Fine-grained binder jetted tungsten heavy alloys with in situ nano-La2O3 addition via a novel metal salt binder

Binder jetting (BJ) holds immense potential for manufacturing complex tungsten heavy alloy (WHA) parts with high efficiency and low cost. However, sintered BJ WHA parts often face the challenges of coarse grains and poor mechanical performance, which can be attributed to low green density and stringent sintering conditions (e.g., high temperature or long duration). In WHA powder metallurgy, oxide nanoparticles are often introduced to pin grain boundaries, limiting grain growth during the sintering process and thereby enhancing the mechanical properties. This work introduced oxide nanoparticles through the binder, which could effectively avoid the problems of uneven mixing, process complexity and impurity introduction. La(NO₃)₃ binder, the key component of which was La(NO₃)₃, a water-soluble inorganic metal salt, would generate nano-La₂O₃ (200 nm) in situ among the base powders during pretreatment, aiming at refining W grains and enhancing mechanical performance. The effects of La(NO₃)₃ binder on the microstructure and properties of sintered BJ WHAs were systematically investigated and compared with those printed by the commercial binder. The average W grain size of sintered samples was 26.85 μm, finer than that printed by the commercial binder (34.53 μm). The ultimate tensile strength and yield strength of sintered samples were 926.54 MPa and 661.72 MPa, which were 8.46 % and 5.86 % higher than those printed by the commercial binder, respectively. Furthermore, the contributions of fine-grained strengthening, dispersion strengthening, solid-solution strengthening, and dislocation strengthening to the yield strength of sintered WHAs printed by La(NO₃)₃ binder were all enhanced. This work offers a promising approach for grain refinement and performance enhancement of BJ metallic materials.