Electron-beam powder bed fusion (EPBF) has been demonstrated to enable crack-free additive manufacturing of the traditionally non-weldable IN738 Ni-based superalloy. This is related to grain boundary (GB) segregation and precipitation phenomena during EPBF thermal cycling. We investigate such GB microstructures around typical interphase boundaries in IN738. Cyclic reheating results in γʹ dissolution, reprecipitation, and formation of layers enriched in refractory elements at γʹ-γʹ interfaces. Interfacial excess shows that >10 atomic layers of Cr and 3.5 of Co at the GB suppress the segregation of W, B, and C. GBs around heterogeneously nucleated γ grains are decorated with less Cr and Co. This is linked to microsegregation of carbide and boride-forming elements, facilitating diffusion of minor elements during cooling. A heterogeneous interfacial excess profile at a γʹ-γʹ interface is reported. These findings improve the current understanding of interphase boundaries and segregation in EPBF-manufactured IN738, possibly contributing to crack-free additive manufacturing.

中文翻译：

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通过电子束粉末床熔融制造的 IN738 中的相边界偏析

电子束粉末床熔合 (EPBF) 已被证明能够实现传统不可焊接 IN738 镍基高温合金的无裂纹增材制造。这与 EPBF 热循环过程中的晶界 (GB) 偏析和沉淀现象有关。我们研究了 IN738 中典型相间边界周围的晶界微观结构。循环再加热导致γ′溶解、再沉淀，并在γ′-γ′界面处形成富含难熔元素的层。界面过量表明，GB 处 >10 个 Cr 原子层和 3.5 个 Co 原子层抑制了 W、B 和 C 的偏析。异质成核 γ 晶粒周围的 GB 装饰有较少的 Cr 和 Co。这与碳化物和碳的微观偏析有关。硼化物形成元素，促进冷却过程中微量元素的扩散。据报道，γ′-γ′界面处存在异质界面过剩轮廓。这些发现提高了目前对 EPBF 制造的 IN738 相间边界和偏析的理解，可能有助于无裂纹增材制造。