Tailoring the Mechanical Properties of L‐DED‐Fabricated γ‐TiAl Alloys Through Heat Treatment: Correlating Microstructural Evolution With Fracture Mechanisms

ABSTRACT

Laser‐directed energy deposition (L‐DED) offers a flexible route for fabricating γ‐TiAl components, but the as‐deposited microstructure requires post‐processing to overcome limited deformation capability. Here, an L‐DED Ti–48Al–2Cr–2Nb alloy was subjected to solution and solution‐aging treatments. Its phase constitution, microstructure, mechanical properties, and fracture behavior were characterized using synchrotron X‐ray diffraction and multiscale microscopy. Increasing the solution‐treatment temperature from 1200°C to 1320°C transforms the microstructure from near gamma to duplex and then near‐lamellar. The duplex microstructure obtained after the 1260°C solution‐aging treatment provides the best property balance, increasing the room‐temperature compressive strength by 17.4%. At 750°C, the tensile strength reaches 449.99 MPa, 40.6% higher than that of the as‐deposited alloy, whereas the tensile elongation increases to approximately 3.31 times the as‐deposited value. Fracture analysis shows that coarse lamellar interfaces act as preferred crack‐initiation and propagation paths because of local deformation incompatibility between the γ and α ₂ phases. Equiaxed γ grains and refined lamellar colonies promote crack deflection and improve deformation compatibility. These results establish a microstructure‐property‐fracture relationship for heat‐treated L‐DED TiAl and identify the duplex microstructure as the optimal state among the conditions examined.