The role of phase transformation in electron-beam welding of TiAl-based alloys

The weldability of two TiAl-based alloys, Ti-45A1-2Nb-2Mn and Ti-48Al-2Nb-2 Mn, was investigated with the electron-beam welding process. It was found t hat the alloys were susceptible to solid-state cracking due to high thermal ly induced stresses and, more significantly, to the intrinsic brittleness o f the microstructures. This work correlated the quality of the TiAl welds, made using different sets of welding parameters which gave rise to differen t cooling rates, to the microstructures that developed during welding, It w as found that the welds were crack-free if the weld cooling rates were such that decomposition of the high-temperature alpha phase in the weld was not suppressed. It was shown that the Ti-48Al-based alloy was less susceptible to the solid-state cracking and, thus, was more weldable than the Ti-45Al- based alloy because the alpha phase in the alloy with a higher aluminum con tent could decompose more readily. A continuous cooling transformation (CCT ) diagram is suggested to be used as an appropriate reference for the selec tion of welding parameters which induce suitable microstructures in the wel ds and result in crack-free welds.