Microstructural evolution and mechanical properties of brazed IN718 ultrathin-walled capillary structure using different particulate reinforced filler alloy

The development of hypersonic precooled combined cycle engine provides a reliable power system for the future intercontinental navigation and reusable space orbital transportation. The compact heat exchanger precooler is the key component of the cooling cycle system, which provides efficient heat management for the hypersonic engine. This investigation mainly focused on the manufacturing process of precooler, and the typical structure of the precooler, ultrathin-walled capillary structure, was facilitated by the vacuum brazing using the particle reinforced composite filler alloy. The effects of different types and contents of the reinforced particle on the spreading behaviour, microstructural evolution, mechanical performance changes were investigated in detail. During the cooling process, the nucleation and growth of the γ-Ni solid solution on the surface of the reinforced particles was the main reason for the microstructure homogenization. Compared to the Ni particles, the more obvious mechanical properties improvement could be achieved by using IN718 particles reinforced composite filler alloy. The tensile strength and elongation of the brazed ultrathin-walled structure present 9.36% and 47.27% higher than that using initial filler alloy. Moreover, the micro-hardness distribution result revealed that the reinforced particles reduced the overall micro-hardness of the brazed region, dispersed the eutectic structure and increased the hardness dispersion, which would reduce the stress concentration tendency and improve the structural properties.