| Abstract Scope |
In additive manufacturing, scanning strategies are critical because they shape distinct thermal histories during printing. Thermal history variations directly affect grain growth, phase distribution, and thermal gradient, which are factors collectively determining the final microstructure. Strong texture, i.e., grains with crystallographic orientation alignment, induced by high thermal gradient, promotes anisotropic properties in printed specimens. To address anisotropic properties in laser powder bed fusion (LPBF), a bi-directional scanning strategy with layer rotation is extensively utilized. Such strategy, when implemented with a 90° rotation between layers, produces texture with a chessboard-like pattern on the plane perpendicular to the build direction. In the literature, the chessboard texture has been reported for both body-centered cubic (BCC) and face-centered cubic (FCC) metals printed by LPBF. However, the mechanism for forming such texture is currently not well understood.
To explore the formation mechanism of the chessboard pattern, LPBF experiments were conducted on Rene65 Ni-based superalloy using three different laser spot sizes, each maintaining the same volumetric heat input. Electron backscatter diffraction (EBSD) analysis was used to investigate the pattern formation and grain orientation. Results showed the chessboard structure varied with spot size: samples printed with intermediate spot size exhibited distinct patterns with [100] grains at borders, samples printed with large spot size had fragmented [100] borders, and samples printed with small spot size showed fewer [100] borders. The results demonstrated that [100] columnar grains formed at the molten pool centers, aligning with the preferred growth direction of FCC crystals. These [100] centerlines grew continuously through the sample height, with epitaxial growth in non-centerline regions of molten pools in successive layers oriented at 90° to their own centerlines. This study helps to refine the theoretical understanding of chessboard pattern formation in LPBF, offering new insights into grain growth mechanisms and texture control strategies for enhanced microstructural design. |