Influence of oxide layers on plastic properties of metals: From atomistic to mesoscopic scale

• Applicant: Professorin Dr. Nina Merkert
• Subject Area: Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452407863

• Final Report Year: 2024

Final Report Abstract

Since in oxidation-rich environments an oxide layer will form on metallic surfaces, the influence of oxidation on dislocation nucleation and propagation needs to be considered. This is particularly important for materials with high surface-to-volume ratio as porous matter and lightweight materials as aluminum. For the latter, even under high vacuum conditions, an oxide layer may form within seconds. This will influence the mechanical properties of materials. The main aim of this research is therefore to examine the impact of oxide layers on the mechanical characteristics of metals, with a specific focus on how oxides affect the plastic deformation stage of materials. Our objective is to utilize the knowledge gained from comprehending these processes at the atomic level to make practical applications at the larger mesoscale. Key Research Insights: • Mechanical Property Alterations: Many different sets of molecular dynamics simulations and examinations have shown that nanoscale oxide layers have an impact on the mechanical properties of aluminum and titanium. The oxide layer on both of the assessed materials exhibits brittleness. Oxide layers have been shown to affect the overall mechanical characteristics of titanium and aluminum by modifying the nucleation process and preventing dislocation migration. On the other hand, aluminum nanofoams and nanowires that have undergone oxidation exhibit a substantial enhancement of Al-O bonds resulting in increased ductility. • Transition to Mesoscale: In this work, we examined the indentation and nanoscratching method as case studies. We analyzed various instances and materials, including high-entropy alloys at the nanoscale scale, using molecular dynamics simulations. On top of that, we employed the Discrete Dislocation Dynamics Simulations approach to build related models. In high-entropy alloys, the size of twinned regions in the plastic zone is greatest for the individual elements, but reduces for the alloys. We demonstrate that the chemical compound has a substantial impact on the buildup of dislocations.

Publications

• Thermodynamic dislocation theory: application to bcc-crystals. Modelling and Simulation in Materials Science and Engineering, 29(1), 015003.
  Le, K. C.; Dang, S. L.; Luu, H. T. & Gunkelmann, N.
  
• Data-mining of dislocation microstructures: concepts for coarse-graining of internal energies. Modelling and Simulation in Materials Science and Engineering, 29(3), 035005.
  Song, Hengxu; Gunkelmann, Nina; Po, Giacomo & Sandfeld, Stefan
  
• Molecular dynamics simulations of the machining of oxidized and deoxidized titanium work pieces. Results in Surfaces and Interfaces, 9, 100085.
  Homann, Simon; Luu, Hoang-Thien & Merkert, Nina
  
• Nanoindentation in alumina coated Al: Molecular dynamics simulations and experiments. Surface and Coatings Technology, 437, 128342.
  Luu, Hoang-Thien; Raumel, Selina; Dencker, Folke; Wurz, Marc & Merkert, Nina
  
• Multiple Scratching: An Atomistic Study. Tribology Letters, 71(2).
  Alabd, Alhafez Iyad; Kopnarski, Michael & Urbassek, Herbert M.
  
• Scratching a soft layer above a hard substrate. Philosophical Magazine, 103(15), 1411-1422.
  Alabd, Alhafez Iyad; Kopnarski, Michael & Urbassek, Herbert M.
  
• Simulated nanoindentation into single-phase fcc FexNi1-x alloys predicts maximum hardness for equiatomic stoichiometry. Scientific Reports, 13(1).
  Alabd, Alhafez Iyad; Deluigi, Orlando R.; Tramontina, Diego; Ruestes, Carlos J.; Bringa, Eduardo M. & Urbassek, Herbert M.
  
• Statistical analysis of discrete dislocation dynamics simulations: initial structures, cross-slip and microstructure evolution. Modelling and Simulation in Materials Science and Engineering, 31(7), 075003.
  Demirci, Aytekin; Steinberger, Dominik; Stricker, Markus; Merkert, Nina; Weygand, Daniel & Sandfeld, Stefan
  
• Nanoindentation into a bcc high-entropy HfNbTaTiZr alloy—an atomistic study of the effect of short-range order. Scientific Reports, 14(1).
  Alhafez, Iyad Alabd; Deluigi, Orlando R.; Tramontina, Diego; Merkert, Nina; Urbassek, Herbert M. & Bringa, Eduardo M.