In-situ aluminum control for titanium aluminide via electron beam powder bed fusion to realize a dual microstructure

Abstract

With electron beam powder bed fusion (PBF-EB), an additive manufacturing (AM) technique, complex-shaped components with excellent properties from high-temperature materials can be manufactured. The latest research on the PBF-EB technique reveals the possibility of establishing different microstructures and differing mechanical properties inside a component made of titanium aluminides (TiAl). In detail, two different well-adjusted process parameter sets lead to varying melt pool characteristics and a significant change in localized aluminum (Al) loss during melting. After heat treatment, the as-built microstructure containing two different levels of Al is transformed into differing customized microstructure and properties. Areas with high Al concentration will be transformed into a nearly lamellar microstructure (NL+γ) with enhanced strength. In contrast, areas with lowered Al concentration will be changed into a fully lamellar microstructure (FL) that displays an increased creep resistance. The presented dual microstructure concept, based on the functionally graded material (FGM) concept, is a groundbreaking benefit from the PBF-EB process necessary to overcome prevailing design limitations. For the first time, components such as TiAl turbine blades can consist of creep-resistant airfoil sections and high strength root sections taking advantage of new design possibilities and additional weight savings at robust dual microstructure designs. • The local adjustment of the beam focus in the PBF-EB process allows governing the degree of Al evaporation for TiAl. • With the FGM concept, a dual microstructure and different properties can be realized in one part by heat treatment. • High c Al areas show a NL+γ microstructure with enhanced ductility, low c Al results in FL and increased creep resistance.