钛-铌合金激光选区熔化双道扫描过程中热历史对非平衡凝固组织影响的多物理场研究

Multi-physics Study of Thermal History Effect on Non-equilibrium Solidification Microstructure of Ti-Nb Alloy During Dual-Track Selective Laser Melting

摘要:

通过多物理场方法来量化工艺参数（激光功率、扫描速度、扫描间距和扫描策略）的变化对Ti-25Nb（原子分数）合金激光选区熔化（SLM）双道扫描过程的热历史以及相应的显微组织演变的影响。模拟结果表明，在双道扫描下，提高激光功率会形成更大的热积累，从而导致重熔时熔池体积增大和晶粒变粗。降低扫描速度会增强重熔，并促进熔池顶部的胞状晶生长，而更快的扫描速度会产生更粗糙的熔体轨迹和更细小的晶粒。扫描间距显著影响熔池尺寸和显微组织形态，较小的扫描间距有助于重熔。此外，采用往复式扫描时，第二熔道中晶粒的取向与第一熔道中的取向明显不同。更重要的是，与第一道次扫描相比，第二道次扫描后重熔熔池边界处的温度梯度和冷却速率都降低了，导致界面速度降低，凝固微观结构发生了显著变化。本研究为非平衡凝固组织调控提供了理论基础，并为钛合金的SLM工艺参数优化提供了新的见解。

Abstract:

A multi-physics approach was used to quantify the effect of process parameters (laser power, scanning speed, hatch spacing, and scanning strategy) on the thermal history and corresponding microstructure evolution of Ti-25Nb (at%) alloy during the dual-track selective laser melting (SLM) process. Simulation results reveal that during the dual-track SLM process, increasing laser power results in greater thermal accumulation, leading to a molten pool of larger volume and coarser grains. Reducing scanning speed enhances remelting and promotes cellular growth at the top of molten pool, whereas faster scanning speed leads to rougher melt tracks and finer grains. Notably, hatch spacing significantly influences the molten pool dimensions and microstructures, and smaller hatch spacing promotes remelting. Furthermore, the orientations of grains in the second track during zigzag scanning differ markedly from those in the first track. More importantly, compared with those after the first track, both the temperature gradient and cooling rate at the boundaries of remelting molten pool are reduced after the second track scanning, resulting in slower interface velocity and significant change in solidification microstructure. This research provides a theoretical foundation for controlling non-equilibrium microstructure and offering novel insights into the optimization of SLM process parameters of titanium alloys.