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.

View full abstract

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.

View full abstract

Noritake investigated the application of 3D printers to the manufacturing process of ceramic cores. Noritake have developed a powder with excellent recoat ability consisting of ceramic core powder and water-soluble resin. It was confirmed that the produced test piece had the same bending strength, porosity, and cristobalite content as the actual product. In addition, high dimensional accuracy was achieved by considering the firing shrinkage rate. Noritake succeeded in fabricating a ceramic core with a complex shape that is difficult to fabricate using current ceramic molding technology.

View full abstract

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.

View full abstract