Ti-Al-based alloys with Mo: high-temperature phase equilibria and microstructures in the ternary system

Molybdenum is one of the major alloying elements in TiAl-based alloys for high-temperature structural applications developed over the last decades. This is due to its stabilising effect on the (beta Ti) phase at high-temperatures, which crucially improves the hot-workability of such alloys. For further alloy development, an exact knowledge of the phase equilibria in the Ti-Al-Mo system is essential. However, there are still uncertainties and inconsistencies related to the ternary phase diagram. In this study, a series of ternary alloys was produced and heat-treated between 700 and 1300 degrees C. Composition, structure, and thermal stability of the phases were analysed and the resulting phase equilibria were established by applying a combination of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), differential scanning calorimetry (DSC), and high-energy X-ray diffraction (HEXRD). From these results, a series of partial isothermal sections is obtained illustrating the phase equilibria in the Ti-rich part of the Ti-Al-Mo system.