Unlocking ultra-fine grains and superior strength-ductility synergy in a peritectic TiAl alloy by additive manufacturing

Peritectic-solidifying TiAl alloys are prone to developing coarse microstructures under conventional casting conditions, making effective grain refinement challenging. In this work, electron beam selective melting (EBSM) was used to process a boride-reinforced peritectic TiAl alloy and to investigate the effects of rapid solidification on its microstructure and tensile behavior. The EBSM-processed (EB) alloy exhibited an average grain size of 5.2 μm, together with uniformly distributed borides shorter than 5.0 μm. Numerical simulation predicted a millisecond-scale characteristic local melt duration, reflecting the highly transient thermal conditions of the EBSM melt pool, which limit the time available for long-range solute redistribution and microstructural coarsening. The EB specimen exhibited an ultimate tensile strength of approximately 726.1 MPa at room temperature and maintained an ultimate tensile strength of approximately 662.1 MPa with an elongation of approximately 6.8% at 700 °C. TEM observations revealed dislocation accumulation and interactions at the γ/α 2 interfaces and in the vicinity of dispersed borides, indicating that both features provide resistance to dislocation motion. At 700 °C, extensive deformation twins were observed in the γ phase. Longitudinal nanotwins parallel to the γ/α 2 interfaces provide an additional mode of plastic-strain accommodation. These results demonstrate that the rapid solidification inherent to EBSM provides an effective route for suppressing microstructural coarsening in peritectic TiAl alloys and achieving a favorable strength–ductility balance without post-processing heat treatment.