Effect of microstructure on fatigue crack growth in TiAl intermetallics at elevated temperature

The fatigue crack growth behavior of Gamma titanium aluminides was investigated by scanning electron microscope in situ observation in vacuum at 750°C and room temperature. Three kinds of microstructures: lamellar, duplex and equiaxed-grain were chosen as testing materials. The results showed that the crack growth rates at 750°C were higher than those at room temperature in every kind of materials. If the stress intensity factor range was modified by Youngʹs modulus, crack growth rates at 750°C and room temperature could fall in the same data band. This indicated that the difference of crack growth rates between room temperature and 750°C in vacuum primarily resulted from the difference of Youngʹs modulus. The crack growth resistance of the duplex structure was higher than that of the equiaxed grain under the same grain size of 200 μm. The lamellar structure shows the best fatigue crack resistance due to bridging effects of the lamellar laths.