Scratch-resistant behavior of NbC/Nb nanolaminates: insights from molecular dynamics atomistic simulations

Molecular dynamics atomistic simulations were used to investigate the tribological properties of NbC/Nb ceramic/metal nano-laminates (CMNLs) during nano-indentation and nano-scratching. The study compared the scratching behavior of the CMNLs to that of NbC and Nb single crystals. Two CMNL models were considered, both featuring a top layer of NbC with differing metallic layer thicknesses of 2 nm and 8 nm. Spherical indenters with radii of 5, 10, and 20 nm were used to scratch the CMNLs with a 3 nm penetration depth, avoiding penetration into the metallic layer beneath the ceramic layer. The results revealed that the alternating metallic and ceramic layers in the CMNL models reduced the amount of material removed during scratching compared to NbC single crystals. The model with the thickest metallic layer showed lower friction coefficient and material removal. The simulations demonstrated that the indenter size had a significant effect on the scratch behavior of CMNLs, with the friction coefficients for the larger indenters being notably lower. The study revealed that larger indenters show less sensitivity to the individual layer thickness in terms of friction coefficients and material removal. The scratching response of the models was linked to the atomic-level deformation mechanisms during the scratching process. The dominant factors affecting the scratching behavior were individual layer thickness, indenter size, and the scratching attack angle. Overall, the study provides valuable insights into the tribological behavior of CMNLs and sheds light on the design of scratch-resistant coatings.