Temperature Estimation and Al Content Prediction Focusing on Microstructural Change in a Thermal Barrier Coating

A superalloy with a thermal barrier coating (TBC) simulating a gas turbine blade is exposed to a high-temperature environment to develop a method for predicting the local temperature and Al content in a bond coat (BC). The Al content decreases with an increase in the test time due to the Al transport induced by the oxidation of the BC and the interdiffusion between the BC and the substrate. This brings about Al-decreased layer (ADL) at the boundary between the BC and the top coat. The thickness of the ADL increases in proportion to the square root of the test time, and the temperature dependence of the growth rate shows an Arrhenius-type behavior. Based on this relation, the local temperature of an in-service blade can be estimated by measuring the ADL thickness when the operation time is known. The Al content decreases in proportion to the ADL thickness. The prediction method of the Al content based on the relation is also presented.     

Densification of rare-earth (Lu, Gd, Nd)-doped alumina nanopowders obtained by a sol-gel route under seeding

Rare-earth (RE: Lu, Gd, Nd, 0.10 mol%)-doped alumina nanopowders were prepared by a new sol-gel route using polyhydroxoaluminum (PHA) and RECl₃ solutions under α-alumina (∼ 75 nm) seeding. Among the rare-earth dopants studied, Lu yields the most suitable nanopowders for low-temperature densification. The 0.10 mol% Lu-doped nanopowders, which were obtained at a calcination temperature of 900 °C under 5 mass% α-alumina seeding, consisted of ∼ 80-nm α-alumina particles and γ-alumina nanoparticles. Using these Lu-doped alumina nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average size of 0.61 μm could be obtained at 1400 °C by pressureless sintering. Clearly, the Lu-doped nanopowders obtained here represent a viable option for fabricating dense, finer-grained alumina ceramics because an undoped sample with 5 mass% seeds gave a microstructure with an average grain size of 1.78 μm at 1400 °C.     

Differences in knowledge production between disciplines based on analysis of paper styles and citation patterns

To identify the differences in the knowledge production between disciplines, we analyzed the relation between the average paper length and impact factor of 100 journals from 5 disciplines. We found negative correlation between the average length and the impact factor in the natural sciences, but not in the social sciences. We also analyzed the structures of paper and the citation patterns. These analyses are expanded to the comparison between Mode 1 and Mode 2. All results showed the natural sciences articles could emphasize the differences from previous studies and be diffused effectively by the short standardized style of paper. This research is partly funded by International Program in Special Coordinating Funds for Promoting S&T from Science and Technology Agency of Japan.     

Increase of stress intensity near interface edge of elastic-creep Bi-material under a sustained load

The transition from small-scale creep to large-scale creep ahead of a crack tip or an interface edge with strong elastic stress singularity at the loading instant causes stress relaxation and the decrease of stress intensity in general. However, this study shows that the stress near the interface edge of bi-material with no or weak elastic stress singularity increases after the loading instant and brings about the stress concentration during the transition. In addition, the creep strain distribution of this bi-material after the loading instant is different from that occurred in the transition of an interface edge with strong elastic stress singularity or a crack tip (notch root). The criterion for the increase or decrease of stress intensity near the interface edge proved by the finite element method is proposed in this study. The stress intensity near the interface edge increases when the elastic stress singularity is lower than the creep stress singularity (λ^el < λ^cr) and vice versa.     

Microstructure Control of Sintered Porous Yttria-Stabilized Zirconia as a Durable Thermal Shielding Material

The microstructure of a thermal shielding material affects its thermal conductivity and mechanical property. In this study, the effects of the sintering temperature and the polymethyl methacrylate powder as a pore-former on the microstructure of a sintered porous yttria-stabilized zirconia (YSZ), which is used as a durable thermal shielding material, were investigated. It became clear that the microstructure of the sintered YSZ could be controlled by the particle size and the amount of the pore-former and the sintering temperature. The effect of the yttria amount in the YSZ on the microstructure was also clarified.     

Photoluminescence of Rare-Earth-Doped Ca-α-SiAlON Phosphors: Composition and Concentration Dependence

Rare-earth-doped Ca-α-SiAlON phosphors, with the compositions of (Ca_{1−3/2 x} RE _x ) _{m /2}Si_{12− m − n} Al _m+n O _n N_{16− n} (RE=Ce, Sm, and Dy, 0.5≤ m =2 n ≤3.0), were prepared by sintering at 1700°C for 2 h under 10 atm N₂. The concentration of rare earths varied from 3 to 30 at.% with respect to Ca. The photoluminescence (PL) properties were investigated as functions of the composition of the host matrix (i.e., m ) and the concentration of rare earths (i.e., x ). The results show that the emission properties can be optimized by tailoring m and x . The Ce³⁺ luminescence originating from the 4 f –5 d interconfigurational transitions is greatly affected by the environment surrounding the Ce³⁺ ions, which differs from the Sm³⁺ or Dy³⁺ luminescence arising from the 4 f –4 f intraconfigurational transitions. X-ray diffraction and scanning electron microscopy were used to explain the composition and concentration dependence of PL properties.     

Multiple‐valued immune network with apoptosis system

In this paper, we describe a new model of immune network based on biological immune response network. We propose an immunity like multiple‐valued network with apoptosis mechanism. The model is based on the interaction between B cells and T cells and the biological apoptosis mechanism in the human body. With the mechanism, a naturally immune system can be reproduced. The model is also applied to pattern recognition. It becomes possible with a conventional model to restrict the category increase of memory patterns. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(3): 51– 57, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20320