This paper investigates the axial flow range where the particle velocities are maximized, and where kinetic energy of spray powder is maximized in high-velocity oxy-fuel (HVOF) thermal spray process, regardless of the particle diameter and material density of the particle. The ranges of diameter and material density of the spray particles selected in this paper are 10-60μm and 6000-16000 kg/m³. The gas/particle velocities are calculated by using one-dimensional simulation, with the equivalence ratio of the HVOF thermal spray gun to be 0.5, 1.0 and 1.5. It was assumed that a single particle travels along the centerline of the gun and jet-flow outside the gun. The present research reveals that 1) The particle velocities are maximized within the flow direction range of x = 108-113mm, 2) The kinetic energy of particles is maximized within the range of x = 121- 154mm for three different particle-diameter distributions, 3) The aforementioned results 1) and 2) are valid for the Stokes number, S_t, in the range of approximately 7 < S_t < 100.

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The aerosol deposition (AD) method is a technique to achieve ceramic coating at room temperature. AD films are dense films composed of nanocrystals, and it is not clear how the large number of grain boundaries and small crystals affect their physical properties. This paper presents measurements of dielectric breakdown strength, nanoindentation hardness, and thermal conductivity of AD alumina films, which the authors have investigated for application to insulating heat-dissipating substrates. The AD alumina film exhibits excellent dielectric breakdown strength in the thickness range of 1-100 μm and thermal conductivity of 15-31 W m^-1 K^-1, which is almost the same as that of sintered materials, indicating that the AD film is promising as an insulating heat-dissipating substrates.

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セラミックコアの製造プロセスへ 3D プリンターを適用する検討を行った. セラミックコア粉末と水溶性樹脂から成るリコート性に優れた粉末を開発した. 作製したテストピースは, 現品と同等の曲げ強度, 気孔率, クリストバライト含有率を有することを確認した. また, 焼成収縮率を考慮することで, 高い寸法精度を実現した. 現在のセラミックス成形技術では作製が難しい複雑形状のセラミックスコアの作製に成功した.

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High-efficiency gas turbine blades, which must withstand increasingly severe temperature and steam environments, are effectively protected by thermal/environmental barrier coatings. However, their inherent brittleness often leads to crack formation, thereby compromising their function. To address this issue, this study proposed a self-healing approach. Yb₂Si₂O₇ matrix dispersed with SiC particles or whiskers exhibit crack healing and strength recovery above 750℃. At elevated temperatures, the flexural strength increases beyond its initial value due to the reinforcing effect of compressive stresses. Under steam exposure, Yb₂Si₂O₇ partially decomposes into Yb₂SiO₅ , which reacts with SiO₂ to reform Yb₂Si₂O₇ that removes residual SiO₂ and maintains a single-phase structure, although cracking may occur at high temperature in a steam atmosphere. Alternatively, Y₂Ti₂O₇ provides a regeneration pathway by converting to TiN at the surface in a N₂ atmosphere. Upon re-oxidation, TiN transforms into TiO₂ , whose volumetric expansion effectively closes surface cracks. These findings underscore the potential of advanced ceramic coating that integrates efficient crack healing with long-term stability under the harsh conditions of turbine operation.

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