Cold spray additive manufactured dense Cu-Ti+Y₂W₃O₁₂ composite filler layers for interface and stress regulation of SiC_f/SiC and GH4169 brazed joints

Negative thermal expansion (NTE) reinforced composite filler with superior mechanical performance and a controllable coefficient of thermal expansion (CTE) are urgently required for heterogeneous materials joining. However, conventional approaches for preparing low-CTE composite fillers with a high NTE content often suffer from poor weldability, primarily due to particle agglomeration and inadequate melt fluidity. This study proposes a new strategy to prepare Cu-Ti composite filler with high Y₂W₃O₁₂ content using cold spray additive manufacturing (AM). Owing to its solid-state deposition mechanism, cold spray AM effectively anchors the Y₂W₃O₁₂ particles within the composite fillers, thereby mitigating the agglomeration issues commonly encountered in conventional powder fillers. By optimizing parameters, including spraying temperature, gas pressure, and Y₂W₃O₁₂ content, high quality Cu-Ti + Y₂W₃O₁₂ composite fillers were successfully fabricated. Under the optimal brazing condition, the joint shear strength achieved its maximum value of 63.6 MPa, which recovers to 92.3% of the ideal limit of a thermal-mismatch-free homogenous SiC_f/SiC joint. Crucially, at an elevated temperature of 650 °C, the optimized joint retained a high shear strength of 40.2 MPa due to the synergistic effect of NTE-induced stress mitigation and matrix thermal softening. Furthermore, finite element simulations were performed to elucidate the residual stress relief mechanism within the brazed joints. These results demonstrate that cold spray fabricated NTE reinforced composite fillers provide an effective pathway for residual stress regulation and reliability enhancement in heterogeneous brazed joints, offering a promising design approach for low-CTE composite fillers.