Crystal plasticity study of the effect of asymmetric structure of diffusive film cooling hole on heterogeneous creep and fracture behavior of NBSC superalloy

Abstract

The heterogeneous creep and fracture behavior of nickel-based single crystal (NBSC) superalloys with inclined and diffusive holes are investigated. The analyses are made by creep experiments and crystal plasticity (CP) simulation with a modified creep constitutive model that accounts for both plastic and creep shear slip near the cooling hole. The study indicates that the cooling hole has a creep-strengthening effect on the NBSC superalloy, resulting in an extended creep duration for specimens with cooling holes than those without holes. Meanwhile, the asymmetric structure of diffusive and machined-tapered inclined cooling holes causes localized stress concentration around outlet side of the holes, which leads to asymmetric deformation and decreased rupture strain. Moreover, the interaction between neighboring holes causes shear slip and creep deformation more dominantly at side holes than at the center hole. Thus, preferential initiation of microcrack occurs around the side holes. The specimen without a hole displays typical ductile fracture, whereas the specimen with cooling holes displays a combined cleavage-like and ductile fracture due to the localized stress concentration induced by plastic shear slip around the hole. In addition, as loading stress increased, the creep lifetime and rupture strain decreased, while the characteristics of cleavage-like rupture increased.