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Advancements in Molybdenum-Copper Brazing: Techniques for High-Temperature Thermal Management

This paper reviews recent advancements in molybdenum-copper (Mo-Cu) brazing, focusing on techniques that enhance joint reliability and thermal performance for high-temperature applications in power electronics, aerospace, and nuclear systems. Key innovations include novel filler materials, process optimization, and microstructural control to mitigate thermal stress and oxidation, ensuring stable operation in extreme environments.

1. Introduction

The integration of Mo-Cu composites in high-temperature thermal management systems is driven by their unique combination of:

  • High thermal conductivity (Mo: ~138 W/m·K, Cu: ~400 W/m·K).
  • Low coefficient of thermal expansion (CTE) mismatch between Mo and Cu.
  • Resistance to thermal cycling and oxidation at elevated temperatures (up to 800°C).

Challenges include:

  • Interfacial reactions between Mo, Cu, and filler metals.
  • CTE mismatch-induced stress in heterogeneous joints.
  • Oxidation susceptibility of Mo at high temperatures (>600°C).

1. Innovations in Brazing Techniques

1.1 Active Brazing Fillers

  • Titanium-based fillers (e.g., Ag-Cu-Ti) improve wetting on Mo surfaces, reducing porosity.
  • Nanostructured fillers (e.g., TiC-reinforced Ag-Cu alloys) enhance thermal conductivity and mechanical strength.

Key Techniques for High-Temperature Performance

  1. Active Brazing Alloys (ABAs)
    • Mechanism: Alloys containing Ti, Zr, or Hf form reactive interlayers with Mo and Cu, improving wettability and joint strength.
    • Example: Ag-Cu-Ti brazing filler reduces porosity and enhances thermal conductivity at interfaces.
  2. Interlayer Design for Thermal Stress Mitigation
    • Copper-Invar-Molybdenum (CIM) composites or graphite interlayers reduce thermal expansion mismatch between Mo and Cu.
  3. High-Temperature Stability Enhancements
    • Oxidation-resistant coatings (e.g., Mo-Cu-Ni alloys) improve joint performance at 600–1,000°C.
    • Microstructural control (e.g., fine-grained Cu phases) enhances thermal fatigue resistance.

Key Techniques for High-Temperature Applications

  1. Hybrid Brazing Methods
    • Laser-assisted brazing: Reduces thermal stress and oxidation risks during Mo-Cu joining.
    • Vacuum brazing: Prevents oxidation and porosity, critical for Mo-Cu joints in high-temperature environments.
  2. Material & Process Innovations
    • Brazing Alloy Development:
      • High-temperature active brazing fillers (e.g., Ag-Cu-Ti alloys) improve wettability and joint strength at elevated temperatures.
  3. Thermal Management Applications
    • Power Electronics: Mo-Cu brazed heat sinks improve thermal dissipation in IGBT modules by reducing thermal resistance by 30–40%.
    • Aerospace Components: Mo-Cu brazed heat sinks withstand temperatures up to 800°C, critical for rocket engine nozzles and satellite thermal control systems.