Defects, microstructure and properties in additive manufacturing of TiAl alloys: Formation mechanisms, influencing factors and improvement strategies

TiAl alloys are pivotal for aero-engine applications due to exceptional high-temperature properties, yet their inherent brittleness challenges traditional manufacturing. Additive manufacturing (AM) techniques, including electron beam melting (EBM), laser-based methods (LAM), and directed energy deposition-arc (DED-arc), offer innovative pathways to overcome these limitations. This review systematically analyses defects (cracking and Al loss) formation mechanisms of AM-fabricated TiAl alloys. EBM, with high preheating, effectively suppresses cracking but exacerbates Al loss under vacuum, while LAM minimizes Al evaporation yet suffers from thermal stress-induced cracks. DED-arc balances cost-efficiency and density but faces compositional inhomogeneity. Subsequently, we discuss microstructural characteristics, evolution mechanisms, and property features and failure mechanisms, including tensile strength, fracture toughness, creep, fatigue, oxidation, and wear resistance. Regulation strategies, such as process optimization, alloying and heat treatment, are also analysed systematically to address defects and enhance performance. Additionally, the current research status of AM-fabricated TiAl-based bimetallic structures is scrutinized, revealing challenges in interface bonding and properties enhancement. Finally, we outline future research directions, emphasizing the need for standardized AM processes, advanced alloying designs, and multi-energy field coupling techniques to achieve large-scale, crack-free TiAl components with superior mechanical properties. This review serves as a valuable reference for advancing high-quality AM of TiAl alloys.