Effect of the scanning strategy on microstructure and mechanical anisotropy of Hastelloy X superalloy produced by Laser Powder Bed Fusion

Four types of scanning strategies, i.e. 0°, 90°, 67° hatch angle and a chessboard with 67° hatch angle strategy (CB + 67°), were adopted to study the microstructure and mechanical anisotropy of Hastelloy X superalloy produced by Laser Powder Bed Fusion (LPBF). The tensile tests show that all the horizontal specimens perform higher yield strength and lower elongation than the vertical counterparts, indicating that tensile anisotropy appears in as-fabricated Hastelloy X. According to the electron backscatter diffraction (EBSD) analysis, there are more grain boundaries and geometrically necessary dislocations (GNDs) hindering dislocation motion when tested along the horizontal direction. Therefore, various degrees of grain boundary strengthening and dislocation strengthening effect are responsible for yield strength anisotropy. Because highly ordered microcracks along the building direction are much more detrimental to horizontal plasticity, the elongation anisotropy can be ascribed to different crack sensitivity along with two tensile directions. Besides, specimens produced using diverse scanning strategies exhibit varying extent of anisotropy, as well as yield strength and elongation. The yield strength of the 0° and CB + 67° specimen is lower than the 90° and 67° one regardless of the tensile direction. Among all horizontal specimens, the 0° specimen shows the lowest elongation and the CB + 67° one performs the highest.