Directed energy deposition (DED) with a coaxial wire-laser configuration has gained significant attention in recent years for the production of large-scale metallic components because of its low directional dependence, fast deposition rate, high feedstock efficiency, and low manufacturing costs. This work studies the coaxial wire-laser DED process of Inconel 718 alloy under a stable deposition condition with a relatively low input volumetric energy density (55.5 J/mm³). Post characterization reveals a cluster of refined grains at the center-bottom region of the as-printed track. Operando high-energy synchrotron X-ray experiments and multi-physics modeling are applied innovatively to study the fundamental mechanism responsible for the formation of this microstructure. The X-ray diffraction experiment provides direct evidence, which is supported by the simulation, that the feeding wire can reach the melt pool bottom and release solid particles (primarily carbides) near the mushy zone owing to insufficient melting. Consequently, these sub-micron sized particles suppress the growth of large columnar grains and cause the formation of unique microstructural heterogeneity. This discovery offers new opportunities for tailoring the solidification microstructure by controlling the melting state of the feedstock wire in DED process, in addition to commonly known factors such as the thermal gradient and solidification velocity.

近年来，采用同轴线激光配置的定向能量沉积（DED）因其方向依赖性低、沉积速率快​​、原料效率高和制造成本低而在大型金属部件的生产中获得了广泛关注。这项工作研究了 Inconel 718 合金在稳定沉积条件下的同轴线激光 DED 工艺，输入体积能量密度相对较低 (55.5 J/mm ³ )。后表征显示在打印轨道的中心底部区域存在一簇细化颗粒。创新性地应用Operando高能同步加速器 X 射线实验和多物理场建模来研究形成这种微观结构的基本机制。X射线衍射实验提供了直接证据，并得到了模拟的支持，证明送丝可以到达熔池底部，并由于熔化不充分而在糊状区附近释放固体颗粒（主要是碳化物）。因此，这些亚微米尺寸的颗粒抑制了大柱状晶的生长，并导致独特的微观结构不均匀性的形成。除了热梯度和凝固速度等众所周知的因素之外，这一发现还为通过控制 DED 工艺中原料线材的熔化状态来定制凝固微观结构提供了新的机会。