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<p>In this study, failure of a rocket engine thrust chamber during vacuum brazing was analysed. The failure was attributed to the cracking of AISI 321 flexure used for brazing of inner (Cu-0.7Cr-0.05Ti-0.05Zr) and outer (06X15H6MBT) walls, where nickel and copper were coated for brazing. Detailed metallurgical investigations (through scanning electron microscopy coupled with energy dispersive spectroscopy) of the failed flexure indicate extensive grain boundary cracking near the fracture edge with presence of Cu-Ag eutectic. This is indicative of liquid metal embrittlement (LME) on flexure, due to its unintentional exposure with molten Cu-Ag eutectic, during brazing. In order to study the critical strain and temperature to avoid LME, the brazing thermal cycle and strain conditions were simulated. Results revealed that the specimen coated with Cu + Ag has failed during simulation test with 0.1 strain due to LME, whereas application of Ni coating was effective to avoid LME up to strain of 0.22.</p>

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Understanding the Liquid Metal Embrittlement Phenomenon in AISI 321 by Eutectic Cu-Ag Liquid Metal During Vacuum Brazing: An Approach Using Gleeble Based Process Simulation

  • 期刊论文

  • 发表日期：

    2026年3月2日

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  • Varsha Florist,
  • Ravi Ranjan Kumar,
  • R. Santhoshkumar,
  • Vineet Sinha,
  • Shubham Kumar,
  • Sai Teja Dasari,
  • S. V. S. Narayana Murty,
  • M. Arumugam

摘要

In this study, failure of a rocket engine thrust chamber during vacuum brazing was analysed. The failure was attributed to the cracking of AISI 321 flexure used for brazing of inner (Cu-0.7Cr-0.05Ti-0.05Zr) and outer (06X15H6MBT) walls, where nickel and copper were coated for brazing. Detailed metallurgical investigations (through scanning electron microscopy coupled with energy dispersive spectroscopy) of the failed flexure indicate extensive grain boundary cracking near the fracture edge with presence of Cu-Ag eutectic. This is indicative of liquid metal embrittlement (LME) on flexure, due to its unintentional exposure with molten Cu-Ag eutectic, during brazing. In order to study the critical strain and temperature to avoid LME, the brazing thermal cycle and strain conditions were simulated. Results revealed that the specimen coated with Cu + Ag has failed during simulation test with 0.1 strain due to LME, whereas application of Ni coating was effective to avoid LME up to strain of 0.22.