High-cycle fatigue of a TiAl alloy in three-point bending test

Experimental investigation of the ultra-high cycles fatigue life and associated fracture behavior of the TiAl alloy subjected to bending fatigue deformation has been conducted. Tests have been performed at stress ratio R=0.1, R=0.5 and R=0.7 and ambient temperature in air. The three-point bending ultrasonic fatigue technique at a frequency of 20 kHz was developed to study the very high-cycle fatigue properties of TiAl alloy. The S-N curves obtained shows that between 105 and 1010 cycles, there are specimens cracked. The asymptote of S-N curve is inclined gently, but not horizontal for R=0.1 and R=0.5, fatigue limit appears after 107 cycles for R-0.7, surface roughness has no influence on the fatigue properties. TiAl alloy studied here shows two phases in microstructure composed of α2-Ti3Al and γ-TiAl with near lamellar microstructure. The fractographic study showed that fatigue failures are mostly initiated at the surface of the test specimens. Interlamellar fatigue crack initiation is predominant in the Ti-Al alloy with near lamellar structure, fatigue crack growth is mainly in transgranular mode. In the very high cycle regime subsurface fatigue crack initiation can been found.