• Holec, David
• Stark, Andreas
• Clemens, Helmut
• Güther, Volker
• Hatzenbichler, Lukas
• Spörk-Erdely, Petra
• Musi, Michael
• Allen, Melissa
• Kardos, Stefan

Abstract

In recent years, Zr has emerged as a promising alloying element for intermetallic γ-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 γphase 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 α2 / γcolonies. 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 γphase, this essentially results in a narrowing of the single αphase 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 βphase are formed in both alloys prior to the transition into the peritectic α+ β+ 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 γphase, resulting in a decreasing c/a ratio.

Topics

• phase
• x-ray diffraction
• experiment
• zirconium
• hardness
• phase transition
• intermetallic
• phase diagram
• lamellae
• isostatic pressing