Structure Of Surface Layer Research Articles

Influence of structure and properties of surface layer on fatigue durability of hardened steels strengthened by combined electromechanical treatment

Using the example of hardened carbon steels (steel 45, U8), the effect of combination of various surface hardening technologies is considered (using electromechanical processing, surface plastic deformation, non-abrasive ultrasonic finishing and their combination) on changes in structural state and surface microhardness, cyclic durability of hardened specimens and fatigue failure mechanisms. The studies were carried out by the methods of optical and scanning electron microscopy and by microhardness and fatigue tests. It is shown that for the investigated steels in quenched state, a high-speed pulsed thermo-deformation effect during electromechanical processing is accompanied by an increase in the surface microhardness (by more than 50 %) and decrease in the fatigue limit (by 20 – 30 %). Such a change in properties is associated with formation in the surface layer of substantially non-equilibrium, inhomogeneous in chemical composition, ultradispersed phases with increased hardness. At the same time, in the near-surface metal volumes tempering processes of the hardened structure proceed with the formation of softening zones and tensile residual stresses, accompanied by a decrease in the microhardness in these zones and the fatigue limit of the specimens. Such effects reduce some of the materials performance characteristics during surface hardening. The ways to improve the properties of such products due to additional technological operations require further studies. Combined surface hardening (based on electromechanical processing, surface plastic deformation and non-abrasive ultrasonic finishing) of carbon steels allows, due to variations in the intensity of temperature and deformation effects, to purposefully change the structural-phase composition and stress-strain state of the surface and near-surface metal layers. As a result, it becomes possible to form a balanced complex of strength and fatigue characteristics of the samples, depending on the preliminary heat treatment of steel. The operations of surface plastic deformation and non-abrasive ultrasonic finishing after electromechanical hardening, due to intensive plastic deformation provide smoothing of the surface and healing of near-surface defects and allow correction of stress-strain state of the processed metal. It provides an increase in microhardness in the tempering zone by 20 – 25 % and the fatigue limit of the samples by 25 – 30 %.

Ellipsometric Diagnostics of a Transient Surface Layer in Optical Glass

Optical properties of a transient layer with a broken structure that arises at the surface of optical glass at its treatment have been considered. Rather often, the surface of optical elements is considered to be perfect, although the actual inhomogeneous surface structure can have a significant effect for precision physical experiments or novel technological problems. Furthermore, the simulation of the surface layer structure and the corresponding optical characteristics, as well as the study of a possibility to determine those parameters from the results of optical researches, is also of theoretical interest, which is demonstrated in this work. Ellipsometric measurements of optical glass specimens with a broken surface layer are carried out. When modeling the angular dependences of the ellipsometric parameters tan ф and cos б, the near-surface specimen region is considered as a stack of 500 thin layers, and the matrix method of light reflection in this structure with regard for the interference phenomenon is used in calculations. Five models are tested for the optical profile of a nonuniform layer, whose parameters are fitted to achieve the minimum of the target function describing the discrepancy between the calculated and measured data. It is found that the theoretical models describe the optical properties of the specimens more accurately, if they make allowance for the inhomogeneous surface layer. Nevertheless, the solution of the inverse ellipsometric problem turns out ambiguous, so that additional measurements are required for the final choice of a model that would be adequate to the actual morphological structure of the broken layer to be made. However, the key advantage of the applied method consists in that it allows a direct registration of the optical response of the system.

Modification of surface layer of hypoeutectic silumin by electroexplosion alloying followed by electron beam processing

The analysis of structure, phase composition and tribological properties of surface layers of hypoeutectic silumin after complex treatment including the electroexplosion alloying by yttrium oxide powder in different modes and subsequent electron beam processing was done by the methods of modern physical material science. The complex treatment is accompanied by the formation of multi–phase submicro – nanocrystalline layer up to 80 μm thick enriched by yttrium atoms and being responsible for the increase in wear resistance. It is shown that Y atom concentration in the modified layer depends on electroexplosion alloying (EEA) mode. The distribution of Y atoms in the layer depends on the mode of EEA as well.

Characterization of Surface Changes on Molybdenum Nitride Thin Films during the Oxygen Reduction Reaction Using Operando Grazing Incidence X-Ray Absorption Spectroscopy

Coupled water electrolysis systems and proton-exchange membrane fuel cells (PEMFC) are a promising technology for clean energy storage and conversion, respectively.1 The efficiency of the hydrogen PEMFC is limited, in part, by the poor performance of catalysts for the oxygen reduction reaction (ORR). Due to problems with low activity and conductivity, the majority of non-platinum group catalysts for the ORR are conductive-carbon-supported nanoparticulate transition metal nitrides and/or carbides. It is difficult to determine the active surface of these catalysts during reaction conditions due to their high surface area, inhomogeneous size and distribution, complicated support-catalysts interactions, and surface oxidation in air. To overcome these complications, our work has focused on the operando structural and compositional characterization of the surface of active molybdenum nitride thin films. These films, prepared via reductive sputtering,2 are an ideal template for study due to their tunable thickness, lack of carbon support, moderate electrical conductivity, and well-defined surface. Using a specifically designed electrochemical cell for grazing incidence x-ray absorption and diffraction, we have been able to characterize changes in our Mo x N surface under ORR conditions. These same surface changes are not apparent at similar non-ORR reducing conditions, supporting our hypothesis that we are characterizing the active surface during ORR. ­ This work highlights the role of nitrogen, oxygen vacancies, and electrical conductivity on electrochemical activity and allows us to probe the structure and thickness of the active surface layer as well as the active site geometry. Understanding the role and importance of nitride bulk and the distinct surface structure will allow us to re-think our typical rational design of catalyst materials and help us design more active and stable catalysts in the future. References (1) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F. Combining Theory and Experiment in Electrocatalysis: Insights into Materials Design. Science (80-. ). 2017, 355, 1–12. (2) Hones, P.; Martin, N.; Regula, M.; Francis, L. Structural and Mechanical Properties of Chromium Structural and Mechanical Properties of Chromium Nitride , Molybdenum Nitride , and Tungsten Nitride Thin Films. J. Phys. D Appl. Phys. 2003, 36, 1023–1029.

TESTING THE STRUCTURE AND PROPERTIES OF STEELS AFTER HARDFACING AND LASER TREATMENT

This paper analyses the structure, hardness, and frictional wear resistance of surface layers formed on steels after hardfacing by means of the SSA arc method with self-shielded flux cored welding wire, with a content of carbon 5% and chromium 30% as well as boron alloying with the CO2 laser. S355J2 steel after being hardfaced with one up to three layers is characterized by the martensitic structure with chromium carbides and its surface hardness is 50–55HRC. In the weld deposit zone, with a thickness of up to approx. 2 mm, there is a constant distribution of hardness with the average value of 700 HV0.1, and then the hardness decreases to approx. 160 HV0.1 in the steel substrate. After hardfacing, the carbon content in S355J2 steel (0.23% wt.) increases to a similar content as in steel C90U in the initial state (0.96% wt.). After laser alloying with boron and after rapid cooling, C90U steel obtains distinctive paths with a zone structure and thickness reaching up to approx. 380 μm. In the remelted zone, there is a eutectic structure consisting of a mixture of iron borides and martensite with a hardness of approx. 1200–1800 HV0.1, and beneath it, there is heat affected zone with a martensitic-bainite structure with a hardness of approx. 700HV0.1. Hardfacing and laser heat treatment significantly decrease the frictional wear of the tested steels.

Potentialities of differently-stabilized silver nanoparticles for spectrophotometric determination of peroxides

One of the possible ways for using silver nanoparticles (AgNPs) in spectrophotometry is their application for the determination of oxidizing agents, based on oxidative destruction of these nanoobjects. This process depends on the structure of AgNPs surface layer, which is essentially affected by the chosen stabilizer. To assess influence of the nanoparticle stabilizer and the nature of the analyte, possibilities of AgNPs covered with stabilizers of three types (citrate, polyvinylpyrrolidone, and polyhexamethylene guanidinium) for the spectrophotometric determination of hydrogen peroxide and differently substituted organic peroxides were studied. The approach is based on AgNPs oxidation leading to discoloration of the solution monitored spectrophotometrically. Different selectivity of the oxidation depending on the stabilizer was shown. Effects of various factors (time of interaction, pH, concentration of AgNPs) on the oxidation and analytical performance of the procedure were investigated. The method allows for the determination of hydrogen peroxide, peracetic acid, m-chloroperbenzoic acid, and t-butylhydroperoxide in the range of 0.3–1.5, 0.1–0.8, 1.0–7.5, and 1–7 μg mL−1 and with the limits of detection of 0.1, 0.04, 0.3, and 0.3 μg mL−1, respectively. The analysis can be performed using either spectrophotometry or naked-eye detection.

Development and modeling of a device for strengthening the channels of gun barrels by the method of vibration-centrifugal processing

The paper proposes a fundamentally new method of vibration-centrifugal hardening of internal cylindrical surfaces of long-length steel parts, in particular artillery guns, belonging to a group of methods of surface plastic deformation, and is characterized by providing a significant level of energy for deformation of the material being processed. Artillery cannons, along with a system for targeting shooting guns, are perhaps the most responsible component, which not only provides range and accuracy of the aiming shot, but also regulates the durability of the gun in general. During each of the gun shots, the surface layers of the metal of the channel of its trunk are exposed to the destructive effects of high (up to 10000 °C) temperatures, the chemical action of powder gases, excessive pressures and mechanical wear on the movement of the shell. This leads to the destruction of the structure, strength and density of the metal surface layers, its burning and wear, which in the rest, leads to violations of the geometry of the working surface of the trunk channel. Violation of the geometry of the working surface of the channel of the gun barrel negatively affects the range, and most importantly, the precision of gunfire and other precision related tactical and technical characteristics of gun armament. Excessively worn internal working surface of the canal of the trunk of repair and restoration is practically not subject. This determines the availability of such characteristics for cannon weaponry as the permissible number of gunfire shots, which to a certain extent limits the duration of the effective use of guns. A rather common practice in mechanical engineering is that when the strength characteristics and capabilities of the materials used are practically exhausted, designers and developers draw their views on the technological capabilities to improve the operational properties of parts and units. Not the last position in their list is the reinforcing operations of the surface layers of the material of the details by various methods of surface plastic deformation, widely known in the literary primary sources under the acronym “PPE methods”. The common advantage of the best of a fairly wide variety of varieties (rolling, rolling, smoothing, blasting and vibrating processing, etc.) is that, without substituting the part for energy-intensive high-temperature heating, the strength characteristics and performance properties of the most loaded surface layers of the material of parts are improved. Accordingly, the use in manufacturing processes of the details of PPD methods helps to increase their reliability and longevity. The developed design of the reinforcement on the basis of the proposed method of vibration-centrifugal hardening treatment is used to strengthen the internal cylindrical channels of the trunk of large-caliber artillery cannons. The reinforcement is simple in structure, energy-saving, does not provide for the maintenance of highly skilled service personnel. The solid-state model of the device for the vibration-centrifugal hardening of the internal cylindrical surfaces of steel parts has been created

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

Evaluation of the suitability of a fluidized bed process for the coating of drug-eluting stents

Drug-eluting stents are often coated using single-stent coating techniques. In pharmaceutical industry, single-tablet coating is unthinkable. Instead large batches of tablets are coated in fluidized bed apparatuses or pan coaters. Therefore, it was the aim of this work to evaluate whether stents can be coated using a fluidized bed process. For this purpose stents were coated with the model fluorescent drug triamterene embedded in ammonium methacrylate copolymer. Different stent lengths as well as different coating yields were assessed and also a drug-free topcoat was evaluated. The coated stents were analysed regarded coating layer mass, drug content, surface structure, coating thickness and drug release. Furthermore, coating yield and stent defect rate were examined. Except for one stent configuration good results were obtained without optimization of process parameters which indicates the suitability of the method to coat large amounts of stents simultaneously in principle. Drug release was tuneable over a wide range of time spans and a wide range of drug loadings was produced. Further work will be necessary to transform the results of this study from a model stent to a clinically relevant product.

On the Dynamic Annealing of Ion-Induced Radiation Damage in Diamond under Irradiation at Elevated Temperatures

The structure and properties of the near surface layer of diamond after high-fluence irradiation at elevated temperatures with 30-keV Ar+, Ne+, N+, $${\text{N}}_{{\text{2}}}^{ + }$$ and C+ ions are studied. Dynamic annealing at temperatures above 500°С results in recrystallization of the diamond phase only in the case of irradiation with carbon ions, and irradiation with impurity ions causes graphitization of the ion-modified layer of diamond. According to Raman spectroscopy and reflection high-energy electron diffraction data, a nanographite structure is formed in the modified layer when irradiated with noble-gas ions. When irradiated with carbon ions, diamond grows and recrystallizes with a thin (~1 nm) graphite-like layer on the surface. In the case of nitrogen ions, a graphite layer is observed up to 720°С. Graphite-like layers on the surface of diamond are thermostable and, according to X-ray photoelectron spectroscopy, are layers of sp2 carbon. The Raman spectroscopy of visible light shows the different optical transparency of ion-induced structures on the surface of diamond, which correlates with the resistivities. The diamond structure disordered during ion irradiation at room temperature and the nanographite structure are more transparent than the graphite structure.

Effect of the Composition of the Lubricating Medium on the Structure of Surface Layers Formed by the Friction of a Servovite Film

The tribological characteristics of a brass–steel friction pair in aqueous solutions of saturated carboxylic acids are studied. With an increase in the length of the carbon radical in the acid molecule used as the organic component of the lubricant composition upon the friction of brass on steel, the coefficient of friction decreases and wear reduces. A servovite film is found to form on tribocoupled surfaces during frictional interaction. In the series of monobasic carboxylic acids R–COOH (R = CnH2n + 1, n = 0–5) used as a lubricating medium, from formic acid to caproic acid, the roughness of the film surface decreases and its continuity increases. The servovite film is formed by copper nanoclusters of predominantly ellipsoidal shape up to 40 nm in height, tightly packed and directed along the slip of the counterbody.

A Comprehensive Study of Steel Powders (316L, H13, P20 and 18Ni300) for Their Selective Laser Melting Additive Manufacturing

The determination of microstructural details for powder materials is vital for facilitating their selective laser melting (SLM) process. Four widely used steels (316L, H13, P20 and 18Ni300) have been investigated to detail their powders’ microstructures as well as laser absorptivity to understand their SLM processing from raw material perspective. Phase components of these four steel powders were characterized by X-ray diffraction (XRD), synchrotron radiation X-ray diffraction (SR-XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were utilized to reveal the surface structure of these four steel powders. It is found that phase components of H13, P20 and 18Ni300 are mainly composed of martensite and a small amount of austenite due to the high cooling rate during gas atomization processing, while 316L is characterized by austenite. XPS results show that the four steel powders all possess a layered surface structure, consisting of a thin iron oxide layer at the outmost surface and metal matrix at the inner surface. It is found that the presence of such oxide layer can improve the absorptivity of steel powders and is beneficial for their SLM process.

Determination of the optimal parameters of the structure of functional gradient materials using mathematical modelling approaches

Purpose: Functioning of mechanical friction systems largely depends on the characteristics of the structure of their surface layers. By controlling these parameters, it is possible to significantly adjust the reliability and durability of parts under the conditions of contact interaction. Design/methodology/approach: he proposed approach, which is based on the principle of nonlocality of the operational properties of materials, allows determining the optimal microhardness values of the surface layers and the gradient of this parameter, at which the contact durability of friction pair elements significantly increases. Findings: It is established that by adjusting the ratios of the surface strength of materials and its gradient, it is possible to achieve a significant increase in the operational parameters of friction units. Practical implications: The engineering relationship considered in the work allows to establish functional distributions of microhardness in the structure of surface layers, at which their wear reaches minimum values. Originality/value: Mathematical approaches are proposed, which allow determining the parameters of the structure of the surface layers of parts to increase their durability under conditions of friction contact loads.

Invеstigation of mechanical stability of the АMA Fe82Nb2B14RE2 (RE = Y, Gd, Tb, Dy)

The aim of study is to evaluate the mechanical properties of amorphous metallic alloys samples: Fe 84 Nb 2 B 14 , Fe 82 Nb 2 B 14 Y 2 , Fe 82 Nb 2 B 14 Gd 2 , Fe 82 Nb 2 B 14 Tb 2 , and Fe 82 Nb 2 B 14 Dy 2 after the temperature treatment. The investigated amorphous metallic ribbons were synthesized by melt spinning technique in helium atmosphere onto a copper wheel with a circumferential speed of about 30 m/s. Features of the technological process of Fe 82 Nb 2 B 14 RE 2 (where RE = Y, Gd, Tb, and Dy) amorphous ribbons producing cause the difference between their contact and external surfaces in mechanical properties. By X-ray diffraction method has been established that the Fe 82 Nb 2 B 14 RE 2 (RE = Y, Gd, Tb, and Dy) initial amorphous alloys have an amorphous structure. The microhardness of the samples in ribbon form has been measured by the use of Vickers technique. It shown the external side of the initial amorphous metallic alloys was characterized by higher the average microhardness than the contact side. It was established that base alloy of the Fe 84 Nb 2 B 14 after alloyed by the rare-earth elements (RE) increase microhardness on 0.85–1.90 GPa for contact surfaces and 3.04–3.89 GPa for external surfaces. The amorphous alloy Fe 82 Nb 2 B 14 Dy 2 has the highest value of microhardness (10.63–13.33 GPa) among alloyed initial samples. The difference between the mechanical properties of the both contact and external surfaces of the corresponding alloys decreases because of annealing at the nanocrystallization temperature. That could by explained by large number of clusters and the change of the free volume in the amorphous matrix of the alloys. The main influence on the mechanical properties causes annealing of ribbon samples in the air atmosphere because of changes of the AMА structure and formation of dense surface layers. Keywords: Amorphous metallic alloys, rare earth metals, thermal annealing, microhardness.

Mg-Co-Al-LDH nanoparticles with attractive electrochemical performance for supercapacitor

In order to strengthen the utilization of abundant magnesium resources in seawater, magnesium-based LDH nanoparticles (Mg-Co-Al-LDH nanoparticles) with attractive specific capacity and cycling stability were synthesized. The nanoparticles were prepared through coprecipitation of Mg(NO3)2, Co(NO3)2, and Al(NO3)3, and then characterized by SEM, FT-IR, and XRD. The electrochemical performances of Mg-Co-Al-LDH nanoparticles were evaluated and researched by galvanostatic charge-discharge test, cyclic voltammogram (CV), and electrochemical impedance spectroscopy (EIS). The results show that the nanoparticles own smooth surface and hexagonal layered structure, particle size is uniformly distributed between 350 and 450 nm. Electrochemical tests reveal that Mg-Co-Al-LDH nanoparticles display superior cycling stability at large current work conditions in charge-discharge tests, good capacitive performance at high scanning rate in CV tests and indicate a small internal resistance through EIS. The nanoparticles display an initial specific capacitance of 381.3 F g−1 at current density of 1 A g−1, with the value remaining 86.32% after 10,000 cycles. In addition, the prepared electrode performs an energy density of 13.09 Wh/kg and a power density of 149.49 W/kg. Besides, owing to the effective utilization of magnesium resources in seawater, Mg-Co-Al-LDH nanoparticles with attracted electrochemical performance are expected to achieve potential applications in supercapacitor.

Surface Hardening of Titanium Under Non-Vacuum Electron-Beam Cladding of an Aluminum-Containing Powder Mixture

Special features of the structure of surface layers formed on billets of commercial-purity titanium VT1-0 by cladding a powder aluminum-titanium mixture with an electron beam removed into air atmosphere are studied. X-ray phase analysis and transmission electron microscopy are used to show that the material remelted by the electron beam is Ti3Al titanium aluminide. The hardness of the deposited layer is 540 – 610 HV. The behavior of the material is studied under the conditions of sliding friction and friction against fixed abrasive particles. The results reflect decrease in the friction factor and increase in the wear resistance of the clad material as compared to commercially pure titanium.

Effect of Electron Beam Power Density on the Structure of Titanium Under Non-Vacuum Electron-Beam Treatment

The structure of surface layers of titanium alloy OT4 subjected to non-vacuum electron-beam treatment with power density of the beam equal to 0.28 – 0.90 kW/cm2 is analyzed. The microstructure of different zones of the material after the treatment and the crystallographic texture appearing in the surface layers as a result of the electron-beam impact are studied. The microhardness of the remelted layers and of the heat-affected zone is measured. Mathematical modeling is used to obtain the distribution of the temperatures and the heating and cooling rates over cross section of the treated material.

New Estimate of Osmium Melting Heat

The value of the osmium melting heat, ΔHm= 57.85 kJ/mol, presented in reference handbooks was obtained about 35 years ago from a wide extrapolation (in temperature) of experimental data on the melting entropy of the FCC and the HCP elements of the Periodic Table. Using the correlation of data on the surface tension (developed by B. D. Summ), the melting heat, and the surface layer structure for osmium, the authors obtain a new estimate, ΔHm = 30−40 kJ/mol, which is half of the reference value.

The Effect of Implantation of Nitrogen Ions on Corrosion-Electrochemical and Other Properties of Armco-Iron. Part I. Preparation and Standardization of Specimens

The results of an investigation of the chemical composition, structure, topography, and mechanical properties of surface layers of armco-iron after implantation of nitrogen ions under various conditions are given. Using X-ray electron spectroscopy, the implanted nitrogen distribution profiles are determined and the formation of nonstoichiometric iron nitrides and oxynitrides is shown. Using X-ray analysis and electron energy-loss spectroscopy of dimensional fine structures, the atomic and local atomic structure of the ion-modified layers is studied.

Redistribution of Erbium and Oxygen Recoil Atoms and the Structure of Silicon Thin Surface Layers Formed by High-Dose Argon Implantation through Er and SiO2 Surface Films

Using analytical high-resolution electron microscopy, the Si structure and the redistribution of Er and O recoil atoms embedded in thin (~10 nm) surface layers by Ar+ implantation with an energy of 250–290 keV and a dose of 1 × 1016 cm–2 through Er and SiO2 films, respectively, and subsequent annealing are studied. It is established that Si recrystallization fails at a distance of ~20 nm from the surface, where the erbium concentration of 5 × 1019 cm–3 critical for failure is achieved at T = 950°C. It disproves the generally accepted model of Er-atom transfer by the recrystallization front into SiO2 on the surface. Instead, it is shown that the redistribution of O recoil atoms to the initial oxide during annealing for immobile Er atoms provides the formation of surface-inhomogeneous erbium phases in such a way that the oxygen-enriched Er–Si–O phase turns out to be concentrated in the oxide, while the depleted Er–Si phase remains in Si. It explains the partial loss of implanted Er after removal of the oxide together with the Er–Si–O phase. It was shown that the formation of a high density of microtwins (locally up to 1013 cm–2) is associated with the formation of Ar bubbles and clusters, which is atypical for (100)–Si recrystallization.