Formation of a bi-directional α2/γ lamellar microstructure through crystallographic texture control in a γ-TiAl alloy fabricated by laser powder bed fusion

This study presents, for the first time, a bi-directional α 2 /γ lamellar microstructure achieved in a γ-titanium aluminide (γ-TiAl) alloy via laser powder bed fusion (LPBF). In the as-built condition, the microstructure was predominantly composed of the α 2 phase, in which a crystallographic lamellar microstructure (CLM) consisting of two differently oriented crystallographically textured layers was established. In the major layer, the {0001} direction was oriented perpendicular to the building direction (BD), whereas in the minor layer, it was nearly aligned parallel to the BD. After heat treatment the previously formed CLM was preserved, thereby governing the orientation of the subsequently formed α 2 /γ lamellae according to the Blackburn orientation relationship. Therefore, a bi-directional α 2 /γ lamellar microstructure was obtained, with lamellae oriented parallel (0°) and perpendicular (90°) to the BD in the major and minor layers, respectively. The individual nano-hardness measurements revealed values of 9.3 ± 0.4 GPa for the major layer and 10.4 ± 0.8 GPa for the minor layer, which are much higher than those of γ-TiAl alloys produced by other processing methods. This unique microstructural formation was primarily enabled by a peritectic reaction-based alloy design combined with process-induced crystallographic texture control, highlighting a new pathway for microstructural design of γ-TiAl alloys and potentially enabling improved mechanical performance.