Numerical study and experimental validation of deformation of <111> FCC CuAl single crystal obtained by additive manufacturing

The importance of taking into account directional solidification of grains formed during 3D printing is determined by a substantial influence of their crystallographic orientation on the mechanical properties of a loaded material. This issue is studied in the present study using molecular dynamics simulations. The compression of an FCC single crystal of aluminum bronze was performed along the axis. A Ni single crystal, which is characterized by higher stacking fault energy (SFE) than aluminum bronze, was also considered. It was found that the first dislocations started to move earlier in the material with lower SFE, in which the slip of two Shockley partials was observed. In the case of the material with higher SFE, the slip of a full dislocation occurred via successive splitting of its segments into partial dislocations. Regardless of the SFE value, the deformation was primarily occurred by means of the formation of dislocation complexes involved stair-rod dislocations and partial dislocations on adjacent slip planes. Hardening and softening segments of the calculated stress–strain curve were shown to correspond to the periods of hindering of dislocations at dislocation pileups and dislocation movement between them. The simulation results well agree with the experimental findings

Aluminum bronze crystallization on deformed base during electron beam additive manufacturing

To obtain products by using additive manufacturing (AM) methods, it is necessary to take into account the features of the formed internal structure of the material. The internal structure depends on the 3D printing parameters. To predict it, it is effective to use computer modeling methods. For this purpose, using the example of aluminum bronze, the influence of the base structure and heat input during surfacing on the grain structure of the deposited layers was studied. To create numerical models, we used data obtained from electron backscatter diffraction (EBSD) analysis of samples. The heterogeneity of the formation of the structure in each selected zone is established, which indicates the heterogeneity of heat input in local areas of the material in one mode of surfacing. For typical cases of crystallization, modeling using the molecular dynamics (MD) method of crystallization processes with different heat inputs to the base with characteristics specified based on experimental data was carried out. It was established that the amount of heat input determines the degree of melting and the inherited defectiveness of growing crystals. The formation of misorientation boundaries and crystallization centers of new grains is determined by the conditions of joint growth of grains with given crystallographic parameters of the computational model. The grain structure obtained as a result of simulation is consistent with the experimentally observed structure of the samples

Growth and Deformation Simulation of Aluminum Bronze Grains Produced by Electron Beam Additive Manufacturing

When working out 3D building-up modes, it is necessary to predict the material properties of the resulting products. For this purpose, the crystallography of aluminum bronze grains after electron beam melting has been studied by EBSD analysis methods. To estimate the possibility of sample form changes by pressure treatment, we simulated structural changes by the method of molecular dynamics during deformation by compression of individual grains of established growth orientations. The analysis was carried out for free lateral faces and grain deformation in confined conditions. Simulation and experiments on single crystals with free lateral faces revealed the occurrence of stepwise deformation in different parts of the crystal and its division into deformation domains. Each domain is characterized by a shear along a certain slip system with the maximum Schmidt factor. Blocking the shear towards the lateral faces leads to selectivity of the shear along the slip systems that provide the required shape change. Based on the simulation results, the relationship between stress–strain curves and structural characteristics is traced. A higher degree of strain hardening and a higher density of defects were found upon deformation in confined conditions. The deformation of the columnar grains of the built material occurs agreed with the systems with the maximum Schmidt factor

Molecular dynamics study of aluminum bronze nanograin surfacing

The amount of heat input during surfacing affects the structure and properties of a product. Features of the crystallizing structure depend on the structure of the already deposited layers. The process of structural changes during the interaction of a melt drop with the basis of three grains has been traced by modeling using the molecular dynamics method. The grain parameters in the model are set from the experimental characteristics of the sample obtained by electron-beam surfacing of aluminum bronze. Increasing the temperature of the melt drop improves its spreading and increases the melting depth. The grain growth during crystallization inherits the grain orientation of the basis. During crystallization, stacking faults and twins are formed, oriented similarly to defects in the basis. The grain boundaries change orientation in the direction of the maximum temperature gradient

Deformation and wear of Hadfield steel single crystals under dry sliding friction

Severe deformation of Hadfield steel occurs via different deformation mechanisms (slip or twinning) depending on the crystallographic orientation and direction of the applied load. The development of these mechanisms under dry sliding friction was investigated by comparing the calculated values of slip stresses for and single crystals. Shear stress calculations with allowance for the friction force showed that twinning is not the predominant deformation mechanism for the considered orientations. TEM studies of the dislocation structure, repolished and etched surface revealed agreement between the experimental and numerical data. According to EBSD analysis, reorientation on the worn surface and in the subsurface region changes depending on the combination of principal stresses in different areas of the worn surface. These results confirmed that conditions for the deformation mechanisms (slip and twinning) are determined by the local conditions in the sample mesovolume. The wear curves demonstrate two stages of even and uneven wear. The uneven wear mechanism is substantiated by the analysis of the structure in the subsurface region, wear debris, and the worn surface. An empirical scheme of the wear and damage accumulation mechanisms is proposed

Side effects of statins in patient with compensated hypothyroidism and SLCO1B1 *5 (c.521T>C) polymorphism

Aim: to assess the influence of compensated hypothyroidism and SLCO1B1 *5 (c.521TC) gene polymorphism on the clinical and laboratory signs of the muscle damage during statin therapy. Methods: assessment of symptoms and markers of the muscle damage and SLCO1B1 *5 (c.521TC) genotyping were performed in 33 patients with primary hypothyroidism taking statins, in 31 patients taking statins without hypothyroidism and in 33 patients with primary hypothyroidism without statins taking. Results: muscle pain was observed more often in the group of the patients with compensated hypothyroidism on the background of statins taking compared with other groups (45,5, 16,1 and 30,3 %, respectively, p=0,048). Only in this group the pain was associated with increased levels of creatine- kinase (171,0108,12 and 110,043,81U/L, in the presence and absence of the pain, p=0,049), LDH (369,566,22 and 305,641,98 U/L, р=0,007), myoglobin titer (90,7109,89 and 41,128,56, р=0,005), and more frequent occurrence of TC and CC genotypes of SLCO1B1*5 (c.521TC) (68,4 и 28,6%, р=0,0027). Conclusions: the patients with compensated hypothyroidism have a higher risk of statin-induced myopathy increasing if the TC heterozygotes or CC homozygotes of SLCO1B1 *5 (c.521TC) gene are present, which requires thorough monitoring of clinical and biochemical muscle damage signs in case of its detection

Molecular Genetic Characteristics of Different Scenarios of Xylogenesis on the Example of Two Forms of Silver Birch Differing in the Ratio of Structural Elements in the Xylem

Silver birch (Betula pendula Roth) is an economically important species in Northern Europe. The current research focused on the molecular background of different xylogenesis scenarios in the birch trunks. The study objects were two forms of silver birch, silver birch trees, and Karelian birch trees; the latter form is characterized by the formation of two types of wood, non-figured (straight-grained) and figured, respectively, while it is currently not clear which factors cause this difference. We identified VND/NST/SND genes that regulate secondary cell wall biosynthesis in the birch genome and revealed differences in their expression in association with the formation of xylem with different ratios of structural elements. High expression levels of BpVND7 accompanied differentiation of the type of xylem which is characteristic of the species. At the same time, the appearance of figured wood was accompanied by the low expression levels of the VND genes and increased levels of expression of NST and SND genes. We identified BpARF5 as a crucial regulator of auxin-dependent vascular patterning and its direct target—BpHB8. A decrease in the BpARF5 level expression in differentiating xylem was a specific characteristic of both Karelian birch with figured and non-figured wood. Decreased BpARF5 level expression in non-figured trees accompanied by decreased BpHB8 and VND/NST/SND expression levels compared to figured Karelian birch trees. According to the results obtained, we suggested silver birch forms differing in wood anatomy as valuable objects in studying the regulation of xylogenesis