Microstructures of the TiAl joints brazed with Ti-Zr-based filler metals

Abstract

TiAl is brazed with Ti-Zr-Fe and Ti-Zr-Cu-Ni-Fe brazing foils at 1,323 and 1,373 K for 5 min. Ti-rich, Ti3Al, and white blocky Ti-Zr-Al-Fe phase are found in the joint brazed with Ti-Zr-Fe filler metal at 1,323 K. Ti2Al phase is formed with the improved brazing temperature. When using Ti-Zr-Cu-Ni-Fe filler metal, the joints are mainly comprised of Ti-rich, Ti3Al, and Ti2Al and white blocky Ti-Zr-Al-(Cu, Ni, Fe) phase. The joint widths and the size and amount of white blocky Ti-Zr-based phases in the center of the joints are increased when the brazing temperature is increased. And under the same brazing condition, the joint width, the size of Ti3Al and Ti-Zr-Al-(Cu, Ni, Fe) phase in the joint brazed with Ti-Zr-Cu-Ni-Fe filler metal, are larger than that of Ti-Zr-Fe filler metal. More TiAl base metal dissolved into the joint induces the wider joint and the higher concentration of element Al in the joint, which lead to form Ti2Al phase. Too large size compounds such as Ti-Zr-based phases and Ti3Al would deteriorate the joint property. A lot of these phases also might have a negative effect on the joint property.