V.V. Uglov

The effect of dense compression plasma flow on silicon surface morphology

Abstract The dense compression plasma flow action on silicon surface layers is investigated. Samples of monocrystalline silicon of (111) and (100) orientations were subjected to plasma flow processings. Values of energy absorbed by the silicon surface range from 5 to 25 J per pulse, the latter corresponding to the flow power density range 0.5·10 5 –3·10 5 W/cm 2 . Microreliefs of sample surfaces and slices were recorded by means of high-resolution scanning microscopy. The action of the compression plasma flow on the sample results in the melting and subsequent modification of silicon material down to the depth of 6 μm. Micrographs of surface layers clearly show regular cylindrical structures that are the first of their kind ever observed. Cylindrical fragments measure 50–100 μm in length and 0.7–1.5 μm in diameter. These fragments are located on the surface of the sample at intervals of 1–2 μm with a surface density of (2–6)·10 6 cm −2 . Possible mechanisms of cylindrical periodic structure formation are discussed. The roles of Rayleigh–Taylor instability, Kelvin–Helmholtz instability and Benard instability in transformations of molten surface layers are considered. It may be inferred that structural-phase changes in the state of silicon surface are related to the fast crystallization of molten layer accompanied by the development of various instabilities in the presence of an induced magnetic field.

Compressive plasma flows interaction with steel surface: structure and mechanical properties of modified layer

The interaction of a dense compressive nitrogen plasma flow with carbon steel specimens has been investigated. The flows were generated by a magnetoplasma compressor, in which the acceleration of a plasma is accompanied by its compression due to interaction between the longitudinal constituent of electric current and the intrinsic azimuth magnetic field. As a result, a layered structure with a total depth of up to 25 μm is formed at a specimen surface. Investigations of a surface structure and its phase composition were carried out using X-ray diffraction, Mossbauer conversion electronic spectroscopy, and optical microscopy methods, along with the studies of mechanical properties.

The use of preliminary ion implantation and heating on the substrate for modifying TiN coating properties and TiN/substrate interface

The influence of preliminary implantation of argon ions on a carbon steel substrate and deposition temperature on the texture and adhesion of TiN coatings deposited by cathodic arc plasma deposition has been investigated. The samples have been evaluated by glancing X-ray diffraction, Auger-electron spectroscopy and scratch adhesion testing. Strengthening of the (220) TiN texture with increasing ion implantation dose on the substrate has been revealed. An increment of deposition temperature (from 450 up to 720 K) leads to a more chaotic orientation of TiN crystallites. An increase of transitional layer thickness (by 60% for the Ti profile) is only observed when depositing the coating at high temperature (720 K). However, both the preliminary implantation process and the heating of the substrate lead to an adhesion improvement of TiN coatings.

Structural and phase composition changes in aluminium induced by carbon implantation

Abstract The results of Rutherford backscattering analysis, Auger electron spectroscopy, transmission electron microscopy and X-ray diffraction analysis of the surface aluminium layer after carbon implantation are presented in this work. The energy of implanted ions was 20 keV, the implantation dose varied in the range of 0.4–4.0×1017 ions/cm2. The growth of carbon implantation dose resulted in an increase of carbon concentration over the stoichiometric level. Phase composition analysis showed that carbon implantation led to the formation of a Al4C3 compound. The possible mechanism of carbide formation based on ion-induced crystallisation was proposed. The behaviour of stress induced by carbon implantation in the aluminium lattice was also discussed.

Friction coefficient, microstructure and thermal stability of amorphous a-C coatings

Abstract Correlation between the microstructure, friction properties and ratio of sp 2 /sp 3 carbon bonds in amorphous a-C coatings on AISI M2 steel was studied in this work. The coatings were formed using pulsed cathodic-arc vacuum deposition (CAVD), with negative bias voltage of 0.2–20 kV applied to the sample. The dose of assisting ion fluence was 3×10 15 –10 17 ions cm −2 . The best friction properties were found for amorphous a-C coatings formed with a negative bias voltage of 5–20 kV and ion assistance dose of 10 17 ions ?m −2 . Raman spectra with a diffused asymmetric maximum at 1545 ?m −1 and I D / I G ratio in the range 2.3–2.7 are characteristic for these coatings. Deterioration of the friction properties of a-C coatings occurs with an increase in annealing temperature from 300 to 600 °C. This is accompanied by a transformation of the amorphous carbon into submicron graphite crystallites.

Evolution of microstructure of instrumental AISI M2 steel after plasma immersion nitrogen and carbon implantation

Abstract Investigations of the elemental and phase composition, microstructure, microhardness and tribological properties of AISI M2 steel subjected to nitrogen and carbon plasma-immersion ion implantation (PIII) at different regimes are presented. Elemental composition was studied by Auger electron spectroscopy (AES) and X-ray microanalysis. Phase composition was identified by means of conversion electron Mossbauer spectroscopy (CEMS) and X-ray diffraction (XRD). Using these methods it was established that nitrogen PIII at a target temperature of 380°C resulted in phase transformations: from α′-Fe(C,M)+M 6 C+MC (M: Fe,Cr,W,Mo) to e-(Fe,M) 2+ x (N,C)+M 6 (C). With increasing temperature up to 500°C in nitrogen PIII the retained martensite, in addition to e-(Fe,M) 2+ x (N,C), was observed. Joint nitrogen and carbon PIII leads to the formation of e-(Fe,M) 2+ x C and (Fe,M) 7 C 3 (M:Cr,W,Mo) carbides. Theoretical analysis of the distribution of thermoelastic stresses during PIII demonstrated the essential increase in the mass transport process of implanted atoms into the target volume. On the basis of the estimations conducted, it has been shown that migration processes of nitrogen into steel during PIII have a complicated character and can be described with the help of mechanisms stimulated by the reaction of a crystal lattice under the impulse influence.

Nitriding of steel and titanium surface layers under the action of compression plasma flows

The elemental and phase compositions of St3 steel and VT1-0 titanium surface layers nitrided by the action of compression plasma flows (CPFs) have been investigated. The plasma flow parameters are shown to be correlated with the modified-layer nitrogen content. The basic mechanism by which the steel and titanium surface layers are saturated with nitrogen has been revealed. The performed experiments indicate that an increase in the absorbed energy density leads to a decrease in the nitrogen concentration because a shock-compressed layer is formed in the near-surface region, impeding nitrogen diffusion into the sample. The higher nitrogen concentration of surface layers treated by CPFs is achieved by increasing the pressure of the residual nitrogen atmosphere. It has been established that γN-Fe nitrous austenite, α″-Fe(N) and α′-Ti(N) martensitic phases, and γ′-Fe4N and δ-TiNx nitrides can be produced by nitriding the surface layers of St3 steel and VT1-0 titanium.

Phase formation and structural changes in the chromium-silicon system exposed to compressed plasma fluxes

The results of the study of structural and phase transformations in the silicon substrate-chromium coating system exposed to compression plasma fluxes with power densities of 0.3–1.2 GW/m2 are discussed. The formation of hexagonal chromium disilicide and an amorphous phase, the growth of silicon dendrites, and the appearance of a chromium-enriched near-surface layer are revealed effects. The mechanisms of structural and phase transformations caused by rapid cooling of a mixed melt and concentration overcooling during solidification are analyzed.

The effect of nitrogen implantation on the tribological properties of composite aluminium alloys

Abstract In this work the tribological properties of powder aluminium alloys (Al + Al 2 O 3 , Al + C) and cast aluminium were investigated after nitrogen implantation (energy 30 keV, implantation dose 2 × 10 17 ions cm −2 ). Phase analysis of the surface modified layer was conducted using X-ray diffraction. Auger electron spectroscopy measurements were also performed to obtain composition and depth profiles of the implanted layer. It was found that implantation led to an increase in the initial friction coefficient of the powder alloy Al + C and cast aluminium. The formation of the AlON phase in the surface layer took place during implantation, according to data of the phase and element composition analysis.

Properties of coatings based on Cr, Ti, and Mo nitrides with embedded metals deposited on cutting tools

The relation between the phase-structure state and mechanical and operating characteristics of coatings based on solid solutions of (Ti, Cr)N, (Ti, Mo)N with Cr and Mo formed on a hard tool T15K6 alloy by condensation and ion bombardment of combined plasma flows in nitrogen is studied. A tool with the coating based on the solid solution (Ti, Cr)N is shown to have high hardness, low friction coefficient, and maximal resistance to cracking and oxidation, resulting in increased service life in mechanical working of steel.