PSI - Issue 71

Gnaneshwar Sampathirao et al. / Procedia Structural Integrity 71 (2025) 484–491

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1. Introduction Al, α -Al 2 O 3 coated with thin Al is widely used in aerospace, automotive, and semiconductor manufacturing due to their properties such as light weight, high strength-to-weight ratio, and excellent corrosion resistance. Nanoscale mechanical behaviour has drawn interest in recent years, as understanding deformation mechanisms can guide improved fabrication and performance. Previous studies have shown that film thickness and substrate effects influence plasticity. For instance, T. Ohmura et al. (2000) identified a critical penetration depth of about 1/5 to 1/6 of the film thickness an d linked sudden “pop - in” events to surface oxide layers. Atomistic simulations by Youngmin Lee et al. (2004) revealed dislocation nucleation mechanisms such as the formation of embryonic loops and prismatic partial loops, while Ping Peng et al. (2010) highlighted substrate-induced changes in pile-up and hardness. Peng Zhang et al. (2013) further demonstrated that nano-scratching behaviour depends on feed, depth, and crystal orientation. Whereas, in this study, a systematic examination of the nanoindentation and nano-scratch behaviour of nanocrystalline Al, Al coated with a 10 Å α -Al 2 O 3 layer using atomistic simulations were performed. The findings aim to clarify the underlying deformation mechanisms and mechanical properties at the nanoscale, ultimately contributing to better design according to industry processes. 2. Models description All the MD (molecular dynamics) simulations were performed using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) Thompson, A.P et al. (2022) . Nanocrystalline Al and α -Al 2 O 3 samples, as well as spherical indenters, were modelled within LAMMPS. The simulation domains measured 100 Å × 100 Å × 100 Å for indentation and 100 Å × 100 Å × 200 Å for scratch experiments. When required, a 10 Å- thick α -Al 2 O 3 layer was added, and a spherical indenter with a radius of 26 Å was employed, as illustrated in Fig. 1.

Fig. 1. Configuration of the Al, α -Al 2 O 3 with Al substrate simulation system.

Al-Al, Al-O interactions were modelled using an (EAM) Embedded Atom Method potential Mishin, Y et al. (1999), which effectively captures metallic bonding by accounting for pairwise interactions and the embedding energy associated with electron density. Al-C interactions were described by a Lennard-Jones (LJ) potential, and C-C interactions were modelled with the Tersoff potential Tersoff, J. (1988) — approaches that have been followed in previous studies on indentation of metals Zhaoyang Ma et al. (2010), Tavazza, F et al. (2015). Periodic boundary conditions were applied along the X, Z directions, while a fixed boundary condition was along the Y direction (direction of indenter penetration). Prior to indentation, the samples were equilibrated at respective temperatures. Indentation simulations were then conducted under an NVT ensemble at indentation velocities ranging from 0.1-0.6 Å/ps, with step size of 0.1 Å/ps. The resulting load-displacement data were analysed using the Oliver-Pharr method Oliver, W.C. et al. (2004). 3. Results and Discussion Here, it has present our interpretations of the results of our MD simulations of nano-indentation and nano-scratch on nanocrystalline Al and Al coated with a 10 Å- thick α -Al 2 O 3 film. It begins by trying to understand how indentation velocity influences hardness, stiffness, and friction. Then, how crystallographic orientation affects dislocation behaviour. Then, consider the role of grain boundaries and grain size on deformation mechanisms. Finally, it has been explored the impact of an amorphous α -Al 2 O 3 layer on the substrate’s mechanical properties. Throughout, it will be emphasized on atomic-scale processes — dislocation nucleation, movement, and accumulation.