Abstract
In single crystal Superalloys, fatigue crack prefers to propagate on crystallographic slip plane at lower temperature, while prefers to propagate perpendicular to the loading axis independent of crystal orientation at higher temperature. The former cracking mode is called as shearing mode cracking, and the latter is called as mode-I cracking. The aim of this work is to understand the determining factor of cracking mode in single crystal superalloys, and we focus on the influence of γ/γ’ microstructure and anomalous increase of yield strength of γ’ phase at elevated temperature on deformation behavior around crack-tip. First, the relation between macroscopic tensile strength and γ/γ’ microstructural phase strength was studied by using unit-cell FE simulations, and yield strength of γ phase and critical resolved shear stress (CRSS) of γ’ phase was evaluated. Second, a constitutive equation which considered γ/γ’ microstructure was made by using Eshelby’s inclusion theory. Finally, FE simulations were performed to understand the influence of γ/γ’ microstructure on crack tip deformation behavior. A series of FE simulations revealed that γ/γ’ microstructure and anomalous increase of yield strength in γ’ phase at elevated temperature strongly affect the slip deformation behavior around crack-tip.
