The Effect of Plastic Strain Range on the Intergranular Cracking under Low Cycle Fatigue Conditions for Lamellar Structured TiAl Alloy

초록

Because lamellar structured TiAl alloys designed for light and high temperature environments are generally exposed to creep-fatigue interaction conditions. Evaluation of low cycle fatigue properties under practical application conditions is necessary for the purpose of safety and performance improvement. Therefore, total strain range controlled low cycle fatigue tests (strain rate=4X10-3/sec., R=-1) for lamellar structured TiAl alloy have been conducted at 800°C. It was found that the slope of the Coffin-Manson plot was changed with plastic strain range and fatigue fracture mode was also changed from transgranular at low strain range to intergranular at high strain range under continuous fatigue. For general metallic materials, it is well known that the slope change in the Coffin-Manson plot is due to the change in fatigue fracture mode from transgranular to intergranular, which results in the reduction of fatigue life. However, the effect of plastic strain range on the intergranular cracking for lamellar structured TiAl alloy has not been reported yet. In the present study, the effect of plastic strain range on the intergranular cracking is investigated and it is found that strain induced 2 phase transformation at the grain boundary under higher strain range results in the intergranular cracking.