Fatigue cracking in additively manufactured titanium aluminides

Over the last decade, additive manufacturing technologies have been used to effectively produce gamma-TiAl alloys suitable for structural components. In this work, the fatigue crack growth properties of a high-Nb containing TiAl alloy (Ti-45Al-8Nb-2Cr) produced by additive manufacturing by Electron Beam Melting (EBM) technology is experimentally analyzed. Fatigue crack growth experiments with sub-size SENT specimens have been conducted with the aim of highlighting the behaviour of fatigue cracks in the threshold region of this TiAl alloy with fully lamellar microstructure. Compression pre-cracking procedure and subsequent fatigue crack growth tests with constant loading amplitudes are reported and compared with fatigue crack growth tests conducted with standard C(T) specimens. Experimentally measured crack closure levels and comparison with the roughness induced closure geometric model by Suresh, Ritchie (1982) provide information on the role of the coarse fully lamellar microstructure on the fatigue properties of TiAl alloys, in view of the application of TiAl intermetallics to structural components.