The development of high-performance joints for high-entropy carbides (HECs) represents a critical advancement for applications in extreme high-temperature environments, including hypersonic vehicles and nuclear reactors. Conventional solid-phase diffusion bonding of HECs typically requires elevated temperatures to overcome the sluggish diffusion effect inherent to high-entropy interfaces. While introducing liquid phases at bonding interfaces effectively accelerates atomic diffusion and reduces bonding temperatures, these liquid alloys generally contain low-melting-point elements or form intermetallic compounds during eutectic transitions (e.g., 1,118 ºC for TiNi-based alloys). These characteristics significantly compromise the high-temperature durability of the resulting joints. Until recently, creating reliable HEC bonding structures capable of service at high temperatures (800-1200°C) using liquid-phase techniques has remained an elusive goal in materials science.
A breakthrough in this field has been achieved by a research team led by Prof. Ying Wang and Prof. Zhenwen Yang from Tianjin University, China. Their strategy has successfully fabricated high-strength HEC joints capable of withstanding temperatures up to 1000°C at relatively low bonding temperatures of 1200-1250°C. The key innovation in their work is the in-situ construction of a high-melting-point Nb₂Ni layer without generating low-melting-point compounds. This was accomplished by precisely controlling the eutectic liquid phase formed by a designed Ni/Nb/Ni composite interlayer under optimized bonding temperature and pressure synergy. The result is a reliable HEC joint with HEC/Nb₂Ni diffusion-bonded interfaces. These findings provide valuable insights for designing high-temperature interfaces for HEC joints.
The team published their work in Journal of Advanced Ceramics on January 17, 2025.
Prof. Ying Wang of the School of Materials Science and Engineering at Tianjin University (China) explained: "The intrinsic interfacial stability and sluggish diffusion effect of the HEC enabled the development of bonding interface with the in-situ-formed Nb₂Ni layer, rather than interaction with the diffusion-assisted liquid film. The reliability of the HEC/Nb₂Ni interface was confirmed by a coherence of (141) Nb2Ni // (11 3) HEC and a calculated lattice misfit of 0.044."
They further discovered that "HEC joints with a high-melting-point interfacial product depended on increasing the proportion of Nb above 64 at.% in the Ni/Nb/Ni composite interlayer and extruding excess eutectic liquid phase at a bonding pressure of 10MPa, while facilitating multi-elemental diffusion at the bonding interfaces. When the Ni/Nb proportion exceeded 36% or when the bonding temperature decreased to 1150°C, the bonding structure transformed from HEC/Nb₂Ni to HEC/Ni₃Nb."
"The HEC joints maintained their strength even when tested at 1000°C, showing a 49% increase compared to HEC/Ni/HEC diffusion-bonded joints," noted Professor Wang. "We anticipate that these joints could potentially operate at much higher temperatures nearly equivalent to the actual bonding temperature."
Despite these promising results, further research is needed to evaluate the performance of these HEC joints in other extreme service environments, such as corrosive conditions and high-temperature water vapor exposure. Additionally, ongoing research should focus on designing interfacial bonding structures for high-temperature applications, particularly the development of high-entropy alloy filler materials suitable for HEC joints in non-planar components where uniform pressure application is difficult.
Co-authors, Prof. Zhenwen Yang at School of Materials Science and Engineering at Tianjin University (China) contributed equally to this work. Other contributors include Ruijie Mu, Shiyu Niu, and Kongbo Sun from the School of Materials Science and Engineering at Tianjin University in Tianjin, China.
This work was supported by the National Natural Science Foundation of China (Nos. 52175357 and 52222511).
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen . JAC's 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in "Materials Science, Ceramics" category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
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