Igor Stanislavovich Yasnikov

1. A deformable solid is an extremely complex system that can be described using modern methods of the dynamics of nonlinear open systems [1]. In the case of deformation of metal materials, the mai...

Biocompatibility makes magnesium alloys attractive functional materials in terms of their use as biodegradable implants. However, the technologies for manufacturing semi-finished products carry a possible diversity of the local strain rate and temperature within a rather wide range, which affects the processed material structure and properties. The purpose of the study is to determine the range of temperatures and resistance to deformation, at which there is no negative effect on the main structural characteristics of the processed material, using the example of a medical purposes alloy of the Mg–Zn–Y alloying system. The authors carried out mechanical tests of a biodegradable Mg–1Zn–2.9Y magnesium alloy at various temperatures and strain rates. The influence of temperatures in the range of 20...400 °C on the structure and properties of the Mg–Zn–Y system alloy is disclosed. Starting from a temperature of 350 °C, the process of dynamic recrystallization is accompanied both by the complete restoration (return) of the original microstructure and by coarsening of the grain size, which can adversely affect the material functional characteristics. The high thermal stability of the biodegradable Mg–1Zn–2.9Y magnesium alloy is revealed, which probably results from the presence of the LPSO phase in it. The study shows that the deformation process is accompanied by twinning. At a strain rate of 2∙10−2 s−1 over the entire temperature range, the grain size distribution slightly narrows and shifts towards smaller diameters. The application of the obtained results in technological processes for manufacturing medical semi-finished products will help to solve the issue of microstructure instability at the stage of transition from a semi-finished product to a finished product during subsequent thermomechanical treatments.

As a result of the application of recurrence quantification analysis to acoustic emission time series obtained in uniaxial tensile testing of copper and silver, we detected the existence of a characteristic interval in which the Shannon information entropy (as a parameter of the quantitative analysis of recurrence plots) increased rapidly. Using statistical analysis of the behavior of the dislocation ensemble, we established a relation between the physical parameters of the given interval and the global stability loss parameters of the plastic flow of metals, indicating the predictability of the distinctive point determined long before the critical state was attained.

—This report presents the experimental facts which demonstrate the possibility of controlling the habit of microcrystals that are structural units of electrodeposited nickel coatings. The introduction of additives (inhibitors) into an electrolyte with a certain chemical composition influences the competition in the evolution of individual crystallographic facets of growing microcrystals and initiates the growth of microcrystal facets with a certain crystallographic orientation. This leads to the preparation of a nickel coating mainly consisting of microcrystals containing disclination-type defects and exhibiting the pentagonal symmetry.

The formation of microcrystals with fullerene-like truncated icosahedral habit observed in experiments on the electrodeposition of copper has been explained. The analysis has been performed in terms of the behavior of the total energy upon the evolution of the truncated icosahedron to the regular icosahedron, and a significant role of the surface energy in this evolution has been indicated. Reasons have been presented for the st-ability of rare experimentally observed fullerene-like habit of single-component small particles and microcrystals.

Using the acoustic emission method, we have determined the probability density distribution function of shear band lengths in a metallic glass and demonstrated its independence of stoichiometric composition of glass and experimental conditions. The power-law form of this distribution confirms independently the observed quadratic scaling in the time dependence of the rate of shear processes in metallic glass.