has been realized by heat treatment at 800°C, 1000°C and 1100°C for 30h, 10h and 5h, respectively. The crack-healing mechanism is attributed to the formation of SiO2 caused by high temperature oxidation during heat treatment. [ABSTRACT FROM AUTHOR]

Abstract: Silicon carbide–aluminium nitride ceramic composites were prepared by gelcasting method. The effect of the solid contents of the slurry on the relative densities, mechanical properties of the green bodies and the pressureless sintered ceramic composites were investigated. When the solid contents increased from 35 to 40vol.%, the mechanical properties, such as elastic modulus, flexural strength and fracture toughness simultaneously increased due to the improving of the relative density. But when the solid contents reached to 42vol.%, the mechanical properties became noticeably worse, which caused by the sharply increase of the slurry viscosity, and many defects such as large scale and uneven pores also can be observed in the green bodies and the sintered ceramic composites. [Copyright &y& Elsevier]

Abstract: Multiferroic BiFeO3 (bismuth ferrite, BFO) ceramics were sintered using a rapid heating and quenching technique in an atmosphere of argon or oxygen. The resulting ceramics were phase pure with the space group R3c. BFO ceramics sintered under an argon atmosphere contained more oxygen vacancies and Fe2+ ions compared with those sintered under an oxygen atmosphere, which resulted in high dielectric loss and large dielectric dispersion. It confirms that the unavoidable Fe2+ ions may play a fundamental role in these special materials, such as in the evaporation of the Bi component and valence change of the Fe component. This work also discusses the dielectric response mechanism in BFO ceramics. [Copyright &y& Elsevier]

Abstract: Translucent α-SiAlON ceramics were synthesized by hot pressing and spark plasma sintering. The in-line transmittance of the visible-infrared light through the α-SiAlON ceramics was discussed in correlation with the SiAlON compositions, rare earth dopant types, microstructures, and the refractive index anisotropy of the α-SiAlON grains. The results showed that the α-SiAlON ceramics had a refractive index about 2.17 and a refractive index anisotropy about 0.014. The birefringent losses due to the index anisotropy were the main reason for the severe transmission degradation in the visible light regions in the transmission curves. Accordingly, smaller grain sizes could be used to counteract the large birefringent losses to improve the in-line transmittance of the short wavelength light. [Copyright &y& Elsevier]

Abstract: This paper concentrates on the influence of gadolinia on structure and thermal expansion property of ZrO2–4.5mol%Y2O3 (YSZ) ceramics. The YSZ–xGd2O3 (0≤ x ≤7.5 in mol%) ceramics were synthesized by solid state reaction method at 1500°C for 2h in air. The relative density, phase structure and thermal expansion property of YSZ–xGd2O3 ceramics were investigated by the Archimedes method, X-ray diffraction and high-temperature dilatometer. The thermal expansion coefficients of YSZ–xGd2O3 ceramics increase with the increase in temperature. The thermal expansion coefficients of YSZ–xGd2O3 ceramics first decrease with increasing the mole fraction (x) of gadolinia from x =0 (YSZ) to x =4.5 (YSZ–4.5Gd2O3), and then increase from x =4.5 (YSZ–4.5Gd2O3) to x =7.5 (YSZ–7.5Gd2O3) in the temperature range of 50–1200°C. The YSZ–4.5Gd2O3 ceramics have the lowest thermal expansion coefficient in YSZ–xGd2O3 ceramics, which is due to formation of the () ionic vacancy clustering. [Copyright &y& Elsevier]

Abstract: Dy3+-doped barium zirconate ceramics, BaZr1–x Dy x O3–δ (x =0, 0.05, 0.10, 0.15, 0.20), have been synthesized by pressureless-sintering method at 1973K for 10h in air. The structure and electrical conductivity of BaZr1–x Dy x O3–δ ceramics were investigated by means of X-ray diffraction, scanning electron microscopy and complex impedance spectroscopy. BaZr1–x Dy x O3–δ ceramics exhibit a cubic perovskite structure. The total conductivity of BaZr1–x Dy x O3–δ ceramics obeys the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1073K. The BaZr0.90Dy0.10O3–δ ceramic exhibits the highest total conductivity at 1073K. The measured total conductivities of the BaZr0.90Dy0.10O3–δ ceramic in wet hydrogen (4% H2O/H2) and in air are 7.90×10−3 Scm−1 and 7.31×10−3 Scm−1 at 1073K, respectively. The activation energy of BaZr1–x Dy x O3–δ (x =0.10, 0.15, 0.20) ceramics is clearly lower than that of undoped BaZrO3 ceramic in both wet hydrogen and air atmospheres, and it can be concluded that the Dy3+-doped BaZr1–x Dy x O3–δ (x =0.10, 0.15, 0.20) ceramics are potential proton conductors. [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 phase composition, relative density, mechanical properties and dielectric properties of silicon nitride porous ceramics with different content of CaHPO4 as an additive prepared by gelcasting method were investigated. The addition of CaHPO4 can improve the sintering ability and the phase transformation from α-Si3N4 to β-Si3N4, so the relative density and β-Si3N4 content both increase with the increase of CaHPO4 content. As a result, when the CaHPO4 addition content is 15wt.%, the flexural strength, elastic modulus, fracture toughness of Si3N4 ceramic reach to 365.1MPa, 107.9GPa and 3.82MPam1/2, respectively. The dielectric constant of Si3N4 ceramics increases with the increase of CaHPO4 addition content due to the increase of relative density and the relative content of β-Si3N4. [Copyright &y& Elsevier]

Abstract: Polycrystalline GdSm1−x Ca x Zr2O7−x/2 (0≤ x ≤0.20) ceramics have been prepared by the solid-state reaction method. The effects of CaO addition on the microstructure and electrical properties of the pyrochlore-type GdSmZr2O7 ceramic were investigated. GdSm1−x Ca x Zr2O7−x/2 (x ≤0.05) ceramics exhibit a pyrochlore-type structure; however, GdSm1−x Ca x Zr2O7−x/2 (0.10≤ x ≤0.20) ceramics consist of the pyrochlore-type structure and a small amount of CaZrO3. The total conductivity of GdSm1−x Ca x Zr2O7−x/2 ceramics follows the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173K. GdSm1−x Ca x Zr2O7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0×10−4–1.0atm at each test temperature. The highest total conductivity is about 1.20×10−2 Scm−1 at 1173K for the GdSm0.9Ca0.1Zr2O6.95 ceramic. [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: Porous silicon nitride/silicon oxynitride composite ceramics were fabricated by silica sol infiltration of aqueous gelcasting prefabricated Si3N4 green compact. Silica was introduced by infiltration to increase the green density of specimens, so suitable properties with low shrinkage of ceramics were achieved during sintering at low temperature. Si2N2O was formed through reaction between Si3N4 and silica sol at a temperature above 1550°C. Si3N4/Si2N2O composite ceramics with a low linear shrinkage of 1.3–5.7%, a superior strength of 95–180MPa and a moderate dielectric constant of 4.0–5.0 (at 21–39GHz) were obtained by varying infiltration cycle and sintering temperature. [Copyright &y& Elsevier]

Novel in situ toughened ScLu–α-SiAlON ceramics with high optical transmittance were prepared by hot-pressing. The obtained material achieves the maximum transmittance of ∼60% in the region of 2500–5000nm for the sample of 1.0mm in thickness. The development of elongated microstructure does not result in an obviously adverse effect on optical transmittance. This indicates that it is possible to produce α-SiAlON ceramics with good mechanical and optical properties. [Copyright &y& Elsevier]