The role of scale factor in the formation of prod-uct properties under the action of surface modifi-cation

Based on theoretical and experimental research in the fields of solid-state physics and physical materials science, it is proved that the surface layer of a solid body, which is deformed, is an independent functional subsystem and radically affects large-scale levels of plastic flow and destruction of the product as a whole. As is known, the most effective method of improving the performance of products is the grinding of grain, because it is the grain boundary (substructural) mechanism of strengthening which provides an increase in the structural strength of the product. In this regard, special attention is paid to submicro- and nano-structuring of the surface. Goal. The aim of the work is to study the process of structure formation of the surface layer under the action of ion bombardment (IB) and its effect on the properties of products taking into account the scale factor. To achieve this goal, the following tasks were set: to evaluate the characteristics of the surface microstructure after IB and to study its tensile behavior in cylindrical and flat samples of low-carbon steel in order to take into account the scale factor in changing their properties. The submicro-structuring of the surface by ion bombardment is carried out in the work and its influence on the behavior of products during tensile deformation is investigated. It is established that the presence of a thin modified layer (with a constant core) significantly changes the properties of the product under force. The decisive role belongs to the contribution of the surface layer (scale factor) – the ratio of the area of the modified layer to the volume of the product: if it is <1 the effect of hardening is better realized while maintaining plasticity, and if ˃ 1, it is a significant effect of plasticization which maintains (or even increases) hardening.

Cathodic nitriding and anodic polishing of Ti6Al4V alloy by plasma electrolysis

The paper presents the results of studies on modifying the surface of Ti6Al4V titanium alloy by combined exposure to cathodic nitriding and anodic polishing in electrolysis plasma. The morphology and roughness of the surface, microhardness of the modified layer have been investigated. Wear resistance was studied under dry friction conditions. The effect of combined treatment on corrosion resistance of Ti6Al4V alloy was examined by means of potentiodynamic polarization in Ringer’s solution. It has been established that cathodic nitriding at 750 °C for 10 min leads to the hardening of the surface layer up to 820 HV with an increase in roughness by 2 times and wear resistance almost 3 times. Subsequent anodic plasma electrolytic polishing of the nitriding surface in solution of ammonium sulfate leads to a decrease in roughness and friction coefficient with an increase in corrosion resistance.

Method for the modification of graphite subsurface layer to a solid mixture of SiC and graphite

We studied the interaction of molten Si and graphite surface during annealing in different atmospheres (CO, vacuum, Ar). The studies have shown that during annealing in CO atmosphere a composite material of SiC and graphite in a thick subsurface layer of the graphite is being formed, whereas at vacuum and Ar atmosphere the modified layer is either thin or absent. The composition and structure of both the composite material itself and the interface between the composite material and the graphite matrix were investigated using the methods of scanning electron microscopy and Raman spectroscopy. Studies have shown that the composite material obtained by this method has a branched fibrous structure consisting of small tubular layers of silicon carbide interspersed with large monocrystalline grains of silicon carbide of the cubic polytype, which leads to significant strengthening of the material. Thus the proposed method can be used to form a thermal protective, chemically resistant coating on graphite surface.

Surface modification of hypereutectic silumin subjected to a millisecond modulated electron beam treatment

In this work, using a unique feature of the “SOLO” electron source with a grid plasma cathode based on a low-pressure arc discharge, which consists in the possibility of controlled operation of the beam power during a pulse of submillisecond duration, and, accordingly, the rate of energy input into the sample surface, we investigated the modes irradiation of samples of hypereutectic silumin. The irradiation modes had the same energy density during the first 200 μs of the pulse, equal to 20 J/cm2 and differed in different durations of further maintaining the surface temperature at 600°C for a time of up to 1 ms. The results of tribological tests and methods of diffraction microscopy of the investigated defect structure, the elemental and phase composition, the morphology of the strengthening phases of the modified layer of the hypereutectic silumin samples are presented.

Influence of plasma electrolytic hardening modes on the structure and properties of 65G steel

This work presented a study of the structure, hardness and wear resistance of 65G steel treated with electrolyte-plasma hardening under different conditions. The electrolyte-plasma hardening technology and a laboratory installation for the realisation of electrolyte-plasma hardening are also described. After electrolyte-plasma hardening, we have established that a modified layer consists of the a-phase (martensite) and M3C cementite. The study results showed that electrolyte-plasma hardening makes it possible to obtain layers on the 65G steel surface that provides an increase in microhardness by 2.6 times, wear resistance by two times, resistance to abrasive wear by 1.7 times compared to the original samples. In addition, local hardening ensures the achievement of technical and economic effects due to the absence of the need to isolate an unwanted site of parts, processing only the areas requiring hardening.

Acceleration of Plasma Nitriding at 550 °C with Rare Earth on the Surface of 38CrMoAl Steel

In order to explore the effect of the addition of rare earth (RE) to a steel microstructure and the consequent performance of a nitrided layer, plasma nitriding was carried out on 38CrMoAl steel in an atmosphere of NH3 at 550 °C for 4, 8, and 12 h. The modified layers were characterized using an optical microscope (OM), a microhardness tester, X-ray diffraction (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), and an electrochemical workstation. After 12 h of nitriding without RE, the modified layer thickness was 355.90 μm, the weight gain was 3.75 mg/cm2, and the surface hardness was 882.5 HV0.05. After 12 h of RE nitriding, the thickness of the modified layer was 390.8 μm, the weight gain was 3.87 mg/cm2, and the surface hardness was 1027 HV0.05. Compared with nitriding without RE, the ε-Fe2-3N diffraction peak was enhanced in the RE nitriding layer. After 12 h of RE nitriding, La, LaFeO3, and a trace amount of Fe2O3 appeared. The corrosion rate of the modified layer was at its lowest (15.089 × 10−2 mm/a), as was the current density (1.282 × 10−5 A/cm2); therefore, the corrosion resistance improved.

Low-Temperature Plasma Nitriding of 3Cr13 Steel Accelerated by Rare-Earth Block

The plasma nitriding of 3Cr13 steel occurred at 450 °C for 4, 8 and 12 h in NH3 with and without rare earth (RE). The nitrided layers were characterized using an OM, SEM, TEM, XRD, XPS, microhardness tester and electrochemical workstation. The modified layer, with and without La, are composed of a compound layer and diffusion layer from surface to core. After the addition of La during nitriding, the maximum increase of layer thickness, mass gain and average microhardness was 15.6%, 35.8% and 212.50HV0.05, respectively. With the increase of the proportion of ε-Fe2-3N, the passivation zone of the corrosion resistance curve increases from 2.436 to 3.969 V, the corrosion current density decreases, the corrosion potential and pitting potential both increase, and, consequently, the corrosion resistance is significantly improved. Most of the surface microstructures of the nitrided layer was refined by the addition of La. The presence of La reduces the N content in the modified layer, which accelerates the diffusion of N atoms and, thus, accelerates the nitriding process.