Phase transformation study during diffusion brazing of γ-TiAl intermetallic using amorphous Ni-based filler metals

Abstract

The paper aims at understanding the microstructure evolution of the diffusion brazing of γ-TiAl intermetallic compound using two Ni-based filler metals, a ternary Ni-Si-B, and a quinary Ni-Cr-Fe-Si-B. It was found that the joint region comprised of two distinct zones: analogous reaction layers adjacent to the TiAl substrates and a solidified zone at the middle of the joint region. The reaction layers consisted of separate intermetallic phases regions including ternary and binary Ti-Ni-Al intermetallic compounds. The solidified zone mainly composed of the Al1-xNi3Six isostructural solid solution and athermally Ni-boride or Ni-Cr rich borides containing eutectic microstructures at the joint centerline. The maximum shear strength was 240 MPa, and obtained by using Ni-Cr-Fe-Si-B filler metal. Fracture of the joint with Ni-Cr-Fe-Si-B filler occurred in the reaction layer/solidified zone interface, but joint with Ni-Si-B filler was fractured at solidified zone. GRAPHICAL ABSTRACT

Effect of filler metal chemical composition on the TiAl/IN738 dissimilar brazed joint

“…It is noteworthy that due to high tendency of alloying elements of IN738 substrate no evidence of boron diffusion in the TiAl side was observed. On the other hand, Ti-borides has been reported as blocky morphology on our previous study [22], and no blocky Ti-boride precipitate was observed in the TiAl side of the dissimilar IN738/Ni–Si–B/TiAl.…”

“…Wang et al [21] studied the brazing of Ti-48Al-2Cr-2Nb with Cu-based amorphous filler alloy and reported that the highest achievable strength of the joint could be obtained at 940°C in 10 min. In our previous studies the microstructural evolution of similar TiAl joints using BNi-2 and BNi-3 filler alloys [22], and dissimilar TiAl/Ni-based superalloy using BNi-2 amorphous filler alloy [23] were investigated.…”