Effect of configuration and composition of interlayer on TLP joints of FSX-414 superalloy

Different interlayers including commercial foils of MBF-80, MBF-60 and MBF-100 with the thickness of 50 μm and pure Ni-coating with the thickness of 10 μm were used for TLP bonding of FSX-414 superalloy. TLP bonding was conducted at the optimum condition (1150 °C/5 min). The joints microstructures were studied using SEM and WDS/SEM was used for phase analysis. For MBF-80 interlayer, no eutectic phases were seen at the joint but some granular and needle-like phases were visible at the diffusion affected zone. Considerable amount of eutectic phases were visible at the joint made using MBF-60 interlayer which were identified as NiP2 and CrP. These phases were detected for MBF-100 interlayer as Co and Cr-rich borides. Isolated eutectic phases, analysed as Ni, Co, Cr and W-rich ones, were seen at the joints made using pure Ni-coating as the interlayer. Mechanical tests including microhardness and shear strength were conducted for all the samples. The highest shear strength and the lowest hardness of eutectic compounds were observed for the joints made using MBF-80 interlayer. This was in agreement with the lowest concentration of alloying elements at these compounds, obtained from SEM/WDS analysis.