PSI - Issue 71

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

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the α -Al 2 O 3 film on Al(110) at 300 K, highlighting significant structural modifications along with the increase in hardness. This behaviour may be because of the instability of α -Al 2 O 3 at 300 K or due to the chosen potential used in our simulations, leading to the observed non-standard mechanical response.

Fig. 8. RDF Plot of Amorphous Region during full load when substrate is Al single crystal with (110) orientation

4. Conclusions In this paper, it has been presented the results and insights of MD simulations where we performed nanoindentation and nanoscratching of Al specimens — both single and bi-crystalline — as well as α -Al 2 O 3 thin films on Al substrates. It has been examined the effects of grain size, indentation velocity, and temperature on the computed mechanical properties to understand the system better. Our findings highlight the difficulties arised while performing indentation (or) scratch on our system with given configuration, and indicate its effect on mechanical constants measured at grain boundaries and in bulk regions, and there were able to observe, mechanical constants measured at grain boundaries are lower than those in bulk regions, grain size increases, hardness also increases, consistent with the inverse Hall – Petch relation at the nanoscale range of 100 – 300 Å. For the α -Al 2 O 3 /Al system, similar trends in hardness were observed comparable to that seen when indenting pure Al crystals, but for friction coefficient it was not able to conclude as for the operating indentation/scratch rate used in our experiments (even when velocity of indenter during indentation is 0.6 Å/ps) the dislocation pileup takes place, and as operating at higher velocities lead to less realistic behaviours, it needs to increase the crystal/system size to avoid this cause for erroneous results. However, the amorphous alumina layer undergoes localized changes via shear transformation zones (STZs) resulting into lower hardness of the system. Notably, at 300 K and on an Al(110) substrate, a detectable phase- like transformation occurs in the α -Al 2 O 3 , which could be because of instability of amorphous phase at 300 K or due to the chosen potential, other simulation settings, leading to the non-standard behaviours. Ohmura, T., Matsuoka, S., Tanaka, K., and Yoshida, T., 2001. Nanoindentation load displacement behavior of pure face centered cubic metal thin films on a hard substrate. In: Thin Solid Films, 385(1):198 – 204. Oliver, W.C., Pharr, G.M. 2004. Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology. Journal of Materials Research 19, 3 – 20. Ma, Z., Gamage, R.P., and Zhang, C., 2021. Mechanical properties of α -quartz using nanoindentation tests and molecular dynamics simulations. International Journal of Rock Mechanics and Mining Sciences, 147:104878. Mishin, Y., Farkas, D., Mehl, M.J., Papaconstantopoulos, D.A.,1999. Interatomic potentials for monoatomic metals from experimental data and ab initio calculations. Physical Review B 59, 3393 – 3407. Peng, P., Liao, G., Shi, T., Tang, Z., and Gao, Y., 2010. Molecular dynamic simulations of nanoindentation in aluminum thin film on silicon substrate. Applied Surface Science, 256(21):6284 – 6290 Stukowski, A. 2010. Visualization and analysis of atomistic simulation data with OVITO – The Open Visualization Tool. Modelling and Simulation in Materials Science and Engineering 18, 015012. Tavazza, F., Senftle, T. P., Zou, C., Becker, C. A., and van Duin, A. C. T., 2015. Molecular Dynamics Investigation References