In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (for example, 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser powder bed fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67°rotation between layers.
a b s t r a c tThe CoCrFeMnNi high-entropy alloy is a promising candidate for metal additive manufacturing. In this study, single-layer and multi-layer builds were produced by laser powder bed fusion to study microstructure formation in rapid cooling and its evolution during repeated metal deposition. CoCrFeMnNi showed good printability with high consolidation and uniform high hardness. It is shown that microstructure in the printed alloy is governed by epitaxial growth and competitive grain growth. As a consequence, a bidirectional scanning pattern without rotation in subsequent layers generates a dominant alternating sequence of two crystal orientations.
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