High-temperature tensile and fatigue properties of Ti-48Al-2Cr-2Nb alloy additively manufactured via twin-wire directed energy deposition-arc

Recently, additive manufacturing of titanium aluminide has attracted widespread attention. Since titanium aluminide is an ideal structure material for high-temperature, corresponding mechanical properties are of great significance. In present work, tensile properties from 25 degrees C to 1050 degrees C and fatigue properties at 650 degrees C were examined for the first time on twin-wire directed energy deposition-arc (TW-DED-arc) manufactured Ti-48Al2Cr-2Nb (TiAl-4822) alloy. Importantly, fracture characteristics and deformation mechanisms were systematically investigated. Similar with extensively investigated titanium aluminide, TW-DED-arc manufactured TiAl4822 alloy generally tends to decrease strength while increase elongation versus temperature during tensile process. Meanwhile, anomalous increase of strength is detected at 750 degrees C, and brittle-to-ductile transition temperature (BDTT) is around 850 degrees C. At 25 degrees C and 550 degrees C, gamma/alpha 2 lamellar interface and lamellar colony boundary as well as special microstructures are weak positions and susceptible to microcracking, and mechanical twining dominates deformation mode. By comparison, in temperature range of 650 degrees C-950 degrees C, gamma/alpha 2 interface and colony boundary are weaker, while deformation mechanism shifts to mechanical twinning and dislocation slip. Moreover, dynamic recrystallization (DRX) starts at 850 degrees C and further affects tensile behaviors, especially at 1050 degrees C. The fatigue limit (107 cycles) at 650 degrees C is approximately 335 MPa, ratio of which to tensile strength is calculated to be 0.71, indicating good fatigue resistance of as-manufactured TiAl-4822 alloy. Irrespective of stress level, crack prefer to initiate and propagate at gamma/alpha 2 interface and colony boundary. Both mechanical twining and dislocation slip are activated during fatigue process, but their morphologies vary with stress level. In sum, these findings provide a valuable reference for mechanical properties of additively manufactured titanium aluminide.