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A series of ZrB 2 -ZrC-SiC composites with various SiC content from 0 to 20 vol% were prepared by reactive hot-pressing using Zr, B 4 C and SiC as raw materials. Self-propagating high-temperature synthesis (SHS) occurred, and ZrC grains connected each other to form a layered structure when the SiC content is below 20 vol%. The evolution of microstructure has been discussed via reaction processes. The composite with 10 vol% SiC presents the most excellent mechanical properties (four-point bending strength: 828.6±49.9 MPa, Vickers hardness: 19.9±0.2 GPa) and finest grain size (ZrB 2 : 1.52 µm, ZrC: 1.07 µm, SiC: 0.79 µm) among ZrB 2 -ZrC-SiC composites with various SiC content from 0 to 20 vol%. [ABSTRACT FROM AUTHOR]

The residual stresses in ZrB 2 SiC ceramics with the addition of WC or ZrC were measured using Raman spectroscopy (RS) and X-ray diffraction (XRD). The temperatures at which the residual stresses began to accumulate were calculated. The resistance to high-temperature deformation of ZrB 2 SiC-based ceramics was evaluated via four-point flexure test under a static load (15, 25 MPa) for 5 h at 1600 °C and 1800 °C. The results indicate that a compressive residual stress existed in SiC particles and a corresponding tensile stress applied in ZrB 2 matrix. The values of thermal residual stresses increase in order of ZSZ (ZrB 2 SiC ZrC) < ZS (ZrB 2 SiC) < ZSW (ZrB 2 SiC WC). The temperature composite begin to accumulate the residual stresses also increases in the same order. The apparent different behaviors are resulted from their dissimilar grain boundary state and third phase nature in three ceramics. The phenomenon was explained by a proposed model. The results provide a path to design material compositions with an ideal mechanical properties and guidance role for applications. [ABSTRACT FROM AUTHOR]

Despite of good oxidation resistance and ablation resistance, challenge to densify and tendency to loss high temperature (H.T.) strength have limited its potential applications in aerospace for HfB 2 –SiC ceramic. In this work, dense HfB 2 –SiC ceramic with improved H.T. flexural strength was prepared using WC as sintering aid. Pure HfB 2 –SiC ceramic exhibited creep deformation at 1600 °C with measured strength value of 389 ± 82 MPa, whereas WC doped sample showed much higher flexural strength of 658 ± 69 MPa with linear elastic behavior prior to fracture. In addition to clean grain boundary, the addition of 5 vol.%WC into HfB 2 –SiC ceramic promoted the formation of fine (Hf,W)B 2 , (Hf,W)C and WB precipitates. This combinative effect is responsible for its excellent H.T. mechanical property of WC doped HfB 2 –SiC ceramic. [ABSTRACT FROM AUTHOR]

ZrB2–20vol% SiC (ZS) ceramics based on ZrB2 starting powders obtained by different boro/carbo-thermal reductions involving ZrO2 +B4C, ZrO2 +B4C+C, and ZrO2 +B, were fully densified by hot pressing at 1900–2000°C. The flexural strength of these ZS ceramics was measured from room temperature up to 1600°C. At 1600°C, the flexural strength of the ceramics is 460±31, 471±32 and 345±11MPa, respectively. The evolution of the strength as function of temperature is explained in terms of the differences in oxygen content, nature of fracture, grain sizes, grain boundary phases and microstructural defects. [ABSTRACT FROM AUTHOR]

ZrB2–SiC–ZrN composites were fabricated by reactive hot pressing using Zr, Si3N4, and B4C powders as starting materials. Sintering was conducted at temperatures of 1800 to 2000°C under a load of 20MPa in Ar atmosphere. The composite was densified at 2000°C. The in situ formed BN flakes which distributed uniformly at the grain boundaries were identified by X-ray diffraction and scanning electron microscopy. The formation of h-BN phase and its effect on the mechanical properties of the composite are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Dense ZrB2–20vol% SiC ceramics (ZS) were fabricated by hot pressing using self-synthesized high purity ZrB2 and commercial SiC powders as raw materials. The high temperature flexural strength of ZS and its degradation mechanisms up to 1600°C in high purity argon were investigated. According to the fracture mode, crack origin and internal friction curve of ZS ceramics, its strength degradation above 1000°C is considered to result from a combination of phenomena such as grain boundary softening, grain sliding and the formation of cavitations and cracks around the SiC grains on the tensile side of the specimens. The ZS material at 1600°C remains 84% of its strength at room temperature, which is obviously higher than the values reported in literature. The benefit is mainly derived from the high purity of the ZrB2 powders. [Copyright &y& Elsevier]

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

Abstract: Mo–Si alloy sheets with different silicon content were fabricated by powder-metallurgical and thermo-mechanically processing. The effect of Si content and annealing temperature on microstructure and hardness of the Mo–Si alloys were studied by using optical microscopy (OM), transmission electron microscopy (TEM) and Vickers hardness tester, respectively. The results indicated that the presence of Si can effectively refine the grain sizes and improve the hardness of Mo–Si alloys. Si can also increase the recrystallization temperature of alloys and play a significant role in restraining the grain growth at high temperatures. Increasing the annealing temperature, the microstructure of Mo–Si alloy sheets is gradually coarsened and changed from fibrous to equiaxed structure, causing reduction in hardness. The hardening effect in the Mo–Si alloys came from the refined grain strengthening, solid solution strengthening, and second phase particle strengthening, which are closely dependent on the Si content and annealing temperature. [Copyright &y& Elsevier]

Abstract: Oxidation behavior and effect of oxidation on the room-temperature flexural strength were investigated for ZrB2–10vol% SiC (ZB10S) and ZrB2–30vol% SiC (ZB30S) in air at 1500°C with times ranging from 0.5h to 10h. The oxide scale of both ZB10S and ZB30S was composed of an outer glassy layer and an inner extended SiC-depleted layer. The changes in weight gain, glass layer thickness, and extended SiC-depleted layer thickness with oxidation were measured. Analysis suggested that the extended SiC-depleted layer was most indicative for evaluating the oxidation resistance. Compared to the ZB10S, the improved oxidation resistance in ZB30S was attributed to the viscosity increase of glassy layer and the lower number of ZrO2 inclusions in the glassy layer. Because of the healing of surface flaws by the glassy layer, the strength increased significantly by ∼110% for ZB10S and by ∼130% for ZB30S after oxidation for 0.5h. [Copyright &y& Elsevier]

Highly c-axis oriented ZrB2-based ultrahigh-temperature ceramics (UHTCs) were prepared via strong magnetic field alignment during slip casting, followed by spark plasma sintering, using ZrB2 and β-SiC as starting materials. Results showed that hardness was superior on the surface perpendicular to the grain alignment. Oxidation resistance was obviously better on the surface of (001) direction. The anisotropic properties of the textured materials would provide an opportunity to the material design and selection of UHTCs. [Copyright &y& Elsevier]

This work reported the grain growth kinetics of high‐entropy diboride (HEB) and HEB‐SiC ceramics containing 10, 20, and 30 vol% SiC during heat treatment at 1800°C. The coarsening of HEB phase occurred in the four kinds of ceramics during heat treatment, especially in HEB ceramics. The kinetic analysis showed that the grain growth of HEB phase in HEB and HEB‐SiC ceramics is controlled by interface‐controlled kinetics and grain‐boundary pinning, respectively. The growth rate constant of HEB grains is lower than ZrB2, which is related to the low grain‐boundary energy and the sluggish diffusion effect in dynamics of high‐entropy materials. The growth rate of matrix phase in HEB‐SiC ceramics is similar to that in ZrB2–SiC ceramics, indicating that the pinning effect of the SiC second‐phase played the dominant role in inhibiting the grain growth of the high‐entropy matrix phase and disguised the sluggish diffusion effect. This study reveals that the grain growth inhibition through sluggish diffusion effect in a high‐entropy ceramic system may be magnified by the possible existence of segregated second‐phase particles located at the grain boundaries. [ABSTRACT FROM AUTHOR]

Hierarchical porous silicon carbide (SiC) attracts great attention due to its superior chemical resistance, high thermal shock resistance, and excellent thermal stability. The preparation of a porous SiC monolith via a simple sol–gel method is limited by either the high cost of the raw materials or the special time-consuming drying process. Herein, we report an ambient drying sol–gel approach for the synthesis of organic–inorganic hybrid monolithic gels which can be converted into hierarchical porous SiC monoliths upon pyrolysis at 1400 °C. The as-synthesized SiC monoliths possess hierarchical pores with macropores of 4.5 µm and mesopores of 2.0 nm. The porosities, specific surface areas and compressive strengths of the hierarchical porous SiC monoliths are 71.3%, 171.5 m2/g and 7.0 ± 0.8 MPa, respectively. [ABSTRACT FROM AUTHOR]

SiC and HfC were used to tailor microstructures and improve properties of hot pressed HfB 2 -based ceramics. SiC and HfC particle, as the second phase, could hinder grain growth of HfB 2 . Compared with HfC, SiC grains grew slower, which was more effective to hinder grain growth of HfB 2 . The ternary ceramics HfB 2 –20vol%HfC–20vol%SiC had the finest microstructure, indicating the effect of SiC and HfC on grain growth. Several SiC clusters were found on related fracture surfaces. Large SiC clusters can cause high levels of residual stress and stress concentration, which are harmful to mechanical properties of boride-SiC ceramics. The predominant fracture mode of HfB 2 –20vol%SiC was transgranular, however, in HfB 2 –10vol%HfC–10vol%SiC and HfB 2 –20vol%HfC–20vol%SiC ceramics, the dominating fracture mode shift from transgranular to intergranular. With the incorporation of HfC, the fracture toughness of HH10S10 and HH20S20 increased to 4.34 MPa m 1/2 and 5.05 MPa m 1/2 , which were 17.3% and 26.7% higher than HS20 (3.72 MPa m 1/2 ), respectively. The flexural strengths of HfB 2 –HfC–SiC ceramics were improved to ~750 MPa, which were about 1.3 times higher than that of HfB 2 –20SiC. [ABSTRACT FROM AUTHOR]

It is thought that the sintering of high‐entropy (HE) ceramics is generally more difficult when compared to that of the corresponding single‐component ceramics. In this paper, we report a novel approach to densify the HE carbide ceramics at relatively low temperatures with a small amount of silicon. Reactive spark plasma sintering (SPS) was used to densify the ceramics using powders of HE carbide and silicon as starting materials. Dense ceramics can be obtained at 1600 ‐1700°C. X‐ray diffraction analysis reveals that only non‐stoichiometric HE carbide phase with carbon vacancy and SiC phase exist in the obtained ceramics. The in‐situ formed SiC phase inherits the morphology of the starting silicon powder owing to the slower diffusion of silicon atoms compared to that of the carbon atoms in HE carbide phase. The mechanical properties of the prepared ceramics were preliminarily studied. [ABSTRACT FROM AUTHOR]

Toughened ZrB 2 –SiC composites have been prepared by an introduction of amorphous carbon spheres. After hot pressing, microstructure observation showed that the carbon phases were present in the form of thin layer at grain boundaries, or in the form of agglomerates at the multigrain junctions. The carbon spheres led to significant improvement of fracture toughness from 4.96 ± 0.46 MPa m 1/2 to 7.52 ± 0.19 MPa m 1/2 . The toughening mechanism was attributed to the weak interfaces, which occurred due to the presence of carbon layer formed at grain boundaries after sintering. [ABSTRACT FROM AUTHOR]

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

Abstract: Using WC as sintering aid, nearly full dense (∼99%) HfB2–20vol% SiC ceramics were sintered at 2200°C for 2h without external pressure. The densification mechanism, microstructure evolution, mechanical properties and oxidation resistance were investigated. The results indicated that complex chemical reactions of WC in HfB2–SiC system strongly related to the densification, microstructure and properties. The Young''s modulus, fracture toughness and 3-pt bending strength of HfB2–20vol% SiC with 10wt% WC were 511GPa, 4.85Mpam1/2 and 563MPa, respectively, which were comparable to some hot pressed HfB2–SiC ceramics in literature. The oxidation of HfB2–20vol% SiC with 10wt% WC at 1500°C in air exhibited parabolic kinetics. After oxidation at 1500°C for 10h, its weight gain and SiC-depleted layer thickness were 3.7mg/cm2 and 43μm, respectively, and its residual flexural strength was comparable to or even a little higher than the value before oxidation. [Copyright &y& Elsevier]

Abstract: HfB2 and HfB2–10vol% HfC fine powders were synthesized by carbo/boronthermal reduction of HfO2, which showed high sinterability. Using the as-synthesized powders and commercially available SiC as starting powders, nearly full dense HfB2–20vol% SiC (HS) and HfB2–8vol% HfC–20vol% SiC (HHS) ceramics were obtained by hot pressing at 2000°C/30MPa. With the incorporation of HfC, the grain size of HHS was much finer than HS. As well, the fracture toughness and bending strength of HHS (5.09MPam1/2, 863MPa) increased significantly compared with HS (3.95MPam1/2, 654MPa). Therefore, it could be concluded that the incorporation of HfC refined the microstructure and improved the mechanical properties of HfB2–SiC ceramics. [Copyright &y& Elsevier]

Abstract: This work compared phase composition, microstructures and mechanical properties of ZrB2—20vol.% SiC—5vol.%Yb2O3 prepared by hot pressing (HP) and spark plasma sintering (SPS) in vacuum. Despite the same raw material composition, the two densification techniques led to the appearance of different secondary phases. The HP ceramics had coarsened microstructure, predominantly intergranular fracture characteristic and high fracture toughness. The SPS ceramics exhibited refined microstructure, transgranular fracture model and high bending strength. [Copyright &y& Elsevier]

Abstract: ZrB2–20vol% SiC composites with 3vol% Re2O3 rare-earth oxide (Re=La, Nd, Y or Yb) were hot pressed to near full-density at 1900°C. The La2O3 and Nd2O3 additions not only caused the formation of an amorphous grain boundary phase and enhanced densification, but also resulted in substantial ZrB2 and SiC grain growth. In contrast, the Y2O3 and Yb2O3 additions resulted in the formation of crystalline (Y/Yb)2Zr2O7 and enhanced densification without ZrB2 and SiC grain growth. The hardness was improved by the rare-earth oxide addition, especially with Y2O3 and Yb2O3. The La2O3 and Nd2O3 only had a minor effect on the fracture toughness, whereas the Y2O3 and Yb2O3 additions increased the fracture toughness. The type of Re2O3 addition was found to influence the nature of the grain boundary and the concomitant fracture and toughening mechanisms. [Copyright &y& Elsevier]

A pressureless densification mechanism and microstructure development in ZrB2–20vol.% SiC ceramics with boron additive were investigated. Results showed that the boron addition removed oxygen impurity and improved the densification process. By adding 1wt.% boron, fully dense ZrB2–SiC ceramics with a fine-grained microstructure was obtained. However, a higher boron addition would lead to fast grain growth of both SiC and ZrB2 grains and a deteriorated densification behavior by forming a liquid phase. The mechanical properties of the sintered ceramics with 1wt.% boron addition were also evaluated. [Copyright &y& Elsevier]

Abstract: Three ZrB2–SiC composites were prepared from polycarbosilane (PCS)-coated ZrB2 powders. Powders with or without additions of Si or Zr were densified by hot pressing at 1800°C. Finally, the oxidation resistance of the composites was studied at 1500°C in air. The phase composition and microstructure were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) along with energy-dispersive spectroscopy (EDS). Results showed that Si addition, which reacted with free carbon coming from the pyrolyzed PCS to produce the SiC, improved the oxidation resistance of ZrB2–SiC composites with PCS as a precursor, whereas Zr addition, which reacted with the carbon to produce the ZrC, decreased it. [Copyright &y& Elsevier]

Abstract: Structure-property relations of ZrB2–SiC composites fabricated by spark plasma sintering reactive synthesis (SPS-RS) method were investigated. The effects of the holding time and pressure on the density, mechanical properties and microstructures were characterized. The results showed that the density increased with both holding time and pressure increased. Hardness was not affected much by the processing condition when the density was above 96.3%. However, fracture toughness values were found to depend on holding time. The value increased from 4.3±0.2MPam1/2 to 5.3±0.3MPam1/2 when the holding time prolonged from 9min to 12min for the grain size of ZrB2 and SiC increased. [Copyright &y& Elsevier]

Using TCAD simulations, the silicon carbide metal–oxide–semiconductor field-effect transistor with p-type floating islands (SiC FLIMOSFET) is systematically investigated in this paper. The doping concentration (NFLI), length (L), and position (D1) of floating islands are optimized according to breakdown voltage (BV), electric field distribution, and on-resistance. The results show that $\text{N}_{\textsf {FLI}} = \textsf {1} \times \textsf {10}^{\textsf {17}}$ cm $^{\textsf {-3}}, \textsf {L}= \textsf {2.5}\,\,\mu \text{m}$ , and $\textsf {D1}=9.0\,\,\mu \text{m}$ are superior values for FLI structure considering tradeoff between BV and on-resistance. With the same BV capacity, the on-resistance of SiC FLIMOSFET is decrease by 32% comparing to the conventional SiC VDMOSFET. Besides, the dynamic property shows 16.5% reduction of FoM $\text{R}_{\textsf {on}}\cdot \textsf {Q}_{\textsf {GD}}$ in the SiC FLIMOSFET. Significantly, comparing to the conventional structure, the electro-thermal simulation indicates that the SiC FLIMOSFET has a higher robustness under short-circuit condition owing to the reduction of thermal stress in SiC/SiO2 interface. All the results show that the SiC FLIMOSFET has a good potential in SiC power device. [ABSTRACT FROM AUTHOR]

Abstract In-depth structural characterization has been performed to investigate the structural evolution in ZrC-SiC under irradiation by high dose of 4 MeV Au2+ ions. XRD, SEM, TEM and Raman examinations have been utilized in the present study. The damage depth in SiC (∼1.55 μm) is found deeper than in ZrC (∼1.22 μm). SiC became amorphous under irradiation accompanied by volume expansion. ZrC kept crystalline but enhanced the formation of carbon vacancies and exhibited high density of dislocations whose structures varied with depth. Compressive stress due to swelling in amorphization of SiC result in 0.49% shrinkage of lattice parameters of ZrC unit cell. The grain boundaries kept structural integrity without occurrence of cracks or broadening, which implies absence of large degradation in mechanical properties of ZrC-SiC composite after irradiation. [ABSTRACT FROM AUTHOR]

Abstract: A volatility diagram of zirconium carbide (ZrC) at 1600, 1930, and 2200°C was calculated in this work. Combining it with the existing volatility diagrams of ZrB2 and SiC, the volatility diagram of a ternary ZrB2‐SiC‐ZrC (ZSZ) system was constructed in order to interpret the oxidation behavior of ZSZ ceramics. Applying this diagram, the formation of ZrC‐corroded and SiC‐depleted layers and the oxidation sequence of each component in ZSZ during oxidation and ablation could be well understood. Most of the predictions from the diagrams are consistent with the experimental observations on the oxidation scale of dense ZrB2‐SiC‐ZrC ceramics/coatings after oxidation at 1600°C or ablation at 1930 and 2200°C. The reasons for the discrepancy are also briefly discussed. [ABSTRACT FROM AUTHOR]

Coating refractory ceramics onto alloys has been considered to be a feasible way to enhance the mechanical properties along with the corrosion and radiation resistance of the cladding materials. Here, we report a room-temperature magnetron sputtering method to deposit SiC films onto Zircaloy-4 substrate. By optimizing variety of processing parameters including target-substrate distance, sputtering power and deposition pressure, we finally obtained a dense SiC film with high values of hardness (25.61 GPa), elastic modulus (214.9 GPa) and critical load (8.24 N). Structural characterization indicates nanocrystalline (∼10 nm) structures of the SiC films, which is expected to show better radiation resistance than bulk SiC. Effects of processing parameters especially the deposition pressure on film microstructures and mechanical properties have been investigated in depth, which involve difference in energy of sputtering particles, nucleation and growth of grains, and stress states of the deposited films. [ABSTRACT FROM AUTHOR]

Immersion corrosion tests of TiC 0.8 , TiC, TiC–20 vol% SiC, TiC–40 vol% SiC and SiC have been performed in molten FLiNaK salt at 800 °C for 25–200 h under argon cover gas. All of these five samples showed small mass loss and relatively good corrosion resistance in molten FLiNaK salt. The corrosion patterns of TiC 0.8 , TiC, TiC–20 vol% SiC and TiC–40 vol% SiC were inter-granular corrosion, which were attributed to the depletion of Ti along the grain boundaries. SiC exhibited a general corrosion process in which a carbon-rich layer formed on the surface, resulting from the depletion of Si. The carbon-rich layer protected SiC against further corrosion, hence lowering the corrosion rate. The corrosion results of TiC–20% SiC and TiC–40% SiC revealed the corrosion resistance of TiC could be improved by adding SiC. And the contribution of SiC to better corrosion resistance has been elucidated. [ABSTRACT FROM AUTHOR]

ZrC–SiC composite nanopowder is synthesized via a simple sol–gel process. First, stable precursor sols are prepared from zirconium oxychloride and tetraethoxysilane respectively. Two sols are mixed and sucrose is added as the carbon source. The mixed precursor sol is converted to ZrC–SiC composite nanopowders after ceramic conversion at 1500 °C for 1 h under vacuum. The particle sizes of the as-synthesized ZrC–SiC composite powders are strongly affected by their compositions. It appears that the coexistences of silica and zirconia hinder the particle growth, leading to smaller and more uniform products. Particles of an average diameter at 180 nm are obtained when SiC volume content is around 12%. The powders are systematically characterized by XRD, SEM, TEM, TG-DSC and TEM-EDS. [ABSTRACT FROM AUTHOR]

The suitability of ZrC–SiC-based ceramics was assessed as candidate materials for fluoride. An immersion corrosion with ZrC–SiC composites was performed in molten FLiNaK salts (LiF–NaF–KF: 46.5/11.5/42 mol%) at 850 °C. Results indicated that ZrC–SiC-based ceramics were more corrosion resistant than the ZrC ceramic. ZrC–40SiC ceramic exhibited 50% weight-loss to ZrC. This carbide exhibited minimal corrosion attack because of strong resistance to dissolution in molten fluorides. Furthermore, XRD results were consistent with weight-loss and SEM results. The corrosion behavior of ZrC–SiC-based ceramics was affected by impurities, particularly oxygen content. Oxygen and/or oxygen ion participated in corrosion of ceramic. Corrosion of carbide ceramics is mainly due to C 4− in ceramics. This ion is oxidized to elemental C by oxidants or impurities in the molten salt. The addition of C may inhibit corrosion of molten salts and thus improve the corrosion resistance of carbide ceramics. [ABSTRACT FROM AUTHOR]

Monolithic ZrB 2 , ZrB 2 SiC, ZrB 2 ZrC and ZrB 2 SiC ZrC were prepared by hot pressing in ternary ZrB 2 SiC ZrC system. They exhibited different microstructural features. Grain sizes of each phase were smaller in the ternary composites. Contour maps of mechanical properties were also plotted in ZrB 2 SiC ZrC ternary diagram based on experiments and software fitting. They established the relationships between chemical composition and properties in a visual way. Young’s Modulus and Vickers hardness had linear relationships with composition, while the evolution of the strength and toughness was complicated. [ABSTRACT FROM AUTHOR]

Oxidation behavior of ZrB 2 –SiC ceramics containing 0, 10 and 20 vol% ZrC was studied at 1600 °C in stagnant air. The structures of oxide scales depended on ZrC content. The thickness of the SiO 2 -rich glass layer on the outermost surface decreased steeply with the addition of ZrC. One “ZrC-corroded layer”, containing ZrC x O y , SiC and ZrB 2 , was observed in ZrB 2 –SiC–ZrC. The oxidation kinetics was converted from parabolic to linear for the ceramics with 20 vol% ZrC. [ABSTRACT FROM AUTHOR]

The porous nature of carbon nanotube (CNT) arrays allows for the unique opportunity to tailor their mechanical response by the infiltration and deposition of nanoscale conformal coatings. Here, we fabricate novel photo-lithographically defined CNT pillars that are conformally coated with amorphous silicon carbide (a-SiC) to strengthen the interlocking of individual CNTs at junctions using low pressure chemical vapor deposition (LPCVD). We further quantify the mechanical response by performing flat-punch nanoindentation measurements on coated CNT pillars with various high-aspect-ratios. We discovered new mechanical failure modes of coated CNT pillars, such as 'bamboo' and brittle-like composite rupture as coating thickness increases. Furthermore, a significant increase in strength and modulus is achieved. For CNT pillars with high aspect ratio (1:10) and coating thickness of 21.4 nm, the compressive strength increases by an order of magnitude of 3, towards 1.8 GPa (from below 1 MPa for uncoated CNT pillars) and the elastic modulus increases towards 125 GPa. These results show that our coated CNT pillars, which can serve as vertical interconnects and 3D super-capacitors, can be transformed into robust high-aspect-ratio 3D-micro architectures with semiconductor device compatible processes. [ABSTRACT FROM AUTHOR]

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

Abstract: A comparative study of phase components and compositions was performed for the pressureless sintered HfB2–SiC–WC composites by various analytical methods. The relative decrease of HfB2 phase leads to a new reaction of HfO2 removal by WC to create B2O3. By using SiC instead of Si3N4 as milling medium, the WB phase was suppressed to the trace level while the W solid-solution in HfB2 phase was favored. The W solution in both the primary HfB2 and resultant HfC phases indicates that the WC additive was involved throughout the sintering process by dissolving into sintering liquid, which remains at the intergranular regions to form amorphous oxides as well as trace W-rich phases. This is effectively a reactive liquid-phase sintering to realize the reaction, solid-solution and densification collectively to achieve a designable HfB2–SiC–HfC composite by pressureless sintering, which may also be extended to other sintering methods. [Copyright &y& Elsevier]

Abstract: The influence of the pressure loading cycle on spark plasma sintered ZrB2–SiC–Yb2O3 ceramics was investigated. Spark plasma sintering consists of three stages, i.e., a heating-up, isothermal and cooling stage. Applying the load during isothermal stage allowed evaporation of volatile species. Applying the load during the heating-up and isothermal stages resulted in the entrapment of volatile species and the formation of nanometer-sized spherical SiO2 particles. The presence of SiO2 particles led to a large thermal residual stress, and improved fracture toughness in the ZrB2–SiC–Yb2O3 ceramics. [Copyright &y& Elsevier]

Abstract: Wood with its rational and magical inner structures was used as a template to fabricate C/Al and (C+SiC)/Al composites in this research. The carbon frame was first pyrolyzed from the wood template. The final composites were then obtained by infiltrating Al alloy and silicone resin into the carbon frame. The microstructures and the wear properties of these products were analyzed. The results show that the structures of the C/Al and (C+SiC)/Al composites are controlled by the natural structures of the wood. Moreover, the carbon in the composites reduced the wear rate of the Al alloy as an efficient lubricant. Compared with the C/Al composite, the (C+SiC)/Al composite shows better wear resistance because of silicon carbide. [Copyright &y& Elsevier]

The effects of nanoscale conformal coatings of amorphous silicon carbide on the mechanical properties of carbon nanotube pillars are investigated. Several interesting mechanical failure modes such as bamboo and brittle‐like composite rupture are observed as coating thickness increases. On page 5737, G. Q. Zhang and co‐workers report on their remarkable increase in strength, making the fast growing coated CNT arrays useful as structural material for high‐aspect‐ratio 3D micro‐architectures. [ABSTRACT FROM AUTHOR]