Requirements and strict regulations for high-performance racing applications involve the use of new and innovative lightweight structural materials. Therefore, intermetallic γ-TiAl-based alloys enable new opportunities in the field due to their lower density compared to commonly used Ni-base superalloys. In this study, a β-solidifying TiAl alloy was examined toward its use as structural material for inlet and outlet valves. The nominal composition of the investigated TNM alloy is Ti-43.5Al-4Nb-1Mo-0.1B (in at%), which enables an excellent formability at elevated temperatures due to the presence of bcc β-phase. Different hot-extrusion tests on an industrial scale were conducted on the cast and hot isostatic pressed material to determine the ideal microstructure for the respective racing application. To simulate these operation conditions, hot tensile tests, as well as rotational bending tests, at room temperature were conducted. With a higher degree of deformation, an increasing strength and fatigue limit was obtained, as well as a significant increment of ductility. The fracture surfaces of the rotational bending test specimens were analyzed using scanning electron microscopy, revealing the relationship between crack initiation and microstructural constituents. The results of this study show that the mechanical performance of extruded TiAl material can be tailored via optimizing the degree of hot-extrusion.
Keywords: casting methods; electron microscopy; fatigue; fracture behavior; grains and interfaces; intermetallics; microstructural characterization; titanium aluminides.