Single-crystals of Co8.4Al9.4W1.9Ta alloy with macrosegregation of Al and W were directionally solidified with a flat front. Mini-specimens of different composition were cut at different heights of the single-crystals and tested for compression and oxidation at 900°C. It was found that W increases yield strength while Al retards oxidation.

An analytical analysis of the problem of the longitudinal tension of two-layered tubes with walls made of tetragonal crystals was carried out together with numerical calculations of the effective Young's moduli and Poisson's ratios of the tubes, using the known experimental data on the elastic characteristics of such crystals. The study of the effective elastic properties of two-layered tubes was carried out in the cases of layers of the same thickness, equal volumes, and greater arbitrariness. The effective Young's modulus often exceeds the largest Young's modulus of a pair of layers, and the effective Poisson's ratio can be negative, even if the Poisson's ratios are positive in both layers. In other words, an auxetic of the two-layered tube may correspond to a pair of non-auxetics in two layers of this tube.

The success of dental titanium implants depends on the interaction of the implant with the surrounding bone, including the type of coating that promotes osseointegration. The most popular are calcium phosphate coatings, in particular tricalcium phosphate (TCP). Since cases of delamination of coatings from titanium have been observed in practice, it is important to be able to evaluate and predict the adhesion strength of coatings of different compositions to titanium. The work involves ab initio quantum chemical modeling of the interaction of TCP with titanium oxide and calculation of their binding energy. Considering that titanium instantly oxidizes in air, calculations were carried out with titanium dioxide. The Gaussian09 DFT B3LYP package with the 6-31G basis set was used. We synthesized tricalcium phosphate stepwise by assessing the binding energies between its constituents and titanium dioxide, as well as other structural characteristics including bond lengths, bond angles, dihedral angles, and charges. A method for assessing adhesion strength at the macro level using binding energy values calculated at the nano level is proposed. The values obtained are in reasonable agreement with experimental data and other numerical calculations. Using the methods of micromechanics of inhomogeneous media for the polycrystalline/amorphous structures of hydroxyapatite (HA) and beta-TCP coatings, their anisotropic elastic characteristics were averaged and the degree of their closeness to the characteristics of the Ti substrate was compared. A comparison of two CFs showed that HA has an advantage over TCP both in terms of greater chemical affinity with the titanium substrate (higher adhesive bond energy) and in terms of proximity to the substrate in terms of mechanical characteristics (lower stress concentration at the bond boundary).

Graphyne (two-dimensional one-atom-thick carbon allotrope) a promising semiconductor distinct by the number of acetylenic bonds. The study of mechanical properties is of key importance for electronics, composite fabrication, and fundamental understanding of the mechanical behavior of 2D structures. Molecular dynamics and analytical calculations were used to obtain the elastic constants (stiffness and compliance constants, Young's and shear modulus, Poisson's ratio) for five graphynes. For the first time, the direct link between stiffness and compliance constants for 2D materials were presented. Among hexagonal graphynes, gamma(1) has the largest Young's modulus (154 N/m). The deformation is attributed to the competition between the rotation and elongation of bonds in graphyne under loading. An analysis of stationary and extreme values of Young's and shear modulus, Poisson's ratio was carried out for the first time based on the search for the extremum of a function of one variable. A strong mechanical anisotropy was observed for orthorhombic graphynes (beta(3) and gamma(2)). Orthorhombic graphynes possess extremely large in-plane Poisson's ratio. Explanation of how elastic constants depend on structure density and atomic arrangement was given. The obtained results open new opportunities for the development of new nanomechanical devices based on such 2D materials.

The mechanical properties of metamaterials with different cellular internal structures were experimentally studied when perforated along the normal by a rigid spherical striker. Auxetic and non-auxetic samples of metamaterials with a chiral structure of cells, respectively, in the form of concave or convex hexagons, were produced using a 3D printer from e-PLA plastic. Based on the penetration experiments, the properties of chiral auxetic and non-auxetic samples of the same mass were compared for the cases when there was air inside the cells and when the cells were filled with gelatin. The relative loss of kinetic energy of the striker when perforating gelatin-filled samples was significantly higher for the auxetic metamaterial than for the non-auxetic one. For unfilled (“air”) samples, the relative loss of kinetic energy was slightly higher for the nonauxetic.

Negative creep of single crystals of two nickel-based superalloys has been studied. This phenomenon was observed for both alloys at temperatures of 980–1000°C and low or zero loading stresses. It is assumed that the main reason for negative creep is the formation of short-range order of atoms in the highly alloyed lattice of the matrix γ-phase. Additional factors influencing the magnitude and anisotropy of negative creep deformation can be the relaxation of residual stresses: at the microscopic level - misfit stresses between the γ-matrix and the strengthening γ′-precipitates, and at the mesoscopic level - dendritic stresses between the dendritic axes and interdendritic regions.

Based on the results of performed thermophysical measurements and available experimental data for adiabatic elastic stiffnesses, isothermal elastic characteristics of the single crystal nickel-based superalloy CMSX-4 have been calculated for a wide temperature range, from room temperature to 1300°C. According to the results obtained, the adiabatic and isothermal values of such elastic characteristics as elastic stiffnesses c_11 , c_12 and bulk modulus of elasticity B differ significantly at high temperatures. The reasons for this are significant changes in the thermophysical properties of the alloy with temperature and a temperature increase of its Poisson’s ratio approaching the limiting value for cubic crystals, equal to 0.5. It is shown that the use of adiabatic elastic constants instead of isothermal ones in engineering calculations affects the relationship between the volumetric strain and hydrostatic stress, and this effect is similar to introducing a field of thermal dilatation into the analyzed object. At low temperatures, this effect is small, but at high temperatures, typical for the service conditions of the blade material of aircraft gas turbine engines, it increases many times.

An analytical solution for residual stresses and their energy in an elastically anisotropic two-component plate structure, where the components have an identical type of elastic anisotropy, identical or proportional elastic constants and coinciding principal axes of elastic anisotropy is obtained. The obtained solution has been applied to analyze the anisotropy of the elastic energy of such crystalline structures as the raft structure γ/γ' of single-crystal nickel-base superalloys, multilayer erosion-resistant nanocoatings ZrN/CrN and single-layer coatings of various types. It has been shown that the factor of minimizing the elastic energy of residual stresses has a significant effect on the crystallographic orientation of the interface in multilayer structures and the direction of axis of the growth texture axis of coatings.

The results of calculations of the effective Young’s modulus of longitudinally stretched two-layered plates made of identically oriented cubic crystals are presented on the basis of analytical analysis and the numerical finite element method. Analytical dependences of effective Young’s modulus on Young’s moduli and Poisson’s ratios of crystals in layers are presented. Combinations of pairs of crystals with a significant deviation of the effective characteristics from ones found by the rule of mixtures are determined. The dependences of the effective Young’s moduli on extreme values of the Young’s moduli and Poisson’s ratios of crystals in layers are established. They are presented graphically, and in some cases are reflected in the form of a table.

Some properties of metamaterials with a negative Poisson’s ratio (auxetics) have been studied experimentally when punched along the normal by a rigid spherical impactor. Samples of a metamaterial with a chiral structure (hexachirals honeycomb) are made of e-PLA plastic using a 3D printer. In experiments, a deviation of the direction of movement of the impactor after leaving the punched sample from the approach direction (normal to the side surface) is observed. The dependence of the impactor projection direction on the orientation of the elements of chiral symmetry of the samples is established. A FE model for calculating the penetration of a chiral structure has been developed. Numerical results are presented and their agreement with experimental data is noted.

The properties of metal honeycomb metamaterials with different internal structures were experimentally studied when they were punched along the normal by a rigid spherical striker. Experiments with metal samples of metamaterials with a negative Poisson’s ratio (auxetics) showed a greater resistance to penetration by impactors than experiments with metal samples having a honeycomb structure with a positive Poisson’s ratio.

Some properties of metamaterials with a negative Poisson’s ratio (auxetics) have been studied experimentally when punched along the normal by a rigid spherical impactor. Samples of a metamaterial with a chiral structure (hexachirals honeycomb) are made of e-PLA plastic using a 3D printer. In experiments, a deviation of the direction of movement of the impactor after leaving the punched sample from the approach direction (normal to the side surface) is observed. The dependence of the impactor projection direction on the orientation of the elements of chiral symmetry of the samples is established. A FE model for calculating the penetration of a chiral structure has been developed. Numerical results are presented and their agreement with experimental data is noted.

A model for the porosity formation which occurs in single-crystal nickel-based superalloys when the non-equilibrium eutectic melts during high-temperature heat treatment is proposed. It is assumed that the porosity formation results from plastic deformation of the γ-solid solution of nickel caused by dilatation of the melting eutectic. This mechanism of porosity formation is described analytically using the elasto-plastic properties of superalloy experimentally measured at near solidus temperatures. The proposed model was used to predict the pore formation in the 3rd generation single-crystal nickel-based superalloy CMSX-10. Comparison of the obtained theoretical and experimental results showed a good agreement.

Diamane is a two-dimensional carbon-based structure coated with hydrogen atoms. The stiffness constants of diamane are studied by molecular dynamics simulation. These constants are used for an analytical calculation of Young’s modulus, Poisson’s ratio, and shear modulus. Two different morphologies are considered, namely, AA diamane and AB diamane. Moreover, both morphologies can contain hydrogen or be without it. It is found that pristine diamane without hydrogen demonstrates higher stiffness constants due to the changes in hybridization. At the same time, the difference in the values of the constants for the two diamane morphologies AA and AB is insignificant. All the obtained results are compared with elastic constants of graphene and diamond calculated by the same method and obtained from literature. Young’s modulus of pristine diamane equal to 1182 GPa is close to that of for graphene diamond.

The dependence of the elastic properties of monatomic (simple substances) and diatomic (AB type compounds) crystals of the cubic syngony on the types of their crystal structure and interatomic bond is analyzed. It is shown that the elastic properties of these crystals follow one of two trends, covalent or ionic. The auxetics (materials with a negative Poisson’s ratio) are identified among monatomic crystals with the A1 structure (fcc), such as to alkaline earth, transition and post-transition metals, actinides, and lanthanides, as well as among monatomic crystals with the A2 structure (bcc), such as to alkali metals. Among binary diatomic compounds, the largest number of auxetics is found among diamond-like crystals with the B3 structure (zinc blende) and stoichiometry A N B 8–N .

The problem of longitudinal tension for a two-layered plate of hexagonal and cubic crystals with different orientations of crystallophysic coordinate systems is discussed. Analytical dependencies of effective Young's modulus and Poisson's ratios on thicknesses ratio are obtained. Variability of effective properties is analyzed for all possible combinations of hexagonal and cubic crystals. Significant difference between effective Young's modulus and predictions by rule of mixtures takes place in the case when one of the layers is auxetic. Effective Young's modulus can exceed Young's modulus of the stiffer layer. The ratio of Young's moduli of crystals has significant influence on effective Poisson's ratio. A FEM (finite element method) analysis of this problem was performed and its results were compared with analytical ones. Between the analytical and numerical results qualitative and quantitative correspondence takes place.

Bulk c-oriented CeF3 single crystals (sp. gr. P3¯c1) were grown successfully by the vertical Bridgman technique in a fluorinating atmosphere. A description of the crystal growth procedure and the solution of the difficulties during the growth process are presented in detail. The anisotropy of the mechanical, thermal and electrophysical properties were studied for the first time. The maximum values of the thermal conductivity coefficient (α = 2.51 ± 0.12 W·m−1·K−1) and the ionic conductivity (σdc = 2.7 × 10−6 S/cm) at room temperature are observed in the [0001] direction for the CeF3 crystals. The Vickers (HV) and Berkovich (HB) microhardnesses for the (0001), (101¯0) and (112¯0) crystallographic planes were investigated. The HB values were higher than the HV ones and decreased from 3.8 to 2.9 GPa with an increase in the load in the range of 0.5–0.98 N for the hardest (0001) plane. The {112¯0}, {101¯0} and {0001} cleavage planes were observed during the indentation process of the CeF3 crystals. The variability of Young’s, the shear modules and Poisson’s ratio were analyzed. A significant correlation between the shapes of the Vickers indentation patterns with Young’s modulus anisotropy was found. The relationship between the anisotropy of the studied properties and the features of the CeF3 trigonal crystal structure is discussed.

The study analyzes the elastic properties of chiral metallic nanotubes formedby rolling up thin crystal plates with the [011] and [111] orientations withintwo frameworks of anisotropic elasticity and molecular statics. Iron, copper andaluminum nanotubes are discussed. It is shown that the tubes have a positivePoisson’s ratio in the entire range of chiral angles, unlike nanotubes obtainedby rolling up crystal plates with the [010] orientation. Poynting’s coefficientof nanotubes rolled up from plates with the [011] orientation becomes negativeat certain chiral angles, which corresponds to a change in the twistingdirection of the nanotubes under tension. The description of the dependence ofthe elastic properties of nanotubes on the chiral angle and thickness withinanisotropic elasticity theory agrees qualitatively with the results of molecularstatics simulations. The results for some chiral metallic nanotubes arequantitatively different.

The extreme values of Young’s modulus for six- and seven-constant tetragonal crystals are found using the necessary and sufficient conditions for the extrema of the functions of two variables. Theoretical and numerical analyzes of stationary and extreme values are performed based on experimental data on elastic constants collected in the Landolt–Börnstein reference book. Five such Young’s moduli are formed in the case of six-constant and seven-constant tetragonal crystals. It is found how the stationary and extremal values of Young’s modulus depend on three anisotropy coefficients that disappear in the limit of an isotropic material. Simple analytical dependences of some stationary and extreme values of Young’s moduli of six-constant crystals are obtained. In the case of stationary values of Young’s modulus of seven-constant tetragonal crystals, the coefficients included in the sufficient conditions for the extremum of the function of two variables are estimated numerically. Tetragonal crystals (Hg2I2, Hg2Br2, Hg2Cl2, TeO2, (NH2)2CO, LiY0.5Tb0.5 F4 and C(CH2OH)4) with a large difference between the maximum and minimum values of Young’s modulus are revealed. It is shown that six-constant tetragonal crystals may have a greater difference between global extrema than seven-constant tetragonal crystals. It is found that six-constant tetragonal crystals with a large difference between the global extrema of Young’s modulus have a negative Poisson’s ratio. In the case of seven-constant tetragonal crystals, such relationship has not been identified. A classification scheme based on the dependence of three stationary values of Young’s modulus on two dimensionless parameters is proposed.

The extreme values of Young’s modulus for rhombic (orthorhombic) crystals using the necessary and sufficient conditions for the extremum of the function of two variables are analyzed herein. Seven stationary expressions of Young’s modulus are obtained. For three stationary values of Young’s modulus, simple analytical dependences included in the sufficient conditions for the extremum of the function of two variables are revealed. The numerical values of the stationary and extreme values of Young’s modulus for all rhombic crystals with experimental data on elastic constants from the well-known Landolt-Börnstein reference book are calculated. For three stationary values of Young’s modulus of rhombic crystals, a classification scheme based on two dimensionless parameters is presented. Rhombic crystals ((CH3)3NCH2COO·(CH)2(COOH)2, I, SC(NH2)2, (CH3)3NCH2COO·H3BO3, Cu-14 wt%Al, 3.0wt%Ni, NH4B5O8·4H2O, NH4HC2O4·1/2H2O, C6N2O3H6 and CaSO4) having a large difference between maximum and minimum Young’s modulus values were revealed. The highest Young’s modulus among the rhombic crystals was found to be 478 GPa for a BeAl2O4 crystal. More rigid materials were revealed among tetragonal (PdPb2; maximum Young’s modulus, 684 GPa), hexagonal (graphite; maximum Young’s modulus, 1020 GPa) and cubic (diamond; maximum Young’s modulus, 1207 GPa) crystals. The analytical stationary values of Young’s modulus for tetragonal, hexagonal and cubic crystals are presented as special cases of stationary values for rhombic crystals. It was found that rhombic, tetragonal and cubic crystals that have large differences between their maximum and minimum values of Young’s modulus often have negative minimum values of Poisson’s ratio (auxetics). We use the abbreviated term auxetics instead of partial auxetics, since only the latter were found. No similar relationship between a negative Poisson’s ratio and a large difference between the maximum and minimum values of Young’s modulus was found for hexagonal crystals.