Papers by Keyword: Pulsed Laser Irradiation

Abstract: The work is devoted to the study of the phenomenon of grain boundary slippage (GBS) in the ARMCO pure iron at the periphery of the laser treatment zone. Using optical metallography and high-resolution scanning electron microscopy (SEM), the characteristic features of the GBS mechanism were revealed: stepped boundaries, accommodation zones, and grain rotation. It was found that under laser irradiation in the heat-affected zone, the plastic deformation of the ferrite matrix is ​​fully realized by the GBS. Slipping of boundaries is carried out under conditions of ultra-high-speed heating of the ferrite matrix not lower than 700 °C, and the degree of deformation by the GBS mechanism does not exceed 5-6%.

Abstract: In general, the form generation theorem of laser removal processes has not yet been established. The cause of this is that laser is a light source and has no tool shape as conventional machining tools. Therefore, its transcription characteristics could not be determined. In this paper, the application of the form generation theorem to laser removal process is examined experimentally. In order to establish the form generation theorem, first the “equivalent tool shape” of the focused beam is determined. To determine the equivalent tool shape, a groove is machined with the laser intensity just above the removal threshold of the work piece material. From the machining result, the cross-section of the groove is machined in to a V-shape. The V-shape is peculiar to the workpiece material, thus can be determined as equivalent tool shape of laser machining. The groove shape can be simulated numerically by considering the removal threshold and dependence of absorption characteristics to incidence angle. The numerical simulation and the experimental result were in good agreement. Based on the equivalent tool shape and the form generation theorem, a rectangular cross-section groove is experimented. As a result the groove was finished with a flat bottom having ruggedness like a saw-blade. This result indicates that the laser shaping based on the form generation theorem can be possible by laser irradiation with properly suppressed intensity.

Abstract: Thermal shock and thermal fatigue of ferroelectric (FE) thin films were investigated by the pulsed laser tests. The power density was gradually increasing in the single pulsed laser heating test which simulated a thermal shock, the part melting threshold of Pb(Zr0.52Ti0.48)O3 (PZT) thin films was found by scanning electron microscopy (SEM). After thermal shock resulted the highest temperature below Curie point at the surface of PZT thin film, X-ray diffraction (XRD), SEM and RT66A standard ferroelectrics analyzer were used to study the microstructure, crystal grain sizes, and ferroelectric failure behavior. It was found that XRD peak of PZT thin film after laser beam heating was stronger than that before laser beam heating, crystal grain sizes decreased, and the ferroelectric properties were degraded. However there was no crack observed by SEM, until PZT thin films were melted. The fined grain effects on ferroelectric properties and XRD patterns of PZT thin film, depolarization due to the single pulsed laser heating were discussed respectively. The pulsed cycles with a certain power density were gradually increasing in the repetition pulsed laser heating test. It was interesting to find that the cracks will initiate and propagate due to the thermal fatigue induced by the repetition pulsed laser. The possible origins of the thermal fatigue cracks were also discussed.