Insights into the gradient-characteristic precipitation behaviors of laves phase induced by Fe/W/Mo addition in Ti42Al5Mn alloy

Abstract

At service temperature ordered β phase (βo), a (meta)stable phase in novel β-solidifying γ-TiAl alloy, is believed undergoing an unexpected phase-transformation procedure, which strongly depends on the prevailing composition. In this study the impacts of alloying with Fe, W and Mo on the precipitation behaviors of Laves phase from the βo region and the concomitant elemental redistribution during isothermal annealing of a Mn-containing β-solidifying γ-TiAl alloy were systematically investigated. Electron microscopy analysis provides evidence that the formation of Laves phase is facilitated by Fe but retarded to a certain extent by W. In sharp contrast, alloying with Mo is confirmed to be capable of effectively suppressing the precipitation of Laves phase due to the intensive restraint of βo→α2 transformation. Moreover, effects of alloying elements on phase stability are carefully evaluated by theoretical calculations, revealing a thermodynamic destabilization of the Laves phase in the presence of W or Mo, whereas Laves phase is stabilized energetically by Fe, which shows good agreement with the experimental results. Additionally, a classical DSC evaluation is supplemented to support a better understanding of the heat events and precipitation kinetics regarding the formation of Laves phase.