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<p>Joining ultra-high-temperature Nb alloys to carbon-fiber-reinforced carbon composites (C<sub>f</sub>/C) is essential for creating graded thermal structure components. However, conventional precious metal brazes typically produce porous seams, brittle interfaces, and inefficient load transfer. In this work, C<sub>f</sub>/C was brazed to Nb alloys using AuNiPd filler, and NiCo foam was introduced as an in-situ diffusion scaffold. Results showed that the foam fundamentally restructured the joint, supplying Ni and Co, promoting wetting, suppressing Au/Pd segregation, and generating a denser Nb‑side diffusion layer (NiNb, CoNb, NiPd₂, Au₄Nb₃) atop the intrinsic NbC layer adjacent to the C<sub>f</sub>/C. Brazing temperature mapping revealed a narrow optimum at 1180&#xa0;°C; lower temperatures resulted in insufficient interfacial reactions, whereas temperatures above 1200&#xa0;°C led to overreaction and phase coarsening. The foam‑assisted joint achieved a shear strength of 41.77&#xa0;MPa, approximately 37% higher than the foam‑free baseline at the same temperature. The fracture mode transitions from brittle fiber pull‑out to multiphase crack propagation with pronounced fiber embedment. These results demonstrated that NiCo foam enabled a chemically graded, crack‑resistant C<sub>f</sub>/C joint and established the processing window.</p>

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NiCo foam–driven microstructural and mechanical upgrading in the Cf/C composites and Nb alloy brazed joint

  • 期刊论文

  • 发表日期：

    2026年6月18日

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  • Yu Zhang,
  • Wei Guo,
  • Md Shahin Alam,
  • Jiapeng Dong,
  • Han Mei,
  • Datao Xu,
  • Hongqiang Zhang

摘要

Joining ultra-high-temperature Nb alloys to carbon-fiber-reinforced carbon composites (Cf/C) is essential for creating graded thermal structure components. However, conventional precious metal brazes typically produce porous seams, brittle interfaces, and inefficient load transfer. In this work, Cf/C was brazed to Nb alloys using AuNiPd filler, and NiCo foam was introduced as an in-situ diffusion scaffold. Results showed that the foam fundamentally restructured the joint, supplying Ni and Co, promoting wetting, suppressing Au/Pd segregation, and generating a denser Nb‑side diffusion layer (NiNb, CoNb, NiPd₂, Au₄Nb₃) atop the intrinsic NbC layer adjacent to the Cf/C. Brazing temperature mapping revealed a narrow optimum at 1180 °C; lower temperatures resulted in insufficient interfacial reactions, whereas temperatures above 1200 °C led to overreaction and phase coarsening. The foam‑assisted joint achieved a shear strength of 41.77 MPa, approximately 37% higher than the foam‑free baseline at the same temperature. The fracture mode transitions from brittle fiber pull‑out to multiphase crack propagation with pronounced fiber embedment. These results demonstrated that NiCo foam enabled a chemically graded, crack‑resistant Cf/C joint and established the processing window.