Abstract A widely known feature of grain growth during powder-bed fusion selective electron beam melting (SEBM) is columnar growth with grains cross many layers along the building direction. Conditions for disrupting this growth direction dominancy have not been well studied. In this study, two different focus offset values were used while other parameters were kept unchanged to result in the shape of melt pool/track being varied significantly and thus the grain growth direction changed considerably for a significant portion of the track. It has been found that as the beam became more focused, the cross section of the melt track became more U-shaped. The lateral heat transfer dominance in top region then resulted in the growth of dendrites, epitaxial and in columnar form, horizontally. The layer thickness of these horizontal dendrites is up to 80 μm and is significant considering the additive layer thickness being 70 μm.

中文翻译：

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钴基合金选择性电子束熔炼过程中枝晶凝固的水平生长方向

摘要 粉末床熔融选择性电子束熔化 (SEBM) 过程中晶粒生长的一个广为人知的特征是柱状生长，晶粒沿构建方向跨越多层。破坏这种增长方向优势的条件尚未得到很好的研究。在这项研究中，使用了两个不同的焦点偏移值，而其他参数保持不变，导致熔池/轨道的形状发生显着变化，因此对于轨道的重要部分，晶粒生长方向发生了显着变化。已经发现，随着光束变得更加聚焦，熔体轨道的横截面变得更加U形。顶部区域的横向传热优势然后导致枝晶的生长，外延和柱状形式，水平。