Microstructure evolution and mechanical properties of tungsten alloy prepared by laser directed energy deposition

Tungsten heavy alloys (WHAs) are widely applied across military, medical, and other advanced industries. Laser-directed energy deposition (LDED) is an innovative approach to fabricate WHAs with intricate microstructures. This study explored the manufacturing processes and forming characteristics of three distinct tungsten alloy compositions to elucidate the microstructural formation mechanisms and performance evolution of WHAs prepared by LDED. Electron backscatter diffraction analysis revealed the occurrence of heterogeneous nucleation and dendritic precipitation in supersaturated solid phases across different alloy compositions. By applying the drag force equation derived from the two-phase flow theory, the Gaussian energy distribution inherent to the LDED process, and the low flowability of WHAs, this study reveals the microstructural layering mechanisms within LDED-produced samples. Through process optimization, 90 W samples that exhibited an ultimate tensile strength of 1093 MPa and elongation of 16.8 % were obtained. In situ mechanical testing revealed that the reduced elongation of the WHAs produced by LDED is due to their unique fracture mechanism driven by the interconnection of cracks between fractured tungsten particles. However, by incorporating smaller W particles and optimizing the gap ratio, the stress concentration can be effectively mitigated and crack propagation can be curtailed, thereby significantly enhancing elongation.