Fizika Nizkikh Temperatur: Volume 46, Number 11 (November 2020), p. 1336-1345 ( to contents , go back )
Nanoindentation of pure and gas-saturated fullerite C60 crystals: elastic-to-plastic transition, hardness, elastic modulus
S. N. Dub1, G. N. Tolmachova2, S. V. Lubenets3, L. S. Fomenko3, and H. V. Rusakova3
1V. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kyiv 04074, Ukraine
2National Science Center “Kharkov Institute of Physics and Technology” of the National Academy of Sciences of Ukraine, Kharkiv 61108, Ukraine
3B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine Kharkiv 61103, Ukraine
Received June 18, 2020, published online September 21, 2020
Elastic-plastic transition at nanoindentation of (111) plane of pure С60 fullerite single crystals was studied. The onset of plastic deformation in the contact was noted due to the plateau formation in the initial part of loading curve. The estimated stress of plasticity beginning was found to be on the order of the theoretical shear stress re-quired for homogeneous dislocation nucleation in the ideal crystal lattice of С60. The empirical values of elastic modulus E ≈ 13.5 GPа, hardness of the ideal crystal lattice H ≈ 1.4 GPа, and hardness at different indentation loads were obtained. The hardness vs load dependence was found consistent with the model of geometrically necessary dislocations. The loading diagrams shape and the dependencies of contact pressure vs indentation depth were strongly affected by gaseous interstitial impurities (hydrogen, oxygen, nitrogen) in С60 crystal; transition stress was essentially less and plateaus formation was observed at elevated indentation loads and depths as compared with pure fullerite crystal. For crystals, saturated with hydrogen, the enhanced value of elastic modulus (~ 20.4 GPа) and hardness (~ 1.1 GPа) were obtained. The results acquired at room temperature for C60 with face-centered cubic lattice are important for the description of the physical-mechanical properties of simple cubic lattice phase of C60 below 260 K (S. V. Lubenets, L. S. Fomenko, V. D. Natsik, and A. V. Rusakova, Fiz. Nizk. Temp. 45, 3 (2019) [Low Temp. Phys. 45, 1 (2019)]).
Key words: С60 fullerite single crystals, nanoindentation, elastic-plastic transition, dislocation nucleation, theoretical shear stress, molecular interstitial impurities.