This paper describes the detailed high-temperature properties of monophasic Al3BC3, including the thermal expansion characteristics of its crystal structure and thermal shock resistance. We examined the differences in physical properties between Al(3)BC(3)and Al8B4C7, which was previously thought to be Al3BC3. Compared with the thermal conductivity and CTE of Al(3)BC(3)measured in the present study, those reported for Al(8)B(4)C(7)in a previous study were higher, which is attributable to residues of Al and B. The densification of Al8B4C7 is supported by gas-phase diffusion via Al- and B-based gases or liquid, whereas the sintering of Al(3)BC(3)is dominated by solid-phase diffusion. The bending strength of Al(3)BC(3)was 226 MPa at RT and was maintained even at high temperatures. Al(3)BC(3)was found to exhibit a good thermal shock fracture resistance parameter R' of 3.3, equivalent to that of Al2O3 and substantially better than that of commonly used engineering ceramics Al(4)SiC(4 )and Al6Si2O13, mainly because of the higher thermal conductivity and lower elastic modulus of Al3BC3. The dense Al(3)BC(3)sample exhibited excellent thermal stability under N-2 and inert gas atmospheres but was easily oxidized to monophasic Al2O3 at 1300 degrees C under ambient air.

BaTiO3–BaO–B2O3–Bi2O3 (BBB) glass composites were investigated to clarify how BBB content and sintering route control low-temperature densification, pore evolution, glass-derived phase redistribution, and crystalline phase development. Densification was assessed using 15 and 30 wt% BBB glass with pressureless sintering (PS) at 600–800 °C and spark plasma sintering (SPS) at 500–800 °C. Monolithic BaTiO3 exhibited limited densification at 800 °C, suggesting that solid-state diffusion was inadequate for consolidation. The addition of BBB facilitated the formation of a transient liquid phase, enhancing glass softening and pore filling. Densification improved with temperature and BBB content under PS, although residual porosity remained, particularly for 15 wt% BBB. SPS significantly modified microstructural evolution, achieving a relative density of 98.28% for 30 wt% BBB at 800 °C due to SPS-assisted liquid redistribution. SEM analysis revealed a shift from interconnected pores to isolated pinholes, with Bi-rich BBB regions redistributing in the BaTiO3 framework. Tetragonal BaTiO3 was the primary crystalline phase, while 30 wt% BBB, after SPS, formed secondary borate phases. These results establish a processing–microstructure–phase relationship for BaTiO3–BBB glass composites and show that BBB-assisted SPS enables low-temperature densification.

Practical techniques to identify heat routes at the nanoscale are required for the thermal control of microelectronic, thermoelectric, and photonic devices. Nanoscale thermometry using various approaches has been extensively investigated, yet a reliable method has not been finalized. We developed an original technique using thermal waves induced by a pulsed convergent electron beam in a scanning transmission electron microscopy (STEM) mode at room temperature. By quantifying the relative phase delay at each irradiated position, we demonstrate the heat transport within various samples with a spatial resolution of ~10 nm and a temperature resolution of 0.01 K. Phonon-surface scatterings were quantitatively confirmed due to the suppression of thermal diffusivity. The phonon-grain boundary scatterings and ballistic phonon transport near the pulsed convergent electron beam were also visualized.

Al4SiC4 shows excellent heat resistance, thermal shock resistance, machinability, and oxidation resistance. We focused on Al4SiC4-based ceramics with SiC as a non-oxide matrix for ceramic matrix composites for aircraft jet engines. In this study, monolithic Al4SiC4 and Al4SiC4/SiC ceramics were fabricated by hot-pressing, and a corrosion test against molten calcium-magnesium-alumino-silicate (CMAS) was conducted at 1350(degrees)C for 12-100 h in air, and their corrosion behavior was investigated. Scanning electron microscopy and energy-dispersive X-ray spectroscopy results revealed that severe damage was not observed at the interface between CMAS and the samples after the CMAS corrosion test. The recession of Al4SiC4-100, -10, and SiC-100 after corrosion for 100 h was 80-90 mu m, and that of Al4SiC4-50 was the highest of all samples and the value was 130 mu m. The dissolution behavior of the oxidation layer into molten CMAS via a corrosion reaction was dependent on the composition of both the sample and the oxidation layer, the thickness, and the microstructure of the oxidation layers. The dominant mechanism of reaction between CMAS and Al4SiC4-100, -90, and -50 samples was concluded to be the dissolution of the oxidation products, while in SiC-100 and Al4SiC4-10 samples, the dominant reaction was determined to be direct corrosion of the surface with CMAS.

In this study, TiC-50 wt% W, TiN-50 wt% W, TiC0.7N0.3-50 wt% W, Ti0.55C0.13N0.32-50 wt% W, TiC0.5N0.5-50 wt % W and TiC0.5N0.5-70 wt% W cermet specimens with grain sizes smaller than 1 mu m were prepared by blending TiC, TiN, TiC0.5N0.5, W and Ti powders followed by the spark plasma sintering of the blended powders. Under Ar gas flow conditions at 1973 K, the TiC0.5N0.5-50 wt% W and TiC-50 wt% W cermet specimens exhibited the first and second highest strengths, respectively, whereas the TiN-50 wt% W and Ti0.55C0.13N0.32-50 wt% W cermet specimens exhibited the lowest strength among all the cermet specimens prepared in this study. In contrast, the Ti0.55C0.13N0.32-50 wt% W and TiC0.5N0.5-50 wt% W cermet specimens exhibited the first and second highest strengths, respectively, at room temperature in laboratory air. Coherent interfaces, whose type differed from those of the TiC0.5N0.5-50 wt% W and TiC0.5N0.5-70 wt% W cermet specimens, were found in (Ti, W)C grains in the TiC-50 wt% W cermet specimen. The coherent interfaces in the TiC-50 wt% W cermet specimen were considered to suppress the grain growth because these interfaces normally suppress the interdiffusion of Ti, W and C atoms. Moreover, the grain growth seemed to be suppressed in the TiC0.7N0.3-50 wt% W, Ti0.55C0.13N0.32-50 wt% W, TiC0.5N0.5-50 wt% W and TiC0.5N0.5-70 wt% W cermet specimens owing to the core-rim structures with coherent interfaces in the cermet specimens. The coherent interfaces and core-rim structures are thus considered to contribute to improving the high -temperature strength of all the cermet specimens except for the TiN-50 wt% W cermet specimen, which contained neither core-rim structures nor coherent interfaces.

In this reply, we stress again the discovery that the lattice size effect is indicated to also contribute to the Seebeck coefficient.

In this study, TiC–50wt% W, TiN–50wt% W, TiC0.7N0.3–50wt% W, Ti0.55C0.13N0.32–50wt% W, TiC0.5N0.5–50wt% W and TiC0.5N0.5–70wt% W cermet specimens were prepared by blending TiC, TiN, TiC0.5N0.5, W and Ti powders with particle sizes of less than 1.2 μm followed by the spark plasma sintering of the blended powders. The microstructure and high-temperature compressive strength of the cermet specimens were investigated by scanning electron microscopy–energy-dispersive X-ray spectroscopy and transmission electron microscopy–energy-dispersive X-ray spectroscopy analyses and high-temperature compression tests after sintering. Coherent interfaces, whose type differed from those of the TiC0.5N0.5–50wt% W and TiC0.5N0.5–70wt% W cermet specimens, were found in (Ti, W)C grains in the TiC–50wt% W cermet specimen. Moreover, the TiC0.5N0.5–50wt% W cermet specimens exhibited the highest strength at 1973 K under Ar gas flow conditions among all the cermet specimens prepared in this study.

Reactive consolidation of medium entropy diboride in the ZrB 2 –TaB 2 –NbB 2 system was performed by spark plasma sintering of diboride powders at 2000 °C. The 3:2:1 ratio between Zr, Ta, and Nb showed the highest specific strength at room temperature during the initial screening of the mechanical properties . The flexural strength gradually decreased from 700 ± 42 MPa at RT to 518 ± 30 MPa at 1600 °C with the Weibull parameter exceeding 15. Diborides with an equimolar composition did not show a maximum in their strength, fracture toughness or hardness.

During the spark plasma sintering at 1900 ?, SiB6 decomposes into cubic silicon carbide and boron carbide, owing to the reducing environment of the furnace. For the HfB2-SiB6 ceramic improvement in hardness (24.5 +/- 0.7 GPa) was attributed to the formation of the B12(C,Si,B)3. Fracture toughness by indentation (6.8 +/- 2.4 MPa.m1/2), single-edge notched bend specimens (4.6 +/- 0.4 MPa.m(1/2)) and room-temperature strength (513 & PLUSMN; 21 MPa) of the HfB2-SiB6 composite produced by spark plasma sintering was higher or on the same level as the HfB2-SiC ceramics. The high-temperature flexural strength tests suggested that the strength would decrease monotonically with an increase in temperature. At or below 1600 C, only a linear stress-strain response was observed, and resulted into a mean strength of-320 MPa. During the tests at 1800 ?, we observed a nonlinear deformation indicating ongoing plastic deformation which led to a strength decrease down to 230 & PLUSMN; 30 MPa.

A technique for measuring the coefficient of thermal expansion (CTE) of ceramic protective coatings from 25 degrees C to 1400 degrees C is proposed. The surface of a self-standing mullite coating heated in a furnace was observed by a scanning laser microscope which detects only the blue laser light reflected from the sample surface as an image source and thereby eliminates the effect of thermal radiation. Images with constant contrast independent of temperature without halation by thermal radiation were obtained. The series of images from 25 degrees C to 1400 degrees C was used for the digital image correlation and the thermal strain was measured for each temperature; the CTE was calculated from the data as a function of temperature. The reliability of the measurement was confirmed through the CTE measurement of a c-plane sapphire plate and practically applied to the measurement of a mullite coating. For cases in which a self-standing coating cannot be obtained, we also proposed a method of CTE measurement for a coating adhered to a substrate, with consideration for the effect of substrate constraint.

Ultra-high temperature ceramics (UHTCs) are most recently getting much attention for structural parts of hypersonic missiles with their cruising speed of more than Mach 5. Most of the UHTCs are poor sinterability carbides, nitrides, and borides. Therefore, they have been studied and developed for a long time. However, there are still many problems to solve. In this paper, based on the solid-state reaction presented as an equation of (x + y)·ZrC + 2·y·B → x·ZrC + y·ZrB2 + y·C, three-phase ZrC/ZrB2/C composites have been fabricated from ZrC and amorphous B powders using pulsed electric-current pressure sintering at 1373 to 2173 K for 6.0 × 102 s under 50 MPa in a vacuum. ZrC/ZrB2/C = 30/70/C~70/30/C vol% composites with the relative densities Dr of 96.6 to 98.7% were obtained at 2073 K. The 60/40/C vol% composite revealed high bending strength σb (554 MPa), Vickers hardness Hv (19.2 GPa) and moderate fracture toughness KIC (5.25 MPa·m1/2) at room temperature. Furthermore, all composites showed elastic deformation up to 1873 K and revealed σb more than 600 MPa at this temperature, in addition, some composites showed higher σb than 900 MPa at the same temperature. These high mechanical behaviors are discussed with those of the simple binary ZrC/ZrB2 composites which were fabricated under the same conditions except for their starting materials. The best mechanical properties of binary composites were σb (474 MPa), Hv (18.5 GPa), and KIC (4.45 MPa·m1/2) at room temperature, and σb of 400 - 700 MPa at 1873 K. Overall, three-phase composites, nevertheless including soft carbon, have higher mechanical properties than the binary composites.

Carbon-fiber-reinforced ultrahigh-temperature ceramic (C/UHTC) matrix composites are an attractive candidate for fabricating various hot structures. The present study aimed to establish a Si-free Zr–Ti melt-infiltration method for fabricating C/UHTC matrix composites. To achieve this, the wettability of Zr–Ti alloys on carbon and their reactivity to carbon were examined. The alloys were melted on graphite plates and infiltrated into model preforms, which were made of porous carbon and had median pore diameters of 3 μm. The results showed that the apparent contact angle between Zr–Ti and C measured from melted alloys on carbon in room temperature was ~20–42° and that the alloys infiltrated into the preforms regardless of the Zr or Ti content. However, with an increase in the Zr content in the alloys, carbon disappeared and was absorbed into the alloys since the reactivity of Zr was higher than that of Ti and the specific surface area of the porous preform was higher than that of carbon-fiber-reinforced carbon composites, which are a typical preform of C/UHTC matrix composites. These results clearly indicate that not only the capillary flow during infiltration but also the reactivity of alloys to preforms should be considered in the process design for fabricating high-density composites via Zr–Ti infiltration.

We investigated the feasibility of the co-doping effect of zinc and chromium for copper and vanadium substitution, respectively, and reported the first successful Cr incorporation within the bulk Sn-based colusite structure.

Ultra-high temperature ceramics (UHTCs) are most recently getting much attention for structural parts of hypersonic missiles with their cruising speed of more than Mach 5. Most of the UHTCs are poor sinterability carbides, nitrides, and borides. Therefore, they have been studied and developed for a long time. However, there are still many problems to solve. In this paper, based on the solid-state reaction presented as an equation of (x + y)·ZrC + 2·y·B → x·ZrC + y·ZrB 2 + y·C, three-phase ZrC/ZrB 2 /C composites have been fabricated from ZrC and amorphous B powders using pulsed electric-current pressure sintering at 1373 to 2173 K for 6.0 × 10 2 s under 50 MPa in a vacuum. ZrC/ZrB 2 /C = 30/70/C~70/30/C vol% composites with the relative densities D r of 96.6 to 98.7% were obtained at 2073 K. The 60/40/C vol% composite revealed high bending strength σ b (554 MPa), Vickers hardness H v (19.2 GPa) and moderate fracture toughness K IC (5.25 MPa·m 1/2 ) at room temperature. Furthermore, all composites showed elastic deformation up to 1873 K and revealed σ b more than 600 MPa at this temperature, in addition, some composites showed higher σ b than 900 MPa at the same temperature. These high mechanical behaviors are discussed with those of the simple binary ZrC/ZrB 2 composites which were fabricated under the same conditions except for their starting materials. The best mechanical properties of binary composites were σ b (474 MPa), H v (18.5 GPa), and K IC (4.45 MPa·m 1/2 ) at room temperature, and σ b of 400 - 700 MPa at 1873 K. Overall, three-phase composites, never-theless including soft carbon, have higher mechanical properties than the binary composites.

The heat resistance of carbon fiber-reinforced ultra-high-temperature ceramic matrix composites (C/UHTCMCs) was characterized by arc-wind tunnel testing with heat fluxes of 2, 4.54, and 6.68 MW/m2. C/UHTCMCs were fabricated via Zr-Ti binary alloy (Zr-20at%Ti, Zr-64at%Ti, Zr-80at%Ti) melt infiltration. The thickness and weight changes of the specimen were dependent on the composition of the infiltrated Zr-Ti alloy. Microstructural and thermodynamic analyses revealed that formed oxides on the surface of composites are composed of ZrO2 solid solution, ZrTiO4 solid solution, and TiO2 solid solution. The composition of oxides also depends on the composition of infiltrated alloys. The difference originates from the formation and composition of oxide scales and the dynamic pressure. Especially, formation of liquid oxides accelerates the recession of composites because liquid oxides are disappeared from the surface owing to the dynamic pressure during arc-wind tunnel testing. To withstand aerodynamic heating above 2000 °C, formation of a solid (and liquid) oxide on the exposed surface is required to reduce recession.

In this study, we explored the consolidation, solid-solution formation, and high-temperature properties of carbides in the Ta-Nb-C system. The tantalum niobium carbide bulks can be consolidated by spark-plasma sintering only at a temperature of 2200 degrees C using a 30-min dwell. The ceramics were homogeneous solid solutions and a linear dependence of the lattice parameters on the NbC content was observed. The average grain size varied between 10 and 30 mu m, while the reference monolithic tantalum carbide consolidated under similar conditions had a grain size exceeding 40 mu m. The room temperature strength linearly decreased from TaC to NbC. The 75 mol% NbC ceramic showed almost an unchanged strength up to 1600 degrees C (450 +/- 20 MPa), following the linear decrease in strength to 290 MPa at 2000 degrees C. The monolithic tantalum carbide had showed the lowest strength at 2000 degrees C among the studied ceramics.

In this study, we explored the consolidation, solid-solution formation and high-temperature properties of tantalum hafnium carbide with the 1 TaC:4 HfC ratio, that is, Ta0.2Hf0.8C. Tantalum hafnium carbide bulks can be consolidated using spark-plasma sintering only at temperatures exceeding 2200 degrees C. The bulks prepared using a 40-min dwell at 2200 degrees C had the lattice parameter a = 4.571(9) A. Based on the three-point flexural tests, it was observed that the toughness and strength of Ta0.2Hf0.8C remained high at 2000 degrees C (3.4 +/- 0.4 MPa m(1/2), 500 +/- 20 MPa). At 2000 degrees C, majority of carbides show a plastic behavior, but the strain-stress curves of the SPSed Ta0.2Hf0.8C ceramic were linear. Using the shrinkage rate data during the SPS and the strain-stress data from the high-temperature flexure, we estimated the activation energies for the densification and flexure as 820 +/- 20 kJ/mol and 1180 +/- 120 kJ/mol, respectively.