Microstructure optimization for strengthening and toughening of LPBF-fabricated WHAs: Insight into the effect of microstructure on mechanical properties

Laser powder bed fusion (LPBF) technology enables microstructural design of tungsten heavy alloys (WHAs) but poses challenges for strengthening and toughening. In this work, 90W-7Ni-3Fe alloy was fabricated via LPBF, and spot-like γ phase (SL-γ), fine equiaxed/coarse columnar grain (FG/CG) heterogeneous structure, and γ phase abnormal agglomeration zone (γ-AZ), were successfully tailored by regulating processing parameters. The experimental results revealed that SL-γ was the dominant strengthening phase in LPBF-fabricated (LPBFed) WHAs, effectively hindering dislocation motion and contributing over 39% to the total yield strength. FG/CG heterogeneous structure achieved effective toughening: CG retarded crack propagation, while FG coordinated the plastic deformation of CG, and the optimal crack-inhibition performance was obtained at a CG area fraction of 68%. γ-AZ mitigated the toughness degradation caused by increased CG size and area fraction. It exhibited dual functions of crack blunting and plastic deformation coordination, and a unique pore-encapsulated microstructure eliminated the risk of pores acting as crack initiation sources. Benefiting from the synergistic effects of the three characteristic microstructures, the optimized WHAs achieved a compressive strength of 2705 MPa. This work systematically clarified the structure-mechanical property relationships of LPBFed WHAs and provided a reliable reference for the customized performance of WHAs via rational microstructure design.