Atomistic simulation study of influence of Al2O3-Al interface on dislocation interaction and prismatic loop formation during nano-indentation on Al2O3-coated aluminum

A large-scale molecular dynamics (MD) simulation of nano-indentation was carried out to provide insight into the influence of the Al-Al2O3 interface on dislocation evolution and deformation behavior of Al substrate coated with Al2O3 thin film. Adaptive common neighbor analysis (a-CNA), centro-symmetry parameter (CSP) estimation, and dislocation extraction algorithm (DXA) were implemented to represent structural evolution during nano-indentation deformation. The absence of elastic regime was observed in the P-h curve for this simulated nano-indentation test of Al2O3 thin film coated Al specimen. The displacement of oxygen atoms from Al2O3 to Al partly through the interface greatly influences the plastic deformation behavior of the specimen during nano-indentation. Prismatic dislocation loops, which are formed due to pinning of Shockley partials (1/6 < 112 >) by Stair-rod (1/6 < 110 >) and Hirth dislocation (1/3 < 001 >), were observed in all cases studied in this work. Pile-up of atoms was also observed and the extent of the pile-up was found to vary with the test temperature. A distorted stacking fault tetrahedron (SFT) is formed when a nano-indentation test is carried out at 100 K. The presence of a prismatic dislocation loop, SFT and dislocation forest caused strain hardening and, consequently, there is an increase in hardness as indentation depth increases.