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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.

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.

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.

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.

Surface and Interface Science, 2020

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.

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.

In the area of manufacturing, surface coating of materials is a widely-used process representing ... more In the area of manufacturing, surface coating of materials is a widely-used process representing a multi-billion pound per annum industry. the choice of a suitable coating allows the design engineer to choose a material for its optimum bulk properties but, at the same time, tailor the surface properties for a specific application. For example, components made of iron have good mechanical strength but, because the iron surface forms an oxide, a suitable coating (usually chromium-based) is used to protect the product. Over the last decade interest has surged in the potential use of more exotic coatings with controlled micro- and nano-structure. Professor John Colligon and Dr Vladimir Vishnyakov have developed techniques for production of such coatings.

Nanomechanical testing has been a revolutionary technique in improving our fundamental understand... more Nanomechanical testing has been a revolutionary technique in improving our fundamental understanding of the basis of mechanical properties of thin film systems and the importance of the nanoscale behaviour on their performance. However, nanomechanical tests are usually performed in ambient laboratory conditions even if the coatings being developed are expected to perform at high temperature in use. It is important to measure nanomechanical and tribological properties of materials under test conditions that are closer to their operating conditions where the results are more relevant. We can then better understand the links between properties and performance and design advanced materials systems for increasingly demanding applications. However, high temperature nanomechanics is highly challenging experimentally and a high level of instrument thermal stability is critical for reliable results. To achieve this stability the NanoTest Vantage has been designed with (i) active heating of t...

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.