Characterization of Ti–48Al–2Cr–2Nb fabricated by directed energy deposition

The additive manufacturing process known as directed energy deposition (DED) is an effective method for repairing parts in aerospace and other industries. In this study, a DED system equipped with a heating component and an inert gas shield system to mitigate the effects of cracks and oxidation was applied for the deposition of Ti-48Al-2Cr-2Nb (at.%), a gamma titanium aluminide used in turbine blades for commercial engines. The microstructure obtained from the proposed DED process was dominated by the γ phase (area ratio of 99.38%) with a small grain size (mean diameter of 7.4 μm) as a result of massive transformation. A γ/γ lamellar structure was also identified. Massive transformation was induced because the DED met certain conditions, such as a high cooling rate, high Al content (above 49 at.%), and a fine microstructure attributed to the powders. The microstructure obtained by DED contributed to excellent mechanical properties, including a tensile strength of 471 MPa at 750°C and a creep life of 357 h at 750°C/200 MPa, which are even superior to those of conventional HIPed TiAl casting materials. The EBSD and TEM analyses suggested that the hybrid microstructure consisting of lamellae separated by high-angle grain boundaries with random orientation and lamellae separated by low-angle grain boundaries within a γ grain, combined with fine γ/γ lamellar spacing of 253 nm, would act as a barrier to dislocation shear. This microstructure is distinct from the widely observed α 2 /γ lamellar grain with semi-coherent boundaries that follow the Blackburn orientation relationship. Finally, our experiments indicate that powder DED, when well managed with heating and an inert gas system, is a potential method for repairing parts. • Directed energy deposition (DED) was applied to TiAl4822 to develop a repair process for jet engine parts. • The microstructure consists of fine γ grains and γ/γ lamellae, formed via massive α→γ transformation. • The material exhibited superior tensile and creep properties at high temperatures, outperforming conventional cast material.