The transient liquid phase bonding process of a γ-TiAl alloy with brazing solders containing Fe or Ni

Abstract

The high Nb-containing γ-TiAl alloy Ti-45Al-5Nb-0.2B-0.2C (in at. %) was successfully brazed by transient liquid phase (TLP) bonding using two brazing solders with different melting point depressing elements (MPD): Ti-24Ni and Ti-29Fe (in at. %). The brazing process was executed for 24 h at 1110 °C. An additional annealing was performed for 168 h at 1000 °C for a better homogenization. The joints were characterized with high-energy X-ray diffraction (HEXRD) and scanning electron microscopy (SEM) using energy dispersive X-ray spectroscopy (EDX). Depending on the MPD and if the specimens were annealed two to three symmetrically arranged transition zones developed between the substrate and the middle of the joint with different microstructures, phase compositions, and chemical compositions. Beside α2 and γ which have been present in the substrate additional phases as β, βo, ωo, τ3, and τ2 were identified in the joints. We discuss the different solidification paths and the following solid-state transformations. The Fe-containing joint solidified via a single βo phase field leading to large βo grains. In contrast, the Ni-containing joint solidified via a two-phase field resulting in a finer grained microstructure.