Daram Phuangphaga, Kusano Masahiro, Watanabe Makoto
Research Center for Structural Materials, National Institute for Materials Science, Tsukuba 305-0047, Japan.
Materials (Basel). 2025 Apr 21;18(8):1890. doi: 10.3390/ma18081890.
The purpose of this study is to investigate the effects of process parameters on the microstructure and mechanical properties of the Hastelloy X (HX) alloy using a laser powder bed fusion (L-PBF) process. A combined experimental and numerical approach was used to evaluate the influence of the energy density distribution and temperature evolution on the microstructure, defects, and mechanical properties. After the specimens were built on SUS304 substrate by the L-PBF, the microstructure and defects in the specimens were analyzed by SEM and EBSD analysis methods, and then the hardness and the tensile tests were performed. The cooling rate under different laser conditions was obtained by the finite element method (FEM). The results show that a low volume energy density (VED) was applied to the unmelted powder particles, and a high energy density resulted in spherical defects. In addition, the microstructures were found to coarsen with increasing the energy density along with a tendency to strengthen the (001) texture orientation in both x-y and x-z planes. Compared to the parts with the thermal history from numerical results, the low cooling rate with high energy density had larger crystal grains elongated along the building direction, coarser sub-grains, resulting in a reduction in microhardness and yield strength together with an increase in elongation for the L-PBF HX alloy. The presented results provide new insights into the effects of parameters and the cooling rates. It can play an important role in optimizing the L-PBF processing parameters, identifying the cause of defects, and controlling the cooling rates for the crystallographic texture in such a way as to guide the development of better metrics for designing processing parameters with the desired mechanical properties.
本研究的目的是利用激光粉末床熔融（L-PBF）工艺研究工艺参数对哈氏合金X（HX）合金微观结构和力学性能的影响。采用实验与数值相结合的方法来评估能量密度分布和温度演变对微观结构、缺陷及力学性能的影响。通过L-PBF工艺在SUS304基板上制造出试样后，采用扫描电子显微镜（SEM）和电子背散射衍射（EBSD）分析方法对试样中的微观结构和缺陷进行分析，然后进行硬度测试和拉伸试验。利用有限元方法（FEM）获得不同激光条件下的冷却速率。结果表明，低体积能量密度（VED）作用于未熔化的粉末颗粒，而高能量密度会导致球形缺陷。此外，发现随着能量密度的增加，微观结构会粗化，同时在x-y和x-z平面上都有强化（001）织构取向的趋势。与数值结果中具有热历史的零件相比，高能量密度下的低冷却速率使得L-PBF HX合金的晶粒沿构建方向拉长、亚晶粒更粗大，导致显微硬度和屈服强度降低，同时伸长率增加。所呈现的结果为参数和冷却速率的影响提供了新的见解。它在优化L-PBF工艺参数、识别缺陷原因以及控制晶体织构的冷却速率方面可发挥重要作用，从而指导开发更好的指标以设计具有所需力学性能的工艺参数。
