Formation Of Diffusion Layer Research Articles

Investigation of the Features of the Formation of Diffusion Layers During Nitrocementation of High-Chromium Steels in a Carbon Black Medium

The purpose of the work is to establish the regularities of the formation of the structure and phase composition of surface (modified) layers on 20X13 chromium stainless steel under intense saturation with carbon and nitrogen and, on this basis, to substantiate the possibility of surface hardening of parts made of high-chromium steels by nitrocementation.Methods. The studies were carried out on samples made of high–chromium steel 20X13, which were subjected to high-temperature nitrocementation in a paste-like medium including fine soot, sodium carbonate and potassium ferruginous oxide (paste-forming agent is an aqueous solution of carbomethylcellulose). The microstructure was studied using an optical metallographic microscope OLIMPUS OX 51 and a scanning electron microscope Qanta FEG-650 with an X-ray microanalysis system EDAX. The microhardness was determined on the Duramit-5 microhardometer, the phase composition on the XRD-7000S X-ray diffractometer.Results. Nitrocementation of high chromium steel 20X13 in the temperature range of 820–950°C provides the formation of diffusion layers on the surface, the structure of which is represented by three zones: a crust of solid carbonitrides on the surface, an eutectoid zone with a solid matrix and inclusions of carbonitrides under the crust and a transition zone including a solid solution enriched in carbon and nitrogen with grains of the base metal. The microhardness of the nitrocemented layers on 20X13 steel after quenching from 1050°C in oil and tempering at 600°C reaches Nm 750–800 on the surface and decreases smoothly enough in depth of the nitrocemented layer. The depth of nitrocemented layers with increased microhardness (more than 400 Nm), depending on the duration of treatment, can reach ~ 0.5 (860°C, 6 hours).Conclusion. Nitrocementation of high-chromium steel 20X13 at 820–880°C in an active carbon black paste with the addition of potassium ferrocarbon leads to an increase in the hardness of the surface layers by about 4 times the hardness of the base, which, combined with the high mechanical properties of the base, will significantly increase the service life of parts made of high-chromium stainless steels of type X13 operating under high contact conditions loads.

Electropulsing-enhanced atomic diffusion and recrystallization to optimize mechanical properties of Al/Cu laminated metal composites

This work adopted the combined processing of electropulsing bonding (EPB) and electropulsing rolling (EPR) to prepare high-performance Al/Cu laminated metal composites (LMCs). The results show that electropulsing (EP) significantly accelerates the diffusion of Al and Cu atoms, thus facilitating the formation of diffusion layer. Through EP treatment, the recrystallization behavior of the Al and Cu layers is enhanced. The microstructure composed of a diffusion layer with suitable thickness and fine recrystallized grains contributes to the mechanical properties. Due to the introduction of intermetallic compounds (IMCs), the hardness and elastic modulus of Al, Cu, and diffusion layers exist large differences. The hard diffusion layer can exert a rigid deformation constraint on the ductile Al and Cu layers, and promote the interface deformation. Meanwhile, the tensile strength of as-EPRed samples increases and then decreases with the increasing EP frequency, the maximum is ∼215.2 MPa at 20 kHz. Theoretical analysis indicates that the local Joule heating and athermal effect should be the principal factors for microstructure evolution and property optimization. These results are expected to clarify the EP-related mechanism on atomic diffusion and recrystallization, which provides guidance for the fabrication of Al/Cu LMCs.

Chromium–Aluminum Coatings for Oxidation Protection of Titanium–Aluminum Intermetallic Alloys

This article explores the utilization of cathodic-arc deposition Cr-Al overlay coatings as oxidation protection for Ti-Al-Nb intermetallic alloys. The primary objective is to investigate PVD Al-Cr coatings deposited via cathodic-arc deposition without subsequent vacuum annealing. The microstructure, phase, and chemical composition of the coatings were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis. Isothermal exposure of samples in a laboratory air furnace was conducted, revealing the efficacy of Cr-Al coatings in protecting the Ti49-11Al-40Nb-1.5Zr-0.75V-0.75Mo-0.2Si (mass%) intermetallic alloy VTI-4 against oxidation. The findings highlight that the as-deposited coatings possess a layered structure and contain Al-Cr intermetallics. Post-exposure to the furnace without prior vacuum annealing results in coatings exhibiting a porous microstructure, raising concerns regarding oxidation protection. This investigation of Cr-Al coatings on a VTI-4 alloy substrate yields valuable insights into their nanolaminate structure and challenges associated with aluminum droplet fractions. The proposed additional vacuum heat treatment at 650 °C for 500 h effectively homogenizes the coating, leading to predominant Cr2Al and Ti-Al phases. Additionally, the formation of diffusion layers at the “coating–substrate” interface and the presence of oxide barriers contribute to the coatings’ heat resistance. Our research introduces possibilities for tailoring coating properties for specific high-temperature applications in aerospace, energy, or industrial contexts. Further refinement of the heat treatment process offers the potential for developing advanced coatings with enhanced performance characteristics.

Analysis of Effect of Concentration Dependence of Exchange Current on the Metal Electrodeposition into Template Nanopores

Metal electrodeposition into the nanopores of template of porous anodic alumina type under the conditions of mixed kinetics is studied theoretically using analytical and numerical methods. Two main stages of the process are studied: the non-steady-state formation of diffusion layer in the template pores and much longer process of pore filling with metal. The effect of nonlinearity of the concentration dependence of exchange current density of metal electrodeposition on the current density of the diffusion layer formation and pore filling with metal is studied.

Влияние продолжительности боромеднения на толщину диффузионного слоя и микротвердость углеродистых и легированных сталей

Introduction. Borocoppering is one of the methods of thermochemical treatment (TCT) aimed at forming diffusion layers with high physical and mechanical properties on the surface of carbon and alloy steels. The thickness of the diffusion layer is the most important characteristic of the TCT, which determines the depth of hardening. Consequently, the intensity and main characteristics of the TCT (layer thickness, alloying element concentration profile) depend on the process conditions (temperature, duration, and amount of alloying element). The purpose of this work is to determine the temperature-time parameters of diffusion borocoppering, which contribute to the formation of diffusion layers with a maximum thickness. The paper considers the results of surface hardening of carbon and alloy steels (for example, Steel 45 (0.45% C), Steel U10 (1.0% C), and 0.5C-Cr-Ni-Mn steel) by high-temperature soaking in powder mixtures containing boron and copper. Borocoppering was carried out in sealed containers with the powder mixture consisting of boron carbide, copper oxide, and sodium fluoride as an activator at a temperature of 950 °C for 3–5 h. The resulting specimens with a diffusion layer were examined using an optical microscope and a scanning electron microscope (SEM); the microhardness, elemental and phase composition of the layers were also determined, as well as the roughness of the obtained surfaces. Results and discussions. The microstructure of the obtained diffusion layers is studied; diagrams of the changes in the layers’ thickness and the microhardness distribution over the layers’ thickness are shown. It is established that with an increase in the soaking time from 3 to 5 h, the thickness of the diffusion layer increases from 120 to 170 μm on Steel 45 (0.45% C); from 110 to 155 µm on Steel U10 (1.0% C) and from 130 to 230 µm on 0.5C-Cr-Ni-Mn steel. A gradual decrease in the concentration of boron and copper along the layer thickness from 15–16% and 2–3% on the surface, respectively, to zero values at the boundary with the base metal is revealed. It is established that borocoppering to the formation of more thick boride layers on the surface of carbon and alloy steels compared to pure boriding. Moreover, an increase in the duration of soaking during the process contributes to the greatest increase in the thickness of the layer on 0.5C-Cr-Ni-Mn steel. A study of microgeometry is carried out, microtopographies and profilograms of specimens’ surfaces are shown before and after borocoppering. It is established that the roughness after borocoppering increases by 2-3 times compared to the initial one, and an increase in the duration of the process does not have a significant effect on the roughness.

Effect of tool pin length on interfacial behaviors and mechanical properties of friction stir-welded lap joints of 430/304 stainless steels

In this study, the effect of tool pin length on friction stir lap welding of 430 and 304 stainless steels has been investigated. The thermal history of interface was measured by thermocouple. The interfacial macro- and micro-structures under different tool pin lengths were analyzed via optical microscope and scanning electron microscope. Also, tensile shear tests were carried out to evaluate the strength of the lap joint. The results show that increasing the pin length from 0.5 to 1.3 mm increases the peak temperature of the interface, which has a significant effect on diffusion layer formation and hook geometry. The fracture mode of the joints shifts from shear fracture to tensile fracture with the increase of the pin insertion depth. When the pin length is 1.0 mm, i.e., a slight penetration into the 304 plate, the joint presents a maximum failure load of 2.86 kN. The findings reveal that the effective top plate thickness (Teff) used to describe the hook geometry is an important factor determining the joint strength and fracture mode.

Зносостійкість титанового сплаву ВТ1-0 з модифікованою поверхнею в умовах абразивного впливу

The cost of rebuilding machine parts as a result of wear is enormous and rising every year. At a US symposium on reducing wear in machinery, the general consensus was that wear management is central to solving national problems such as energy conservation, material reduction, and ensuring the reliability and safety of mechanical systems. Nitriding significantly increases the wear resistance of metals and alloys. The formation of chemical compounds in titanium alloys by introducing nitrogen or increasing its concentration limit changes the rate of chemical reactions and the kinetics of oxide film growth, and increases their adhesion to the substrate. This leads to a decrease in the intensity of adhesive node formation and improves the tribological characteristics of titanium alloys. Therefore, it is necessary to study a titanium alloy with a hardened nitrided layer to obtain experimental results to determine the regularity of the influence of diffusion saturation parameters on wear resistance under abrasive conditions. The universal installation "VIPA-1" was used for vacuum ion nitriding in the pulse mode and the formation of diffusion layers on the surface. Technological parameters of vacuum ion nitriding in the pulse mode: temperature - 550°C, pressure - 25-150 Pa, processing time - 10 hours, ratio of reaction gases - 80% Ag + 20% N2. For experimental studies, samples of VT1-0 titanium alloy with dimensions of 30x30 mm and a thickness of 5 mm were used. The surface hardening of the samples was carried out uniformly around the entire perimeter, which ensures a uniform thickness of the diffusion layer. The analysis of the operating conditions of the friction surfaces of most structural elements made it possible to use the installation for bench tests according to the scheme of wear with a free abrasive (Brinell method). Wear tests were carried out on an experimental setup in accordance with GOST 23.208-79 (Fig. 2). The friction process was modelled in the presence of a free, not rigidly fixed abrasive, which coincides with the American standard ASTM C 6568. The experiment was carried out at a sliding speed of 0.158 m/s, a load of 20 kg (with a shoulder of 272 mm) and a friction path of 50 m. Steel 45, hardened to a hardness of 480-500 HB, was used as a reference. The wear body was a disc made of VT1-0 titanium alloy with a diameter of 100 mm and a thickness of 3.5 mm. On the basis of experimental studies, it has been established that the main mechanisms for increasing the wear resistance of titanium alloys as a result of the process of diffusion saturation of the surface with nitrogen during vacuum ion nitriding in the pulse mode are strengthening of the surface layers; creation of a favourable residual stress pattern; change in the patterns of deformation of the surface layers; change in the chemical and adhesive properties of the surface; transfer of diffusing nitrogen atoms into the depth of the matrix during friction due to the tribodiffusion effect. Conclusions. 1. Maximum wear rate of titanium alloy VT1-0 without hardening. 2. The effect of thermocyclic nitriding increases the wear resistance of VT1-0 alloy: in sand - 3 times; in water + sand - 3.5 times; in salt + sand - 2.5 times. 3. The effect of isothermal nitriding increases the wear resistance of VT1-0 alloy: in sand - 4 times; in water + sand - 3.5 times; in salt + sand - 2.5 times.

Fabrication of MoSi2 coatings on molybdenum and its high-temperature anti-oxidation properties

Industrial spent MoSi2-based materials were used to fabricate oxidation-resistant coatings on molybdenum via slurry painting in air. The microstructure, phase constituent and high-temperature oxidation behaviors of the coatings at 1500 °C were explored. The results show that the bonding layer is generated in the coatings after sintering, which strengthens the metallurgical combination between the coating and the substrate because of the formation of diffusion layers. Rare cracks appear in the coating using pure MoSi2 (PM coating) while the coating using spent MoSi2 (SM coating) is free of cracks due to decreased thermal expansion mismatch. After oxidation, the oxide scale of PM coating possesses large-sized pores while a relatively dense oxide scale is acquired by SM coating. Compared with PM coating, thinner glassy oxide scale with lower mass gain is obtained by SM coating, exhibiting better anti-oxidation properties at 1500 °C.

Surfacing of stamping tools with subsequent nitrocarburizing for their effective restoration

The possibility of restoration and hardening of stamping tools by surfacing them with special electrodes OZSh-1 and TsN-4 with subsequent nitrocarburizing is shown. The microstructure of nitrocarburized surfacings on transverse sections was studied using a Quanta 650 FEG microscope by scanning electron microscopy. The dependence of the abrasive wear of the deposited coatings on the carbonitriding temperature has been experimentally established. It has been established that the increased wear resistance of nitrocarburized surfacings is due to the characteristics of the carbonitride structure of the diffusion layers, which depend on the alloying of the deposited metal and on the nitrocarburizing modes. The features of chemical-thermal treatment in a highly active nitrogen-carbon paste, which leads to the formation of diffusion layers with excess carbonitrides having high hardness on the surface of the deposited metal, are considered. The high efficiency of a pasty coating based on amorphous carbon and nitrogencontaining components (urea and potassium ferricyanide) has been experimentally shown. It has been established that for the restoration of small die tools with small allowable wear, it is advisable to use chromium-molybdenum surfacing with an OZSh-1 electrode, nitrocarburized at a temperature of 700 °C, for large-sized dies, manganese surfacing TsN-4. At the same time, carbonitriding of manganese coatings deposited with TsN-4 electrodes must be carried out at a temperature of 900 °C in order to obtain carbonitride layers of great depth on the surface of the restored stamps.

Features of the Structure Formation of Diffusion Boride Layers upon Preliminary Activation

The features of the structure formation of diffusion layers obtained by technology, including preliminary surface treatment of steel products made of U8 steel and subsequent boriding in powder media, have been investigated. The pretreatment consisted of dynamic alloying in the superdeep penetration (SDP) mode with a SiC-based powder composition. As a result, the thickness of the diffusion layer increases, its porosity decreases, and the proportion of the high-boron FeB phase in the layer increases.

Microstructure evolution and growth mechanism of Si-MoSi2 composite coatings on TZM (Mo-0.5Ti-0.1Zr-0.02 C) alloy

The Si-MoSi2 composite coatings with a high silicon concentration were prepared on TZM alloy through a hot dip siliconizing method (HDS). The evolution behavior of microstructure and phase composition of Si-MoSi2 composite coatings with different diffusion times were studied. The Si-MoSi2 composite coatings have a very dense and uniform microstructure with a submicron roughness, and the lowest Sa, Sq, and Sz are only 0.258, 0.312, and 5.08 µm, respectively. A typical three-layer diffusion structure is observed at cross-section of coatings, the MoSi2 phase and carbide phases form in the outer layers, and the intermediate layer only consists of MoSi2 phase. Whereas the transition layer mainly consists of Mo5Si3 phases. The formations of globular SiO2 and carbide dispersion particles on coating surface are due to the reduction reaction between Si and (Ti,Zr)O2 dispersion phase, and the carbonation reactions. The growth process of silicide ceramic coating can be divided into four different stages: wetting stage, initial diffusion stage, stratification stage of diffusion layer, and final stage of diffusion layer formation.

Grain-boundary nitrogen diffusion model in multilayer materials

The paper presents the dependencies for the formation of diffusion layers in materials having a laminar structure, when they are saturated with nitrogen. The influence of chemical composition on the thickness of the nitrided layer has been determined. Models for formation of diffusion layers depending on permeability of interlayer boundaries and chemical formula of the composition are proposed.

Activation of diffusion during the formation of boride layers on the surface of steel parts

The features of structure formation of diffusion layers obtained by the technology, including preliminary surface treatment of steel products and subsequent thermal diffusion boriding in powder media, have been investigated. Pretreatment consisted in surface activation by superdeep penetration with a powder composition based on SiC of steel samples made of У8 steel. The features of the activation zones and their distribution over the surface are noted. The features of the activation zones and their quantitative characteristics are noted. A structural analysis of the obtained diffusion layers for the variants of low-temperature (650 °C) and high-temperature (920 °C) boration has been carried out. The chemical composition of the layer and the distribution of the main elements in it are analyzed. In both cases, a change in morphology was noted, consisting in the formation of a more compact diffusion layer and rounding of boride needles in the zone adjacent to the base metal. An increase in the layer thickness by 20–50 % and an increase in the proportion of the high-boron FeB phase relative to the variant of borating without preliminary activation were established.

Fe/Ni diffusion behavior in the shear-extrusion solid state bonding process

• A diffusion layer about 3 μm thick can be formed through Fe/Ni interdiffusion during the SEB process. • The main composition of the diffusion layer is Fe-Ni substitutional solid solution distributed in Ni base. • The maximum actual interdiffusion coefficient of Fe/Ni atoms can achieve 5.4 × 10 −13 cm 2 /s during the SEB process. • Relative diffusion layer thickness increases with the increase of deformation degree with a linear relationship. The shear-extrusion bonding (SEB) of pure iron (99.9 %) and pure nickel (99.5 %) are carried out under the experiment condition of heating temperature 1050℃, top die speed 12 mm/s with different deformation degrees. The Fe/Ni diffusion behavior is analyzed through experimental studies and theoretical analysis. The results indicate that a diffusion layer about 3 μm thick is formed through Fe/Ni interdiffusion and the main compositions of the diffusion layer are Ni and Fe-Ni solid solution. It is found a large number of vacant clusters are formed at the Fe/Ni interface in the SEB process. The diffusion of matrix atoms or substitutional solute atoms is mainly realized by vacancies, so the diffusion mechanism of Fe/Ni in SEB process is vacancy diffusion mechanism or vacancy pair diffusion mechanism. The actual interdiffusion coefficient of Fe/Ni in SEB process is 100∼1000 times higher than the interdiffusion coefficient of Fe/Ni atoms under thermal action. So the plastic deformation provides additional vacancies to promote the formation of diffusion layer. The relative diffusion layer thickness increases from 6.02 μm to 12.01 μm when the deformation degree increases from 50 % to 74.2 %, and the relative diffusion layer thickness increases linearly with the increase of deformation degree.

Strengthening the Surface Layer of Tools with State-of-the-Art Technologies

Increasing both the service life and the wear resistance of the tool by surface hardening is an urgent issue. Its solution contributes to a significant increase in the performance of products. Available methods of surface hardening of tools, based on coating or changing the surface condition, are becoming increasingly important due to the complexity of the operation of products. Plates made of the T5K10 (85%WC–6%TiC–9%Co) and T15K6 (79%WC–15%TiC–6%Co) hard alloys as well as cylindrical samples made of the W6Mo5Cr4V2 and W18Cr4V high-speed steels are used for the study. Studies have shown that, after processing the T15K6 alloy plates with a pulsed magnetic field, the cutting tool life improved by more than 200% as compared to the untreated ones. The proposed method will increase the strength of carbide plates and stabilize the physical and mechanical properties of the cutting tool. For tools made of alloy steels, the hardening treatment is carried out by the boron method in pastes with nanodisperse powders. As shown, the thickness of the boride layer for high-speed steels increases with the duration of the process; however, its growth rate depends on the composition of the steel. An increase in the holding time of the chemical and thermal treatment leads to the growth of boride layers. The layer thickness changes quadratically (as a second-degree polynomial) with duration time. A feature of formation of diffusion layers is revealed. The dependences of both the surface hardness and the thickness of boride layer on the borating time for high-speed steels are also shown. Studies have shown that boriding in a nanodisperse medium can significantly increase the wear resistance of steels. The method of expert assessments of the maximum values of the surface properties of the studied steels is carried out. As shown, it is more rational to use W6Mo5Cr4V2 steel as a cutting tool after hardening the surface layer by boriding in a nanodisperse boron-containing powder. The proposed processing method demonstrates the prospects of using it to improve the performance of products. In addition, this method of hardening can significantly increase the wear resistance of materials (by ≈3.38–3.75 times) as compared to steels without processing.

THERMODYNAMIC ANALYSIS OF THE GAS MEDIUM IN THE FORMATION OF DIFFUSION COATINGS USING COMPOSITE SATURATING CHARGES

Review of the main processes of formation of diffuse coatings doped with molybdenum,vanadium and tungsten. The basic features of the formation of diffusion layers during chemicalthermaltreatment are considered.: When the SHS is tested, the container is heated to temperaturesof 1173-1330 K. Within 1-2 hours, a diffusion coating is formed due to the saturation of thesurface of structural materials with atoms of saturating elements - Cr, Al, V, Ti, B, W, Mo. Assaturating elements, the defects of these elements and the chemical compounds of these elementswere used, and to determine the possibility of using specific substances, chemical reactionswere considered that can occur in the temperature range of diffusion saturation usingSOS. It should be noted that the metallothermal Reduced oxide, which is used in the synthesisof powder media for CHT, is very fast. When obtaining diffuse layers using the composition ofsaturating the medium, a gas phase is formed, containing spolo-I, I2, I3, H, H2, H3, Cl2, Cl3 withchemical elements. With an increase in temperature, an increase in the amount of halides isobserved. This confirms the possibility of transferring alloying elements for the formation of diffusioncoatings. Also, the amount of products in the gaseous phase increases and condensedproducts are released. It is characteristic that in the temperature range of 700-1500 K, the decompositionof reaction products occurs during CHT, which is confirmed by the production ofdecomposition substances and a sharp increase in the number of gas moles.

(Invited) Short Introduction of Brenner’s Paradigm on the Steady State Diffusion Layer Model of Alloy Electrodeposition Composition Control, and Its Possible Extensions

Understanding the composition control of alloy electrodeposition is the prerequisite of pursuing fundamental understandings of phase and morphology evolution in the deposit. It is well known that a constant electrolyte concentration boundary, called diffusion layer, will form when the system is under forced convection or natural convection.[1] Given enough time, the thickness of diffusion layer, which in the beginning follows the Cottrell equation, will reach a steady state value, and thus a steady state deposition flux rate and deposition current could be estimated using the ionic diffusivity and diffusion layer length. For alloy electrodeposition, using the steady state deposition flux rate, ideally, the composition of the deposit could be predicted by the concentration ratio in the electrolyte and the mass-transfer coefficient ratio of the depositing ions.Despite being proposed by Essin in the 1930s and systematically documented in Brenner’s famous alloy electrodeposition book in the 1960s,[2, 3] nowadays, this behavior seems to be set aside when investigating the alloy electrodeposition properties. We decided to summarize the recent evidence for the composition control at the limiting case of diffusion layer control (limiting current condition) and discuss the confusions we are facing when applying this paradigm of alloy electrodeposition composition control at steady state.In this presentation, we will tentatively present the following topics: Levich in the 1960s has estimated the diffusion layer thickness of the electrodeposition on a vertical plate without any forced convection: when depositing in low viscosity electrolytes without forced convections, the natural convection will be induced by the tiny variation of local electrolyte density of the electrolyte and lead to the formation of diffusion layer.[4, 5] We will briefly present his model and derivation. From this model, the diffusion layer thickness due to 0.01mM Ni(II) at the height of 1 cm on the vertical electrodecould be as much as 0.21 cm. The time for reaching the steady state diffusion layer thickness and the initial layer thickness of the deposit (assuming two elements start to be deposited simultaneously) is estimated using the Cottrell equation.Expansion of mass-transfer coefficient to higher orders with respect to concentration, under the circumstances of multi-component, multi-element alloy electrodeposition. The matrix for multicomponent system could be fitted from the experimental data with a designated order of approximation on the mass-transfer coefficient. We will give the example for fitting the simplest case: binary system with linear behavior, based on data mentioned in our AgFe DMH-citrate work, where both ions are complexed as anions and deposited under limiting current condition. Meanwhile, a tentative construction of multi-element electrodeposition is given from the tabulated ionic diffusivities and a fixed diffusion layer thickness.Non-linear behaviors of deposit composition ratio - electrolyte concentration ratio sometimes happen in the alloy electrodeposition comparing with the prediction from the diffusion layer model. We will conceptually discuss the several possible causes for this non-linear behavior: the existence of homogeneous reaction inside the diffusion layer due to the pH and ligand concentration variation,[6] the transition from laminar flow to turbulent flow of the electrolyte near the electrode due to hydrogen bubbles and high deposition rate,[1] the formation of extended charge region at the cathode under overlimiting current,[7] and the situations where charge transfer kinetics governs the overall deposition rate.

Possibilities of Obtaining Diffused Layers upon Saturation of Multilayer Materials with Nitrogen and Carbon

The paper analyzes the processes of saturation of multilayer metal materials with interstitial elements: nitrogen and carbon. The formation of diffusion layers is presented. It is found that the thickness of the laminar layer and the degree of structuring of the sample affect the penetration depth of the diffusant.

Features for formation of diffusion layers during vacuum carburizing of 12Kh2N4A-Sh and 20Kh3MVF-Sh steels

The patterns reflecting the influence of controlling technological parameters on the characteristics of the carburized layer during vacuum carburizing of 12Kh2N4A-Sh and 20Kh3MVF-Sh steels are considered. The need is shown to take into account the presence or absence of active carbide-forming elements in the composition of carburizing steels when developing of vacuum carburizing modes.

Combustion synthesis of SiC-based ceramics reinforced by discrete carbon fibers with in situ grown SiC nanowires

This study proposes a combustion-based ceramic matrix composite processing technique intended on single-step in situ deposition of single-crystal SiC nanowires (SiCnw) on the surface of carbon fibers (Cf) and formation of SiCnw–reinforced SiC matrix. This was accomplished by Ta-catalyzed combustion of poly-(C2F4)-containing reactive mixtures with pre-mixed chopped Cf. Depending on the combustion conditions, carbon fiber surface is subjected either to formation of diffusion layers, ceramic particle incrustation or growth of continuous arrays of carbon-coated single-crystal SiCnw with a nearly defect-free lattice, 10–50 nm diameter and 15–20 μm length. Thermodynamics, phase and structure formation mechanisms are explored, and the optimal conditions are outlined for reproducible Cf/in situ SiCnw dual reinforcement of SiC-based ceramics. Hot pressing at 1500 °C produced Cf/in situ SiCnw-reinforced ceramic SiC–TaSi2 specimens with a relative density of 97%, 19 GPa Vickers hardness, 3-point flexural strength σ = 420 ± 70 MPa and fracture toughness K1C = 12.5 MPa m1/2.