Residual Stress Relief in Graphite/Cu Brazed Joints by Inserting Carbon Fiber Felt

Abstract

Relief of residual stress is an effective strategy for enhancing brazed joints, especially for dissimilar materials with large mismatches in their coefficients of thermal expansion. In this study, an AgCuTi/carbon fiber felt composite filler was designed to improve graphite/Cu joint bonding. The carbon fiber felt exhibited excellent compatibility with the brazed seam, resulting in the formation of a dense and continuous reaction layer. Due to its extremely low coefficient of thermal expansion along the fiber axis, the uniformly distributed felt significantly reduced the cooling shrinkage deformation of the brazed seam. As a result, finite element simulations predict that the simulated equivalent plastic strain at the brazed seam is reduced by 26.4%, and the simulated maximum principal residual stress at the G/brazed seam interface is reduced by 25%. The shear strength of the joint increased by 103%, from 27.2 to 55.3 MPa, reaching 92% of the strength of the graphite matrix itself. This work demonstrates that introducing a low-expansion, well-compatible reinforcement into filler metal is an effective approach for residual stress relief and joint performance enhancement.