Thermoplastic brazing of TiAl- and Ni-based alloys utilizing a Ni-based bulk metallic glass as the filler metal

Abstract Good high-temperature property is of great significance for TiAl/Ni joint. In this work, a (Ni60Nb15Zr15Ti10)98Co2 BMG was designed and applied as the filler metal to join TiAl- and Ni-based superalloy utilizing TPB method. Good physical prebonding was firstly achieved at temperatures much lower than the melting point by superplastic filling of the BMG and metallurgical bonding was then realized through solid-state atomic diffusion at higher temperatures. Superplastic filling and crystallization behaviors of the BMG in the superliquid region were analyzed and the experimental results indicated that after superplastic deformation in the superliquid region, no crystallization occurred and a compact contacting between base metals and filler metal was achieved. Temperature plays an important role in microstructure evolution of the joint. With increasing the diffusion temperature, the reaction layer between the Ni-based alloy and BMG become thicker. Small isotropic phases derived from crystallization of the amorphous with the dimension ranging from nanoscale to several micro of the joint were formed in the joint after bonding. Focused Ion beam (FIB), transition electron microscope (TEM) and selected area electro diffraction (SAED) were applied to further determine the small isotropic phases. Shearing tests performed at room temperature and 1023K were used to examine the strength of the joint and the results showed that the shear strength at room temperature and at 1023K were as high as 365MPa and 260MPa.