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

Abstract

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 (βTi) 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 °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.