Laser deposition of graded γ-TiAliTi2AlNb alloys: Microstructure and nanomechanical characterization of the transition zone

Additive manufacturing (AM) is a transformative technology to the aerospace industry. As one of the AM techniques, laser metal deposition (LMD) enables the fabrication of engine blades and a disk, as a single component, known as blisk. In this study, we use the LMD technique to fabricate a gamma-TiAl/Ti2AlNb graded metallic alloy by depositing gamma-TiAl powder on a Ti2AlNb alloy substrate. High-resolution scanning electron microscope (SEM) and high-speed nanoindentation are employed to characterize the microstructure and mechanical properties of the transition zone from the Ti2AlNb substrate (disk) to the gamma-TiAl alloy (blade). The results show that the transition zone includes three layers (I, II and III) with gradient compositions and phases: (I) mainly beta/B2 matrix with randomly distributed alpha(2) and gamma phases, (II) (alpha(2) + gamma) lamella with gamma and beta/B2 phases, and (III) similar microstructure with Layer II but finer 7 and [beta/B2 phases. The results of nanoindentation mapping show good correlations between the mechanical properties (nanohardness and elastic modulus) and microstructure in the transition zone. Attributing to the rule of mixtures, the nanohardness and elastic modulus gradually increase from the substrate Ti2AlNb to Layer I, and gradually decrease from Layer I to gamma-TiAl. This work demonstrates that the microstructure and phase analysis in combination with high-speed nanoindentation offers a new opportunity to study graded materials made using LMD. (C) 2021 Elsevier B.V. All rights reserved.