Comprehensive microstructural investigation during dissimilar transient liquid phase bonding cobalt-based superalloys by BNi-9 amorphous interlayer foil

Abstract Cobalt-based X-45 and FSX-414 superalloys with interlayer BNi-9 have been bonded by a transient liquid phase bonding process at a constant temperature of 1150 °C with the holding times of 1, 10, 60, 120, 180 and 240 min. Microstructural changes of base metals showed that the conditions of 1150 °C/240 min can be used to joint base metals, in such a way that the primary carbides of M6C and M23C6 are significantly dissolved in the matrix, forming a supersaturated solid solution. Examination of the bonded specimens showed that during heating up to the bonding stage, Nickel-rich carbo-boride deposits are formed at the interface between the filler metal and the base alloys due to the solid-state diffusion of boron element. The next generation of carbo-borides is formed in the diffusion affected zone of the base metals, which are also Cobalt–Chromium–Tungsten–Molybdenum-rich carbo-borides. Bonding at 1150 °C/1 min resulted in lack of complete diffusion of boron element into the base metals; quasi-eutectic compounds γ, Ni3B and CrB were formed in the centerline of the bond and, increasing the holding time causes the interdiffusion of alloying elements of base metals and the interlayer and leads to the uniformity of the chemical composition along the joint. Bonding under standard solution heat treatment condition (1150 °C/240 min) completely removes the diffusion affected zone on the 45-X side.