Slip Band Evolution Behavior near Circular Hole on Single Crystal Superalloy: Experiment and Simulation

Abstract

Circular holes on single crystal (SX) superalloys are widely utilized as film cooling structures on SX turbine blades, while their failure is a persistent issue. This study presents in-situ tests using digital image correlation (DIC) to reveal the slip band (SB) evolution behavior near the circular hole on SX superalloy, and proposes a mechanism-based model to capture the SB-associated evolutions of stress, strain, and damage fields. In the experiment part, high-temperature in-situ tensile tests are carried out under scanning electron microscope on plate-like SX specimens with circular hole, which can achieve the in-situ measurement and observation for the SB-induced strain concentration and microcrack nucleation. Experimental results reveal the effects of secondary orientation and temperature on stress-strain curve, SB evolution and SB direction. Besides, the microstructure observation shows that the γ´ phase shear is the primary cause of strain concentration inside SB. In the simulation part, a physics-based SB evolution model is proposed under the framework of crystal plasticity. For the regions inside and outside SB, different critical resolved shear stresses are utilized as the plasticity criteria, and different slip resistances are used as internal state variables in the flow rule to simulate the SB-induced strain concentration. A damage evolution rule is developed based on the plastic work density in slip systems to simulate the microcrack nucleation near the hole edge. Finally, the proposed model is validated through the experiments. The model can effectively simulate the SB initiation/evolution, SB direction, SB-induced strain concentration, and the microcrack nucleation near circular hole on SX superalloy.