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Metastable c-Al xT1− xN is an important and well-established hard coating in the tool industry. To improve the mechanical and thermal properties, Al-rich c-Al xTi1− xN coatings with controllable preferred crystal orientations were fabricated via low-pressure chemical vapor deposition ( LP- CVD) in an industrial plant, using an AlCl3-TiCl4-NH3-Ar-H2 precursor system. The c-Al xTi1− xN coatings with (100)- and (111)-preferred orientations and average x values of 0.82 and 0.73, respectively, comprised c-Al(Ti)N/c-Ti(Al)N nanolamellae with average compositions of c-Al0.9Ti0.1N/c-Al0.6Ti0.4N and c-Al0.80Ti0.20N/c-Al0.50Ti0.50N; the average lamellar periods were 7.7 and 4.5 nm, respectively. High-resolution transmission electron microscopy indicated that the c-Al(Ti)N/c-Ti(Al)N nanolamellae were modulated along the <100> direction, implying coherent spinodal decomposition of c-Al xTi1− xN in the as-deposited state. The hardness of the c-Al xTi1− xN coatings varied from 33 to 36 GPa, depending on the (100)- or (111)-preferred orientation. Residual stress measurements in the as-deposited state showed tensile stress values of 1.8 and 4.6 GPa for the (100)- and (111)-oriented c-Al xT1− xN coatings, respectively. This stress may be generated by the difference in the thermal expansion coefficient of the c-Al xT1− xN coating and the carbide substrate and by coherency stress in the c-Al(Ti)N/c-Ti(Al)N nanolamellae. In situ high-temperature X-Ray diffraction results revealed high thermal stability up to 1000°C. [ABSTRACT FROM AUTHOR]

The mechanical properties of a ZrB2-10 vol% ZrC ceramic were measured up to 2300°C in an argon atmosphere. Dense billets of ZrB2-9.5 vol% ZrC-0.1 vol% C were produced by hot-pressing at 1900°C. The ZrB2 grain size was 4.9 μm and ZrC cluster size was 1.8 μm. Flexure strength was 695 MPa at ambient, decreasing to 300 MPa at 1600°C, increasing to 345 MPa at 1800°C and 2000°C, and then decreasing to 290 MPa at 2200°C and 2300°C. Fracture toughness was 4.8 MPa·m½ at room temperature, decreasing to 3.4 MPa·m½ at 1400°C, increasing to 4.5 MPa·m½ at 1800°C, and decreasing to 3.6 MPa·m½ at 2300°C. Elastic modulus calculated from the crosshead displacement was estimated to be 505 GPa at ambient, relatively unchanging to 1200°C, then decreasing linearly to 385 GPa at 1600°C, more slowly to 345 GPa at 2000°C, and then more rapidly to 260 GPa at 2300°C. Surface flaws resulting from machining damage were the critical flaw up to 1400°C. Above 1400°C, plasticity reduced the stress at the crack tip and the surface flaws experienced subcritical crack growth. Above 2000°C, microvoid coalescence ahead of the crack tip caused failure. [ABSTRACT FROM AUTHOR]

A glucose sol-gel combustion method has been developed to synthesize composite nanopowders with equal volume fractions of Y2O3 and MgO. The synthesis involves the generation of precursor foam containing Y3+ and Mg2+ cations via the chemical and thermal degradation of glucose molecules in aqueous solutions. Subsequent calcination of the foam gave the composite nanopowders uniform composition and surface areas of 44-62 m2/g depending on the relative amount of glucose. Then the nanopowder with an average particle size of 19 nm was consolidated by the hot-pressing technique with different sintering temperatures. The fabricated nanocomposite is mid-infrared transparent as the result of fine grains, narrow grain size distribution, and uniform phase domains. The transmittance increases with increase in the sintering temperature and reaches 83.5% at 3-5 μm mid-infrared wave range once the temperature reaches 1350°C, which is close to the theoretical value of 85%. And it is noteworthy that the cutoff wavelength reaches 9.6 μm, which is superior to those of spinel, AlON, and sapphire. And the Vickers hardness of the sample reaches 10.0 ± 0.1 GPa, which is significantly higher than those of the coarse grained single-phase MgO and Y2O3. The results indicate that the glucose sol-gel combustion and hot-pressing technique is an effective method to fabricate infrared transparent Y2O3-MgO nanocomposites. [ABSTRACT FROM AUTHOR]

A rapid synthesis method for preparing homogeneous and submicrometer-sized cerium-doped yttrium aluminum garnet (Ce: YAG) particles was proposed in this work. Instead of precipitating the YAG amorphous precursor prior to the solvothermal process, cerium, yttrium, and aluminum nitrates were dissolved in alcoholic solvents to form transparent and clear solutions that were directly transferred into the stainless autoclave to undergo the solvothermal reaction. Four different alcohol solvents, that is, ethanol, 2-propanol, 2-butanol, and tert-butanol, were used as the reaction medium. The crystallization mechanisms in correlation with the alcohol solvent properties, such as the supercritical point and the dielectric constant, were discussed. The interaction between the alcohol solvent and the precursor salts were also investigated. Well-dispersed and spherical Ce: YAG particles in size ranging from 200 to 350 nm were obtained in one pot via solvothermal reaction at 285°C from 5 to 8 h. [ABSTRACT FROM AUTHOR]

A sol-gel combustion method has been used to synthesize Y2O3-50 vol%MgO composite nanopowders. Solutions of the precursor nitrates were mixed with citric acid and ethylene glycol, heated from 200°C to a predetermined temperature gradually, giving nanocrystalline ceramic powders. The influence of the ratio of yttrium nitrate to the whole precursor mixture and the holding temperature on the properties of the composite nanopowder was investigated using a combination of thermal analysis, X-ray diffraction, specific surface area analysis, and scanning electron microscopy techniques. When the ratio of yttrium nitrate to the whole precursor mixture reaches 22.5 mol%, the average particle size of synthesized composite nanopowder is 13 nm and the specific surface area is 45.9 m²/ g. Then the synthesized Y2O3-MgO composite nanopowder was consolidated by the hot-pressing technique at 1200°C with different dwell time. As a result, the nanocomposite ceramic prepared with a dwell time of 60 min got the highest transmittance of 75% at 5 µm wavelength. The cut-off wavelength of Y2O3-MgO nanocomposite ceramic reaches 9.8 µm, which is superior to other mid-IR transparent materials. In addition, the fabricated sample is more or less transparent in visible wavelengths and the transmittance at 0.8 µm is as high as 14.5%. [ABSTRACT FROM AUTHOR]

This article addresses the effects of small holes (1-2 mm in diameter) on the tensile properties of a woven C/SiC composite. Holes are introduced by one of two methods: by insertion of fugitive rods into the woven preform before adding the matrix or by drilling after panel fabrication. The tensile strength exhibits only a weak sensitivity to the presence of holes, regardless of the manner in which the holes are introduced. Nevertheless, woven holes appear to be somewhat less detrimental to strength. The effects are attributed to the fact that the tows in specimens with woven holes are locally intact and thus contribute to load-bearing. Full-field strain maps reveal strong spatial periodicity, reflecting the underlying crack pattern and weave geometry. Even when averaged over lengths equal to the unit cell dimensions, the strains exhibit periodicity, with a wavelength dictated by the unit cell dimensions. When holes are present, the strain patterns reflect a convolution of the effects of weave geometry and strain concentrations near the holes. The results have implications for development of high-fidelity models for these composites: notably, in selection of a suitable representative volume element and for modeling schemes that capture the stochastic nature of cracking. [ABSTRACT FROM AUTHOR]

The composition of the borosilicate glass layer formed during oxidation of ZrB2-30 vol% SiC was determined to elucidate the extent of B2 O3 retention in the oxide during high-temperature oxidation. Oxidation was conducted in stagnant air at 1300°C, 1400°C, and 1500°C for times between 100 and 221 min. Specimens were characterized using mass change and scanning electron microscopy. After oxidation, the borosilicate glass layer was dissolved from the specimens sequentially with deionized H2 O and HF acid, to analyze the glass composition using inductively coupled plasma optical emission spectrometry. It was found that the average B2 O3 content in the glass scale ranged from 23 to 47 mol%. Retained B2 O3 content in the bulk of the glass decreased with increasing temperature, confirming increased volatility with temperature. Boron depth profiles were also obtained in the near surface region using X-ray photoelectron spectroscopy and energy dispersive spectroscopy. The measured B concentrations were used to estimate the B2 O3 concentration profile and B diffusion coefficients in the borosilicate glass. Implications for the ZrB2-SiC oxidation process are discussed. [ABSTRACT FROM AUTHOR]

The oxidation of highly porous ceramic matrix composites ( PCMCs) based on different Tyranno® fibers has been analyzed by means of thermogravimetry and electron microscopy. Both uncoated fibers and PCMC materials exhibit parabolic kinetics between 900°C and 1250°C, these being faster for Ti-doped than for Zr-doped Tyranno fibers. Oxide layers in Ti-doped fibers are porous and partially crystalline, whereas in Zr-doped materials a significant fraction of relatively coarse β-SiC grains is still found embedded in the amorphous silica matrix. On the other hand, the CVD-SiC coatings exhibit higher oxidation rates from the outer surface than from the inner one, a phenomenon that has been associated not only with the more difficult access of oxygen to the inner face but also with the highly <111> textured structure of these coatings, for which very different oxidation rates have been published for the inward and outward directions. Cracking phenomena observed above 1100°C for long dwelling times do not lead to an acceleration of the oxidation process, which could be due to the simultaneous crystallization of the amorphous silica layers. [ABSTRACT FROM AUTHOR]

Niobium aluminum carbide ( Nb4 AlC3), as a member of the MAX phases, can retain its stiffness and strength up to over 1400°C. However, its applications are limited due to its poor oxidation resistance at high temperatures. In this work, silicon pack cementation has been applied to improve the oxidation resistance of Nb4 AlC3. After Si pack cementation at 1200°C for 6 h, a dense and uniform silicide coating which was mainly composed of NbSi2 and SiC and well bonded to the matrix was successfully formed on the surface of Nb4 AlC3. The Si pack cemented Nb4 AlC3 shows excellent oxidation resistance up to 1200°C due to the formation of protective Al2 O3 layer. The oxidation kinetics of the cemented Nb4 AlC3 obey parabolic law all the way to up to 1200°C, and the parabolic rate constants of cemented Nb4 AlC3 are in the same order of magnitude as those of Ti3 AlC2 in the temperature range 1000°C-1200°C. However, the oxidation of the cemented Nb4 AlC3 was accelerated after oxidation at 1300°C for about 15 h due to the formation of NbAlO4. [ABSTRACT FROM AUTHOR]

Magnesium aluminate spinel solid solutions with the alumina-rich compositions MgO·2 Al2 O3 and MgO·2.5 Al2 O3 have been prepared as polycrystalline ceramics with average in-line transmissions at 550 nm of 85.5 ± 0.3% and 80.9 ± 0.4%, respectively. Starting powders are prepared from combinations of high purity Mg( OH)2 and γ- Al2 O3 thoroughly mixed in an aqueous slurry, and the solids are collected, dried, calcined, mixed with LiF sintering aid, and sieved. The optimum amount of LiF added varies with the alumina composition of the spinel solid solution. The powders are sintered into dense ceramics by hot pressing at 1600°C under vacuum and 20 MPa uniaxial load followed by hot isostatic pressing at 1850°C under 200 MPa in Ar. Both compositions exhibit exaggerated grain growth with average sizes well over 500 μm. Knoop hardness measurements are 11.2 ± 0.3 GPa for MgO·2 Al2 O3 and 11.0 ± 0.4 GPa for MgO·2.5 Al2 O3. [ABSTRACT FROM AUTHOR]

The fabrication of 0.5 mol% Ce:LuAG transparent ceramics starting from synthetic nanosized Ce:LuAG powders was investigated by low temperature vacuum sintering. It was found that high quality optical Ce:LuAG ceramics could be densified successfully by vacuum sintering (<10-3 pa) at 1750°C for 10 h. The in-line optical transmittance of as-sintered Ce:LuAG ceramics with thickness of 0.7 mm could reach 73.48% at the wavelength of 550 nm. The microstructure observations revealed that transparent Ce:LuAG ceramics were composed of uniform LuAG grains with average size of 9 μm and HRTEM morphology indicated that no impurity segregation existed at grain boundaries or within Ce:LuAG grains. It was also demonstrated that the annealing treatment (at 1450°C for 20 h in air) could greatly enhance the luminescent intensity of as-sintered Ce:LuAG ceramics under excitation of X-ray radiation (75 kV, 25 mA), which makes it a potential candidate to be applied in radiation detector. [ABSTRACT FROM AUTHOR]

Application of SiC-based ceramic matrix composites ( CMCs) in combustion environments demands the use of an environmental barrier coating ( EBC) to prevent volatilization of the protective SiO2 scale in flowing water vapor. The EBC only provides protection while present on the surface; cracking and spallation of the coating leaves the underlying SiC vulnerable to the oxidation-volatilization processes. A robust matrix material chemically tailored to regrow a yttrium silicate scale in the event of EBC loss has been developed by incorporating yttrium bearing species including YB2, Y2 O3, and Y5 Si3 into the SiC. During oxidation a borosilicate glass helps seal cracks while Y2 O3 and SiO2 react to form Y2 Si2 O7 for environmental protection. Candidate compositions were oxidized for 10 min to 100 h at 1400°C and for 24 h at 1500°C to understand the scale growth. The prospects for effectively applying this approach in CMCs are discussed. [ABSTRACT FROM AUTHOR]

Oxidation of SiC can occur in a passive mode where a protective film is generated or in an active mode where a volatile suboxide is generated and can lead to rapid material consumption. The transition between these two modes of oxidation is a critical issue. Evidence indicates that this transition occurs via a different mechanism for the active-to-passive transition as compared with that of the passive-to-active transition. In Part I of this article, the former (active-to-passive mode) is explored. Three different types of SiC are examined: Si-rich SiC, stoichiometric SiC, and C-rich SiC. Evidence suggests that the SiO2/ SiC equilibrium requirements as well as formation of SiO(g) at the SiC surface and subsequent oxidation to SiO2(s) are critical issues in the active-to-passive transition. [ABSTRACT FROM AUTHOR]

This study is focused on the effect of the sintering additive on the microstructure and properties of HfB2 composites reinforced with SiC Hi-Nicalon fibers. The materials were spark plasma sintered with addition of 5-10 vol% of Si3 N4 or ZrSi2. The fibers morphology was examined using scanning and transmission electron microscopy and remarkable differences were observed depending on the additive. Local hardness and Young's modulus were measured by nanoindentation to investigate the fiber mechanical behavior. The introduction of 20 vol% SiC short fibers into the HfB2 matrix increased the fracture toughness up to 5.4 MPa m1/2 for the material sintered with ZrSi2. The room temperature flexural strength of the materials containing fibers slightly decreased when ZrSi2 was used, but with the addition of Si3 N4 an improvement of more than the 40%, as compared to the unreinforced material was observed. [ABSTRACT FROM AUTHOR]

Oxidation of SiC can occur in a passive mode, where a protective film is generated, or in an active mode, where a volatile suboxide is generated. The transitions from active-to-passive and passive-to-active are particularly important to understand as they occur via different mechanisms. In Part II of this article, the passive-to-active transition is explored. Three different types of SiC are examined- Si-rich SiC, stoichiometric SiC, and C-rich SiC. In addition to an in situ transition from passive-to-active, the effect of a preformed film on all three types of SiC is explored. It appears that the passive-to-active transition occurs when the SiO2 scale begins to react with the SiC substrate. This reaction generates SiO(g) and CO(g), which build pressure beneath the SiO2 scale, eventually causing the oxide to rupture. In addition, the SiO(g) can oxidize a distance away from the surface leading to the formation of SiO2 needles and further promoting this SiO2/ SiC reaction. Thermodynamic and kinetic data are used to predict transition pressures of oxygen, which show reasonable agreement with those measured. [ABSTRACT FROM AUTHOR]

A dense oxidation protective SiC- Si ceramic coating with well-dispersion SiC nanowires was prepared on carbon/carbon ( C/ C) composites using a two-step technique consisting of chemical vapor deposition and hot-pressing reactive sintering. The results showed that the toughness and thermal shock resistance of the coating were dramatically improved, resulting in an excellent oxidation protection for the coated C/ C composites, which is attributed primarily to the toughening effects of SiC nanowires in the coating including two special energy dissipation mechanisms involving the super-plasticity deformation of SiC nanowires and the plastic fracture at the interface of the nanowire-matrix, except for nanowire pullout, nanowire bridging, and microcrack deflection. More importantly, a novel oxidation protective failure mechanism of the coated C/ C composites revealed that the presence of Al3+ in the coating, damaged the network structure of SiO2 glass and resulted in the slight oxidation of C/ C composites. [ABSTRACT FROM AUTHOR]

Magnesium aluminate spinel with the alumina rich composition MgO · 1.5 Al2 O3 has been prepared as a transparent polycrystalline ceramic with average in-line transmission at 550 nm of 83.3 ± 0.9% and >80% throughout the visible spectrum. This finding significantly increases the compositional range over which polycrystalline magnesium aluminates can be prepared as fully dense ceramics with high transparency to visible light. Starting powders are prepared from combinations of high purity Mg( OH)2 and γ- Al2 O3 thoroughly mixed in an aqueous slurry, and the solids are collected, dried, calcined, mixed with LiF sintering aid, and sieved. The powders are sintered into dense ceramics by hot pressing at 1600°C under vacuum and 20 MPa uniaxial load, followed by hot isostatic pressing at 1850°C under 200 MPa Ar. The crucial parameter for forming highly transparent MgO · 1.5 Al2 O3 ceramic from this procedure is to hold the amount of LiF to 0.25 wt%. [ABSTRACT FROM AUTHOR]

Directionally solidified Al2 O3- Er3 Al5 O12- ZrO2 eutectic ceramic rods were fabricated by the laser-assisted float zone method at growth rates from 25 to 1200 mm/h. The microstructure of the eutectic rods was studied as a function of the solidification rate and the three eutectic phases present in the material were identified by X-ray and electron diffraction. The size of the eutectic phases measured in the plane perpendicular to the growth direction decreased when the growth rate increased. The microstructure showed a geometrical pattern morphology at low growth rates, an irregular faceted and interpenetrating morphology at medium rates, and a nanofibrillar morphology in samples solidified at 1200 mm/h. The fibrous pattern consisted of Al2 O3 trifold shaped nano-fibers surrounded by a jacket of Er-stabilized ZrO2 ( t < 50 nm) and embedded in a matrix of Er3 Al5 O12 of ~150 nm width. The residual stress in the alumina phase due to the thermal contraction mismatch between phases was determined by piezospectroscopy. It decreased with solidification rate from 262 MPa compressive at room temperature in the sample with the coarsest microstructure to 135 MPa in the sample solidified at 1200 mm/h. A linear behavior of the thermoelastic stresses was found in the 110-370 K temperature range. The stress relief temperature at which the stresses become zero markedly decreased with the interphase spacing. The decrease was attributed to thermal activation of diffusional creep in the nanometric ZrO2 phase. [ABSTRACT FROM AUTHOR]

Highly transparent Er:YAG ceramics were fabricated by solid-state reactive sintering using a mixture of commercial α-Al2O3, Y2O3, and Er2O3 powders with tetraethoxysilane and MgO as sintering aids. A fully dense 1.0 at.% Er:YAG ceramic with an average grain size of ~25 μm was obtained by vacuum sintering at 1800°C for 30 h. The in-line transmittance reached 83% near the lasing wavelength of 1645 nm with a scattering loss of ~0.02 cm−1. Laser operation of such a Er:YAG ceramic rod (4.0 mm × 4.0 mm × 10.8 mm) was demonstrated at 1645 nm with a slope efficiency of 51% under resonant pumping at 1532 nm, and the maximum continuous-wave laser output was 13 W. [ABSTRACT FROM AUTHOR]

Experimental data on the oxidation kinetics of SiC-containing diborides of Zr and Hf in the temperature regime of 1473-2273 K are interpreted using a mechanistic model. The model encompasses counter-current gas diffusion in the internal SiC depleted zone, oxygen permeation through borosilicate glass channels in the oxide scale, and boundary layer evaporation at the surface. The model uses available viscosity, thermodynamic and kinetic data for boria, silica, and borosilicate glasses, and a logarithmic mean approximation for compositional variations. The internal depletion region of SiC is modeled with CO/CO2 counter diffusion as the oxygen transport mechanism. Data reported for pure SiC in air/oxygen, for ZrB2 containing varying volume fractions of SiC, and for SiC-HfB2 ultra-high temperature ceramics ( UHTCs) by different investigations were compared with quantitative predictions of the model. The model is found to provide good correspondence with laboratory-furnace-based experimental data for weight gain, scale thicknesses, and depletion layer thicknesses. Experimental data obtained from arc-jet tests at high enthalpies are found to fall well outside the model predictions, whereas lower enthalpy data were closer to model predictions, suggesting a transition in mechanism in the arc-jet environment. [ABSTRACT FROM AUTHOR]

Silicon carbide nanofiber dispersion within a silicon oxycarbide glassy ceramic was achieved through a combination of a fast sol-gel procedure for in situ ceramic matrix synthesis and nanofiber conversion from sacrificial multiwalled carbon nanotube templates. Nanotubes were dispersed using both surfactant adsorption and a covalent sidewall modification scheme with gel-grafting capabilities. The combination of high temperature processing and silicon monoxide precursor concentrations allowed substantial carbothermal reduction of the nanotube templates, yielding silicon carbide nanofibers. The resulting nanocomposites were examined for density, Vickers microhardness, Young's modulus, and fracture toughness. The surfactant-assisted route inhibited ceramic densification, offering virtually no mechanical property enhancement. In contrast, the covalently functionalized nanotube templates at 0.8 wt% loading enhanced tensile modulus of 77% while simultaneously maintaining both Vickers microhardness and fracture toughness. These results indicate strong interfacial adhesion between the nanofiber surface and host matrix despite the abrupt chemical changes experienced during the high temperature processing. [ABSTRACT FROM AUTHOR]

Nanocomposite powders with equal volume fractions of Y2 O3 and MgO have been produced by the thermal decomposition of precursor mixtures of yttrium nitrate and magnesium nitrate. Solutions of the precursor salts were mixed with ammonium acetate fuel, dried to form a gel-like substance, and then calcined to give nanocrystalline ceramic powders. The amount of ammonium acetate added to the metal nitrate precursors was varied systematically, and the morphology and distribution of the component phases in consolidated compacts of the resultant ceramic powders were examined by a combination of focused ion beam sectioning, scanning, and transmission electron microscopy. The dispersion of the Y2 O3 and MgO phases within the synthesized powders improved, and the sizes of the phase domains reduced, with increasing ammonium acetate content up to the quantity required for a stoichiometric redox reaction with the metal nitrates. The addition of excess ammonium acetate gave no further improvement in phase domain dispersion or reduction in phase domain sizes. These phenomena are related to the thermal characteristics for the decomposition of the precursors and their effect on phase separation during oxide crystallization. [ABSTRACT FROM AUTHOR]

The Ce3+-doped Y2O3-Al2O3-SiO2 ( YAS) bulk glasses with low SiO2 (≤40 mol%) were prepared by flame spray-quench method and hot press sintering. YAG nanoglass-ceramics were derived from YAS bulk glass by a controlled crystallization. The differential thermal analysis ( DTA) results showed that the glass-forming ability of YAS system was strongly dependent on SiO2 content and the supercooling degree required for forming YAS glass increased with the decrease of SiO2 content. The YAS glass compositions had been extended to low SiO2 phase region (10-40 mol%) by flame spray-quench method. The study of crystallization process showed that glass matrixes experienced initially a phase-separation followed by crystallization during the heat treatment. The phase-separated grains (100-300 nm) that were composed of YAG nanocrystallites precipitated in the glass matrix. And the intensity of emission spectra increased with the decreasing SiO2 content. [ABSTRACT FROM AUTHOR]

The thermal stability of ZrB2-based composites containing SiC-chopped fibers was tested in a bottom-up furnace at 1200°C, 1500°C, and 1700°C for 30 min. The oxidation behavior was studied by X-ray diffraction, scanning electron microscopy, and weight gain. The degradation induced by oxidation was also evaluated considering the strength decrease of oxidized bars. Baseline ZrB2-composites containing the same amount of SiC particles or SiC whiskers were tested in the same conditions for comparison. [ABSTRACT FROM AUTHOR]

Equiaxed yttrium–lanthanum phosphate nanoparticles (Y0.7,La0.3)PO4·0.7H2O were made and used to continuously coat Nextel™ 720 fiber tows. The particles were precipitated from a mixture of yttrium and lanthanum citrate chelate and phosphoric acid (H3PO4), and characterized with differential thermal analysis and thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The coated fibers were heat treated at 1000°–1300°C for 1, 10, and 100 h. Coating grain growth kinetics and coated fiber strengths were determined and compared with equiaxed La-monazite coatings. The relationships between coating porosity, coating hermeticity, and coated fiber strength are discussed. [ABSTRACT FROM AUTHOR]