Additive manufacturing Hastelloy X with enhanced properties by optimizing strategies

Optimizing laser additive manufacturing (LAM) scanning strategies is crucial for improving the quality and performance of metallic parts formed by laser powder bed fusion (LPBF), particularly for alloys with high susceptibility to cracking. However, there is limited research on the effects of unidirectional and unidirectional-remelting strategies on the temperature field and forming quality of LPBF-manufactured Hastelloy X (HX), a nickel-based superalloy highly susceptible to cracking. This study focused on the temperature field, surface roughness, crack occurrence, and mechanical and thermal properties of LPBF-manufactured HX, employing four different laser scanning strategies: chessboard, bidirectional, unidirectional, and unidirectional-remelting. Specimens manufactured using the unidirectional-remelting strategy showed the lowest surface roughness (4.12 μm), highest density (99.64 %), superior tensile properties (tensile strength of 1068.29 MPa and elongation of 16.82 %), lowest coefficient of friction (0.65), highest thermal conductivity (9.77 W/m·K), and lowest specific heat capacity (0.38 J/g/K) compared to other strategies. This can be attributed to the unidirectional-remelting strategy resulting in specimens with equiaxed grains, the most uniform elemental and residual stress distributions, as well as the strongest grain boundary and dislocation strengthening. Moreover, it exhibited compressive residual stress in HX specimens. Interestingly, the tensile properties of the unidirectional-formed HX parts ranked second only to the unidirectional-remelting formed parts, owing to the efficacy of texture strengthening. These findings provide insights into the underlying mechanisms of optimizing laser scanning strategies for LPBF fabrication of HX, offering essential references for the LAM of crack-sensitive alloys, especially nickel-based superalloys.