Effect of build direction on creep properties of TiAl4822 alloy additively manufactured by electron beam melting

Abstract

In the aviation industry, materials are being developed to improve the performance of jet engines. TiAl is used in turbine blades because of its high strength at high temperatures and its light weight. However, due to the difficulty of machining TiAl, additive manufacturing has been expected in recent years. Electron-beam-melted TiAl4822 has a unique layered microstructure composed of duplex-like fine-grain layers and a band of coarser γ-grains. This unique microstructure is known to bring about the anisotropy of mechanical properties. This study investigated the effects of building direction on creep properties. The creep test was conducted in accordance with the ASTM standard. The creep life of an additive manufacturing specimen was longer than that of a cast specimen due to the higher percentage of lamellar structure in the former. A specimen with building angle θ = 0° (vertical direction) had the longest creep life, which is attributed to the deformation of layers. When the building angle is θ = 45° or 90°, slip occurs between the layers, resulting in the formation of a large void along the vertical grain boundary of the γ band, which may cause high creep elongation.