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A mullite/Si multilayer coating was deposited on a SiC substrate using atmospheric plasma spraying. Mud cracking of the protective surface mullite layer was examined using a high-temperature observation system (HTOS). In-plane surface strain distributions were also measured using the digital image correlation (DIC) method. The experimental results showed that mud cracks nucleated in the mullite layer during heating, primarily due to shrinkage of the mullite during crystallization. The cracking event was detectable by mapping the maximum principal strain distribution. We clearly demonstrated that HTOS and DIC are effective tools for investigating the degradation mechanisms of thick coatings at high temperatures.

A simple interface fracture test for ceramic environmental barrier coatings (EBCs) on ceramic matrix composites (CMCs) was developed. A variation on the asymmetric double cantilever beam (ADCB) test was proposed so that the interface toughness could be measured in a small specimen of simple shape without applying interlaminar loading to the CMC substrate. The proposed test was applied to an EBC consisting of a mullite layer and Si bond coat on a monolithic SiC substrate. A pre-crack was introduced by pop-in cracking, and then a notch overlapping the pre-crack was machined. The pre-crack was opened by inserting a wedge into the notch. From the critical notch opening displacement the crack starts to propagate, interface toughness is calculated. The measured interface toughness was 4.1 J/m2. Finally, the application range of the test was discussed and suggestions were made for introduction of the notch and pre-crack.

Speckle patterns to be used for digital image correlation (DIC) at the micrometer level up to 1400 °C were fabricated by several methods. The quality of the patterns before and after heating was evaluated in terms of the mean intensity gradient (MIG) and the speckle size distribution. The displacement accuracy in simulative translation of images showed that the MIG alone was not enough to evaluate the pattern properties; a large MIG, an even speckle size distribution, and a wide speckle size range pattern were required for a good DIC. The reaction between the patterning material and substrate, the cracking of speckles, and the plastic flow of patterning material may cause changes in the pattern morphology at high temperature. Two patterning methods, spraying a mixture of ceramics powder and binder by a fine-nozzle air brush and abrading a polished surface, yielded a small pattern with high MIG values and even size distributions that was stable at 1400 °C. The potential of the fabricated patterns was shown by measuring the coefficient of thermal expansion of polycrystalline Al 2 O 3 from 800 °C to 1400 °C.

Nanosized composite rods ∼300 nm in length and ∼20 nm in width were produced by deposition of 22-77 wt% of a c-axis-oriented hydroxyapatite (HA) on cellulose nanocrystals (CNCs). The CNCs functionalized with sulphonic groups were covered with the HA nanocrystals through controlled nucleation and growth under a moderately supersaturated condition in a solution system based on a simulated body fluid. Water-resistant transparent coatings 2-4 μm thick were obtained via evaporation-induced assembly of CNC-HA nanocomposites by casting their suspension on a glass substrate and the subsequent growth of HA nanocrystals by vapour hydrothermal treatment. The composite coatings exhibited improved mechanical strength compared to that of crustacean exoskeletons, and potential for bone regeneration.

An in-phase stress controlled thermo-mechanical fatigue test (IP-TMF) on an electron beam physical-vapor-deposition (EB-PVD) 7-wt.% Y2O3-ZrO2-coated CoNiCrAlY bond coat, called an IN-738LC thermal barrier coating (TBC) system, was carried out. The temperature gradient in the through-thickness direction was achieved. Examination of the system's deformation behavior showed clear creep and superimposed ratcheting behaviors similar to those of the substrate superalloy tested by the same IP-TMF test. The EB-PVD TBC also follows the creep deformation behavior of the substrate. Anisotropic undulation of the thermally grown oxide (TGO) layer was observed in polished section observations. The undulation behavior appeared only perpendicular to the loading direction and was not observed parallel to the loading direction. The average compressive stress distribution of the TGO layer depends on the undulation behavior. The compressive stress parallel to the loading direction is nearly constant and the value agrees with the estimated thermal stress, while the stress in the undulating section is distributed unevenly such that the compressive stress is enhanced at the bottom of concave region.

Alternate spin-coating was done to fabricate an organic/inorganic multiplayer composite at room temperature. SiO2/polyacrylic ester multilayer composites were obtained by coating an aqueous alkoxysilane-modified polyacrylic ester emulsion and an alkoxysilane liquid alternately on a substrate. We examined the layer thickness when the concentration of aqueous emulsion and disk rotating speed in spin-coating were changed, and found that the thickness decreased when the concentration was decreased and when the rotating speed was increased. Layers with a submicron thickness were obtained in optimum conditions for both polyacrylic ester and SiO2 layers. A multilayer composite with 31 layers in total was successfully fabricated without interface delamination or discontinuity of any layer; it showed good light transmittance through the visible light range. The potential of alternate spin-coating as a room temperature process for fabricating organic/inorganic multilayer composites was proven.

Among many kinds of “nano-laminar” composites inspired by the brick and mortar structure of nacre in mollusk shells, a bulky, dense and ceramics–base composite has been a missing piece despite its importance. Here we report that such a composite with a submicron-order layered structure can be fabricated by a simple method, sintering aligned flake-like inorganic powder coated with ductile matrix material. The composites fabricated by this method had crack extension resistance by interface delamination, crack deflection, and ligament bridging by the ductile matrix. They showed non-brittle fracture behavior in a bending test despite a quite high flake volume fraction of over 80%, and had a work of fracture (WOF) of more than 300 J/m2, several hundreds times as large as that of monolithic glass.

Bulk nano-laminar composites were fabricated by a novel technique called Hot-press Assisted Slip Casting (HASC) which combines hot-pressing and slip-casting to improve alignment and volume fraction of the reinforcement. Alumina flakes were used as filler in an epoxy matrix. Microstructure of composites and alignment of flakes were characterized by Scanning Electron Microscope (SEM). Three point bending test and Vickers hardness test were done for mechanical characterization of composites. Flexural tests on Chevron-notched specimens revealed a high work-of-fracture in the case of the fabricated composites reaching to 254 J/m 2 . Fracture surface of three point bending samples were examined by SEM. Main fracture mechanism is debonding of flakes from the matrix. With its high volume fraction (60%) of reinforcement phase and high degree of flake alignment, a nacre-like microstructure was achieved with a relatively efficient, cost effective and simple hybrid conventional method.

The mechanical performance of nacre in seashells is generally described in terms of mesoscale mechanisms between mineral plates within the organic polymer matrix. However, recent work has reported nanostructures and organic material within individual plates and associated deformation mechanisms. In this work, we further investigated the nanoscale structure and mechanical behavior within individual plates of nacre by using two methods to induce fracture of plates: microindentation with focused ion beam preparation and ultramicrotomy. Using transmission electron microscopy, we observed deformation nanostructures and organic matrix within plates and identified nanoscale mechanisms, such as separation, shear, and matrix crack bridging.

The deformation behavior of the organic polymer matrix of the biocomposite nacre structure in abalone shell was investigated by in situ straining during transmission electron microscopy (TEM). We observed strong adhesion to mineral plates and high ductility of the organic matrix, confirming a crack-bridging toughening mechanism. In addition, direct observation of reversible mechanical behavior was made in the viscoelastic reformation of matrix ligaments after failure. Crystalline β-sheet structures identified through electron diffraction suggested the presence of protein structures similar to spider or cocoon silk, and the reversible mechanism was attributed to hydration-induced unfolding and refolding of domains in these silklike proteins. This work provides further insight into the molecular and nanoscale behavior of nacre organic matrix and its contribution to bulk mechanical performance.

Hybrid atomization is a new powder-making method and can produce economically very fine, clean, spherical tin alloy powders with average particle size about 10μm and narrow size distributions. The key concept of hybrid atomization is to control the liquid film formation on disk for fine powder production. Low-pressure gas atomization was utilized to promote the formation of a very thin stable liquid film before centrifugal breakup and give a better preparation for the final disintegration of melts. Besides the breakup ability of the rotating atomizer, the characteristics of liquid film on rotating disk affect the atomization mechanism and results remarkably. The main disintegration mode of melt is the breakup type of liquid film, which depends on the film instability and the atomization ability of the rotating disk. On the other hand, the mean powder size relates closely to the film thickness. The powder size distribution is mainly controlled by the atomization mode and the stability, flow type of liquid film on the rotating disk. A very thin, stable liquid film with long ligaments and a small pitch in LF mode results in very fine uniform tin alloy powders.

A nano-laminar glass/metal composite was fabricated. Glass flake powder coated with silver was used as the raw material, and was sintered by hotpressing. Samples fabricated in the optimum condition had a dense, laminar microstructure originating from the aligned flake powder. The result of a three-point bending test for the samples suggested that the alignment of the powder was essential for fracture behavior: When the powder was aligned in advance during the green sample fabrication, the sample fractured stably after the maximum load, while the samples fabricated by simple hotpressing of the powder without pre-alignment fractured unstably. Work of fracture of the sample in which the powder was well aligned was measured with chevron notched specimens; a significantly high value of about 300J/mm2 was obtained.

Nacre is a natural composite material making up the inner structure of mollusk shells. It has been of great interest in materials research due to its mechanical properties far exceeding that of its individual components: well ordered plates of aragonite (a CaCO3 polymorph) within an organic polymer matrix. Generally the aragonite plates had been treated as single crystals and mechanical behavior explained as the result of micro-scale mechanisms between plates and matrix. However, recent work has shown that the plates themselves are made up of smaller nano-scale structures, which are also thought to contribute to the bulk properties. In this work, transmission electron microscopy (TEM) was used to observe the nano-scale structure of nacre from abalone. “Nanograins” of aragonite surrounded by organic material was observed, showing composite structure within aragonite plates.

In this research, the effect of the aluminum addition to cast iron on damping property was investigated by central vibration method, dynamic mechanical analysis, ultrasonic attenuation measurement and impact sound method. All measurement results indicated that the addition of aluminum improve the damping property of cast iron.

The production of aluminum scrap is expected to exceed the domestic demand in japan around the year 2010. The key to the establishment of a "resource recycling-based society" is the zero emission process. However, recycling materials will produce an amount of scrap that cannot be recycled and will become waste. A design that considers the intended usages and includes recycling should be incorporated into the materials development to reduce as much waste as possible. Mixing iron impurities with aluminum leads to the formation of coarse needle-shaped intermetallic compounds during solidification and hinders the recycling capacity of the finished product. The application of ultrasonic vibration during solidification was carried out in this work with the aim of controlling the morphology of the material. Experiments were performed by melting an Al-Si alloy containing 4 mass% Fe (hereafter, mass% is abbreviated by %). The primary crystals formed from the liquidus line of this alloy were intermetallic compounds identified as Al 3 Fe, α-AlSiFe (Al 7.4 SiFe 2 ) and P-AlSiFe (Al 9 Si 2 Fe 2 ). A coarse needle-like intermetallic compound was formed in the Al-6Si-4Fe and Al-12Si-4Fe alloys, but the application of ultrasonic vibration resulted in the formation of a fine grained structure. In the Al-18Si-4Fe alloy, the structure could be modified from a coarse needle-like structure into a fine grained structure.

Fabrication of nano-laminar ceramic composite by a simple sintering technique was examined. Glass flakes with a thickness of 0.7μm coated with silver were used as model materials, and were consolidated by pulsed current sintering with a uniaxial press of 7.1MPa or 30MPa. By sintering the flakes at 943K, we obtained a fairly dense composite where the flakes were aligned by uniaxial press. The silver coating remained on the flakes through the sintering, and an interface layer between the flakes was formed. The sample’s indentation test demonstrated its high resistance to crack propagation through the transverse direction of the lamellar; this result was attributed to crack deflection at the interface and the accumulation of microfractures around the indentation mark.

Production of dense metal products by a three-dimensional inkjet printing system was developed. Carbonyl nickel powder with a mean particle size of 5μm was used as a raw material and two binder supply methods, (i) coating a water soluble polymer on the powder and then supplying thin polymer-dissolved water from the inkjet head; (ii) supplying a binder directly from the inkjet head were examined. The layered green product was sintered in a hydrogen atmosphere at a temperature in the range of 1073-1623K. Microstructure observation was done and sintering procedure was discussed. Sintered samples fabricated from the coated powder had non-uniform microstructure with different densities due to agglomeration of the coated powder. The inhomogeneous microstructure was improved by screening the agglomerated particles, or agglomerating most of the powder to the contrary. However, the elimination of the density variegation was not achieved in the method using the coated powder. In samples made from the powder bonded by the binder directly, microstructure was fairly homogeneous. The homogeneous microstructure helped uniform sintering, and the macroscopic shape was retained after high temperature sintering at 1623K, and a high density of over 90% was achieved.

Iron impurity in aluminum alloys forms coarse needle-shaped intermetallic compounds during solidification and hampers the recycling process. To control the morphology of the material microstructure, an experiment was carried out where ultrasonic vibration was applied to the melt during solidification. Aluminum-Silicon-Iron alloys containing 4 mass% iron were melted and solidified. The primary crystals that formed from the melts were intermetallic compounds that were identified as Al3Fe, � -AlSiFe (Al7:4SiFe2) and � -AlSiFe (Al9Si2Fe2). The refinement of these intermetallic compounds was thought to occur with the application of ultrasonic vibration. Accurate results were obtained when the vibration was applied at the liquidus temperature. The liquidus temperatures of the Al-615Si-4Fe alloys were in the range of 945 to 955 K regardless of the silicon content and that of the Al-18Si-4Fe alloy was 977.2 K. Coarse plate-like intermetallic compounds formed in Al-6 mass%Si-4 mass%Fe and Al-12 mass%Si-4 mass%Fe alloys, which can be refined by the application of ultrasonic vibration on crossing the liquidus temperature on cooling. The coarse columnar structure of an Al18 mass%Si-4 mass%Fe alloy was modified to a fine grained structure. [doi:10.2320/matertrans.F-MRA2007874]

Hybrid atomization is a new atomization technique that combines gas atomization with centrifugal atomization. This process can produce fine, spherical powders economically with a mean size of about 10μm diameter and a tight size distribution. Experiments on the process were carried out using a Sn-9mass%Zn alloy to investigate the influence of processing parameters on powder characteristics in hybrid atomization. The primary atomization mechanism under normal hybrid atomization conditions is predicted to be direct drop formation mode.

C60 nanowhiskers fabricated by liquid–liquid interfacial precipitation method and pristine C60 powder were sintered at 800 °C under 5.5 GPa for 2 h. The specimens showed high micro-Vickers hardness about 1100 kg/mm2 and electrical resistivity as low as several Ωm. Structural characterization by x-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared, and Raman spectroscopy revealed that most of C60 molecules were broken to form turbostratic graphite by high-pressure and high-temperature treatment. Comparison with the pristine C60 powder sintered under the same conditions suggests that the structural change depends microscopically on the C60 molecules, but the size and the morphology of the starting material also affect the macroscopic sintering process.

Considerable R&D efforts in last decade have identified several promising lead-free tin alloys for the replacement of lead-containing solders in microelectronic applications. However, it is difficult or uneconomical to produce high-quality solder balls industrially by means of conventional atomization methods. To produce acceptable lead-free solder balls efficiently and industrially, a novel powder-making process change to active voice. Hybrid Atomization that combines free fall gas atomization and centrifugal atomization effectively, was invented and developed recently by us. This new technique can produce very fine, spherical tin alloy powders with mean diameters of about 10 μm, very narrow size distributions, few satellites and low production costs. Taking Sn-9mass%Zn alloy as an example, process experiments were carried out and the optimal processing conditions obtained. Results show that the influences of processing parameters and optimum conditions are very different from those in conventional atomization processes. The spherical powder with a mean particle size of 10.6 μm and a standard deviation of 1.3–1.7 μm was obtained in the determined optimum condition.

A simple process for fabricating a "nano-laminar" ceramic composite was examined. Glass flakes with a thickness of 0.7 μm coated with silver were used as model materials, and were consolidated by pulsed current sintering with a uniaxial press of 7.1 MPa. The sintering temperature was varied in the range of 873-973 K. The consolidated samples sintered at 943 K were fairly dense, and the flakes were aligned by uniaxial pressing. The silver coating remained on the flakes through the sintering, and became an interface layer between the flakes. The indentation test demonstrated its high resistance to crack propagation through the transverse direction of the aligned flakes; this result was attributed to crack deflection at the interface and the accumulation of microfractures around the indent. The potential for a nano-laminar composite with high toughness were shown.

We studied the 3-Dimensional Printing method to fabricate the metallic components from powder. The laminating fabrication by starch-coated metal powder was proposed as rapid prototyping. In this research, the effects of the drying time, laminating pitch, size of adherent powder, and the starch-coating thickness on the handling of green body were investigated. Based on the obtained results, the optimum process conditions were determined.

The strengthening mechanism of Fe-Cu alloy manufactured from rapidly solidified powder was investigated. Powders of Fe-Cu with copper content ranging from 0.5 to 5 wt-% were prepared by high pressure water atomisation and consolidated by groove rolling at 973, 1073 or 1273 K. Analysis by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) were carried out to evaluate the resulting structures. The microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Yield stress under tensile loading and hardness after aging were measured. The copper states in consolidated specimens were determined based on the results, and the states were correlated to the mechanical properties of the specimens. At each of the consolidating temperatures, the yield stress increased with an increase in copper content. However, the strengthening mechanism differed according to the temperature. Specimens consolidated at 973 and 1073 K were strengthened by microstru...

The effect of oxide inclusions on the tensile properties of a Fe–Cu consolidated alloy was investigated. Fe–Cu powders with a copper content in the range of 0.5–5 mass% were prepared by high-pressure water atomization and reduced in a hydrogen atmosphere to remove surface oxides. The as-atomized and reduced powders were consolidated by groove rolling at 973 K. Microstructures were characterized by scanning electron microscopy and tensile properties were determined. The microstructure where recrystallized grains appeared was observed in the samples from both powders; there were fewer and smaller inclusions in the samples from the reduced powder. Reduction of the oxide inclusions contributed to increased elongation of the consolidated samples. Control of the inclusion at the powder surface is necessary in order to obtain plasticity.

The strengthening mechanism of Fe Cu alloy from rapidly solidified powder was investigated. The powder microstructure was changed by annealing. The as-atomized and annealed powders were consolidated by groove rolling at a warm temperature in order to avoid recrystallizatiuon and to maintain the powder microstructure. Copper was precipitated in the ierrite matrix and at the primary powder boundaries in all of the consolidated samples ; the precipitation was coarser in the samples from the annealed powders. The results of the tensile testing showed strengthening occurred by the addition of copper in all the samples: the magnitude of the strengthening was larger in the samples from the as-atomized powder. The minute and uniform copper distribution in the samples from the as atomized powder resulted in a greater strengthening effect.

Considerable R&D efforts in last decade have identified several promising lead-free tin alloys for the replacement of lead-containing solders in microelectronic applications. However, it is difficult or uneconomical to produce high-quality solder balls industrially by means of conventional atomization methods. A new powder-making technology, Hybrid Atomization, was recently developed in order to inexpensively produce very fine uniform spherical powders with mean particle sizes of about or less than 10 μm. This new method effectively combines free-fall gas atomization with centrifugal atomization. For example, Sn-9 mass%Zn powders obtained by hybrid atomization show very fine particle size, spherical shapes, narrow particle size distributions, few satellites, and low oxidation. In this paper, the optimized production of lead-free tin solder powder by hybrid atomization was investigated, and the influences of the powder's main processing parameters were discussed.