Surface integrity and low cycle fatigue behavior of Ni-based single-crystal film cooling holes processed by ECM, EDM and PLM

Abstract

Surface integrity and low cycle fatigue (LCF) behavior of Ni-based single crystal film cooling hole (FCH) structures manufactured via three different processes—Electrochemical Machining (ECM), Electrical Discharge Machining (EDM), and Picosecond Laser Machining (PLM)—were investigated at high temperature. The surface integrity resulting from different drilling methods was analyzed across three aspects: geometry, metallurgy and roughness. Experimental results indicate that the LCF lifetime is significantly influenced by the drilling processes, with the order being N_ECM > N_EDM > N_PLM. In addition, while the drilling process minimally impacts the macroscopic fracture path and fracture morphology, it greatly influences the microstructural evolution near the cracks around the FCHs. Utilizing geometric reconstruction modeling, the crystal plasticity finite element method (CPFEM) was performed for three kinds of FCH model. The maximum resolved shear stress (RSS) around the three FCH models is mainly affected by surface integrity, with the order being RSS_ECM > RSS_EDM > RSS_PLM. Moreover, the fatigue damage distribution locations in all FCH models align well with the fatigue crack nucleation position observed in experiments. The fatigue life simulated using the damage evolution law falls within the error bands of ±2 times.