EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Due to their low density (roughly 4 g/cm$^3$) and excellent high temperature properties, such as good creep behavior, high specific yield strength as well as good oxidation resistance, intermetallic γ-TiAl based alloys are applied in the automotive and aircraft industry, i.e. as turbocharger turbine wheels or turbine blades in the last stage of the low pressure turbine. One disadvantage of conventional γ-TiAl alloys, however, is their poor workability even at elevated temperatures. To overcome this deficit, a low-cost β-solidifying γ-TiAl alloy with the nominal composition Ti-42Al-5Mn (in at.%) has been developed. This alloy shows an improved hot forgeability and machinability, due to the existence of the ductile disordered β-Ti(Al) phase over a large temperature range. Despite this technological advantage, it has been found that at service temperature (<800 °C) the then ordered β$_\text{o}$-TiAl phase is decomposed and a hexagonal C14 Laves phase is precipitated. Although the formation of the Laves phase is detrimental to the mechanical properties, it has – to the authors’ knowledge – not yet been investigated via in-situ experiments. In this study several heat treatments at different temperatures and holding times have been applied to investigate the decomposition behavior of the β$_\text{o}$-phase as well as the kinetics and thermal stability range of the C14 Laves phase. The investigations were conducted via in-situ and ex-situ high-energy x-ray diffraction at a synchrotron radiation source and have been supported by scanning electron microscopy as well as ab-initio atomistic modelling.