Yukio Nishikawa

Influence of Second Phase Particles on Fracture Toughness in AZ31 Magnesium Alloys

Three kinds of thin AZ31 wrought magnesium alloys sheets were used in order to investigate the influence of the second phase particles on fracture toughness. From the theoretical model, the ratio of λp/dp would be estimated 5~ 6. On the other hand, from the microstructural observation, average particle spacing on each material was sample A: 13.1µm, sample B: 14.1, and sample C: 12 µ. In addition, average particle size on each sample was sample A: 2.1, sample B: 1.9, and sample C: 2.3 µm. Therefore, the ratio of λp/dp calculated from fracture surface observation would be predicted 6 ~ 7. In comparison with the result of the prediction by theoretical analysis was in good agreement with the result of fracture toughness observation. It was found that the variation in plane-strain fracture toughness on AZ31 were affected by both of particle spacing and particle size.

Formation of Ni-Zn-Ferrite Films Using Laser Ablation

Ni-Zn-ferrite thin films were formed on glass substrate by a laser ablation method employing a KrF excimer laser at wave-length 248 nm and frequency 15 Hz. Film was deposited on substrate at room temperature, 200°C and 350°C, to a thickness of 2 ¿m. Ni-Zn-ferrite films thus prepared had the spinel structure when the substrate temperature was raised to 200°C. The saturation magnetic flux densities of Ni-Zn-ferrite films annealed at 400°C were between 1300 and 2020 G. The coercive force of annealed Ni-Zn-ferrite films decreased from 534 to from 70 to 113 Oe as the N2O gas pressure was decreased from 1×10¿2 Torr to 1×10¿5 Torr.

Ion Energy Distribution of KrF Laser Ablation

The KrF laser ablation of Al, Cu, Si, and SrTiO3 targets has been studied using an electrostatic deflection energy analyzer and a quadrupole mass filter. Beam like ions appear to accompany ablation. The average kinetic energies of Si+ and metal ions are about 45 eV and 60 eV, respectively. The energies of ions are ranked in the order of Si<metal (Al, Cu)<SrTiO3. The mean ion energy of Cu+ is not affected by the laser fluence range of 2-7.5 J/cm2.

Structural change of metal targets and particles by excimer laser ablation

We have studied the structural change of targets and the ablated particles to classify the characteristics of laser ablation. Neutral atoms, positive ions and global particles are generated from metal targets irradiated by the KrF excimer laser beam. The average energy of 100∼180 eV per atom is required to ablate atomic particles. The targets after irradiation show the change of surface morphologies and X‐ray diffraction patterns due to heating. The change of chemical compositions and the resolidified layer are not observed.