Microstructural evolution and mechanical properties of TLP bonded joints of Mar-M247 superalloys with Ni-Cr-Co-W-Ta-B interlayer

The three-stage isothermal solidification process of TLP bonded Mar-M247 nickel-based superalloy was studied. The transient liquid phase bonding of Mar-M247 superalloys was conducted at 1150 °C for 1, 60, 120 and 240 min. Dendritic formation and solute partitioning governed the microstructure development. Ni-rich solid solution, Ni-rich boride W-rich boride and other carboborides were formed in the joint area. The maximum tensile strength of 443 MPa was obtained when TLP bonding at 1150 °C for 240 min. It had completed isothermal solidification. After isothermal solidification, the distribution of microhardness across the joints was more homogeneous. Enrichment of refractory elements in the Ni-Cr-Co-W-Ta-B interlayer was detrimental to the process of isothermal solidification. The presence of hard and brittle borides reduced the hardness and tensile strength of the bonded area. Post-bonding heat treatments are suggested to improve mechanical properties in future studies.