Papers by Author: T. Ueda

Abstract: In this study, evaluation of residual stress in nano-TiO2 film on ITO glass is carried out. The films with thickness less than 30 nm are prepared by the dual-arcs magnetron sputtering with gas pressure 10 and 20 Pa. The surface microstructure and grain morphology of the nano-TiO2 films are observed by the atomic force microscopy (AFM). In order to accurately evaluate the residual stress in the film, the Young’s modulus of the film is determined by the nanoindentation with three point bending method at first, then the internal residual stress in the film is measured by high energy X-ray diffraction with the synchrotron radiation facility Spring-8. The measured residual stresses of nano-TiO2 films prepared with gas pressure 10 and 20 Pa are -11.6 and -9.1 GPa, respectively. It is shown that the residual stress of TiO2 films decrease with the increasing of gas pressure.

Abstract: The deformation and fracture behavior at 1773-2023K of the unidirectionally solidified eutectic Al2O3/YAG (Yttrium-Aluminum Garnet with the composition of Y3Al5O13) ceramic composite was investigated. The stress-stain curve and strength of unnotched and notched specimens, measured by bending and tensile tests, showed that (a) both unnotched and notched specimens fractured in a brittle manner at low temperatures and at high displacement speeds, but in a ductile manner at high temperatures and at low displacement speeds, and (b) the notched strength increased, reaching maximum, and decreased with increasing temperature and decreasing displacement speed. The increase in the notched strength with increasing temperature and decreasing displacement speed up to the maximum value was accounted for by the increase in plastic zone size ahead of the notch, and the decrease with further increasing temperature and decreasing displacement speed by the loss of the stress carrying capacity of the yielded ligament, based on the finite element analysis.