Microstructure and Fracture of 50Mo-50Re Vacuum Brazed with Fe-Si-B Filler Metal

Microstructural evolution, interfacial reaction and fracture during vacuum brazing of 50Mo-50Re alloys using amorphous alloy Fe-5.6Si-2.6B(wt%) were investigated. A binary intermetallic compound, sigma(Mo2Re3) formed as parallel contiguous layers in the diffusion zone. In addition, Fe from the braze alloy, in combination with dissolved Mo from the substrate, formed two layers of binary compounds mu-Mo6Fe7 and lambda-MoFe2, adjacent to diffusion zone. The unreacted Fe-based filler metal solidified as alpha-Fe solid solution. Fracture analysis showed that the mode of failure was mainly transgranular cleavage with partly intergranular and the fracture located on the interface of 50Mo-50Re alloy and the central area of brazing seam.