Thermochemical Nitriding and Oxynitriding of Ti Alloys.

Nitrided and oxynitrided coatings that formed on α alloy (c.p.-Ti), near-α alloy (Ti-2.1Al-2.5Zr), (α + ß) alloy (Ti-6Al-4V), and ß alloy (Ti-6Al-2Zr-1Mo-1V) were microstructurally characterized. The nitriding at 950 °C and PN2 ═ 105 Pa for 5 h formed TiN, Ti2N, and α-Ti(N) layers from the surface. The nitriding tendency increased in the order of ß alloy, (α + ß) alloy, near-α alloy, and α alloy. The Ti-N coatings transformed to Ti-N-O coatings when the nitrided alloys were exposed to PO2 ═ 10-2 Pa during cooling at the final stage of the nitriding. This oxynitriding process led to the formation of TiNxO1-x, Ti2N, and α-Ti(N,O) layers from the surface where a small amount of rutile-TiO2 coexisted. Oxynitriding was more effective than nitriding in increasing the surface microhardness, with the former accumulating more compressive residual stress than the latter.

High Temperature Corrosion of TiAlCrSiN Films in N2/0.1%H2S Gas.

Nanomultilayered TiAlCrSiN film was corroded in N2/0.1%H2S-mixed gas at 900 °C for 5-300 h. It corroded to TiO2, α-Al2O3, and Cr2O3. From the early corrosion stage, not only the outward diffusion of Al, Ti, Cr, and Si but also the inward migration of oxygen occurred. As the corrosion proceeded, the outermost TiO2 layer, outer (Ti-depleted, (Al,Cr)-rich)-oxide layer, inner (Ti-rich, (Al,Cr)-depleted)-oxide layer, and partially oxidizing innermost film formed on the oxygenaffected film.

High temperature oxidation of ZrO2/Al2O3 thin films deposited on steel.

Thin ZrO2/Al2O3 films that consisted of alternating monoclinic ZrO2 nanolayers and amorphous Al2O3 nanolayers were deposited on a tool steel substrate using Zr and Al cathodes in a cathodic arc plasma deposition system, and then oxidized at 600-900 degrees C in air for up to 50 h. The ZrO2/Al2O3 films effectively suppressed the oxidation of the substrate up to 800 degrees C by acting as a barrier layer against the outward diffusion of the substrate elements and inward diffusion of oxygen. However, rapid oxidation occurred at 900 degrees C due mainly to the increased diffusion and subsequent oxidation of steel as well as the crystallization of amorphous Al2O3.

Effect of Al2O3 nano-filler on properties of glass-based seals for solid oxide fuel cells.

This study compares the viscosity and strength of three glass-based seals prepared with or without nano or micron-sized alumina powder used as filler material. Measurements of the viscosity and bending strength of the glass-based seals showed that addition of the nano-sized alumina powder to the glass increased both the high-temperature viscosity and the strength of the sintered glass matrix. Strength tests and observations of the microstructure of the fracture surface of the seal samples confirmed the strengthening of the glass network structure. Conversion of non-bridging oxygen to bridging oxygen is presumed to occur upon the addition of alumina to the glass sample. The strengthening of the alumina-glass composite seal was attributed to the alumina nano-filler and prolonged heat treatment at elevated temperatures.

Transmission electron microscopy characterization of thermomechanically treated Al3Ti-(8, 10, 15)% Cr intermetallics.

The ordered L12-type Al3Ti-(8, 10, 15)% Cr intermetallic compounds, namely, Al67Ti25Cr8, Al66Ti24Cr10, and Al59Ti26Cr15, were prepared by induction melting followed by thermomechanical treatment. Their microstructure, compositional variation, and crystal structure were characterized using X-ray diffraction, optical microscopy, and scanning and transmission electron microscopy equipped with energy-dispersive spectroscopy. The Al67Ti25Cr8 alloy consisted of the L12-Al3Ti matrix and precipitates of α2-Ti3Al, D022-Al3Ti, and γ-TiAl. The Al66Ti24Cr10 and Al59Ti26Cr15 alloys consisted of the L12-Al3Ti matrix and grains of α-TiAl and ß-Cr.

Oxidation of nano-multilayered AlTiSiN thin films between 600 and 1000 degrees C in air.

Multilayered AlTiSiN films with a composition of 32.0Al-12.4Ti-4.9Si-50.7N (at.%) were deposited on a steel substrate in a nitrogen atmosphere by cathodic arc plasma deposition. The films consisted of crystalline approximately 8 nm-thick AISiN nanolayers that originated from the Al-Si target and approximately 3 nm-thick TiN nanolayers that originated from the Ti target. Their oxidation characteristics were studied between 600 and 1000 degrees C for up to 20 h in air. They displayed good oxidation resistance due to the formation of a thin, dense Al2O3 surface scale below which an (Al2O3, TiO2, SiO2)-intermixed inner scale existed. They oxidized slower than TiN films because protective Al2O3-rich scales formed on the surface. However, they oxidized faster than CrN films because impure Al2O3 scale formed on the AlTiSiN film. Their oxidation progressed primarily by the outward diffusion of nitrogen and substrate elements, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film.

Effect of resin infiltration on the thermal and mechanical properties of nano-sized silica-based thermal insulation.

Several kinds of nano-sized silica-based thermal insulation were prepared by dry processing of mixtures consisting of fumed silica, ceramic fiber, and a SiC opacifier. Infiltration of phenolic resin solution into the insulation, followed by hot-pressing, was attempted to improve the mechanical strength of the insulation. More than 22% resin content was necessary to increase the strength of the insulation by a factor of two or more. The structural integrity of the resin-infiltrated samples could be maintained, even after resin burn-out, presumably due to reinforcement from ceramic fibers. For all temperature ranges and similar sample bulk density values, the thermal conductivities of the samples after resin burn-out were consistently higher than those of the samples obtained from the dry process. Mercury intrusion curves indicated that the median size of the nanopores formed by primary silica aggregates in the samples after resin burn-out is consistently larger than that of the sample without resin infiltration.

High temperature oxidation of a nanolayer laminated (Cr0.95Ti0.05)2AlC compound in air.

High-purity, dense nano-laminated (Cr0.95Ti0.05)2AlC compounds were synthesized via a powder metallurgical route. Their oxidation characteristics were investigated by exposing them to temperatures between 900 and 1200 degrees C in air. The alloying Ti in the Cr layer of Cr2AlC did not significantly change the crystal structure and microstructure of Cr2AlC. But, it increased the oxidation rate of the Cr,AlC. The scale morphology of the (Cr0.95Ti0.05)2AlC was basically similar to that of the pure Cr2AlC. The main difference was that the (Cr0.95Ti0.05)2AlC contained oxide nodules. These formed because the titanium oxidized to TiO2, making the Cr2AlC susceptible to nodular oxidation. However, alpha-Al2O3 was still the major oxidation product in both the (Cr0.95Ti0.05)2AlC and pure Cr2AlC.

Effect of nanoparticle coating on the thermal conductivity of microporous thermal insulations.

Microporous thermal insulations were prepared from mixtures of nano-sized fumed silica, micron-sized fibers and opacifier particles. Those micron-sized particles were dry coated with nano-sized fumed silica particles by mechanical process using a compressive-shear type mill. The effect of nanoparticle coating on the thermal conductivity of the insulation media was investigated using a hot-wire method. Effect of nanoparticle coating was found to be more pronounced for the insulation composed of fumed silica and fiber than for the one composed of fumed silica, fiber and an opacifier. By adding 15% SiC or TiO2 opacifier, the thermal conductivity of the insulation samples could be lowered to 0.08 Wm(-1) K(-1) at temperature range of 805 approximately 817 degrees C. The temperature dependent thermal conductivity of the sample containing glass fiber did not exhibit any remarkable changes compared to the one containing ceramic fiber.

High temperature oxidation of WC-CrN Nano-multilayered film at 700 and 800 degrees C.

Nano-multilayered WC-CrN films were deposited onto steel substrates by an arc ion plating method. The oxidation characteristics of the films were studied at 700 and 800 degrees C for up to 60 h in air. In each case, during oxidation, carbon and nitrogen escaped from the film into the air, while oxygen from the air diffused into the film. Substrate elements diffused outwards towards the oxide surface. The high-temperature oxidation resistance was not satisfactory, mainly due to the formation of a non-protective, volatile W-oxide scale, and the escape of carbon and nitrogen from the film. The scale formed was prone to cracking and spallation. The oxidation resulted in the destruction of the original nano-multilayers.

Microstructure and Oxidation of (La,Sr)CrO3-Added Ti3SiC2 Composites.

Composites of Ti3SiC2-(10, 20, 40)wt% La0.8Sr0.2CrO3 were synthesized by hot pressing powders of Ti3SiC2 and La0.8Sr0.2CrO3. These powders reacted to form stable TiC carbides and LaTiO3, Cr2Ti4O11, La2O3, and SrCrO4 oxides during hot pressing. The composites consisted primarily of a fine TiC-rich matrix phase and coarse Ti3SiC2 dispersoids. The addition of oxidation-immune La0.8Sr0.2CrO3 into Ti3SiC2 increased the oxidation rate because TiC formed during hot pressing. During oxidation of the composites at 800-1000 degrees C for 100 h in air, Ti diffused outward to form an outer rutile-TiO2 layer, and oxygen transported inward to form an inner oxide layer.

High-Temperature Corrosion of Nano-Multilayered TiAISiN Thin Films in Ar-0.2%SO2 Gases.

Nano-multilayered TiAlSiN films with a composition of 26Ti-16.3Al-1.2Si-56.5N (at.%) were deposited onto steel via arc ion plating, and corroded at 800-900 °C for 30 h in Ar-0.2%SO2 gases. The films were corrosion resistant, because the oxidation process dominated sulfidation. The scales consisted primarily of Al2O3 and TiO2, where a small amount of Si dissolved.

Synthesis of Meltspun Multiwall Carbon Nanotube/Polycarbonate Fibers Through Solvent Casting and Melt Extrusion.

Films and strands consisting of polycarbonate (PC) containing 0.55 or 0.75 wt% multiwall carbon nanotubes (MWNTs) were synthesized through solvent casting and melt extrusion methods, respectively. They were further processed into fibers through melt spinning. Fibers made from melt-extruded strands exhibited a smoother surface, more uniform morphology, and better dispersion of MWNTs in PC than those made from solvent-cast films.

Effect of Al2O3 Nano-Filler on Properties of Alkali/Alkaline-Earth Borosilicate Glass Composite Sealants.

The effect of adding Al2O3 nano-filler (5 and 10 vol%) to two different alkali/alkaline-earth borosilicate glass sealants, particularly on the viscosity and electrical characteristics of the glass composite sealants, was investigated to improve the cyclic sealing performance. The effects of the filler and base glass composition on the viscosities, electrical conductivities, and phase transformations of the sealants were investigated. The glass viscosity was decreased by replacing 20 mol% SrO with alkali and zirconium oxide in a base alkaline-earth glass. Alumina filler increased the high-temperature electrical conductivities, as well as the viscosities, of the heat-treated glass composite sealants. The replacement of 20 mol% SrO with alkali and zirconium oxide in the base alkaline-earth glass decreased the electrical conductivity of the heat-treated glass containing Al2O3 nano-filler.

Effect of Heat Treatment on Properties of Glass Nanocomposite Sealants.

The objective of this study was to investigate the effect of heat treatments on the viscosities and electrical conductivities of glass sealants to be used in solid oxide fuel cells. Glass-based sealants, both with and without an alumina nanopowder added as a nanofiller, were heat treated at temperatures ranging from 750 degrees C to 770 degrees C for periods of up to 240 h. The effects of heat treatments on the viscosities, electrical conductivities and phase transformations of the sealants were investigated. The results showed that alumina nanopowder added to the glass increased both high-temperature electrical conductivities and the viscosities of the sintered glass nanocomposite sealants. However, lengthy heat treatments decreased the electrical conductivities of the glass nanocomposite sealants. This decrease in the conductivities of the heat-treated glass nanocomposites was attributed to the crystallization of glass phase, owing to the dissolution of the alumina nanofiller in the sealing glass.

Oxidation of Nano-Multilayered CrAlCuN Thin Films Between 800 and 1000 degrees C in Air.

Thin CrAlCuN films with a composition of 21.5Cr-18.6Al-5.6Cu-54.3N (at.%) were deposited on steel substrates by the cathodic arc plasma deposition, and oxidized for up to 50 h in air. They consisted of alternating crystalline CrN/AlN nano-multilayers where Cu was incorporated. At 800 degrees C, a thin Cr2O3 layer formed. At 900 and 1000 degrees C, an outer Cr2O3 layer and an inner (α-Al2O3, Cr2O3)-mixed layer formed. Copper diffused outward to a small extent during oxidation. The film had good oxidation resistance, owing to the formation of the protective Cr2O3 and α-Al2O3.

Corrosion of Ti3SiC2 carbides in N2/H2O/H2S gases at 800 and 900 degrees C.

The corrosion behavior of Ti3SiC2 carbides was studied at 800 and 900 degrees C for 30 and 100 h in a gas mixture containing 0.9448 atm of N2, 0.031 atm of H2O, and 0.0242 atm of H2S. The scales consisted primarily of rutile TiO2 and amorphous SiO2. Oxidation prevailed, and a small amount of sulfur was present over the whole scale, including the scale/matrix interface. Despite the hostile oxidizing, sulfidizing, and hydriding gas environments, Ti3SiC2 displayed relatively good corrosion resistance due to the formation of SiO2 in addition to TiO2.

Effect of alumina nanofiller on properties of heat-treated glass composite sealants.

Alkali/alkaline-earth borosilicate glass-alumina composites containing 10 vol% Al2O3 were prepared for use as solid oxide fuel cell sealants. The effect of heat treatment and Al2O3, addition on the viscosities and electrical conductivities was investigated to improve cyclic sealing performance. Upon a 48-h heat treatment, the viscosity of the glass-alumina composites at 750 degrees C was approximately four orders of magnitude higher than that of the base glass owing to the crystallization of the glass in the presence of Al2O3. Heat treatment increased the electrical conductivities of both the base glass and the glass-alumina composites. The electrical conductivities of glass-alumina composites in the range from 400 degrees C to 550 degrees C were three times higher than those of the base glass regardless of heat treatment. This increase in the conductivities and viscosities by heat treatment was attributed to the devitrification and structural densification of the sealing glass and the partial dissolution of the Al2O3 filler in alkali/alkaline-earth borosilicate sealing glass.

Video deblurring algorithm using accurate blur kernel estimation and residual deconvolution based on a blurred-unblurred frame pair.

Blurred frames may happen sparsely in a video sequence acquired by consumer devices such as digital camcorders and digital cameras. In order to avoid visually annoying artifacts due to those blurred frames, this paper presents a novel motion deblurring algorithm in which a blurred frame can be reconstructed utilizing the high-resolution information of adjacent unblurred frames. First, a motion-compensated predictor for the blurred frame is derived from its neighboring unblurred frame via specific motion estimation. Then, an accurate blur kernel, which is difficult to directly obtain from the blurred frame itself, is computed using both the predictor and the blurred frame. Next, a residual deconvolution is applied to both of those frames in order to reduce the ringing artifacts inherently caused by conventional deconvolution. The blur kernel estimation and deconvolution processes are iteratively performed for the deblurred frame. Simulation results show that the proposed algorithm provides superior deblurring results over conventional deblurring algorithms while preserving details and reducing ringing artifacts.

Gas nitriding and subsequent oxidation of Ti-6Al-4V alloys.

Ti-6Al-4V alloys consisting of α-Ti grains and intergranular ß-Ti islands were nitrided at 850°C for 1 to 12 h under a nitrogen pressure of 1 Pa. With increasing nitriding time, the Ti-N compound layer became thicker, and the α-Ti diffusion zone containing dissolved nitrogen became wider. In the Ti-N compound layer, the initially formed Ti2N became TiN as the nitriding progressed. The nitride layers were oxidized to rutile-TiO2 after oxidation at 700°C for 10 h in air.