Microscopic Analysis of Fatigue Damage Accumulation in TiAl Intermetallics

In order to design efficient and light components for the aircraft industry preserving the safety of the design, more sophisticated design criteria are required for the application of new materials. In particular, the usage of novel manufacturing processes to produce advanced materials such as the gamma titanium aluminide alloys (γ-TiAl) requires the investigation of the microstructure influence in the fatigue damage accumulation processes. In this work we examine a Ti-48Al-2Cr-2Nb alloy obtained with an additive manufacturing technique by Electron Beam Melting (EBM) by conducting monotonic and fatigue experiments both on tension and compression samples. The full-field residual strain maps corresponding to different applied stress levels and number of cycles are obtained through the use of high-resolution Digital Image Correlation (DIC). The strain maps were overlaid with the images of the microstructure and detailed analyses were performed to investigate the features of the microstructure where high local strain heterogeneities arise. High local residual plastic shear strains were measured inside lamellar colonies, which are detected as the precursor to fatigue crack initiation. The measure of the residual strains also provides further information on the role of the intermetallic phases on the fatigue behavior of γ-TiAl alloys.