The effect of zirconium on the Ti-(42-46 at.%)Al system

In recent years, Zr has emerged as a promising alloying element for intermetallic gamma-TiAl based alloys to improve their mechanical properties. The present work focuses on the influence of this element on the microstructure and the thermodynamic phase equilibria in the ternary Ti-(42-46)Al-(2-4)Zr (at.%) system. Alloying with Zr was found to increase the amount of the gamma phase in the microstructure of cast material densified by hot-isostatic pressing. Simultaneously, the material's hardness increased due to solid solu-tion strengthening as well as the refinement of lamellae in the alpha 2/gamma colonies. With respect to the phase transformation behaviour, a significant decrease of the solidus temperature was observed in the high Zr alloyed material variants. In combination with the stabilization of the gamma phase, this essentially results in a narrowing of the single alpha phase field region in the Ti-Al-Zr phase diagram derived in this work. In situ high-energy X-ray diffraction was performed on Ti-46Al-2Zr and Ti-46Al-4Zr (at.%) specimens to investigate the phase transitions above and below the solidus temperature by utilizing two different ex-perimental setups. These experiments showed that upon heating, small amounts of ,B phase are formed in both alloys prior to the transition into the peritectic alpha-F,B-F L phase field region. Furthermore, an ad-ditional heat treatment study was conducted to determine the influence of Zr and temperature on the resulting microstructure. The combination of X-ray diffraction techniques with ab-initio calculations re-vealed a significant asymmetric influence of Zr on the lattice parameter of the gamma phase, resulting in a decreasing c/a ratio. (c) 2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )