Phase Formation during Heating of Amorphous Nickel-Based BNi-3 for Joining of Dissimilar Cobalt-Based Superalloys

• Published in: Materials 2021-08, Vol.14 (16), p.4600
• Main Authors: Naalchian, Mojtaba, Kasiri-Asgarani, Masoud, Shamanian, Morteza, Bakhtiari, Reza, Bakhsheshi-Rad, Hamid Reza, Berto, Filippo, Das, Oisik
• Format: Article
• Language: English
• Subjects: Alloys; Bonding; Byggkonstruktion; Cobalt base alloys; cobalt-based superalloy; Crystallization; Energy distribution; Grain size; Heat; Heating; Interlayers; Intermetallic compounds; Liquid phases; mechanical properties; Metal fatigue; microstructural changes; Microstructure; Molybdenum; Nickel; Optical microscopy; Phase transitions; Shear strength; Solid solutions; Solidification; Structural Engineering; Superalloys; transient liquid phase bonding; Vacuum diffusion
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma14164600

Phase transformations and the melting range of the interlayer BNi-3 were investigated by differential scanning calorimetry, which showed three stages of crystallization during heating. There were three exothermic peaks that indicated crystallization in the solid state. The cobalt-based X-45 and FSX-414 superalloys were bonded with interlayer BNi-3 at a constant holding time of 10 min with bonding temperatures of 1010, 1050, 1100, and 1150 °C using a vacuum diffusion brazing process. Examination of microstructural changes in the base metals with light microscopy and scanning electron microscopy coupled with X-ray spectroscopy based on the energy distribution showed that increasing temperature caused a solidification mode, such that the bonding centerline at 1010 °C/10 min included a γ-solid solution, Ni3B, Ni6Si2B, and Ni3Si. The athermally solidified zone of the transient liquid phase (TLP)-bonded sample at 1050 °C/10 min involved a γ-solid solution, Ni3B, CrB, Ni6Si2B, and Ni3Si. Finally, isothermal solidification was completed within 10 min at 1150 °C. The diffusion-affected zones on both sides had three distinct zones: a coarse block precipitation zone, a fine and needle-like mixed-precipitation zone, and a needle-like precipitation zone. By increasing the bonding temperature, the diffusion-affected zone became wider and led to dissolution.