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

本计画旨在开发一种能在多晶材料中产生特殊微结构的雷射点加热系统。本计画包含三个任务：1）晶粒成长的电脑模拟; 2）雷射加热系统的设计与建构; 3）利用雷射加热系统对纯铝与纯钛进行点加热实验。在实验工作之前，采用Monte Carlo模拟方法模拟了从具有双峰晶粒尺寸分布的初始晶粒结构开始的晶粒生长过程。模拟清楚地表明，优先生长的晶粒尺寸比周围的晶粒的两倍大，发生，这表明点加热将创建相当新的显微组织时，它是实际实现。本加热系统使准直激光束聚焦在直径小于10 μm的样品表面上。本点加热方法的有效性验证如下。点加热产生了由变形基体中的再结晶晶粒组成的簇。团簇的尺寸约为160μm，这种人工微结构迄今为止从未报道过。点加热系统可以锁定任何待加热的目标区域，并且进行五点加热以显示具有不同取向的晶粒的五个簇。本加热系统也有望实现织构控制。这些新的发现强烈地表明，具有与诸如晶粒、第二相、颗粒甚至致密位错壁等微观结构参数的尺寸相当的加热区域的点加热方法将使我们能够制造我们设计的特殊微观结构。

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.