Crystal plasticity analysis of fatigue-creep behavior at cooling holes in single crystal Nickel based gas turbine blade components

Abstract

We build a crystal plasticity finite element framework to investigate slip localisation and fatigue-creep behaviour at the cooling holes of single crystal Nickel (Ni) based components under cyclic thermomechanical loading. The total slip rate is decomposed into a thermally activated dislocation glide rate which dominates at moderate/low temperatures (T) and/or high stresses, and a climb rate which dominates at high temperatures and increases as inelastic strain accumulates. This formulation captures the monotonic and long-term creep response of Ni alloys in the wide range 20 <T < 1100 °C and indicates that room temperature plasticity during unloading increases the high temperature creep rate during loading (creep dwell), eventually increasing the total slip accumulation per cycle; the effect depends on the way the inelastic strain accumulates upon successive slip reversals. Elastic material anisotropy is shown to modify drastically the stress concentration around holes such that slip tends to localise at locations where the max principal stress, tangent to the hole surface, aligns with stiff crystallographic directions. This highlights the importance of plastic and creep anisotropy and creates new avenues for optimising hole shape to minimise slip activity. Our study brings to light key material-component relationships that concern the wider material science, high temperature and fatigue communities.