Department of Materials Science and Engineering, National Cheng Kung University, No.1, Daxue Rd., East Dist., Tainan City 701, Taiwan.
Laser and Additive Manufacturing Technology Center, Industrial Technology Research Institute, Tainan City 701, Taiwan.
Sci Rep. 2017 Jan 30;7:41527. doi: 10.1038/srep41527.
There are serious questions about the grain structure of metals after laser melting and the ways that it can be controlled. In this regard, the current paper explains the grain structure of metals after laser melting using a new model based on combination of 3D finite element (FE) and cellular automaton (CA) models validated by experimental observation. Competitive grain growth, relation between heat flows and grain orientation and the effect of laser scanning speed on final micro structure are discussed with details. Grains structure after laser melting is founded to be columnar with a tilt angle toward the direction of the laser movement. Furthermore, this investigation shows that the grain orientation is a function of conduction heat flux at molten pool boundary. Moreover, using the secondary laser heat source (SLHS) as a new approach to control the grain structure during the laser melting is presented. The results proved that the grain structure can be controlled and improved significantly using SLHS. Using SLHS, the grain orientation and uniformity can be change easily. In fact, this method can help us to produce materials with different local mechanical properties during laser processing according to their application requirements.
激光熔化后金属的晶粒结构及其控制方法存在诸多问题。为此，本文采用一种新的模型，基于 3D 有限元（FE）和元胞自动机（CA）模型的组合，通过实验观察进行了验证，解释了激光熔化后金属的晶粒结构。详细讨论了竞争晶粒生长、热流与晶粒取向的关系以及激光扫描速度对最终微观结构的影响。研究发现，激光熔化后的晶粒结构呈柱状，且倾斜方向指向激光移动的方向。此外，本研究表明，晶粒取向是熔池边界传导热通量的函数。此外，提出了利用二次激光热源（SLHS）在激光熔化过程中控制晶粒结构的新方法。结果表明，利用 SLHS 可以显著控制和改善晶粒结构。利用 SLHS，可以方便地改变晶粒取向和均匀性。事实上，这种方法可以帮助我们根据应用要求在激光加工过程中生产具有不同局部力学性能的材料。
