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

The high Nb-containing gamma-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 degrees C. An additional annealing was performed for 168 hat 1000 degrees 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 alpha(2) and gamma which have been present in the substrate additional phases as beta, beta(o), omega(o),tau(3), and tau(2) 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 beta(o) phase field leading to large beta(o) grains. In contrast, the Ni-containing joint solidified via a two-phase field resulting in a finer grained microstructure.