Multiscale simulation of mechanical properties of TiNb alloy

The article presents a numerical simulation of the mechanical properties of a Ti-Nb β-alloy on three different scales. The ab-initio approach is used to estimate the concentrations of the Ti alloy with required elastic properties. On the basis of molecular dynamics simulation, we calculate the adhesive force between individual particles of the alloy. The calculated dependence is implemented within the movable cellular automata method to determine the mechanical properties of Ti-Nb depending on the interparticle free space

Molecular dynamics modelling of boundary migration in bicrystals under nanoburnishing

The paper reports the molecular dynamics simulation results on the behavior of a copper crystallite in local frictional contact. The crystallite has a perfect defect-free structure and contains a high-angle grain boundary of type Σ5. The influence of the initial structure on the specimen behavior under loading was analyzed. It is shown that nanoblocks are formed in the subsurface layer. The atomic mechanism of nanofragmentation was studied. A detailed analysis of atomic displacements in the blocks showed that the displacements are rotational. Calculations revealed that the miso ientation angle of formed nanoblocks along different directions does not exceed 2 degrees

Molecular dynamics study of sliding mechanisms of Ni, amorphous Ni-p and nanocrystalline Ni films

In the paper by using molecular dynamics method we investigate the sliding feature of different nano-scale specimens: single-crystal nickel evolving from amorphous pure Ni during shear deformation, Ni-P a layer and nanocrystalline nickel. Special attentions are paid to the value of resistance stresses and plastic deformation mechanisms manifested during sliding simulations. The study is performed at an ambient temperature. The analysis showed that Ni-P amorphous structure is characterized by lowest resistance stresses and smooth sliding provided by the bond-switching mechanism between pairs of atoms due to shear loading. Similar low resistance stress was also observed for an amorphous pure Ni layer, but only at an early stage of sliding before crystallization occurred. The highest shear resistance was confirmed for single-crystal nickel caused by classical deformation mechanisms like stacking fault formation and dislocation movement. Sliding simulations of a nanocrystalline specimen show both, crystal defect driven deformation in the bulk and sliding along quasi-amorphous grain boundaries. Thus, it was shown that nickel-phosphorous coating in amorphous-like state may exhibit low friction properties, and, therefore, serve as the solid lubricant material

Ab initio calculations for search optimization of multicomponent alloy configurations

The paper presents an algorithm for optimization of searching configurations of multicomponent alloys that have a predetermined value of physical and mechanical properties. Values obtained by Exact MT Orbitals (EMTO) were used for calculations. The algorithm efficiency is demonstrated on an example of estimating the bulk modulus of a three-component alloy based on Ti, Nb and Zr. It is shown that the use of the algorithm can in some cases reduce the amount of calculations by 10 times or more

THE EFFECT OF ELECTRON-BEAM TREATMENT ON THE DEFORMATION BEHAVIOR OF THE EBAM TI-6AL-4V UNDER SCRATCHING

The effect of the continuous electron beam scanning (CEBS) post-treatment on the microstructure, mechanical properties and scratching behavior of the Ti-6Al-4V alloy samples produced by electron beam additive manufacturing was studied experimentally and by using molecular dynamics simulation. It was found that the CEBS post-treatment resulted in the transformation of the microstructure of the samples from the α′-martensite into the α+β structure. The evolution of the sample microstructure was shown to provide improved mechanical characteristics as well as enhanced deformation recovery after scratching. A mechanism was proposed based on the results of molecular dynamics simulation, which attributed to the improved recovery of the scratch groves after passing the indenter to reversible β→α→β phase transformations, which occurred in the vanadium alloyed Ti crystallites

FEATURES OF THE Σ5 AND Σ9 GRAIN BOUNDARIES MIGRATION IN BCC AND FCC METALS UNDER SHEAR LOADING – A MOLECULAR DYNAMICS STUDY

Molecular dynamics simulation of metallic bicrystals has been carried out to investigate the behavior of the symmetrical tilt grain boundaries under shear loading. Σ5 and Σ9 grain boundaries in Ni and α-Fe were analyzed. It is found that behavior of the defect depends not only on the structure of boundaries but also on the type of crystal lattice. In particular it is shown that under external stress the grain boundary (GB) behaves differently in the BCC and FCC metal. A comparison of the values of displacement of various types of GB due to their migration caused by shear deformation is carried out. The results can help us to understand the features of the plastic deformation development in nanoscale polycrystals under shear loading

Features of the microstructure development under conditions, reproducing the process of friction stir welding. Molecular-dynamics study

Friction stir welding is a recently developed technology which is used in various branches of modern engineering. The basis of this technology is the friction of the rotating cylindrical or specially shaped tool between two metal plates brought together either to meet their ends of one above another with the overlap. When applying the FSW process in various economical sectors, the important task is to study the mechanisms and identify the physical laws and factors leading to formation of structural inhomogeneities and discontinuities in the weld seam. This paper analyzes the basic mechanisms behind the structural state generation in the material subjected to severe plastic deformation and heating. To investigate the atomic mechanisms of structural changes in FSW, the modeling at atomic scale has been carried out. Results of work can be a basis for new knowledge about the microstructure evolution in FSW

Geodetic base for the construction of ground-based facilities in a tropical climate

The data on the geodetic base creation for surveys and construction on the example of works to expand the power station capacity, performed in one of the Latin America countries in 2015-2018, are presented in the paper. The points’ coordinates obtained by two methods were established. A comparison of the points’ heights obtained from II class geometric leveling and two-sided trigonometric leveling is also carried out. It was concluded that the high accuracy of determining the points’ coordinates and altitudes can be obtained by ground methods (using a total station) with careful measurements even in tropical climates

Theoretical investigation of the dynamics of friction stir welding process by movable cellular automaton method

The paper is devoted to development of a new approach to study of friction stir welding (FSW) process on the mesoscopic scale. This approach is based on computer-aided simulation by movable cellular automaton (MCA) method. In the framework of developed formalism of MCA method the dynamics of the friction stir welding process of duralumin plates was investigated. It was shown that ratio of rotation velocity to velocity of translation motion of rotating tool greatly influences the quality of welded joint. Optimal choice of the ratio of these parameters could significantly decrease volume content of pores and microcracks in the welded joint