The effect of thickness on the defects and anisotropy of thin-wall Hastelloy X fabricated via laser powder-bed fusion

Laser powder-bed fusion (LPBF) possesses unique advantages in manufacturing complex structures. The mechanical properties of thin-wall structures are crucial for the application. This study investigates the influence of wall thickness on defects and mechanical properties of LPBF Hastelloy X (HX) superalloy. As the wall thickness decreases from 1.5 mm to 0.25 mm, the diameter of sub-grains inside the molten pool increases, exhibiting a progressively enhanced //transverse direction (TD) texture in thin wall structure. Meanwhile, decreasing wall thickness leads to increased porosity and cracks due to unstable molten pool and higher residual stress. The crack initiates at columnar to equiaxed transition (CET) position and propagates along the building direction (BD). The tensile strength of the LPBF HX specimens in the horizontal and vertical directions is 773.5 MPa and 642.1 MPa with thickness of 1.5 mm, respectively, while the elongation of both specimens is close to 35%. When the wall thickness decreases to 0.25 mm, the elongation significantly decreases due to the evolution of microstructure anisotropy and the cracks along the BD, reaching 10.1% and 24.3% for horizontal and vertical specimens. This work illustrates the defects, microstructural evolution and the mechanical properties anisotropy in thin-wall structures of LPBF HX, providing a foundation for adjusting and optimizing the performance of subsequent thin-wall printing processes.