Microstructural characterization of TLP bonded joints of Mar-M247 superalloys with Ni-Cr-B interlayer

Transient liquid phase (TLP) bonding is a promising joining and repairing process for nickel-based superalloys. Understanding the microstructure and secondary phase precipitation behavior in bonded joints is essential for the TLP bonding process. In present work, the Mar-M247 superalloys were joined by TLP bonding using Ni-Cr-B amorphous interlayer at 1230 degrees C for 5 min. The microstructure and precipitation behaviors of joints comprised of non-isothermal solidified zone (NSZ), isothermal solidified zone (ISZ), and diffusion affected zone (DAZ) were investigated. The results showed that the precipitates in central NSZ were mainly eutectic structure of M23(C,B)6 (where M is a mixture of Hf, Ta, Cr and Ni) and gamma/gamma' matrix, and randomly dispersed block MC (where M is a mixture of Hf, Ta and Ti) carbides. A small number of M3B2-type borides could also be observed in NSZ. The ISZ adjacent to NSZ was composed of gamma solid solution phase and fine cuboidal homogeneously distributed gamma' pre-cipitates. The precipitates in DAZ were granular and acicular M5B3-type borides which were both Cr-W-Mo-Ta-Hf elements enriched. The microhardness across the bonding joint was analyzed. Considering that the element B acted as melting point depressant element and significantly affected the solidification behavior of the residual liquid, the precipitation behavior of joints with short bonding time was discussed.

Automated summary

TLP bonding using Ni-Cr-B amorphous interlayer was successfully applied to join Mar-M247 superalloy at 1230°C for 5 minutes. The microstructure of the bonded joints consisting of non-isothermal solidified zone, isothermal solidified zone, and diffusion affected zone was investigated. The results showed the presence of M23(C,B)6 eutectic phase, γ/γ' matrix, and randomly dispersed MC carbides. The microhardness of the bonding joint was also analyzed.