Browsing by Author "Domínguez-Gutiérrez, F. J."

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Nanoindentation of single crystalline Mo: Atomistic defect nucleation and thermomechanical stability
(2021-10-05) Domínguez-Gutiérrez, F. J.; Papanikolaou, S.; Esfandiarpour, A.; Sobkowicz, P.; Alava, M.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The mechanical responses of single crystalline Body-Centered Cubic (BCC) metals, such as molybdenum (Mo), outperform other metals at high temperatures, so much so that they are considered as excellent candidates for applications under extreme conditions, such as the divertor of fusion reactors. The excellent thermomechanical stability of molybdenum at high temperatures (400–1000 oC) has also been detected through nanoindentation, pointing toward connections to emergent local dislocation mechanisms related to defect nucleation. In this work, we carry out a computational study of the effects of high temperature on the mechanical deformation properties of single crystalline Mo under nanoindentation. Molecular dynamics (MD) simulations of spherical nanoindentation are performed at two indenter tip diameters and crystalline sample orientations [100], [110], and [111], for the temperature range of 10–1000 K. We investigate how the increase of temperature influences the nanoindentation process, modifying dislocation densities, mechanisms, atomic displacements and also, hardness, in agreement with reported experimental measurements. Our results suggest that the characteristic formation and high-temperature stability of [001] dislocation junctions in Mo during nanoindentation, in contrast to other BCC metals, may be the cause of the persistent thermomechanical stability of Mo.
Nanoindentation of tungsten : From interatomic potentials to dislocation plasticity mechanisms
(2023-04) Domínguez-Gutiérrez, F. J.; Grigorev, P.; Naghdi, A.; Byggmästar, J.; Wei, G. Y.; Swinburne, T. D.; Papanikolaou, S.; Alava, M. J.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In this study, we employed molecular dynamics simulations, both traditional and machine learned, to emulate spherical nanoindentation experiments of crystalline W matrices at different temperatures and loading rates using different approaches, such as EAM, EAM with Ziegler, Biersack, and Littmark corrections, modified EAM, analytic bond-order approach, and a recently developed machine-learned tabulated Gaussian approximation potential (tabGAP) framework for describing the W-W interaction and plastic deformation mechanisms. Results showed similarities between the recorded load-displacement curves and dislocation densities, for different interatomic potentials and crystal orientations at low and room temperature. However, we observe concrete differences in the early stages of elastic-to-plastic deformation transition, revealing different mechanisms for dislocation nucleation and dynamics during loading, especially at higher temperatures. This is attributed to the particular features of orientation dependence in crystal plasticity mechanisms and, characteristically, the stacking fault and dislocation glide energies information in the interatomic potentials, with tabGAP being the one with the most well-trained results compared to density functional theory calculations and experimental data.