Development of a lock-on type laser spot heating system and its application to coding and de-coding technology of microstructural information

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The present project aims to newly develop a laser spot heating system which can produce peculiar microstructure in polycrystalline materials. This project comprises three missions such as 1) computer simulation of grain growth, 2) design and construction of laser heating system, and 3) spot heating experiments on pure aluminum and titanium utilizing the laser heating system. Prior to the experimental work, a Monte Carlo simulation method was adopted to simulate grain growth process starting from initial grain structure with bimodal grain size distribution. The simulation clearly showed that a preferential growth of grains having twice larger size than surrounding grains took place, suggesting the spot heating would create quite new microstructure when it is practically realized. The present heating system enables a collimated laser beam focus on specimen surface with a diameter less than 10 μm. Effectiveness of the present spot heating method is verified as follows. The spot heating yielded a cluster composed of recrystallized grains in the deformed matrix. Size of the cluster is around 160μm and this artificial microstructure has never been reported so far. The spot heating system can lock-on any target areas to be heated, and five-spot heating was performed to show five clusters having grains with different orientations. Texture control is also expected to be realized by the present heating system. These new findings strongly suggest that the spot heating method with a heating area comparative to the size of microstructure parameters such as grains, second phase, particles and even dense dislocation walls will enables us to fabricate peculiar microstructures that we design.