Vladimir Vishnyakov - Profile on Academia.edu (original) (raw)

Papers by Vladimir Vishnyakov

Materials Today Communications, 2021

TiB 2-SiC-C and TiB 2-TiC-C heteromodulus ceramics were sintered by reactive hot pressing of TiC-... more TiB 2-SiC-C and TiB 2-TiC-C heteromodulus ceramics were sintered by reactive hot pressing of TiC-B 4 C-Si and TiC-B 4 C precursors at 1830 °C and 30MPa. Sintering time at the maximum temperature was between 2 and 8 min. The reactions in TiC-B 4 C-Si green body create submicron (100-400nm) TiB 2 crystals inside silicon carbide grains as well as B x Si y C z nanofibers, which nucleate near SiC surfaces. Low hardness graphite platelets are formed within the hard matrix during the in-situ exothermic reaction. "Soft-hard" grain combination produces substantially improved fracture toughness (up to 9MPa•m 1/2). The materials also demonstrate high thermal conductivity (up to 120W/m•K) and high thermal shock resistance. The thermal shock crack growth is arrested by the graphite platelets.

Handheld Material Analyser

Nanomaterials

Soft TiB2-BN-C hetero-modulus ceramics were sintered with the assistance of in-situ reactions dur... more Soft TiB2-BN-C hetero-modulus ceramics were sintered with the assistance of in-situ reactions during the hot pressing of TiN-B4C precursors. TiB2 formation was observed already after the hot pressing at 1100 °C, remaining the only phase identifiable by XRD even after sintering at 1500 °C. Analysis of reaction kinetics allows us to assume that the most probable reaction controlling stage is boron atoms sublimation and gas phase transfer from B4C to TiN. Reactive sintering route allows almost full densification of TiB2-BN-C composite ceramics at 1900 °C. The processes enable the formation of multilayer h-BN nanosheets inside the TiB2 matrix. The manufactured TiB2-33BN-13C ceramic with K1C = 5.3 MPa·m1/2 and HV = 1.6 GPa is extremely thermal shock-resistant at least up to quenching temperature differential of 800 °C. The sintered UHTC composite can be machined into complex geometry components.

Reactively sintered TiB2-based heteromodulus UHT ceramics with in-situ formed graphene for machinable concentrated solar light absorbers

Ceramics International, 2022

ACS Omega, 2022

Biocompatible Al 2 O 3 −hBN ceramic was sintered from AlN and B 2 O 3 precursors by reaction hot ... more Biocompatible Al 2 O 3 −hBN ceramic was sintered from AlN and B 2 O 3 precursors by reaction hot pressing at 1750°C and 30 MPa for 8 min. The ceramic was compared to nonreactive (NR) one sintered from Al 2 O 3 and BN under the same sintering conditions. The NR ceramic possesses 9% porosity as opposed to only 2% porosity for the reaction sintered Al 2 O 3 −hBN. The reaction sintered ceramic has crack resistance in the region of 5.0 ± 0.1 MPa•m 1/2 , which is approximately 20% higher than previously reported pure Al 2 O 3 or Al 2 O 3 −hBN sintered without reaction support. The higher amount of hBN in the developed Al 2 O 3 −hBN material (27 vol %) facilitates hardness lowering to the region of 6 GPa, which is closer to the bone hardness and makes the ceramic machinable. Reaction sintering of the Al 2 O 3 −hBN composite opens a new area of creation and formation of load-bearing Al 2 O 3 −hBN ceramic bioimplants.

Data for: Thermodynamics of an austenitic stainless steel (AISI-348) through in situ TEM heavy ion irradiations

This dataset contains processed and raw data necessary to reproduce the reported research investi... more This dataset contains processed and raw data necessary to reproduce the reported research investigation. The steps to reproduce this research are detailed described in the Materials and Method section in our paper.

Basic physical and chemical concepts

In order to extract oil from a formation we need to be able to displace reservoir fluids into the... more In order to extract oil from a formation we need to be able to displace reservoir fluids into the production well and move them to the surface. On the first place we need to have or be able to create driving force, either utilize gravity or to have pressure differential, which might eventually move our fluids, hopefully containing hydrocarbons, into the production well. On the second place, for the fluid to flow it needs the interconnected channels (openings, interconnected pores) up to the production well. How fast the fluid flow depends on its viscosity, which is an indication of the liquid “internal friction”, size and concentration of interconnected pores and physical interactions between fluids and the formation stone.

Microcavity Gettering in Silicon

An STM Study of Atomically-Flat Gold Surfaces Irradiated with Energetic Helium and Argon Ions

Ion Beam Modification of Materials, 1996

{111} and {100} oriented crystallites of Au have been irradiated to different fluences, at room t... more {111} and {100} oriented crystallites of Au have been irradiated to different fluences, at room temperature, with 3 keV He + and Ar + ions and changes in surface atomic morphology observed subsequently in an air operated Scanning Tunnelling Microscope. The different ion species produce very different topographic features which also behave differently with respect to long time room temperature annealing. He + bombardment produces raised bumps on the surface which, it is believed, are associated with subsurface gas filled bubbles. These features are thermally stable at room temperature. Ar + bombardment produces a continuously roughening topography with increasing ion fluence which is composed of etch pits and adatom islands. It is concluded that these are produced by sputtering and radiation produced interstitial atom migration from the bulk respectively. Surface and interlayer defect and atom migration may be inferred from the observed infilling of pits from islands during thermal annealing.

Fluid-rock interaction

Primer on Enhanced Oil Recovery, 2020

Nanotechnology, 2020

Near stoichiometric and under stochiometric Cr2AlxC (x=0.9 and 0.75) amorphous compositions were ... more Near stoichiometric and under stochiometric Cr2AlxC (x=0.9 and 0.75) amorphous compositions were deposited onto silicon substrate at 330 K in a layer-by-layer fashion using magnetron sputtering from elemental targets. The film thickness found to be 0.9 µm and 1.2 µm for the near and under stoichiometric compositions respectively. A transmission Electron Microscope (TEM) heating holder was used to heat thin sample lamellae prepared using focussed ion beam milling. Near stoichiometric Cr2AlC thin films consisted of nano MAX phase after crystallisation at 873 K. Under stoichiometric Cr2AlxC (x=0.75) thin films contained MAX phase along with nanocrystalline chromium aluminides after crystallisation at 973 K. Ion irradiations with 320 keV xenon ions were performed at 623 K using a TEM with in-situ ion irradiation (MIAMI) facility. Near stoichiometric Cr2AlC nanocrystalline films irradiated up to 83 displacements per atom (dpa) showed no observable changes. Also, irradiations of under stoichiometric nanocrystalline thin films up to 138 dpa did not show any observable amorphisation and recrystallization was observed. This radiation resistance of near and under stoichiometric thin films is attributed to the known self-healing property of Cr2AlxC compositions further enhanced by nanocrystallinity.

Ceramics International, 2019

Reactive hot pressing of TiC-B4C precursors was undertaken at 1800 ℃ to produce TiB2 with carbon ... more Reactive hot pressing of TiC-B4C precursors was undertaken at 1800 ℃ to produce TiB2 with carbon inclusions. Atomic mechanisms of titanium diboride nucleation, as well as spongelike carbon inclusions and submicron platelets of graphite precipitation has been investigated. Precursor grain size, green body composition and synthesis time were varied to analyse phases transformation. Boron from B4C grain sublimation is shown to result in carbon-based foam formation. Ab-initio calculations confirm that the boron atoms accumulation on (111) TiC plains leads to tensile stress. The developed stress cleaves TiC grains and enhances further reaction. Most of carbon expelled from TiC during its transformation into TiB2 forms graphite platelets.

Advances in Applied Ceramics, 2016

Structure and mechanical characteristics of dense ceramic composites synthesised by reactive hot ... more Structure and mechanical characteristics of dense ceramic composites synthesised by reactive hot pressing of TiC-B 4 C powder mixtures at 1800-1950°C under 30 MPa were investigated by Xray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM and EDX). The results show that during hot pressing solid-phase chemical reaction 2TiC + B 4 C = 2TiB 2 + 3C has occurred with final products like TiB 2-TiC-C, TiB 2-C or TiB 2-B 4 CC hetero-modulus composite formation with around one micrometer size carbon precipitates. The fracture toughness depends on the amount of graphite precipitation and has a distinct maximum K1C = 10 MPa m 1/2 at nearly 7 vol.-% of carbon precipitate. The fracture toughness behaviour is explained by the developed model of crack propagation. Within the model, it is shown that pores (voids) and low-modulus carbon inclusions blunt the cracks and can increase ceramic toughness in some cases.

Materials Today Energy, 2019

The feasibility of depositing a thin film of highly concentrated alloy on zircaloy-4 substrates a... more The feasibility of depositing a thin film of highly concentrated alloy on zircaloy-4 substrates at low temperatures was investigated. Electron microscopy characterisation at meso-and nanoscales showed that the deposited thin film is equiatomic, single-phase and with all alloying elements uniformly distributed throughout the microstructure. Heavy-ion irradiations carried out in situ within a transmission electron microscope revealed the generation of both defect clusters and inert gas bubbles at around 1.5×10 16 ions•cm-2 (15.4 dpa). Post-irradiation characterisation showed that the thin film preserved its solid solution and that, under the studied conditions, no elemental segregation or phase transformations were observed indicating a high radiation tolerance.

Polymer Degradation and Stability, 2018

Use of ion-assisted sputtering technique for producing photocatalytic titanium dioxide thin films... more Use of ion-assisted sputtering technique for producing photocatalytic titanium dioxide thin films: Influence of thermal treatments on structural and activity properties based on the decomposition of stearic acid.

International Journal of Refractory Metals and Hard Materials, 2017

The densification kinetics and structure of TiB2-TiC-C, TiB2-C and TiB2-B4C-C hetero-modulus cera... more The densification kinetics and structure of TiB2-TiC-C, TiB2-C and TiB2-B4C-C hetero-modulus ceramics produced via reaction hot-pressing of B4C and TiС precursors are investigated. The reaction begins at 1100°C with boron carbide decomposition and progresses in two main stages which can be predominantly determined by the boron atoms to TiC grains diffusion mechanisms. The solid phase grain boundary diffusion starts at 1100°C and effective gas phase transport finalises the reaction at temperatures above 1400°C. Two distinctive waves of the charge consolidation allow densifying investigated refractory materials at 1900°C and 30MPa during 16 minutes. The reaction is shown to define the features of the composite structure: submicron TiB2 particles and faceted voids in B4C matrix, flake-like graphite and TiB2 inclusions in TiC matrix. High concentration of carbon atoms (~ 10 at.%) in synthesized diboride titanium grains have been observed.

Surface and Coatings Technology, 2017

Thin films of (Ti,Fe)Nx have been produced on silicon wafers with a wide range of compositions an... more Thin films of (Ti,Fe)Nx have been produced on silicon wafers with a wide range of compositions and mechanical properties to investigate correlations between the mechanical properties measured by indentation and crack resistance in the highly loaded sliding contact in a nano-scratch test. The nano-scratch test data on the thin films using a well-worn Berkovich indenter with ~1 m end radius were supported by high resolution scanning electron microscopic (SEM) imaging and analytical stress modelling. The results show that mechanical properties of the coating, its thickness and the substrate properties all influence the deformation process. They affect the critical loads required, the type of failures observed and their location relative to the moving probe. The differences in coating mechanical properties affect how the interface is weakened (i.e. by initial substrate or coating yielding or both) and determine the deformation failure mechanism. The load dependence of the friction coefficient provides details of the sliding contact zone and the location of failure relative to the sliding probe. Improved performance was achieved at intermediate hardness and H 3 /E 2 in the nano-scratch tests on thin films. The friction and modelling results strongly suggest that failure at low load on the hardest coatings is due to a combination of high tensile stress at the 2 rear of the contact zone and substrate yield. Designing thin films for protective coatings with in-built dissipative structures (such as soft and low elastic modulus inclusions) and mechanisms to combat stress may be a more successful route to optimise their toughness in highly loaded sliding conditions than aiming to minimise plasticity by increasing their hardness.

Ne+, Ar+ and Xe+ ion bombardment induced and suppressed topography on Si

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1995

... 170 (1980) 363. S. Duncan, R. Smith, DE Sykes and JM Walls, Vacuum 34 (1984) 145. K. Elst, Ph... more ... 170 (1980) 363. S. Duncan, R. Smith, DE Sykes and JM Walls, Vacuum 34 (1984) 145. K. Elst, Ph.D. Thesis, University of Antwerp (1993). G. Carter, MJ Nobes, C. Cave and N. AlQuadi, Vacuum 45 (1994) 71. [8] FA Stevie, PM Kahora, DS Simons and P. Chi, J. Vac. Sci. ...

Microelectronic Engineering, 2014

In this study, the effects of dwell time on Ga + focused ion beam machining at 30 keV for differe... more In this study, the effects of dwell time on Ga + focused ion beam machining at 30 keV for different milling currents were investigated. The surface topographies were analysed using atomic force microscopy (AFM) and the substrate structures were investigated by means of Raman spectroscopy. It has been observed that by increasing dwell time the total sputtering yield was increased even though the total dose was remained the same. Also the silicon damage by ion bombardment is reduced as the dwell time is increased. This is mainly due to catalyst behaviour of Ga inside Si which over a period of hours causes recrystallization of Si at room temperature by lowering the activation energy for crystallization.