Rita I. Babicheva

Molecular dynamics simulations were performed to examine the temperature-dependent nanoindentation response of aluminum substrates coated with amorphous or crystalline equiatomic FeNiCrCo layers. The study extends our previous 300 K baseline analysis of the same model system by comparing deformation at 300 and 600 K and by examining the spatial redistribution of local kinetic energy and local nonequilibrium kinetic-temperature indicators during loading and unloading. A spherical virtual indenter with a radius of 30 Å was driven to maximum penetration depths of 35 and 65 Å, representing predominantly coating-controlled deformation and a regime involving the coating–substrate interface and aluminum substrate, respectively. At both temperatures, the crystalline coating exhibited higher indentation resistance and serrated force–depth responses associated with intermittent lattice-mediated plasticity, whereas the amorphous coating showed lower force levels and smoother deformation through distributed local atomic rearrangements. Increasing the temperature from 300 to 600 K enlarged the deformation-affected region and promoted a greater involvement of the interface and Al substrate. Nevertheless, the spatial character of the response remained structure-dependent: the crystalline coating retained a comparatively compact region of elevated local kinetic energy beneath the indenter, whereas the amorphous coating displayed a broader and more diffuse kinetic-energy perturbation. Adaptive common-neighbor analysis was used as a qualitative local-environment descriptor; therefore, structural labels are interpreted together with force–depth curves and atomistic configurations rather than as unique phase identifiers. The results identify temperature-dependent trends in deformation localization and energy redistribution for an idealized FeNiCrCo/Al model system. Because the simulations employ a finite periodic cell, a high indentation velocity, and an empirical potential, the findings are interpreted as qualitative atomistic trends and are not quantitatively extrapolated to experimental indentation conditions.

This study investigates the nanomechanical response of aluminum substrates coated with crystalline or amorphous equiatomic FeNiCrCo compositionally complex alloy (CCA) layers using molecular dynamics nanoindentation. We evaluated the influence of coating microstructure and pre-relaxation via Monte Carlo/molecular dynamics (MC/MD) on deformation behavior at shallow (35 Å) and deep (65 Å) indentation depths. The relaxation process is critical for equilibrating internal stresses and homogenizing the initial stress field in amorphous phases, while preventing chaotic defect multiplication in crystalline lattices, yet it simultaneously promotes Fe and Cr surface segregation consistent with the equilibrium chemical short-range ordering of the alloy. The results reveal distinct deformation mechanisms: crystalline coatings exhibit higher peak indentation forces of about 300 ± 16 eV/Å characterized by discrete force fluctuations indicative of localized plastic events, while amorphous coatings show lower peak loads (~170–220 ± 12 eV/Å), corresponding to a reduction in load-bearing capacity of roughly 25%–40%, and smooth, continuous deformation governed by shear transformation zones. Notably, in amorphous systems, pressure-induced local crystallization occurs under load, with ordered FCC/HCP regions persisting after unloading, indicating partial irreversibility of the phase transition. Upon deep indentation into the substrate, the amorphous system exhibits a sharp increase in stiffness due to substrate compaction, whereas the crystalline system maintains high load-bearing capacity with reduced defect density in the relaxed state compared to the non-relaxed counterpart. Relaxation significantly reduces force-curve fluctuations in both systems, enhancing the stability of the mechanical response. Compared with uncoated aluminum, which exhibits extensive twin propagation and deep defect penetration, the FeNiCrCo-coated systems approximately halve the defect penetration depth and reduce the defective-atom volume fraction in the substrate by about a factor of two, thereby more effectively confining plastic deformation and preserving substrate integrity under the simulated conditions. These findings demonstrate that the synergy between coating crystallinity and rigorous relaxation protocols governs stress distribution patterns—localized hotspots in amorphous phases versus extended networks in crystalline ones—providing key insights for designing advanced protective coating–substrate systems with optimized mechanical performance.

In this work, a comprehensive modeling of the influence of short-range order on the mechanical properties of body-centered cubic high-entropy ZrTiNbV and ZrTiNbHf alloys under shear deformation using a hybrid molecular dynamics (MD) and Monte Carlo (MC) approach has been carried out. High-entropy alloys (HEA) are a new class of materials produced by mixing four or more elements in approximately equal proportions, providing a unique combination of properties and expanding the capabilities of traditional materials science. In recent years, special attention has been paid to the mechanical properties and deformation mechanisms of high-entropy alloys with a bcc lattice, where screw dislocations, interaction with atoms of various elements and the formation of short-range order, which contributes to the strengthening of the material, play a key role. Bicrystalline models with different degrees of atomic ordering resulting from MD/MC relaxation have been constructed, allowing for both chaotic and clustered elemental distributions. A comparative analysis of structural changes, defect evolution and mechanical properties (in particular, yield strength) under shear has been carried out. It was found that in ZrTiNbV alloy the formation of Nb clusters initiates local phase transformations BCC → HCP and reduces yield strength, whereas for ZrTiNbHf the formation of segregations and nanoclusters effectively prevents grain boundary migration and phase transformations, which leads to a significant increase in strength. The results are consistent with the current understanding of the role of near-order in the hardening of high-entropy materials and demonstrate that targeted control of chemical ordering and grain boundary structure can be an effective tool for optimizing the mechanical properties of high-entropy alloys. The work extends fundamental knowledge of plasticity and fracture mechanisms in multicomponent alloys and opens new perspectives for their application under high mechanical loads and aggressive environments.

Our study investigates the interaction of dislocations with hexagonal close-packed (hcp) and chi-phase (χ) particles in body-centred cubic (bcc) tungsten (W) using molecular dynamics simulations. The research aims to understand how these interactions influence the mechanical properties of W, particularly in the context of neutron irradiation environments. The simulations were conducted with spherical and cylindrical particles at various temperatures and cell sizes to observe the effects on critical shear stress. Results indicate that the shape and size of the particles significantly affect the critical shear stress required for dislocation movement, with cylindrical particles requiring higher stresses than spherical ones. Additionally, the study found that temperature variations have a more pronounced effect on χ-phase particles compared to hcp-phase particles. Our findings provide insights into the strengthening mechanisms in W-Re alloys and suggest potential pathways for enhancing the material’s performance under extreme conditions.

In a recent experimental work, as a result of severe plastic deformation, a non-equilibrium solid solution was obtained despite the very limited solubility of zirconium (Zr) in aluminum (Al). This opens up a new path in the development of heat-treatable alloys with improved electrical and mechanical properties, where mechanically dissolved elements can form intermetallic particles that contribute to precipitation strengthening. In the present study, molecular dynamics simulations were performed to better understand the process of mechanical dissolution of Zr within an Al model, with Zr atoms segregated along its grain boundaries. Stress–strain curves, radial distribution functions, and mechanisms of plastic deformation and dissolution of Zr in Al were analyzed. It is revealed that orientation of the grain boundary with segregation normal to the shear direction promotes more efficient mixing of alloy components compared to its parallel arrangement. This happens because in the second case, grain boundary sliding is the main deformation mechanism, and Zr tends to remain within the interfaces. In contrast, the involvement of dislocations in the case of normal orientation of grain boundaries with Zr segregation significantly contributes to deformation and facilitates better dissolution of Zr in the Al matrix. The findings obtained can provide new insights considering the role of texture during mechanical alloying of strongly dissimilar metals.

A molecular dynamics (MD) simulation method is used to investigate the effect of grain boundary (GB) segregation on the deformation behavior of bicrystals of equiatomic nanoscale CoCrCuFeNi high-entropy alloy (HEA). The deformation mechanisms during shear and tensile deformation at 300 K and 100 K are analyzed. It is revealed that upon tensile deformation, the stacking fault formation, and twinning are the main deformation mechanisms, while for the shear deformation, the main contribution to the plastic flow is realized through the GB migration. The presence of the segregation at GBs leads to the stabilization of GBs, while during the shear deformation of the nanoscale CoCrCuFeNi HEA without the segregation at GBs, GBs are subject to migration. It is found that the GB segregation can differently influence the plasticity of the nanoscale CoCrCuFeNi HEA, depending on the elemental composition of the segregation layer. In the case of copper and nickel segregations, an increase in the segregation layer size enhances the plasticity of the nanoscale CoCrCuFeNi HEA. However, an increase in the thickness of chromium segregations deteriorates the plasticity while enhancing maximum shear stress. The results obtained in this study shed light on the development of HEAs with enhanced mechanical properties via GB engineering.

Tungsten is widely used as a material capable of withstanding working conditions in nuclear reactors and other extreme conditions. Under the influence of irradiation, such defects as Frenkel pairs, pores, and dislocation loops are formed in the metal. Therefore, the research aimed at studying the interactions of these defects with each other and their influence on the mechanical properties of the metal are relevant. The paper presents the theoretical study based on the molecular dynamics method, the purpose of which is to investigate the mechanism of strain hardening of tungsten associated with the interaction of dislocations and pores. The authors solved this problem using the LAMMPS package, carried out the integration of atoms motion equations by the fourth order Verlet method. The model under the study is a single crystal of a certain [111], [–1–12], [1–10] orientation along the basic X, Y, and Z coordinate axis relatively, in which the slip of edge dislocations in the main slip system of BCC metals and their interaction with pores is considered. The authors studied the influence of a pore size on the shear stress magnitude: the growth of pore diameter is proportional to the stress growth. The dependences of shear stress on the shear strain in the temperature range of 600–1400 K are calculated, whereby the temperature change does not significantly influence the stress value. The study shows that dislocations cut the pores and, upon the repeated interaction with a pore, a lower value of peak shear stress is observed than during the first one. The presence of pores leads to the flow stress increase, and such an effect becomes more evident with the increasing pore diameter. The flow stress increases thrice for pores with a diameter of 6 nm compared to the material without pores. The authors described the mechanism of interaction between the edge dislocations and pores under the influence of shear stress.

Graphene is a two-dimensional crystal in which sp2-hybridized carbon atoms have valence bonds with three neighbors. Theoretically, other two-dimensional carbon structures were predicted, in...