A. P. Rybalko

Bio: A. P. Rybalko is an academic researcher. The author has contributed to research in topics: Wind wave & Buoy. The author has an hindex of 2, co-authored 2 publications receiving 26 citations.

Unusual Young׳s modulus behavior in ultrafine-grained and microcrystalline copper wires caused by texture changes during processing and annealing

Abstract: Effect of annealing on the dynamic Young׳s modulus E of ultrafine-grained (UFG) and microcrystalline (MC) copper obtained by combined severe plastic deformation (SPD) including repeated hydrostatic extrusion and drawing (UFG copper) or only repeated drawing (MC copper) is investigated. It is established that the Young׳s modulus in the SPD-prepared UFG and MC samples exceeds that in the coarse-grained fully annealed (CGFA) samples by 10% to 20%. Subsequent isothermal annealing at elevated temperatures between 90 and 470 °С leads to a sharp decrease of the Young׳s modulus for annealing temperatures above 210 °С. After annealing at 410 °С, the value of E reaches its minimal value that is 35% lower than E in CGFA samples (total change in E is about 50% of the initial value). Further annealing at higher temperatures leads to some increase in the Young׳s modulus. It is shown that the unusual behavior of the Young׳s modulus is caused by the formation of the 〈111〉 axial drawing texture in the SPD-treated samples which is replaced by the 〈001〉 annealing texture during the post-SPD heat treatments.

Change of Parameters of the Koiwa–Hasiguti Dynamic Dislocation Relaxation in Nanostructured and Polycrystalline Zirconium after Severe Plastic Deformation and Annealing

Abstract: The temperature dependences of acoustic properties of nanostructured and polycrystalline zirconium are investigated in the temperature range of 100–340 K. The effect of severe plastic deformation and subsequent annealing on key parameters of the Koiwa–Hasiguti acoustic relaxation in zirconium is studied in detail. It is established that, due to intensive plastic deformation, the relaxation strength considerably increases, and the temperature and the width of the corresponding relaxation peak systematically decrease with reduction of the mean grain size in the samples. Annealing leads to a partial recovery of the relaxation strength and the peak temperature back to the initial values in undeformed samples, but the width of the relaxation peak shows an additional decrease. The majority of the effects observed can be explained by changes in dislocation subsystems of the samples during intensive plastic deformation and annealing. An influence of a random scatter of the relaxation time on the main parameters of the Koiwa–Hasiguti peak is established using the statistical analysis based on the lognormal distribution. It is shown that the parameter β of the lognormal distribution determines the width, height, and asymmetry of the peak and also allows estimating the relaxation strength from the peak height. An algorithm for retrieving the parameter β from experimental data is presented.

Wave Buoy Measurements at Short Fetches in the Black Sea Nearshore: Mixed Sea and Energy Fluxes

Abstract: Wave buoy measurements were carried out near the northeastern Black Sea coast at the natural reserve Utrish in 2020–2021. In total, about 11 months of data records were collected during two stages of the experiment at 600 and 1500 m offshore and depths of 18 and 42 m. The measured waves propagate almost exclusively from the seaward directions. Generally, the waves do not follow the local wind directions, thus, implying a mixed sea state. Nevertheless, dimensionless wave heights and periods appears to be quite close to the previously established empirical laws for the wind-driven seas. The results of the wave turbulence theory are applied for estimates of spectral energy fluxes and their correspondence to the energy flux from the turbulent wind pulsations. These estimates are consistent with today’s understanding of wind–wave interaction. It is shown that the main fraction of the wind energy flux is sent to the direct Kolmogorov–Zakharov cascade to high wave frequencies and then dissipates in small amounts. Less than 1% of the wind energy flux is directed to the low frequency band (the so-called inverse Kolmogorov–Zakharov cascade), thus, providing wave energy growth.

One-step consolidation and precipitation hardening of an ultrafine-grained Al-Zn-Mg alloy powder by Spark Plasma Sintering

Abstract: In the present work, ultra ne-grained Al-Zn-Mg alloy produced by high energy ball milling and Spark Plasma Sintering was synthesized. The Hall-Petch strengthening due to grain re nement (about 150 nm) is preserved and the Orowan's e ect attributed to the presence of the hardening phase ' is obtained in a single-step during the sintering. Maximum compression stresses as high as 736 MPa and 830 MPa were reached in quasistatic and dynamic conditions respectively. Hardness was increased from 124 HV5 for a consolidated coarse grained material to 196 HV for a consolidated ultra ne-grained (UFG) material. The mechanical properties obtained in this study were all superior to the ones of the reference AA7020-T651.

A review on nanostructured stainless steel implants for biomedical application

Abstract: Over the last two decades, many researchers have developed a variety of stainless steel-based medical implant types,taking full advantage of nanostructuring technologies. In this paper the application, fabrication and development of nanostructured stainless steel based materials with new composition for medical implants will be discussed. It is well established that application of severe plastic deformation (SPD) can decrease the grain size of metals and alloys significantly to the nanometer range. Among all the available SPD methods, equal channel angular pressing (ECAP) is very applicable. Stainless Steel became the raw structural material for the majority of the developed medical implants, and several techniques had to be studied and established in order to fabricate a feasible stainless steel-based neural probe. These nanostructured implants present a superior performance mechanically, biologically and electrically, when compared to the conventional implants. Finally, the effect of alloying elements on the bio-interaction of stainless steel will be explained.

Fiber vs Rolling Texture: Stress State Dependence for Cold-Drawn Wire

Abstract: The texture of the cold-drawn copper wire was investigated along the radius using electron backscatter diffraction. The complex fiber texture of the central region of the wire was considered as the rolling texture consisting of a set of preferred orientations. The texture of the periphery region was revealed to be similar to the shear texture. The orientation-dependent properties of the wire were proven to be determined by the texture of the near-surface layers.

Numeric Loading Simulation of Titanium Implant Manufactured Using 3D Printing

Abstract: The problem of medical implants honeycomb structures loading has been stated. The problem was solved using simulation by the finite element method. Simulation revealed that it is possible to change the elastic modulus of the material more than three times with respect to the bulk titanium alloy. The quality of the simulation was estimated based on the convergence of the simulation data.

Effect of cold drawing strain on the microstructure, mechanical properties and electrical conductivity of low-oxygen copper wires

Abstract: The effects of cold drawing process on the microstructure, mechanical properties and electrical conductivity of low-oxygen copper wires were studied. The results show that at low drawing strains (e ≤ 1.23), the plastic deformation is dominated by planar slip, some of grains are rotated along the drawing direction, giving rise to a texture. At medium strains (1.23 and textures are highly developed. At high strains (e > 1.91), a fibrous structure is formed, with a staggered distribution of and textures. With the increase of drawing strain, the volume fraction of the texture first increases and then decreases, while the volume fraction of the texture increases monotonously. The yield strength first increases and then decreases, yielding the maximum value of 427.5 MPa at the strain of 1.91. Interestingly, the electrical conductivity of the copper wires changes with cold drawing strain and moves in the opposite way to the yield strength. The electrical conductivity first decreases and then increases with the minimum value at a strain of 1.91 (~87.5% IACS). At strains higher than 2.74, dynamic recrystallization occurs, resulting in a decrease in dislocation density and an increase in grain size. In addition to the dislocation density and grain size, the yield strength of the copper wires is further impacted by the texture development. The electrical conductivity is less influenced by dislocations and vacancies. Instead, it is dominated by those grain boundaries perpendicular to the drawing direction. An excellent strength-conductivity combination was achieved by tailoring the microstructure of copper wires. For example, a wire with the yield strength (YS) of 400.5 MPa and electrical conductivity (EC) of 94.3% IACS was acquired when the drawing strain reaches 2.74.