INITIATION AND GROWTH OF SMALL FATIGUE CRACK IN TiAl INTERMETALLICS AT ELEVATED AND ROOM TEMPERATURES

Abstract

The initiation and growth of small fatigue crack in a gamma titanium aluminides (TiAl) have been investigated by scanning electron microscope (SEM) in situ observation in vacuum at 750°C and room temperature. The initiation of crack occurs transgranularly at room temperature, but both transgranularly and intergranularly at 750°C. Small cracks grow at stress intensity factor lower than the threshold value for long crack growth. The fatigue life at 750°C is shorter than that at room temperature. When the stress is modified by Young's modulus, fatigue limit at 750°C is the same as that at room temperature. However, fatigue lives at high stresses showed difference between room and elevated temperatures.