Fabrication of high strength TiAl alloy with nano-lamellar and ultra-fine-grained microstructure by selective electron beam melting

Abstract

The TiAl alloy is a highly promising high-temperature structural material. TiAl alloys can be fabricated using the Selective electron beam melting (SEBM) additive manufacturing method, which avoids the cracking issues commonly encountered in traditional manufacturing methods. However, TiAl alloys produced by SEBM often exhibit complex microstructures and banded structures. Achieving a refined fully lamellar structure in TiAl alloys remains a significant challenge. In this study, T445- TiAl alloy was used for SEBM additive manufacturing. Several printing process parameters were investigated, resulting in highly dense samples. The printed microstructure features ultrafine grains with an average grain diameter of 5.9 μm, representing a 91.87% reduction compared to As-cast T445 alloy. Post-processing achieved a nano-lamellar structure with an average lamellar width of 8.64 nm. The final post-processed microstructure was nearly fully lamellar. Room temperature tensile tests revealed that the mechanical properties of the post-processed material reached the level of deformed TiAl alloys. Compared to the As-built state, tensile strength increased by 102.2%, reaching 932 MPa, and elongation improved to 1.33%. The crack propagation and deformation mechanisms were analyzed, revealing that the nanoscale lamellar structure possesses certain deformation capabilities.