Aqueous partially stabilized zirconia sheets were fabricated using an emulsion of urethane polymer as a binder. The effects of the concentration of dispersant, the organic binder and the solid loading of slurry were measured using a viscometer with a coaxial cylinder sensor system on the properties of the slurry. The degree of cracking on drying was evaluated with eyes on the sheets obtained from the slurries of various compositions. The obtained results are as follows, (1) The slurry containing the high concentration of dispersant and the organic binder exhibited Newtonian flow. The slurry showed the hysteresis characteristics for high solid loading. The change in the apparent viscosity of the slurry with binder content was remarkable at high solid loading. (2) When the concentration of dispersant and the binder were high, and thus the viscosity of the slurry was low, crack-free sheets were obtained. The void resulting from air-bubbles in the slurry remained in the sheet at higher viscosity. (3) At constant solid loading, the apparent density of the sheet was independent of the concentration of dispersant and went down as that of the organic binder rose. At low binder content, the apparent density of the sheet prepared at low solid loading was high. However, at high binder content, the dependence of the apparent density on the solid loading was not observed.
AlN granules, containing 5mass% Y2O3, were sintered at various conditions in a nitrogen flowing atmosphere to investigate its sinterability. The resulting microstructures were characterized as well. AlN granules sintered at 1850°C for 15min were densified to a relative density of 98%. In the granules sintered at 1600°C for 15 min, AlYO3 and Al2Y4O9 secondary phases were identified by XRD, due to the reaction between Y2O3 additive and Al2O3 impurity from AlN granules. Y2O3 was formed in the granules sintered at 1850°C for longer than 3h by the reduction reaction of AlYO3 and Al2Y4O9 with the reducing nitrogen atmosphere. Oxygen content of the granules sintered at 1850°C for 24h decreased to one third of that of dewaxed granules.
To evaluate the capability of candidate materials such as alumina (Al2O3) and yttria stabilized zirconia (YSZ) ceramics for use as environmental barrier coatings (EBCs) on C/C composites, the oxygen and water permeability through each oxide ceramic were measured in dry and/or wet atmospheres at ultra-high temperatures. The oxygen permeability constant of Al2O3 was much smaller than that of YSZ, and was found to be in good agreement with previous values. The surface morphology of Al2O3 after the test displayed significant dependence on the oxygen potential gradients during the test. Deep grain boundary grooves were formed on those surfaces exposed to lower Po2 ; however, on the opposite surface under a higher Po2, the grain boundaries rose, forming ridges. The dependence of the Al2O3 oxygen permeability constant on the Po2 in the testing environment displayed p-type semiconductivity. Therefore, the unique morphological change may be related to the migration of aluminum ions from the lower to the higher Po2 side by the substitution of cation vacancies that segregate at the grain boundaries. The water permeability constant of Al2O3 was under the detection limit (10-10mol/(m·s) at the temperature of 1923K.
Thermal properties of materials at micrometer-scale were quantitatively measured with a thermal microscope, using thermoreflectance and periodic heating. Thermal microscope measures phase lag, which is the delay between the signals of periodic heating laser and the reflectance signals of detecting laser, to calculate the thermal effusivity of the test. In this study, phase lag at an individual point, along a line and within an area on the c plane of highly thermally conductive SiC single crystal (4H-N) was measured to evaluate the reliability of the measurement from such materials. The average value of the measured phase lag was –16.4 ± 0.3deg. The small value of standard deviation suggests thermal properties of highly thermally conductive SiC single crystal can be characterized with a high reliability using a thermal microscope. Furthermore, the thermal effusivity, calculated from the thermal diffusivity using a laser flash technique (JIS R 1611), was 26.1kJ/s0.5m2K. The calibration curve for high thermal effusivity materials was established using the data of SiC single crystal and calibrants such as Si and Ge. Thermal effusivities of 29.0 ± 0.5kJ/s0.5m2K and 28.2 ± 0.6kJ/s0.5m2K for 4H-C and 6H-C SiC single crystals, respectively, were obtained using the calibration curve. Thermal conductivities of 389W/m·K and 368W/m·K, respectively, were calculated from the measured thermal effusivity data.
Polycrystals of yttria stabilized cubic zirconia (Y-CSZ) with small amounts of additives (Al2O3 or TiO2) were deformed at 1523 to 1750K in air. TiO2 is thought to dissolve into lattice, whereas Al2O3 segregates at grain boundaries. The effect of those additives on strain rate gives the information on deformation mechanism. The addition of Ti, as well as Al, to Y-CSZ enhanced the strain rates in deformation of Y-CSZ, and the effective grain-boundary diffusion coefficients were calculated to be higher than those in undoped Y-CSZ, which suggests Ti, as well as Al, at grain boundaries affects the cation diffusion in CSZ.
The internal friction of some ceria stabilized zirconia ceramics were measured in the temperature range of 30-450°C in air using two method, piezoelectric resonance method and forced torsion method. The internal friction was observed for 12%CeO2 doped ZrO2 which was reduced in flowing hydrogen. The doping of CeO2 to cubic ZrO2-Y2O3 suppressed the amplitude of internal friction. The result suggested the lowing effect of CeO2 to the mobility of oxygen in cubic Y2O3-doped zirconia ceramics.
The effects of ZrO2 on the crystallization behaviors of ZnO-Al2O3-SiO2 glasses were investigated in order to prepare transparent glass ceramics containing ZnAl2O4 nano-crystal. Nucleation in 20ZnO·20Al2O3·60SiO2 glass proceeded vigorously at the temperature range between 775°C and 825°C. Though a few silicate phases precipitated in as-quenched 20ZnO·20Al2O3·60SiO2 glasses, addition of ZrO2 and nucleation heat treatments promote the precipitation of ZnAl2O4. As a result, a transparent glass ceramic containing ZnAl2O4 nano-crystal was obtained by crystallization of 20ZnO·20Al2O3·54SiO2·6ZrO2 glass after the heat-treatment at 775°C for 24hr.
Failure strains of some glass fibers were measured by 2-point bending test at liquid nitrogen temperature. The failure strength was estimated from failure strain and Young's modulus of glass. At a face-plate rate of 50μm/sec, failure strains were 12% (failure strength is 8.6GPa) for silica glass, 15% (10GPa) for soda-lime glass and 16% (10GPa) for lead glass, respectively. High failure strength of lead glass fiber suggests that 2-point bending strength of glass fiber is determined not only from interatomic bond strength but also from inelastic energy dissipation on fracture.
It is known that nitrogen and carbon S phases are formed in the diffusion layer on the surface of austenitic stainless steels if nitriding or carburizing is performed at the temperature of 500°C or less. In order to investigate the effect of the nitrogen and carbon S phases on high cycle fatigue properties of type316L austenitic stainless steel, rotating bending fatigue tests were carried out for four specimens with different treatments : One was gas carburized at 470°C. The other three were gas nitrided at 420°C, 460°C and 570°C, respectively. The former three specimens had the carbon or the nitrogen S phase and the last one had no S phase in the diffusion layer, depending on the temperature. As the fatigue tests result, the S phase is effective to enhance the fatigue properties. The effect of fatigue properties improvement of the nitrogen S phase is greater than that of the carbon S phase. The fatigue strength increases with an increase in the thickness of the diffusion layer in the nitrided specimens. External observation suggests that the fatigue crack initiated from the chipped part on the surface due to fatigue loading. Although the chipping behavior depended on the diffusion species, the propagation behavior of fatigue cracks did not depend on them.
Creep-fatigue properties of HR6W, which is Fe-Ni base 0.08C-23Cr-45Ni-7W alloy for piping in 700°C USC power plants, are investigated at 700°C and compared with Ni base superalloy Alloy 617. The fatigue lives of HR6W and Alloy 617 are almost the same under PP (fast-fast) type strain waveform, but the life of HR6W is longer than that of Alloy 617 under CP (slow-fast) and CC (slow-slow) type strain waveforms. In the PP test of both HR6W and Alloy 617 the transgranular fracture is dominant. On the other hand, the intergranular fracture mainly occurred in the CP test. In particular, the intergranular cracking is observed in almost all areas of the fracture surface of Alloy 617, although the transgranular cracking is partly observed in the facture surface of HR6W. It is predicted by three-dimensional FE-analyses that the crack initiation life of HR6W at the ligament parts of superheater outlet headers in the boiler plant operating in the steam condition of 700°C-34.3MPa is longer than that of Alloy 617, because HR6W is superior to Alloy 617 in creep ductility and creep-fatigue properties.
A liquid mercury target system for MW-class spallation neutron source is installed in Japan Proton Accelerator Research Complex (J-PARC). High power proton beams bombard the mercury at 25Hz, the mercury target vessel suffers the repeated stress due to the pressure waves induced by thermal expansion of the mercury. Cavitation will be generated in the propagation of pressure waves, and pitting damage will be formed on the inner wall of the target vessel by the cavitation bubble collapse. In previous research, it was confirmed that the surface hardening treatment is effective to suppress the pitting damage at some level, although crack and/or separation occurred due to poor interface strength. A novel surface modification technique was developed based on the previous research : i.e. double stratified surface modification by plasma nitriding and carburizing. The bending fatigue tests on modified stainless steels with pitting damage were performed. As results, damage suppression and fatigue limit improvement due to the modification were confirmed.
Recently, the asymmetric rolling (ASR) was applied to the material process of aluminum alloy sheet generation to control the micro-crystal structure and the texture in order to improve the mechanical properties, such as the strength and the formability. Until now, many experimental studies aimed to the high formability sheet generation have been carried out, but a numerical scheme to predict the deformation induced texture evolution of the asymmetrically rolled sheet metal have not been accomplished. In this study, the crystallographic homogenized elasto/viscoplastic finite element (FE) code is developed and applied to analyze the asymmetrical rolling process. The textures of ASR sheet metals are measured by the electron backscatter diffraction (EBSD) method, and are compared with these ASR rolling FE simulation results. This multi-scale FEM code shows a comprehensive tool to predict the plastic induced texture evolution.
Due to a strain-induced martensitic transformation (SIMT), TRIP (transformation-induced plasticity) steel possesses favorable mechanical properties such as high strength, ductility and toughness. However, since the SIMT depends on temperature, strain rate and stress state, the desired mechanical properties are obtained only in a fairly restricted working environment. On the other hand, a spatial distribution of geometrical characteristics of martensitic phase, including size, shape, and orientation against the loading axis, are heterogeneous at a microstructure of TRIP steel as observed in micrographs. It can be thought that the mechanical properties of TRIP steel manifest strong dependences on the geometrical inhomogeneity and spatial configuration of martensite. If these geometrical characteristics can be controlled, the enhancement of the mechanical properties of TRIP steel might be expected. Hence, it is necessary to evaluate the geometrical characteristics in TRIP steel to describe and control its deformation behavior. Here, in order to study the geometrical orientation from micrographs, the Fourier transformation image analysis (FTIA) is employed. After the suitable magnification of the micrographs for the FTIA and a spatial frequency are discussed, the dependences of plastic strain, temperature and stress states on the geometrical orientation are investigated by using the FTIA.
In this work, in order to study the effect of the interface roughness between the bond coating and the top coating, two kinds of the CoNiCrAlY powder with the different particle size were used for spraying the bond coating material. In addition, the bond coat was sprayed by either the low-pressure plasma spray (LPPS) method or the high velocity oxy-fuel (HVOF) one. The adhesion strength of the TBC top coat was evaluated as a function of the isothermal exposure time by means of the modified 4-point bending test. In addition, in-situ observations of the initiation and propagation of delamination cracks were carried out. The experimental results indicated that the delamination cracks initiated and propagated at the intersplat boundaries in the top-coating for the as-sprayed TBC specimens. After isothermal exposure at 1000°C, the microcracks were generated in the top-coating and the thermal grown oxides (TGO) grew at the top-coating/bond-coating interface. The delamination of the thermal exposed specimen occurred by the mixed fracture mode of the microcracks and top-coating/TGO or TGO/bond-coating interfaces. There was little difference of the adhesion strength by the bond-coating process in the as-sprayed conditions. On the other hand, the LPPSed bond coat specimen which has the rough interface exhibited lower adhesion strength compared with other specimens after thermal exposure due to the remarkable growth of the mixed oxide type of the TGO.
This paper deals with evaluation of fracture toughness in functionally graded materials (FGMs) consisting of partially stabilized zirconia (PSZ) and austenitic stainless steel SUS 304. FGMs and non-graded composites (non-FGMs) with fine and coarse microstructures are fabricated by powder metallurgy using PSZ and two kinds of SUS 304 powders. The fracture toughness is determined by conventional tests for several non-FGMs with each material composition and by a method utilizing stable crack growth in FGMs. The obtained results on the fracture toughness are as follows : (1) The fracture toughness increases with an increase in a content of SUS 304 on both FGMs and non-FGMs. (2) On the fracture toughness of the non-FGMs, the influence of microstructure is negligible. (3) On the FGMs, the fracture toughness is higher in the FGM with fine microstructure than in the FGM with coarse microstructure. (4) The fracture toughness of the FGMs is higher than that of the non-FGMs especially in the case of fine microstructure. Finally, the residual stress in the FGMs created in the fabrication process is estimated from the difference in fracture toughness between the FGMs and non-FGMs.
Polymer thin films sputtered onto glass slide and copper substrates with argon (Ar) and tetrafluoromethane (CF4) using poly(tetrafuruoroethylene)(PTFE), poly(vinylidenfluoride)(PVDF) and poly(ethylene)(PE) targets were characterized and evaluated their tribological properties. The polymer thin film sputtered with Ar using PVDF target contained only a few fluorine atoms. The fluorine contents of the polymer thin films sputtered with CF4 used with PVDF and PE targets increased, and chemical structures of these polymer thin films were almost the same as that using the PTFE target. Friction coefficients of these sputtered polymer thin films showed higher value than those of the pristine PTFE and PE. Wear durability of these fluorine thin films decreased with increase of fluorine contents in the thin films.
In the previous paper, we showed in a constant strain rate shear test using an amorphous polyethylene terephthalate (PET) thin plate that 1. there were two kinds of yield mode, diffuse slip line (DSL) and localized shear band (LSB) modes and 2. the DSL mode appeared in a range of relatively high temperature and low strain rate and the LSB mode occurred in a range of relatively low temperature and high strain rate. In this paper, we investigated the condition of the yield mode transition in both tensile and shear tests and showed that 1. the yield mode transition occurred in tensile test as well as in shear test depending on test condition and 2. an example of a critical condition for the transition was given as a function of temperature T and strain rate S by T Sm = C where m and C were the constants.