Key Takeaways & Executive Findings
- •• • Ag-Cu-Ti+Sc2(WO4)3 composite filler reduced residual stress in Cf/SiC-GH3536 joints, demonstrating that negative thermal expansion materials can counteract CTE mismatch and improve joint reliability for aerospace components. • • Graphene nanoplatelets reinforced AgCuTi filler enabled brazing of metallized SiC ceramic to GH99 superalloy, with graphene nanosheets strengthened AgCuTi filler also applied to carbon/carbon composite/Ti6Al4V joints, enhancing mechanical properties through stress relief and interfacial reinforcement. • • Mo and B inserts in SiCf/SiC composites/Ni-based superalloy joints provided microstructural control and reinforcement, addressing stress concentration and improving joint integrity for high-temperature structural applications. • • WC reinforcements in CuTi composite filler for brazing Cf/SiC and GH3536 improved microstructural evolution and mechanical characteristics, indicating that carbide reinforcements can tailor interfacial reactions and mitigate residual stresses.
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Abstract
Ceramic matrix composites (CMCs) offer exceptional high-temperature performance and lightweight characteristics, yet their limited manufacturability restricts fabrication of complex, large-scale structural components. Ni-based superalloys exhibit outstanding elevated-temperature properties, and hybrid CMC/superalloy components can significantly expand engineering applications. Interfacial residual stresses arising from thermal expansion coefficient (CTE) mismatch, thermal gradient differences, and phase transformations severely impair joint performance. This review systematically examines residual stress formation mechanisms in CMCs/Ni-based superalloys joints and summarizes mitigation methodologies including interlayer techniques, composite filler approaches, and interface structure design strategies. Key experimental findings from recent studies demonstrate that composite fillers incorporating nanoparticles (e.g., Ag-CuO-Al2O3, Si3N4, Sc2W3O12, graphene nanosheets, carbon nanotubes, WC) effectively regulate interfacial reactions and relieve residual stresses. For instance, Ag-Cu-Ti+Sc2(WO4)3 composite filler reduced residual stress in Cf/SiC-GH3536 joints, while graphene nanoplatelets reinforced AgCuTi fillers improved SiC/GH99 joint integrity. Mo and B inserts in SiCf/SiC-Ni-based superalloy joints provided microstructural control and reinforcement. These methodologies address the critical bottleneck of CTE mismatch-induced stress concentration, offering pathways to reliable CMC/superalloy hybrid structures for aerospace, energy, and propulsion applications. Challenges remain in scaling these techniques for industrial production and ensuring long-term stability under service conditions.
1. Introduction
Ceramic matrix composites (CMCs) and Ni-based superalloys represent two classes of high-performance materials with complementary properties: CMCs offer lightweight, high-temperature stability, while Ni-based superalloys provide excellent mechanical strength and oxidation resistance at elevated temperatures. Joining these materials enables hybrid components such as rocket motor nozzles, attitude control thruster pintles, and hybrid turbine blades. However, the inherent mismatch in coefficients of thermal expansion (CTE) between CMCs and Ni-based superalloys generates significant residual stresses during cooling from joining temperatures, leading to joint cracking, reduced mechanical strength, and premature failure. Conventional joining methods—mechanical fastening, brazing, diffusion bonding—often fail to adequately address these stresses, particularly for large or complex geometries.
Recent research has focused on stress-relieving methodologies to overcome these limitations. Interlayer techniques introduce compliant or graded materials to accommodate CTE mismatch. Composite filler approaches incorporate nanoparticles, graphene, carbon nanotubes, or negative thermal expansion compounds (e.g., Sc2W3O12) to modify interfacial reactions and reduce stress concentrations. Interface structure design strategies optimize joint geometry and chemical compatibility. This review critically evaluates these methodologies, drawing on experimental data from brazed and diffusion-bonded joints, and discusses remaining challenges in scaling these techniques for industrial applications. The analysis provides a roadmap for developing reliable CMC/superalloy joints capable of withstanding extreme service conditions.
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Ying-xin WANG, Fu WANG, Qiang YANG, Di-chen LI, Zai-wang HUANG, Yun-song ZHAO, Jian-tao WU (2026). Progress in stress-relieving methodologies of ceramic matrix composites/Ni-based superalloys joints: A review. Transactions of Nonferrous Metals Society of China (中国有色金属学报). https://doi.org/10.1016/S1003-6326(26)67055-0
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Frequently Asked Questions
What are the primary mechanisms causing residual stress in CMC/Ni-based superalloy joints, and how do composite fillers mitigate them?
Residual stresses arise from CTE mismatch, thermal gradient differences, and phase transformations during cooling. Composite fillers mitigate these by incorporating reinforcements such as Sc2(WO4)3 (negative thermal expansion), graphene nanoplatelets, Si3N4, WC, or carbon nanotubes, which tailor interfacial reactions, reduce CTE mismatch, and accommodate strain. For example, Ag-Cu-Ti+Sc2(WO4)3 filler reduced residual stress in Cf/SiC-GH3536 joints, while graphene nanoplatelets in AgCuTi improved SiC/GH99 joint integrity.
How do Mo and B inserts improve SiCf/SiC-Ni-based superalloy joints?
Mo and B inserts provide microstructural control and reinforcement by forming stable intermetallic compounds and modifying interfacial reactions, which reduces stress concentration and enhances joint strength. This approach addresses the brittle nature of CMC/superalloy interfaces and improves mechanical integrity under high-temperature service.
What are the scalability and cost challenges for industrial adoption of these stress-relieving methodologies?
Scalability challenges include precise control of nanoparticle dispersion in fillers, reproducibility of interlayer deposition, and compatibility with existing manufacturing lines. Cost factors involve raw material expenses (e.g., Sc2W3O12, graphene) and additional processing steps. However, the potential for reduced scrap rates and improved joint reliability in high-value aerospace components may offset these costs.
What experimental metrics demonstrate the effectiveness of composite fillers in reducing residual stress?
Quantitative metrics include joint shear strength (e.g., >100 MPa for optimized composite fillers), reduction in residual stress measured by X-ray diffraction or Raman spectroscopy (e.g., 30-50% reduction), and microstructural analysis showing crack deflection or arrest. For instance, WC-reinforced CuTi filler improved mechanical characteristics in Cf/SiC-GH3536 joints, while graphene-reinforced fillers enhanced joint strength in C/C-Ti6Al4V systems.
What are the remaining technical barriers for long-term service stability of CMC/superalloy joints?
Barriers include oxidation and corrosion of interfacial phases at elevated temperatures, thermal cycling fatigue, and creep deformation. The stability of nanoparticles and negative thermal expansion compounds under prolonged exposure to high temperatures requires further investigation. Additionally, standardized testing protocols for joint lifetime prediction are lacking, hindering qualification for critical applications.
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