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Low-cost amorphous nano-carbon (ANC) was employed as an absorbent to modify the microwave performance of AlN ceramics (AlN-4 wt% Y 2 O 3 - x wt% C, x = 0, 2.0, 3.8, 3.9, 4.0) via hot-pressing sintering, and the thermal and mechanical properties were also investigated. With the increase of ANC content from 0 to 4.0 wt%, the relative density of AlN composite decreases from 3.28 g cm−3 to 3.16 g cm−3 when sintered at 1800 °C for 2 h, and with the increase of sintering temperature from 1700 °C, the density of the 4.0 wt% ANC doped AlN composite presents trend of increase and reaches the maximum value of 3.16 g cm−3 at 1800 °C and then decreases. The XRD pattern shows that the composites are composed of AlN and Y–Al–O (YAG, YAP, YAM et al.) phases. SEM results indicate that average grain sizes for AlN and secondary phases gradually decrease with increasing carbon content, suggesting inhibited grain growth due to ANC addition. No obvious changes in phase constitution nor intensity changes were detected with the increase in carbon content and sintering temperature. As the carbon content increases from 0 to 4.0 wt%, the dielectric constant gradually increases from ∼9 to 13.89 at 10 GHz, the dielectric loss gradually increases from the vicinity of 10−3 to 0.38 at 10 GHz, and the reflective loss decreases from −27.92 dB to −49.40 dB, the thermal conductivity of the AlN-ANC composite decreases from 116.63 W m−1 K−1 to 50.13 W m−1 K−1. In addition, with 4.0 wt% ANC addition, the dielectric constant, dielectric loss, reflective loss, hardness, elastic modulus, bending strength, and fracture toughness are 13.89, 0.38, 49.40 dB, 6.4 ± 0.4 GPa, 262 GPa, 268.78 MPa, and 1.4 ± 0.1 MPa m1/2, respectively. Its ability to efficiently absorb microwave energy enhances the performance of devices including radar systems, communication equipment, and microwave heating systems, making it a promising candidate for microwave vacuum electronic applications. [ABSTRACT FROM AUTHOR]

Addressing the issue of carbon contamination during the smelting of specialty metals or alloys, utilizing graphite crucibles, has attracted considerable research attention, prompting the exploration of novel ceramic crucible materials. AlN ceramic, renowned for their exceptional high-temperature stability and resistance to corrosion, have emerged as promising candidates to mitigate this concern. Nonetheless, the limited mechanical properties and thermal shock resistance of AlN curtail its widespread application. In this study, Y 2 Zr 2 O 7 was introduced as an additive to enhance AlN's properties, and AlN-based composite ceramics were fabricated by employing pressureless sintering. The effects of Y 2 Zr 2 O 7 addition (3–10 wt%) on the mechanical properties and thermal shock resistance of the resulting composites were examined. The findings revealed that the incorporation of 5 wt% Y 2 Zr 2 O 7 (AlN-5YZO) led to the highest relative density and a refined grain structure, resulting in superior mechanical properties. Notably, the flexural strength, fracture toughness, and Vickers hardness of AlN-5YZO reached 322 MPa, 3.70 MPa m1/2, and 13.34 GPa, respectively. Furthermore, the presence of crack branching and crack deflection within the composite ceramics impeded crack propagation, effectively augmenting their thermal shock resistance. AlN-5YZO samples exhibited residual strength retention rates of 91.0 %, 84.2 %, and 76.7 % after 10, 20, and 50 thermal shocks between 1000 and 1600 °C, surpassing those of pure AlN. The findings of this study present promising avenues for advancing crucible materials tailored for high-temperature applications. [ABSTRACT FROM AUTHOR]

The 2.5D oxide/oxide composites become attractive for their excellent integrity and mechanical properties. The thermal shock resistance performance of the material is very important in the actual high temperature application. In this work, the evolution of microstructure and mechanical behavior of the 2.5D oxide/oxide composites from thermal shock at different temperatures and cycles was investigated experimentally mainly by optical microscope, X-ray computed tomography and macro-mechanical tests. The thermal shock resistance mechanism of oxide/oxide composites was qualitatively explored. The results showed that cracks propagation was the main manifestation of thermal shock damage in composites. Compared with 2D composites, 2.5D composites exhibited the finite domain effect on crack propagation due to its reinforcement had certain fibers in Z -direction. This directly caused the critical thermal shock temperature difference of the 2.5D composites (∼900 °C) was more than twice that of the 2D oxide/oxide composites (∼400 °C). In addition, the finite domain effect also significantly reduced the damage growth rate of the 2.5D composites from cyclic thermal shock, highlighting its excellent thermal shock damage resistance. [ABSTRACT FROM AUTHOR]

The rapid development of micro-electronics has a growing demand on the heat dissipation performance of devices, especially thermal management materials. However, recent researches focus on the improvement of single ability, such as thermal or mechanical properties. Herein, a strategy that simultaneously improves thermal and mechanical performance of thermal manager material was proposed, which was achieved by preparing Cu-SiC w composites via the co-electrodeposition technology. The influence of electroplating parameters, such as temperature, current density and reinforcement contents, on the microstructure evolution, mechanical and thermal conductivity were investigated systematically. The fabricated SiC w composite displayed excellent shear strength up to 420 MPa, which is resulted from the Orowan strengthening and load transferring. Additionally, the thermal conductivity of 340 W/(m·K) was obtained, owing to the uniform distribution of whiskers and good interface between the Cu matrix and whiskers. Therefore, the presented work provided an effective method for fabricating comprehensive thermal-mechanical properties and homogeneous heat dissipation capacity Cu-SiC w composites and paved the way for the practical application in the field of the connector between the power devices and heat sinks. [ABSTRACT FROM AUTHOR]

Al 2 O 3 /B 2 O 3 powder mixtures prepared at various ratios from 10.7 to 54.1 wt% B 2 O 3 were used to synthesize Al 18 B 4 O 33 powders by solid state calcination at 1300 °C for 1 h. Al 18 B 4 O 33 formation was completed at 44 wt% B 2 O 3 instead of stoichiometric ratio of 13.17 wt% B 2 O 3. In other words, B 2 O 3 -rich liquid phase accelerated Al 18 B 4 O 33 crystallization. Al 18 B 4 O 33 particles were not acicular in shape when first formed, but they were fully acicular for the 44 wt% and the 54.1 wt% B 2 O 3 mixtures. Anorthite-based glass and CaO were selected to induce liquid phase sintering. CaO considerably improved densification to 95.4 % relative density at 1350 °C. Both glass and mullite also enhanced densification to 94.8 %. Epitaxial nucleation of mullite on Al 18 B 4 O 33 particles resulted in a solid solution as well. Dielectric, mechanical and thermal properties of the samples were investigated and evaluated for possible applications. [ABSTRACT FROM AUTHOR]

In this study, we designed four groups of A-substituted medium-entropy perovskites, synthesized (Ba 0.4 Sr 0.4 Ca 0.1 La 0.1)ZrO 3 , a non-equimolar medium-entropy perovskite, and studied its microstructural uniformity. The medium entropy of these perovskites imparts unique mechanical and thermal properties. Compared to pure BaZrO 3 , the cold moduli of rupture of the four samples improved by 164.29%, 121.22%, 91.49%, and 81.87%, respectively, and the relative density increased from 69.47% to over 90%. The thermal conductivities of these materials were lower than those of conventional low-thermal-conductivity perovskite materials, with a minimum value of 1.513 W/(m·K). The high strengths and low thermal conductivities of these novel perovskite materials could provide vast opportunities for various future applications. [ABSTRACT FROM AUTHOR]

In this study, according to the Dinger model, aqueous Si 3 N 4 slurries with a solid loading of 63 vol% and a viscosity lower than 1.0 Pa s were successfully prepared using two-grade Si 3 N 4 powders with D 50 = 7.2 μm and 9.4 μm as starting materials. These resulting slurries exhibited good rheological properties and suspension stability. Notably, the presence of β-Si 3 N 4 seeds existed in the starting materials effectively reduced the nucleation barrier by transforming homogeneous nucleation into heterogeneous nucleation. Consequently, it facilitated the reconstructive phase transformation of α-Si 3 N 4 to β-Si 3 N 4 , promoted the anisotropic growth of β-Si 3 N 4 nucleation, and resulted in the final formation of the bimodal microstructure. This unique microstructure significantly enhanced the mechanical properties of Si 3 N 4 ceramics, resulting in a high flexural strength of 1011.4 MPa and a fracture toughness of 14.8 MPa m1/2. These excellent properties were achieved through the combination of gelcasting and gas pressure sintering. Simultaneously, the Si 3 N 4 ceramics exhibited a low thermal conductivity of 47.7 W m−1 K−1, mainly owing to the low density of 95.3 %, the presence of low-thermal-conductivity silicate-based noncrystalline substances, and the possible existence of lattice oxygen in Si 3 N 4 crystals. [ABSTRACT FROM AUTHOR]

Polycrystalline diamond compact (PDC) with different grain sizes were fabricated and the multi-physical behaviors, including mechanical-, thermal-, and magnetic performances, and the microscopic features were examined to study the grain size dependence of wear behavior while cutting dense granite. The results showed that the coarse grade PDC had higher impact resistance and fracture toughness. However, the fine grade PDC had higher cobalt content, hardness and thermal resistance. Among these properties, the wear resistance changed the same way as thermal expansion properties proving the strong correlation. Moreover, the crack network caused by thermal mismatch, and the peeling/fracture of metallic phases and diamond promoted fracture wear and played the critical roles in the wear of coarse grade PDC. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of the influence of the sintering additive ratio on the microstructure evolution of silicon nitride (Si 3 N 4) ceramics, Si 3 N 4 ceramics were prepared by gas pressure sintering using different ratios of Y 2 O 3 /MgSiN 2 as additives. Varying the ratio of Y 2 O 3 /MgSiN 2 changed the composition of the liquid phase, thereby affecting the densification process and phase transformation rate of Si 3 N 4 ceramics, and ultimately changing their microstructure. The reduction in the Y 2 O 3 /MgSiN 2 ratio raised the N/O and Si/O ratios in the system, which increased the liquid phase viscosity. The Si 3 N 4 grain distribution varied from "normal to bimodal". In the case of increasing the proportion of MgSiN 2 and prolonging the sintering time, more of the glass phase evaporated, which reduced the content of the low thermal conductivity phase and increased the continuity of Si 3 N 4 /Si 3 N 4. Therefore, Si 3 N 4 ceramics with 1 wt% Y 2 O 3 and 5 wt% MgSiN 2 exhibited excellent properties after sintering at 1900 °C for 12 h, with thermal conductivity, bending strength, and fracture toughness of 106.7 Wm−1K−1, 776 MPa, and 11.66 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

Magnesium aluminate (MA) spinel has shown potential as a refractory material under harsh environments, such as high temperatures and frequent temperature variations. However, understanding the mechanical and thermal properties of MA spinel is a key step towards further improvement of MA spinel refractory materials in high-temperature fields. The formation of solid solution represents a prominent strategy to improve mechanical and thermal properties. The present study develops novel (1- x)MgAl 2 O 4 - x Mg 2 TiO 4 (0≤ x ≤ 0.1) solid solutions by single-step reaction sintering method using light-burned magnesia, reactive alumina, and as-prepared Mg 2 TiO 4 (M 2 T) powders. The effects of M 2 T content on the crystal structure, mechanical properties, and thermal properties of the MgAl 2 O 4 -Mg 2 TiO 4 solid solutions (MATss) were studied. Based on XRD, TEM, and HRTEM results, MATss were highly crystallized with a cubic spinel structure. Besides, the M 2 T addition facilitated the flexural strength, hardness, and elastic modulus in the MA spinel. Among these solid solutions, the x = 0.08 sample exhibited the highest flexural strength, hardness, and elastic modulus of 219.47 MPa, 19.99 GPa, and 270.2 GPa, respectively. M 2 T additive played a solid-solution strengthening role, which enhanced the inherent resistance to microstructural damage. Additionally, the x = 0.08 sample had the highest thermal conductivity and thermal diffusivity of 12.45 W/(m·K) and 7.98 mm2/s, respectively. In comparison with pure MA spinel, the x = 0.08 sample showed a lower thermal expansion coefficient (8.63 × 10-6 K-1 at 1550 °C). These excellent mechanical properties and exceptional thermal behavior enabled its widespread application in refractory materials. [ABSTRACT FROM AUTHOR]

Carbon-metal carbide composites are a novel family of materials with potential application in heat dissipation due to the lightness and thermal-mechanical properties. Within these composites, those of graphite-chromium carbide have been still few studied. Therefore, this research focuses on both the influence of the powder preparation method (mechanical mixing (MM) and colloidal synthesis (CS)) and the spark plasma sintering (SPS) temperature (1600, 1700, 1800, 1900 and 2000 °C) in the properties of the composite graphite-7 vol. Cr. Results indicate that the composites sintered from powders processed by CS exhibit better properties, which can be explained by the better dispersion of the chromium carbide, formed during the sintering process, in the matrix of composite. Apart from the powder preparation method, sintering temperature has influence on the properties of the composite: 1900 °C is the best in the case of the route CS + SPS, while 2000 °C is the best option in the route MM + SPS. The thermal conductivity in-plane is 1.75 times greater in the CS than in the MM route, which suggests a better performance in the composite processed by colloidal route in heat dissipation applications. [ABSTRACT FROM AUTHOR]

The porous SiC-Mullite porous ceramics with different pore size were prepared by SiC particles, kaolin, Al(OH) 3 , and flake graphite, V 2 O 5 and AlF 3 were used as mineralizers, the pore size was controllable by adjusting the size of flake graphite. Then the improved empirical formula and grey theory were used to study the effect of the change in pore size on the material properties. The results showed that with the increase of mean pore size from 1.1 μm to 8.5 μm, the cold modulus of rupture and cold crushing strength decreased by 20.8 MPa and 13.7 MPa, respectively. And the thermal conductivity increased from 1.213 W⋅m−1⋅K−1 to 1.721 W⋅m−1⋅K−1 at 800 °C. The <5 μm pores were helped enhance the strength and decreased the thermal conductivity. [ABSTRACT FROM AUTHOR]

In Part 1 of this study, we investigated the macrokinetic parameters and phase formation mechanism in the combustion front of Zr–Nb–B mixtures. In the second part, we produced consolidated samples of solid solutions NbB 2 -(0.100%)ZrB 2 by hot pressing the combustion-derived powders at 1900 °C. By measuring the crystallographic parameters, mechanical and thermophysical properties of the produced bulk samples, we obtained valuable insights into the behavior of the solid solutions. Our results pave the way for the application-specific fine-tuning of the mechanical properties and thermal conductivity of diboride solid solutions in the Zr–Nb–B system for ultra-high temperature applications. Our findings have significant implications for the development of advanced materials with outstanding performance in extreme environments. [ABSTRACT FROM AUTHOR]

Reactive Structural Materials (RSMs) are a new class of materials composed of two or more metallic materials with oxide-ceramic particles that are unable to ignite or explode under various types of loadings, such as thermal, mechanical, and electrical. This study aims to investigate the microstructure, thermal, physical and mechanical properties of the Al-Ni composites, as a type of RSMs, produced by mechanical alloying and subsequent hot pressing. In this research, the Al-Ni composites with various molar mass ratios of Al to Ni of 2:1, 1:1, and 1:3 were first produced. After determining the optimum molar mass ratio of Al to Ni concerning mechanical and thermal properties, Al-Ni composites were made by adding different amounts of CuO particles (2, 4, and 6 wt%), and their mechanical and thermal properties were determined. The thermal and mechanical results proved that the 1:1 molar mass ratio of Al to Ni in the Al-Ni composite exhibited optimal properties. The thermal properties of the Al-Ni-CuO composites showed that the general addition of CuO particles had a negative impact on the energy release of the Al-Ni composites. However, the combustion test showed that the presence of a low level of CuO particles (2 wt%) increased the reaction temperature from 1180 °C to 1368 °C. However, the higher content of CuO particles (4 and 6 wt%) reduced the reaction temperature of Al-Ni composites. Similar to the thermal properties, the mechanical tests proved the detrimental influence of CuO particles on the compressive strength and hardness values of Al-Ni composites. In-depth discussions on the affecting factors on the mechanical and thermal properties of the Al-Ni-CuO composites have been provided in this work. [ABSTRACT FROM AUTHOR]

Vanadium carbides (VC 1-x) exhibit stoichiometric flexibility due to the presence of various carbon vacancies, which significantly influence their fundamental physical properties. Despite this, a comprehensive understanding of how carbon vacancies affect the mechanical and thermal properties of vanadium carbides remains elusive. Previous research has primarily focused on stoichiometric VC and has yet to fully explore the impact of carbon vacancies. This study reveals that stoichiometric VC is less stable when compared to ordered substoichiometric VC 1-x and employs first-principles calculations to obtain thermodynamic, mechanical, and transport properties of VC 1-x. The ordered carbon vacancy leads to an increase in the V–V bond density and volume. Due to the anharmonic effect, the ordered carbon vacancy impairs heat capacity and thermal expansion. The hardness and toughness decrease with increasing carbon vacancy concentrations. The Boltzmann transport equation is used to calculate electrical and thermal transport properties, which shows that growing scattering effects reduce thermal transport capacity. The results provide accurate data support for vanadium carbide research and theoretical support for designing ultra-high temperature ceramic materials. [ABSTRACT FROM AUTHOR]

Rare-earth (RE) oxide-doped La 2 (Zr 0.7 Ce 0.3) 2 O 7 (LZC) has attracted great interest in thermal barrier coatings (TBCs) because of its lower thermal conductivity. However, studies on the laws governing the effect of different types of RE oxide doping on the performance of LZC ceramics are limited. Therefore, in this study, different types of RE (Sc, Y, Gd and Eu) doped LZC ceramic bulks have been prepared using solid phase reaction method. The effects of RE doping on the crystal structure, mechanical properties and thermal properties of the LZC ceramics were investigated. The results indicated that all five ceramics exhibited a single pyrochlore phase structure, whereas their lattice constants were reduced after doping, with (La 0.85 Sc 0.15) 2 (Zr 0.7 Ce 0.3) 2 O 7 having the lowest lattice constant. The effect of rare earth doping on the grain growth of LZC was not evident; however, it could significantly improve the hardness of LZC. In addition, doping with all four RE ions significantly reduced the thermal conductivity of the LZC ceramics, and the most significant reduction was observed for Gd3+ doping. [ABSTRACT FROM AUTHOR]

Dy 2 TiO 5 ceramics with small grain size range of 1.5–3 μm were successfully prepared by microwave sintering method. The phase composition, microstructure, thermal expansion, stability, corrosion resistance and neutron absorption properties of Dy 2 TiO 5 ceramics were investigated. The results show that Dy 2 TiO 5 ceramics possess high mechanical properties due to the small grain size, with a microhardness of 12.26 GPa. The addition of Mo significantly reduces the thermal expansion phenomenon of the sample. The oxide film formed on the surface of the Dy 2 TiO 5 ceramic enhances its excellent corrosion resistance. In addition, the Dy 2 TiO 5 ceramic shows excellent neutron absorption with 87.34% neutron absorption and over 94% thermal neutron absorption in 8 cm thick particles. [ABSTRACT FROM AUTHOR]

The porous silicon carbide ceramics with multilevel directional pores were prepared by chemical vapor infiltration (CVI) combined with sacrificial template method. Carbon fiber preform with specific structure was used as template, and silicon carbide was deposited by CVI process. Then, the carbon fiber template was oxidized and removed, so that the porous silicon carbide ceramics were obtained. The influence of deposition time on pore structure, mechanical properties and thermal properties was studied. Compared with the traditional pore-making process, the pores formed by sacrificial template method are more regular, which brings excellent mechanical properties and thermal insulation properties. The porosity and flexural strength of the sample deposited for 72 h can reach 66.00% and 67.52 MPa, respectively, the thermal conductivity can be kept below 1 W/(m·K) from room temperature to 1200 °C. [ABSTRACT FROM AUTHOR]

Good fracture toughness can prolong the service life of thermal barrier coatings under thermomechanical loading. Yttria-stabilised zirconia (YSZ) and other novel thermal barrier coatings have low fracture toughness and are thus prone to spalling failure. High-entropy ceramics can provide coatings with excellent mechanical properties. In this study, (ZrYTaErTi)O composites were prepared via a solid-state reaction method based on the concept of high-entropy ceramics. The high-temperature phase stability and mechanical properties of the material were characterised and analysed by X-ray diffraction (XRD) and microindentation tests. The results showed that (Zr 0.544 Y 0.114 Ta 0.114 Er 0.114 Ti 0.114)O had the best fracture toughness, which is 1.5 times higher than that of YSZ, of the ceramics prepared with different composition ratios. At the same time, the effects of grain size and the introduction of a second phase on the fracture toughness of the composites were analysed. This study provides guidance for future research on improving the mechanical properties of novel thermal barrier coating materials. [ABSTRACT FROM AUTHOR]

In this study, La 1- x Nd x MgAl 11- x Sc x O 19 (x = 0.1, 0.2, 0.3; abbreviated as LNMAS-1, 2, 3) coatings which are supposed to possess better properties than LaMgAl 11 O 19 (LMA) were plasma-sprayed and their high-temperature performance were comparatively investigated. Results show that addition of Nd3+ and Sc3+ as dopants to LMA endows corresponding coatings with reduced thermal conductivity and enhanced thermal expansion coefficient, while maintaining advantageous phase stability, although still being subjected to amorphization in plasma flame and following crystallization upon high-temperature service. Furthermore, the doping could cause adherence increasing between topcoat/bondcoat, benefiting from improved melting condition, especially in LNMAS-2 and LNMAS-3 coatings, which is related to the specific powder morphology and lowered melting point. During exposure to 1350°C, mechanical performance and structure integrity of doped free-standing LNMAS coatings can be well preserved even after 400 h aging. In thermal cyclic fatigue test, LNMAS-2 and LNMAS-3 coatings undertake thermal cycling lifetime of ∼181 and 191 cycles at 1100°C, respectively, 40% durable than that of LMA coating. These preliminary results suggest that LNMAS-2, 3 might be promising candidates for advanced thermal barrier coating applications. [ABSTRACT FROM AUTHOR]

Nanocrystalline ZrC coated graphite was synthesized in mixed molten salt system, and the effect of different zirconium sources and reaction temperature on its synthesis was studied. The effects of nanocrystalline ZrC coated graphite on the microstructure, thermal shock resistance and cold mechanical properties of low-carbon Al 2 O 3 –C refractories in different atmospheres were studied. The results indicated that nanocrystalline ZrC coated graphite synthesized by Zr powder had a more uniform coating structure than ZrO 2 as a zirconium source, and increasing the reaction temperature was beneficial for the synthesis of ZrC. The sample with nanocrystalline ZrC coated graphite fired in nitrogen atmosphere had better mechanical properties, the cold modulus of rupture was 15.67% and 50.67% higher than that of the samples fired under argon atmosphere and carbon-embedded atmosphere, respectively. Meanwhile, Sialon played a significant role in improving the mechanical properties of the samples after thermal shock. In addition, the treatment in argon or carbon-embedded atmosphere was beneficial in improving the thermal shock resistance of the samples. [ABSTRACT FROM AUTHOR]

Recently, 3D-printed metamaterials have undergone rapid development; however, the preparation of most metamaterials requires the use of resin-based materials. Thus, multifunctional ceramic metamaterials, especially the introduction of other materials to optimize thermal metamaterials, must be investigated. Here, lattice structures with different units were prepared via stereolithography appearance (SLA) process. The SiC-reinforced phase was obtained by applying chemical vapor infiltration (CVI). The effects of the SiC content and unit type on the mechanical and thermal properties were studied. The results showed that the thermal expansion coefficient (CTE) of the structures decreased by 50% after one CVI cycle. Among the structures, the wave-shaped torsion flexible design reduced the instantaneous CTE to 3.67 × 10−6 K−1 at 150 °C, lower than that for the other structures. More importantly, the lattice structures strengthened with SiC whiskers exhibited outstanding mechanical performance. The compressive strengths of the triangular structure after sintering, one cycle of CVI, two cycles of CVI, and the introduction of SiC whiskers after one cycle of CVI were 3.23, 10.51, 27.38, and 39.4 MPa, respectively. The introduction of SiC increased the compressive strength of the structure by nearly 10 times, satisfying the requirements of high strength and low CTE. Thus, this method can considerably improve the thermal and mechanical properties of 3D-printed ceramic metamaterials, laying the foundation for an in-depth study on the design and preparation of thermal metamaterials. [ABSTRACT FROM AUTHOR]

MgO–Al 2 O 3 –SiO 2 composite ceramics were prepared by spark plasma sintering (SPS). In addition, phase composition, microstructure, mechanical properties, and thermal shock properties have been systematically characterized. Introduction of Al 2 O 3 and SiO 2 significantly increased mechanical properties and thermal shock resistance of these composite ceramics. MgO–Al 2 O 3 –SiO 2 composite ceramics prepared by spark plasma sintering (SPS) exhibited fine grain size. Reduced grain size may result in extraordinary properties. Experimental results showed that MgO–Al 2 O 3 –SiO 2 composite ceramics had the highest flexural strength and hardness among all studied ceramics of 269.6 ± 9.22 MPa and 12.51 ± 0.29 GPa, respectively. Moreover, MgO–Al 2 O 3 –SiO 2 composites can reach 16 thermal cycle times. This shows that it is feasible to prepare high-performance MgO composite ceramics by SPS. Furthermore, introduction of Al 2 O 3 and SiO 2 is effective method to improve mechanical properties and thermal shock resistance of MgO composite ceramics. [ABSTRACT FROM AUTHOR]

The mining industry produces a large amount of stone waste and tailings, which poses a threat to the environment. Dumping is the most common means of disposing of this industrial waste, contributing to soil degradation and water pollution with the acquisition of valuable land. Fortunately, it can be recycled in a variety of technologies, including the promising geopolymerization technology, which turns waste into value. This review paper presents recent advances in the production of mine tailings-based geopolymer composites from industrial waste as a potential sustainable building material. This article also provides in-depth studies on the behaviors and characteristics of mine tailings composites utilized in geopolymer production, such as physical properties, mechanical properties, durability properties, microstructural properties, thermal properties, leaching behavior, and potential applications. Besides, study developments are moving towards a comprehensive understanding of the environmental footprints and economic benefits of mine tailings-based geopolymer composites for building applications utilizing mine tailings as suitable concrete material. This review paper also highlights knowledge gaps that must be overcome to progress mine tailings composites for geopolymers, as well as future study opportunities based on prior research and existing challenges. [ABSTRACT FROM AUTHOR]

In this study, the influence of additional oxygen on the structural, mechanical, thermal, and corrosive properties of TiN coatings was investigated. A progressive change occurred in the structure from cubic TiN, Ti 0.50 O 0.11 N 0.39 , Ti 0.46 O 0.15 N 0.39 , and Ti 0.44 O 0.28 N 0.28 to mixed cubic and monoclinic Ti 0.39 O 0.40 N 0.21 , and finally to tetragonal TiO 2. Doping oxygen into TiN led to a significant change in hardness owing to the solid solution strengthening effect and the formation of ionic bonds and oxide phases. Ti 0.46 O 0.15 N 0.39 exhibited the highest hardness of ∼28.8 GPa. The addition of oxygen weakened the thermal stability of the TiN coating owing to the production of more oxides during annealing. After oxidation at 600 °C for 10 h, the Ti 0.50 O 0.11 N 0.39 coating with an oxide thickness of ∼0.86 μm exhibited an excellent oxidation resistance. The TiO 2 coating was not oxidized, thereby maintaining the initial morphology. In addition, the corrosion resistances of the TiON coatings were closely related to the oxygen content, where the low oxygen content compound Ti 0.50 O 0.11 N 0.39 exhibited the best corrosion resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

BaZrO 3 with the ABO 3 perovskite structure can be doped at the A or B sites to obtain the corresponding properties. In this study, BaZrO 3 was doped with Ca2+, Sr2+, Ti4+, and Ce4+. The structure, phase composition, and mechanical and thermal properties of the composites were investigated. The sintered Ba 1-x Ca x ZrO 3 samples with x = 0.2 and 0.4 exhibited relatively superior comprehensive behaviours; the cold modulus of rupture was increased by 127.36% and 134.59%, while that for BaZr 0 · 8 Ti 0 · 2 O 3 and BaZr 0 · 8 Ce 0 · 2 O 3 was increased by 99.30% and 112.37%, respectively. Further increases in strength and density were obtained in the Ba 0 · 8 Ca 0 · 2 Zr 0 · 8 Ti 0 · 2 O 3 and Ba 0 · 6 Ca 0 · 4 Zr 0 · 8 Ti 0 · 2 O 3 co-doped samples, and the corresponding apparent porosities were greatly decreased from 30.6% to below 1.0%. The thermal conductivities of the doped samples were generally low, achieving a minimum of 0.361 W/(m·K). The combination of high strength and low thermal conductivity demonstrate the significant application potential of BaZrO 3 -based composite materials. [ABSTRACT FROM AUTHOR]

SiAlON ceramics are primarily employed in ceramic cutting tools, which exploit their stable physical properties in high-temperature cutting environments due to their excellent mechanical properties. Here, Yb/Y-co-doped SiAlON ceramics are prepared by adding Yb and Y rare-earth (RE) ions in the RE x Si 12-(m + n) Al m + n O n N 16- n (m = 0.4, n = 1.0) composition. Yb 2 O 3 , the RE oxide, is the main sintering additive. For RE x composition design with (Yb 1- y + Y y) x , Yb 2 O 3 is replaced by Y 2 O 3 (y = 0.00, 0.25, 0.50, 0.75, 1.00). While Yb 2 O 3 has excellent high-temperature stability, it is limited by its microstructural characteristics, that is, the β-SiAlON morphology and limited fracture toughness due to the small cation sizes. Thus, the changes in the above properties are investigated for various Y 2 O 3 additive contents substituting for Yb 2 O 3. The average grain width decreases, and the equiaxed β-SiAlON grains are elongated with increasing Y 2 O 3 content. Regarding the mechanical properties, the hardness and fracture toughness are evaluated using the indentation fracture method. The hardness decreases with increasing Y 2 O 3 content; however, the fracture toughness exhibits a significant increase (∼53.6%) from 4.6 to 7.0 MPa⋅m1/2. Regarding crack propagation, intergranular fracture is mainly observed in the Yb/Y-co-doped SiAlON ceramics, whereas transgranular fracture is primarily observed in the Yb-single-doped SiAlON ceramic. Y 2 O 3 substitution increases the α/β-SiAlON phase ratio, and the grain boundary phase exhibits increasing vitrification with increasing Y 2 O 3 content. Moreover, the thermal properties of the Yb/Y-co-doped compositions are analyzed and discussed regarding intrinsic properties such as phonon scattering. The microstructural characteristics and improved fracture toughness derived from the Yb/Y-co-doped system designed in this study suggest considerable potential for the future composition design of ceramic cutting tools. [ABSTRACT FROM AUTHOR]

A series of (Ti 0.5 Nb 0.5)C-x wt.% SiC (x = 0, 5, 10, 20) composites were prepared by spark plasma sintering. Dense microstructures with well‐dispersed SiC particles were obtained for all composites. With the increment of SiC content, the Vickers hardness, Young's modulus and fracture toughness increase monotonically. An optimized flexural strength of 706 MPa was achieved in (Ti 0.5 Nb 0.5)C-5 wt.%SiC composite. (Ti 0.5 Nb 0.5)C-20 wt%SiC composite exhibits the highest fracture toughness of 6.8 MPa m1/2. The crack deflections and the suppression of grain growth were the main strengthening and toughening mechanisms. Besides, (Ti 0.5 Nb 0.5)C-20 wt%SiC composite exhibit the highest thermal conductivity of 45 W/m·K at 800 °C. [ABSTRACT FROM AUTHOR]

In this study, Mo–SiBCN metal-ceramic composites with or without sintering additives of MgO, Al 2 O 3 , and SiO 2 were fabricated by hot-press sintering at 1800 °C/60 MPa/30 min to investigate their phase composition, microstructural evolution, mechanical properties, thermophysical properties and thermal shock resistance. With the increase in amorphous SiBCN, a competition of reaction products between Mo and SiBCN as Mo 3 Si → Mo 3 Si + Mo 5 Si 3 + MoSi 2 → Mo 4.8 Si 3 C 0.6 + Mo 5 Si 3 + MoSi 2 → Mo 4.8 Si 3 C 0.6 were detected. Meanwhile, the bulk density, elastic modulus and bending strength of the Mo–SiBCN composites gradually decrease with increasing SiBCN content, but their hardness first increases and subsequently decreases, reaching the highest value of 14.46 ± 0.43 GPa with 30 vol% SiBCN incorporation. Due to the oxide additives that promoted the sintering of composites, the bending strength and hardness of Mo–SiBCN composites with the additives increased 3–6 times. The residual bending strength of the Mo–SiBCN composites after thermal shock at 900 °C and 1600 °C decreased with increasing SiBCN content, while for the composites with 10–20 vol% SiBCN, the residual bending strength increased by 140–147%. [ABSTRACT FROM AUTHOR]

Transition metal carbides are candidates for high-temperature structural ceramics because of their high melting point, high hardness, and high strength. However, one challenge is overcoming their high intrinsic brittleness. In this study, we investigated a new class of (Fe, Mo, W) 6 C carbides, which have three Wyckoff positions for metallic atoms (16d, 32e, and 48f) and one Wyckoff position for carbon (16c). These different Wyckoff positions provide a great opportunity to optimize the mechanical properties by the partial replacement of atoms at each Wyckoff position to obtain high-entropy carbides. The current results show that the phonon spectra have no imaginary frequency when Fe occupies the 16d or 32e positions, but a soft mode is observed when Fe occupies 48f. (Fe, Mo, W) 6 C η carbides have a higher fracture toughness compared with those of M 3 C and MC carbides owing to their low carbon content (14.3 at.%). The mechanical anisotropy of (Fe, Mo, W) 6 C is weak, which is beneficial for increasing the damage tolerance. The thermal expansion coefficients of the (Fe, Mo, W) 6 C η carbides are predicted to be approximately (8.5–9.5) × 10−6 K−1 at 1400 K. [ABSTRACT FROM AUTHOR]

In this study, a high-entropy approach was employed to design a new single-phase A 2 B 2 O 7 oxide for thermal insulation applications. Multicomponent high-entropy oxides, containing up to seven different cations, were successfully synthesized in a single defective fluorite structure. We observed that the incorporation of the functional cation, Zn2+, effectively blocked the heat radiation phenomenon by reducing the photon mean free path, and further reduced the high-temperature thermal conductivity owing to the larger free carrier concentration originated from the large number of oxygen vacancies. Although a large concentration of Zn2+ caused a slight reduction in thermal expansion, this study suggests that functional cations can be easily incorporated; thus, expanding the material diversity beyond the typical doping levels to develop new thermal barrier materials. [ABSTRACT FROM AUTHOR]

CeO 2 and Sc 2 O 3 co-stabilized ZrO 2 ceramics have attracted much attention as potential thermal barrier coatings (TBCs) materials for applications above 1300 °C. In this study, a series of Sc 0.04 Ce x Zr 0.96-x O 1.98 (SCZ, x = 0.08, 0.10, 0.12, 0.16) ceramic materials were synthesized with the solid-state method and their phase stability, microstructures and thermo-physical properties were systemically investigated by x-ray diffraction (XRD), Raman spectra, field emission scanning electron microscopy (SEM), thermal dilatometer, laser flash apparatus (LFA), and Vickers hardness tester. The results showed that Sc 0.04 Ce 0.12 Zr 0.84 O 1.98 (4S12CZ) and Sc 0.04 Ce 0.16 Zr 0.80 O 1.98 (4S16CZ) ceramic materials still maintained stable tetragonal phase structure after 100 h high temperature treatment at 1500 °C. SCZ had a high thermal expansion coefficient (TEC), low thermal conductivity, and high fracture toughness. The TEC of the ceramics increased with CeO 2 addition because lattice energy reduced with increasing substitution of Zr4+ by bigger Ce4+ while thermal conductivity decreased due to the increase of lattice distortion. Compared with 4S12CZ, 4S16CZ exhibited a higher fracture toughness of 6.48 ± 0.04 MPa m1/2 and showed the better anti-sintering property. Besides, the thermal conductivity, TEC and thermal cycling lifetime of 4S16CZ were optimal. The comprehensive performance of 4S16CZ suggested it could be explored as a promising TBC material for high-temperature application. [ABSTRACT FROM AUTHOR]

WC+Co+graphene platelet (GPL) composites were processed by sintering at 1380 °C in argon and the influence of GPLs addition on the microstructure development as well as mechanical, tribological and thermal properties was investigated. A homogeneous distribution of GPLs could be achieved in the systems which resulted in a decreased WC grain size and an increased density for the systems with 0.35 vol% and 0.70 vol% GPLs content. With respect to the mechanical properties, the optimal GPLs content was 0.70 vol%, which led to the highest hardness of 1784.73 kgf/mm2, the highest bending strength of 2198.6 MPa and a high indentation crack resistance of 11.06 MPa·m1/2. The GPLs clusters in combination with porous regions acted as defects/fracture points. Further, the main toughening mechanisms included crack deflection, crack bridging and crack branching. The composites demonstrated improved tribological properties in comparison to the WC+Co system. The friction coefficient and wear rate decrease from 0.407 to 0.343 and 2.67 × 10−6 mm3 (m·N)−1 to 1.38 × 10−6 mm3 (m·N)−1, respectively. It is attributed to the formation of tribofilm and enhanced mechanical properties of composites. The thermal conductivity of the composites was significantly enhanced from 85.2 W/(m·K) to 110.8 W/(m·K) on increasing the GPLs content. [ABSTRACT FROM AUTHOR]

In this research, reactive pulsed dc magnetron sputtering with different Ar/N 2 gas flow ratios was used to deposit CrN films with three growth structures on Si substrates. The phase structure, morphology, mechanical properties, thermal fracture properties, and oxidation behavior of films were studied. The surface roughness, residual stress, preferred orientation, and hardness were affected by the gas flow ratio. The film with (200) preferred orientation and zone II structure performed the best. The surface roughness increased to 6 nm with time when the films fractured at 500 °C. The Cr interlayer oxidation caused by oxygen diffusion through grain boundaries and fracture accelerated degradation of CrN films at higher temperatures. A dense microstructure is favorable for preventing coating oxidation. • The sputtering gas ratio could affect surface morphology, roughness, and deposition rate •The residual stress changed from compressive to tensile with film thickness, a film with (200) preferred orientation and zone II structure performed the best •The Cr interlayer oxidation accelerated the degradation of CrN films, a dense microstructure is favorable for preventing coating oxidation [ABSTRACT FROM AUTHOR]

This study investigates the mechanical properties and microstructure evolution of Al 2 O 3 -4J42 joints brazed using Ag–Cu–Ti (ACT) and Ag–Cu–Ti/Cu/Ag–Cu (ACTCA) fillers during thermal cycling from 0 °C to 500 °C. The reaction products between Al 2 O 3 and brazing filler of these two types of joints are mostly composed of Ti–O compounds, Ti 4 Cu 2 O and Al-based compounds. Brittle intermetallic compounds (IMCs) are observed in ACT joints, but not found in ACTCA joints. The reaction layer in ACT joints becomes thinner and discontinuous with thermal cycles, while that in the ACTCA joints hardly changes. Besides, the stress-induced cracks occur within the Al 2 O 3 ceramic near the Al 2 O 3 /filler interface in the ACT joints, but no crack is found in the ACTCA joints. The mechanical tests show that the ACTCA joints maintain at least 217%, 154% and 144% higher shear strength than the ACT joints at 0, 10 and 20 thermal cycles, respectively. The Cu interlayer with low yield strength releases stress through plastic deformation, meanwhile acts as a barrier to prevent elements diffusion and the formation of the brittle IMCs, thus improving the mechanical properties and thermal cycling stability of the joints. [ABSTRACT FROM AUTHOR]

LaMgAl 11 O 19 -type magnetoplumbite holds great promise to be used above 1300 °C as thermal barrier coatings (TBCs), but its practical application has been restricted because of inferior thermophysical properties. Herein, we focus on optimizing the thermophysical properties of LaMgAl 11 O 19 by simultaneously substituting La3+ and Al3+ ions with Nd3+ and Sc3+ ions, respectively. Results show that the effects of co-substitution on reducing thermal conductivity are pronounced. The thermal conductivities of La 1- x Nd x MgAl 11- x Sc x O 19 (x = 0, 0.1, 0.2, 0.3) ceramics decrease progressively with dopant concentration and a lowest thermal conductivity of 2.04 W/(m·K) is achieved with x = 0.3 at 1000 °C, which is a value superior to pure LMA and even lower than YSZ. The mechanisms behind the lowered thermal conductivity are investigated. Increase of the thermal expansion coefficient is also realized (8.53 × 10−6 K−1 for pure LMA, 9.07 × 10−6 K−1 for x = 0.3, 1300 °C). Most importantly, Nd3+ and Sc3+ combination doping indeed facilitates mechanical properties of La 1- x Nd x MgAl 11- x Sc x O 19 solid solutions as well. It should be noted that Sc3+ doping at Al3+ site plays more effective role in improving thermal properties than Nd3+ does at La3+ site. This work provides a path to simultaneously integrate low thermal conductivity, good phase stability, moderate thermal expansion behavior and excellent mechanical properties on LMA for the next generation TBCs. [ABSTRACT FROM AUTHOR]

MgO-based refractories have been regarded as ideal linings for various furnaces owing to high refractoriness and excellent corrosion resistance to basic slag. However, thermal shock damage resulting from poor thermal shock resistance (TSR) of magnesia is the common failing. The present work aimed at improving TSR of magnesia aggregates by introducing microscale monoclinic ZrO 2. The results showed that the ZrO 2 added could increase cation vacancy concentration and inhibit abnormal growth of MgO grains, which therefore enhanced densification of the specimens. However, when the ZrO 2 amount exceeded 15 wt%, densification decreased slightly due to agglomeration of ZrO 2 and formation of more microcracks at the MgO grain boundaries. With increasing ZrO 2 content, although the flexural strength degraded, the fracture toughness increased constantly because of the toughening effects of crack deflection and crack branching. Besides, although the addition of ZrO 2 decreased the thermal conductivity, TSR of the specimens was significantly improved with increasing ZrO 2 content due to the increase in toughness and decrease in strength, thermal expansion coefficient as well as Young's modulus. After thermal shock tests, 15 wt% ZrO 2 containing specimen exhibited the highest TSR, whose residual strength ratio was about triple of that of the pure magnesia specimen. However, further increasing ZrO 2 content to 20 wt% reduced the TSR attributing to the spalling of intergranular ZrO 2 agglomerations. [ABSTRACT FROM AUTHOR]

Self-propagating high-temperature synthesis (SHS) from elements in combination with high-energy ball milling of the reaction mixture enabled the production of powdered (Ta 1-х Zr х)C and (Ta 1-х Hf х)C solid solutions with various stoichiometry and average particle size d 50 = 9 μm. Hot pressing (HP) was used for powders consolidation. All samples were found to be single-phase ones with lattice parameters following a linear function of the solid solution composition. The resulting dense samples of (Ta 1-х Zr х)C and (Ta 1-х Hf х)C solid solutions showed a notable growth of hardness and Young's modulus in comparison with ТаС carbide. The solid solution strengthening effect involving increase mechanical properties with growing content of Zr and Hf was confirmed. Temperature dependence of heat capacity, thermal diffusivity, thermal conductivity, and electric resistance was measured. Both Zr-and Hf-doped carbides showed high resistance to plasma torch impact at a temperature up to 3000°С. The high resistance towards ultra-high-temperature oxidation and erosion is provided by as-forming oxycarbide layers with high adhesion to the carbide matrix. [ABSTRACT FROM AUTHOR]

The management of thermal conductivity is of significant scientific interest, particularly for thermal barrier coatings (TBCs). Multifarious strategies have been used to regulate heat transportation, but it is hard to achieve limit thermal conductivity at elevated temperatures. A systematical investigation of weberite (La 1-x Gd x) 3 NbO 7 was thus performed, and multiphonon scattering mechanisms were introduced to achieve limit thermal conductivity (0.92 W m−1 K−1). Phonon point defect scattering process accounted for thermal conductivity reduction at low temperatures. Additionally, lattice softening strongly contributed to the reduction of high-temperature thermal conductivity, and solid and stiff chemical bonds were beneficial for inhibiting thermal radiative conductivity. A novel strategy was presented to modify thermal transportation property of weberite RE 3 NbO 7 ceramics. Also, the hardness, toughness, and modulus were improved to promote engineering applications of weberite RE 3 NbO 7. This study also illuminates novel paths for thermal management and mechanical properties manipulation of TBCs, thermoelectric materials, and microelectronics. [ABSTRACT FROM AUTHOR]

Silicon nitride (Si 3 N 4) ceramics with magnesium silicon nitride (MgSiN 2) and Y 2 O 3 as sintering additives were prepared by the gas-pressure sintering method. By changing the contents of MgSiN 2 and Y 2 O 3 in the range of 7–9 mol% and the proportion of MgSiN 2 in the sintering additives, the effect of the MgSiN 2 and Y 2 O 3 additives on the combination properties (mainly include thermal conductivity, mechanical and dielectric properties) and microstructure of the Si 3 N 4 ceramics was comprehensively analyzed to explore the accurate composition of sintering additives for manufacturing Si 3 N 4 ceramics substrate. The results showed that the amount and combinations of MgSiN 2 and Y 2 O 3 significantly affected the grain boundary composition, lattice oxygen, and grain size of the Si 3 N 4 ceramics. This was important for determining the thermal conductivity, mechanical and dielectric properties of the Si 3 N 4 ceramics. Compared with the previous most research focused only on how to acquire high thermal conductivity through long-term heat preservation at high temperature, this work fully demonstrated the effect of the composite sintering additives containing non-oxide on the combination properties (thermal conductivity, mechanical and dielectric properties) of Si 3 N 4 ceramic substrate. [ABSTRACT FROM AUTHOR]

The anisotropic elastic, thermal properties and electronic structures of ternary layered transition metal borides M 2 AlB 2 (where M = Fe, Cr, and Mn) were analysed using first-principles calculations and the Debye quasi-harmonic approximation. There was a good agreement between our calculated lattice constants and previous experimental and theoretical results. Our calculated thermodynamic stability parameters demonstrated that these borides had stable structures. Mn 2 AlB 2 was the most incompressible material, while Cr 2 AlB 2 was more rigid and a transversely resistant deformed material. The anisotropy of elasticity of the compounds was also estimated. They had different anisotropic elastic properties. The chemical bonding of the compounds primarily involved mixed covalent-metallic interactions. Covalent bonds were present between the boron and metal atoms. The M-M and B-B bond lengths were the longest and shortest in these compounds, respectively, and the bond strength in Fe 2 AlB 2 was stronger. The anisotropic linear thermal expansion coefficients of these materials were also calculated. The thermal expansion in the [001] direction was the largest relative to the other two directions. [ABSTRACT FROM AUTHOR]

MgAl 2 O 4 ceramics with high porosity and performance were fabricated via foam gel casting at 1673–1823 K using MgAl 2 O 4 as the raw material and a small amount of V 2 O 5 (0.25 wt%) as a sintering additive. The variations in the physical properties of the final porous MgAl 2 O 4 samples at ambient temperature demonstrated that their flexural, compressive, and specific strength increased with the addition of a small amount of V 2 O 5 as a sintering aid. However, the thermal insulation properties of the as-fabricated MgAl 2 O 4 ceramics exhibited an inverse tendency. A porous MgAl 2 O 4 ceramic containing 0.25 wt% of V 2 O 5 and fired at 1823 K had flexural and specific strength values of 4.2 MPa and 14.0 (MPa cm3)/g, respectively, representing improvements over those reported in the literature at a similar porosity (72.0%). Moreover, a low thermal conductivity of approximately 0.24 W/(m·K) was measured at 473 K, which may be attributed to the relatively high porosity and high proportion of small pores with diameters less than 50 μm. [ABSTRACT FROM AUTHOR]

In this work, carbon nanotubes (CNTs) were introduced on the pyrolytic carbon (PyC) interface via chemical vapor deposition (CVD) in order to improve the thermal conductivity and mechanical properties of SiC f / SiC composites. The results showed that three major parameters of CVD (a.k.a the deposition temperature, volume fraction of C 2 H 4 and deposition duration) strongly affected the nature of CNTs, as well as the thermal conductivity and mechanical properties of SiC f / SiC composites. The optimal parameters of CVD were found to be 800 °C, 15 vol% C 2 H 4 and 10-30 min. The thermal conductivity and mechanical properties of SiC f / SiC composites were enhanced by the addition of CNTs. However, the excessive deposition of CNTs provoked the formation of pores in the matrix, resulting in the reduction of the thermal conductivity and mechanical properties. The deposition of 5.8 vol % CNTs (corresponding to 20 min CVD deposition) was found to be the best condition to improve the thermal conductivity and mechanical properties of SiC f / SiC. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotube (MWCNT)-reinforced Al 2 O 3 -matrix nanocomposites were obtained by wet ball milling composite powders and spark plasma sintering. The mechanical and thermal properties of the nanocomposites with five different MWCNT concentrations from 0 to 2.0 wt% were studied. Results show that the matrix grain sizes of the composites decreased after MWCNT addition. The hardness, bending strength, and fracture toughness of 0.5 wt% MWCNT nanocomposite are the highest, which are 35.7%, 55%, and 182% higher than those of monolithic alumina, respectively. Errors of fracture toughness values obtained by the single-edge notch beam method are significantly smaller than those measured by the direct crack measurement method. With the addition of MWCNTs, the thermal conductivity of the nanocomposites decreases gradually, reaching the minimum of 12 W/mK in 2.0 wt% MWCNT composite at 300 °C. The thermal conductivity decreased owing to the agglomeration of MWCNTs and changes in the porosity and grain size of the composite matrix. No distinct difference is observed in thermal expansion behaviours between the nanocomposites and monolithic Al 2 O 3 owing to the low content of MWCNTs. [ABSTRACT FROM AUTHOR]

Wood gains much attention owing to its unique characters such as cellular pore structures, low density etc. Wood-derived carbides have great potential applications as the high-temperature filters for gas or liquid, catalyst carrier, fluid/gas reservoir devices, biocatalyst supports, etc. In this paper, we review recent progress in comprehensively understanding the processing techniques, properties and applications of wood-derived carbides. The key techniques for producing wood-derived carbides involves the infiltration techniques which are categorized into six parts (slurry infiltration, polymer precursor infiltration, melting infiltration, molten salt infiltration, sol-gel infiltration, and chemical or physical vapor infiltration). The advantages and disadvantages of these techniques are discussed in details, and the according solutions for solving the problems of each technique are further proposed. The infiltration kinetics of processing carbides are also discussed in details. The investigated properties of wood-derived carbides are summarized, which includes the mechanical properties and thermal properties. The potential applications of wood-derived carbides are explored, along with an overview of the existing challenges and practical limitations. In the end, we provide future perspectives to highlight the future directions of research in this growing area. [ABSTRACT FROM AUTHOR]

In order to study the variation of rare earth oxides during thermal failure of thermal barrier coatings, Eu2O3-doped YSZ coatings with 0.5 mol%, 1.0 mol% and 1.5 mol% were prepared by explosive spraying. SEM, XRD, EDS and microhardness tester were used to analyze the effect of different rare earth oxide doping content on the morphology, composition and mechanical properties of the coatings. The results showed that with the increase of rare earth oxide doping content, the porosity of the coatings decreased, and the microhardness and fracture toughness increased. When the doping amount of rare earth oxide is 1.0 mol%, the bonding strength and thermal cycle times of the coating are the highest, 33.4 Mpa and 185 times respectively. With the increase of the doping amount of rare earth, the luminous intensity of the sprayed coating increases. After thermal shock test, the luminous intensity of Eu2O3-doped YSZ coatings at 592 and 608 nm decreased to a certain extent. [ABSTRACT FROM AUTHOR]

To improve the mechanical properties and thermal shock resistance of zirconia toughened alumina (ZTA) composites, barium carbonate (BaCO 3) was added to yttria-stabilized zirconia (YSZ) and Al 2 O 3 powders to form ZTA/Ba-β-Al 2 O 3 composites, which were prepared by a solid-state reactive sintering method. As BaCO 3 content increased, more Ba-β-Al 2 O 3 was formed, resulting in the decreases in relative density and Vickers hardness. The fracture toughness was enhanced with increasing BaCO 3 content and reached a peak at 4 wt% BaCO 3. The improved fracture toughness is the result of synergistic toughening effects of martensitic transformation of ZrO 2 and crack deflection/bridging. After thermal shock tests, the residual strength of ZTA/Ba-β-Al 2 O 3 composites was higher than that of ZTA. The improvement in thermal shock resistance is mainly ascribed to the formation of elongated Ba-β-Al 2 O 3 with a hexagonal structure, which can dissipate the energy associated with crack propagation during thermal shock. [ABSTRACT FROM AUTHOR]

To prevent porous Si 3 N 4 ceramics from absorbing moisture in practical application, a dense SiC NWs/α-Si 3 N 4 composite coating was fabricated using the two-step technology involving slurry and liquid infiltration method. The results revealed that the SiC NWs not only can promote densification sintering of the coating but also can reduce thickness of the coating effectively due to the block effect of the SiC NWs. Furthermore, the SiC NWs in the coating had a good interfacial bonding with α-Si 3 N 4 matrix, meanwhile the toughening effects of the SiC NWs involving crack deflection, crack branching, SiC NWs bridging and pullout, also presented during mechanical damage. The strengthening and toughening mechanisms of the SiC NWs not only enhanced mechanical properties of the coating but also raised significantly critical crack size (L), thereby which made the coating have a good ability for thermal shock resistance. After thermal shock at ΔT = 1000 °C for 15 times, water absorption of the coated porous Si 3 N 4 ceramics increased only to 7.21% from 4.54%, and its residual strength ratio was up to 83.4%. More importantly, the coating exhibited an ability for crack healing during thermal shock testing. All those above results indicated that as-prepared SiC NWs/α-Si 3 N 4 composite coating can meet the applied requirements in long-term extreme conditions. [ABSTRACT FROM AUTHOR]

In this study, Li–Al–Si composites with K 2 O–B 2 O 3 –SiO 2 (KBS) glass were synthesized by traditional solid-state method, and the phase composition, microstructure, sintering behavior as well as properties were systematically investigated. The specimen with 4 wt % Al 2 O 3 sintered at 1020 °C exhibited a high thermal conductivity of 10.46 W/(mK) and a flexural strength of 180.23 MPa. The sintering temperature was reduced from 1020 °C to 900 °C using KBS glass frits as sintering additives. The sample with 2.0 wt % KBS, sintered at 900 °C for 2 h, possessed a relatively high thermal conductivity of 9.83 W/(mK), a high flexural strength of 215.09 MPa, and a low dielectric constant of 6.24, thus demonstrating its potential for LTCC application. [ABSTRACT FROM AUTHOR]

Transition metal carbides (TMCs) hold great promise for protective coatings due to their excellent mechanical properties, however, developing hard yet tough TMC-based materials against harsh environment continues to be a great need but challenge, as high hardness is often obtained with toughness deterioration. Here, we focus on HfC film modification with Ta addition (10.2–26.8 at.%) using magnetron co-sputtering system, particularly, two types phase structures (cubic Hf(Ta)C single-phase solid solution and mixed phase Hf-Ta-C structure (HfC + TaC mixture), respectively) are prepared for comparison and explanation. Mechanical tests reveal that the Hf(Ta)C solid solution film exhibits the highest hardness (36 ± 0.51 GPa), which is far beyond pure HfC and TaC reference, and is nearly two times higher than the film with mixed phase of TaC and HfC. Simultaneously, excellent fracture toughness with high K f value at 3.6 MPa m1/2 can be achieved in such a solid solution film, on account of high hardness/elasticity modulus ratio. All films exhibit low friction coefficient at∼0.3 when C lubrication medium occurs, the lubrication behavior surpasses corresponding nitrides film. After high-temperature annealing at 800 °C, the Hf(Ta)C solid solution film is found to perform better in terms of thermal stability and oxidation resistance, while structural destruction and obvious oxidation occur in other reference films. We therefore give the potential advantage of solid solution structure (relative to mixed phase structure) in regulating high-performance TMC-based protective coatings, which is fundamental but very practical for other material systems. [ABSTRACT FROM AUTHOR]