Gradient transition and solution strengthening mechanisms in SiCf/SiC composites joints brazed with medium-entropy alloy filler

Abstract

A Ti-Ni-Nb-Zr medium-entropy alloy filler was developed to achieve a uniform microstructure and effective stress transition in the SiC_f/SiC composites brazed joints. Composition gradients of Ti, Nb, and Ni across the asymmetric interface promoted the formation of a thermal-expansion transition structure, while the solid-solution strengthening contribution of Zr was clarified. A multiscale architecture integrating solution strengthening and stress transition was constructed, enabling synergistic enhancement through thermal-expansion mismatch mitigation and grain-scale stress accommodation. The gradient transition mechanism at the SiC_f/SiC composites asymmetric interface was elucidated by correlating NbC nucleation-growth-induced stress concentration, high-entropy solid solution effect in Ti-Ni-Nb-Zr, and the crystallographic matching between TiSi₂ and γ-(Ni, Cr, Fe) phases. Benefiting from the coupled strengthening mechanisms, the joint strength increased by nearly 300%, with fracture initiating in the interfacial reaction zone and exhibiting a cross-regional mixed mode. This work provides new mechanistic insight into interfacial design for carbon-based ceramic composites and establishes a scientific basis for the high-temperature brazing of advanced ceramic-metal systems.