Microstructure and mechanical properties of TiAl/TiAl joints brazed with a newly developed Ti–Ni–Nb–Zr quaternary filler alloy

Abstract

A novel Ti–Ni–Nb–Zr quaternary filler alloy with the composition of Ti-(19∼25)Ni-(15∼25)(Nb ​+ ​Zr) (wt.%) was designed. The filler alloy was composed of (Ti,Nb)ss, (Ti,Zr,Nb)ss ​+ ​(Ti,Zr)2Ni, α-Ti and Ti2Ni phases. It was fabricated into filler foil with a thickness of about 45 ​μm by a rapid solidification technique. The results indicate that the liquidus temperature of the Ti–Ni–Nb–Zr brazing alloy was about 978 oC, and the brazing alloy presented excellent wettability on TiAl substrate. The TiAl joint mainly consisted of β/B2 phase, Ti2Al, Ti2AlNi and α2-Ti3Al phases. The diffusion of Al atom from base metal to brazed seam led to the formation of Ti2Al and Ti2AlNi. Considering that no previously references on XRD pattern of Ti2AlNi compound can be found, Ti2AlNi cast alloy specimen was specially prepared and XRD peaks were specially labeled. The micro-hardness and bending strength tests of the Ti2AlNi phase were carried out, and the results were 761 HV and 192 ​MPa, respectively. The brazing parameters of 1010 oC/10 ​min offered the joint shear strength of 280 ​MPa at room temperature, and the joints exhibited tensile strength of 372 ​MPa at room temperature and 340 ​MPa at 750 oC, indicating that the newly developed filler alloy could offer a stable high-temperature strength.