The RL10 engine program is exploring the use of IN625 Ni-base superalloy components that are additively manufactured using laser powder bed fusion (LPBF). IN625 alloy powders are commercially available for LPBF to produce dense, complex parts/components. In this study, IN625 components, with both simple and complex geometries with overhangs, were manufactured via LPBF, and subjected to a heat-treatment consisting of a stress relief, hot isostatic pressing (HIP), and a solution anneal. The microstructure was examined with optical, scanning electron, and transmission electron microscopy. Changes in phase constituents and microstructure were documented as a function of heat treatment and component geometry (i.e., bulk section built on support structure versus thin, overhang section built on top of the previous powder bed). The as-built microstructural features included large columnar grains, a sub-grain cellular-solidification structure, approximately ~ 1 µm in diameter, and solute enriched cell boundaries decorated with A 2 B Laves phases. After heat treatment, the bulk section consisted of recrystallized equiaxed grains with annealing twins, and the sub-grain cellular-solidification structure was found to be completely dissolved. However, in the thin, overhang section, the sub-grain cellular-solidification structure persisted within columnar grain structure, which exhibited no recrystallization. An alternate HIP cycle with a higher temperature was employed to produce desired microstructure (i.e., recrystallized grains without sub-grain cells and Laves phases) in components with geometrical complexity for successful testing of RL10 engine.

中文翻译：

---

激光粉末床融合增材制造的已建成和热处理的 IN625 部件的显微结构发展

RL10 发动机计划正在探索使用 IN625 镍基高温合金部件，这些部件是使用激光粉末床融合 (LPBF) 增材制造的。IN625 合金粉末可用于 LPBF 以生产致密、复杂的零件/组件。在这项研究中，具有简单和复杂几何结构的 IN625 组件通过 LPBF 制造，并经过热处理，包括应力消除、热等静压 (HIP) 和固溶退火。用光学、扫描电子和透射电子显微镜检查微观结构。相成分和微观结构的变化被记录为热处理和组件几何形状的函数（即，建立在支撑结构上的主体部分与建立在先前粉末床顶部的薄悬垂部分）。建成后的微观结构特征包括大柱状晶粒、亚晶粒细胞凝固结构，直径约为 ~ 1 µm，以及用 A 2 B Laves 相装饰的富含溶质的细胞边界。热处理后，块体部分由具有退火孪晶的再结晶等轴晶粒组成，亚晶细胞凝固组织完全溶解。然而，在薄的悬垂部分，亚晶细胞凝固结构在柱状晶结构内持续存在，没有表现出再结晶。为了成功测试 RL10 发动机，采用具有更高温度的交替 HIP 循环在具有几何复杂性的部件中产生所需的微观结构（即，没有亚晶胞和 Laves 相的再结晶晶粒）。