Diffusion brazing of Gamma-TiAl-alloys: Investigations of the joint by electron microscopy and high-energy X-ray diffraction

Abstract

Diffusion brazing is a potential method to repair parts made from TiAl-alloys. Two different brazing materials with varying contents of titanium, iron and nickel were investigated. The phases present in the brazed zone were identified by high energy X-ray diffraction (HEXRD) at the material science beamline HEMS at the PETRA III synchrotron facility at DESY in Hamburg, Germany, and the microstructure was characterised by scanning electron microscopy (SEM). The braze zone itself is composed of one to two transitional layers from the substrate material to the middle of the joint. Near the substrate material the phase constitution reassembles a TiAl-alloy while the middle of the joint is similar to α/β-titanium alloys. Besides phases commonly encountered in TiAl-alloys such as γ, α2 and β, additional phases, which are related to the presence of nickel or iron as melting point depressing elements are present. The microstructure of the brazed zone changes significantly during a subsequent heat treatment.