Microstructural stability of the intermetallic Ti–45Al–2W–0.5Si–0.5B in the 800–980 °C temperature range

Abstract

γ-TiAl intermetallic Ti–45Al–2W–0.5Si–0.5B was exposed in the temperature range of 800–980 °C, well over its intended application range, for up to 1000 h to test its thermal stability limit. It was found that, the fine α 2 laths could be broken down by growth of equiaxed γ grains, transformation of α 2 to B2 phase, and coalescence of α 2 laths. With increasing of temperature, needle-like B2 phase became spheral, and its volume fraction increased due to the transformation of α 2 to B2 phase. Addition of boron was demonstrated to be beneficial to the thermal stability of the lamellar structure, by the way of comparison to its boron-free counterpart ABB-2 alloy. Subsurface evolution during long-term aging was also investigated.