Surface Layer Of Metal Research Articles

Wear resistance of strengthened layers with nanocrystalline structure in friction with boundary lubrication

Friction treatment refers to surface strengthening (hardening) methods using highly concentrated energy sources. The source of thermal energy occurs in the contact area of the tool-part due to high-speed friction (60–90 m/s) of the tool on the treated surface. The heating rate of the metal surface layer is 105–106 K/s. After moving the energy source from the contact zone, high-speed cooling of the surface layer of the metal takes place. The cooling rate is 104–5∙105 K/s. Under the action of high-speed heating and cooling of the contact area of the tool-part in the surface layers, a strengthened (hardened) nanocrystalline (white) layer is formed. The formed nanocrystalline surface layer has other physical, mechanical, chemical properties in comparison with the base metal of the part. Studies have shown that in the process of friction treatment of working surfaces of parts made of Steel 40NiCr6 (quench hardening and low-temperature tempering) a strengthened layer with a thickness of 250–320 μm with a hardness of 7.6–9.2 GPa is formed. The grain size of the surface strengthened layer was 20–40 nm near the treated surface. The formation of the strengthened layer is influenced by the shape of the working surface of the tool. Thus, a strengthened layer of greater thickness and hardness is obtained when machining with a tool with transverse grooves on the working part than with a tool with a smooth working part. Experimental studies in friction with maximum lubrication of pair “Steel 40NiCr6 and Grey Cast Iron GG20” showed that the strengthened nanocrystalline layer significantly increases the performance during sliding friction. Only samples made of steel were strengthened, counter-samples made of gray cast iron were not strengthened. The wear intensity of strengthened pair is 2.2–3.1 times less compared to unstrengthened pair. During the friction of the strengthened pair, the coefficient of friction and the temperature in the sliding zone also decrease. The best results were obtained when studying the friction pair in which the samples were strengthened with a tool with transverse grooves on its working part.

Designing of equipment for the synthesis of coatings from nitrides and carbides of intermetallic Ti-Al systems by condensation of plasma flows generated with vacuum arc

The quality characteristics of Ti-TiN multilayer vacuum ion-plasma coatings are studied, among which are as follows: roughness and adhesive strength. It is shown that additional ion bombardment contributes to obtaining high-quality coatings. Ion bombardment has a significant impact on the state of metal surface layer. In the process of ion bombardment, the conditions for formation of active adsorption centers as well as formation of a fine-grained structure, nanoscale grains and layers are created.

INNOVATIVE MATERIALS AND TECHNOLOGIES IN THE OIL AND GAS INDUSTRY

During the exploitation of equipment and piping systems of sulfuric acid, shale, metallurgical, mining, energy and other industries, the metal of a number of structures directly contacts with sulfur-containing agents at high temperatures. This resultsin intense corrosion, loosening and saturation of the surface layer of metal with sulfur (elementalor in the form of variouscompounds, including sulfides, iron, oxides) with a concentration of up to 0.6%. Repair welding of such metal at its partialreplacement is connected with the big labor costs caused by necessity of mechanical removal of a surface layer, as withoutthis operation in weld metal by standard electrodes hot cracks, pores and notfusion are formed.

Improving the quality of aircraft fasteners by transverse running with flat plates

For the strain hardening of aircraft fasteners, a surface plastic deformation method is proposed, based on running of blanks with smooth plates. The method allows processing parts that do not have center holes. Transverse running also eliminates the bending of the workpiece from the transverse loading forces action. Analytical dependences are obtained for determining the maximum possible contact area and relative compression for a transverse running. The quality of fasteners after transverse running with smooth plates provides the following favorable changes in the surface layer of metal: the formation of residual compressive stresses in the surface layers, a significant decrease in the initial roughness, an increase in the microhardness of the surface layer, the formation of a fine-grained structure, and the high accuracy of the machined parts diameter.

Reverse biased nanocrystalline graphite (NCG)/p-Si schottky junction for methane gas sensor

An investigation on the effect of the reverse biased operation of NCG/p-Si Schottky contact during methane gas exposure at room temperature has been presented. The experimental results show the larger current shift at the reverse bias operation, compared to the forward bias by exposing to methane gas. This can be attributed to the adsorption of methane gas into the metal surface layer and produces a negative charge at the junction, thus reduces the barrier height of the device. The reverse barrier height was calculated under the reverse bias condition, demonstrated the value decreased from 0.58-0.53eV towards a higher concentration of methane gas. The Schottky junction also affected by the increase in a free carrier when exposure to the reducing gas such as methane. Raman spectra are reported to be detected at G, D and 2D band with the grain size 1.88nm to exhibit single crystallite graphite properties. The results correlate well with the 3D AFM scans reveal the RMS surface roughness of 1.1 to 2.8nm.

(Invited) Do We Need 3D Metal Structures for Catalysis and Electronics When 2D Metals Are Possible and Perform Better?

This presentation will describe a new material paradigm: contiguous, atomically-thin, epitaxial metal films, one monolayer to several multilayers thick, where the graphene serves as both the growth template for the metal films and also as a ‘chemically transparent’ barrier against catalytic deactivation. In the latter role, graphene does not restrict access of the reactants to the catalyst but blocks the catalyst from dissolution or agglomeration. In other words, a true 2D atomically-thin metal is demonstrated - which the author believes is a first in the scientific community. A fundamental questions we can ask ourselves is whether surface metal atoms rendered in these 2D architectures are as stable as those of their counterparts in bulk. In the Pt/graphene case it is found that the surface atoms exhibit stronger binding than their bulk counterparts, but do so without sacrificing metal-like Fermi level electronic structure. The bulk-like stability of atomically-thin Pt/graphene is possible through a combination of inter-planar Pt-C covalent bonding and inter/intra-planar metallic bonding. It is further shown in a related system that by introducing a single-layer of graphene as an interface between the core and surface metal layers, unwanted surface alloying between the layered metals can be mediated. The room-temperature epitaxial synthesis approach has immediate implications on the science and application of metal catalyst systems that are support-flexible in design. More broadly, however, we reveal a new frontier for the nature of metals themselves, where they can be rendered in 2D films that are single to several atoms thin and are supported on a movable, electronically coupled substrate. Such metal/graphene or graphene/metal architectures will impact not just catalysis, but also electronic, thermoelectric and optical materials

Synthesis of Carbide Phases in Surface Metal Layers Under Electrospark Alloying with Graphite and Transition Metals in Groups IV–VI

The paper examines the electrospark synthesis of carbide phases in the surface layers of some steels (structural and tool) and titanium using graphite and transition metal electrodes: Ti, Cr, Mo, and W. Various options for processing with compact electrodes and powders of these materials were used. The electrospark alloying (ESA) of metal surfaces relies on the phenomenon of polar transfer of the anode tool material to the cathode when pulse discharges flow in a gaseous medium. The specific ESA features include high adhesion of the deposited material to the substrate, lack of heating to the part during processing, and use of pure metals and alloys as processing materials. The electrospark alloying process is very simple, and the required equipment is small, reliable, and transportable.

Regarding a technology of Sulphur removal in acidic induction furnaces

Sulphurremoval is a rather complicated metallurgical task, which require implementation of new energy-saving technologies, including metal desulphurization in induction furnaces. Results of analysis of different methods of metal desulphurization in the acidic induction furnaces. A technology of hot metal refining with Sulphurremoval by basic slags by extraction mechanism in the acidic induction furnaces proposed, tested and implemented at several plants. The essence of the xtraction mechanism applied to desulphurization method is as follows: particles of calcic slag involved by electromagnetic flows deep into an induction furnace. The surface layer of slag particles deoxidizes by carbon of the metal and silicon, resulting in the Sulphursolubility increases sharply due to its absorption by the metal surface layer of slag particles. Next, the metal flows deliver to the surface the slag particles saturated by Sulphur, the surface contacted with the furnace atmosphere, where the surface layer of slag particles is oxidized by oxygen of the atmosphere. It results in the Sulphursolubility decreasing sharply and after precipitating out of the slag; it oxidizes by oxygen to SO2 and removes into the furnace atmosphere. The process repeats multiply. The mechanism of theSulphur removal in the induction furnaces with acidic lining was studied at OJSC ZSMK foundry shop using IChT-10M furnaces when melting hot metal for melt bases and warmth-keeping jackets. To increase the proposed technology efficiency, the influence of different technological parameters on the rate and degree of metal desulphurization in the acidic induction furnaces of industrial frequency studied. Results of the study allowed to make a conclusion that induction furnaces, traditionally used for smelting of burden materials, convert into active refining melting facilities.

Hardness Optimization Based on Nitriding Time and Gas Pressure in the Plasma Nitriding of Aluminium Alloys

Plasma nitriding has attracted much interest to improve the hardness of aluminium alloys. However, the contradictive properties can be produced on the metal surface due to the saturated condition of the diffused nitrogen atom in the metal surface layer. The objective of this work was to investigate the effect of nitriding time and gas pressure to improve the hardness of aluminium using plasma nitriding. The nitriding processes were conducted in a DC glow discharge with nitrogen gas flowing inside the vacuum chamber. Firstly, the sample was nitrided using a fixed gas pressure of 1.2 mbar with the varied nitriding times of 3, 4, 5 and 6 hours. The optimum time producing the highest hardness of the surface was then used in the next nitriding process with varied gas pressure of 1.2, 1.4, 1.6 and 1.8 mbar (1 bar = 105 Pa). The optimum gas pressure producing the highest hardness was then used again in the last nitriding process using varied nitriding time of 3, 4, 5 and 6 hours. The result showed that the highest hardness was achieved using the gas pressure and nitriding time of 1.6 mbar and 4 hours, respectively. The formed AlN phase on the aluminium surface was identified by XRD, whereas the surface morphology was observed by SEM image. Compared to the untreated sample, the hardness of the treated samples was significantly high.

Friction, Wear, and Monitoring of Heavily Loaded Tribosystems: An Innovative Approach to Studying the Processes

This paper focuses on the influence of diffusion and segregation processes on the strength and tribological characteristics of friction units. The application of the quantum chemical method made it possible to reveal that the appearance of segregated atoms at the grain boundaries is the main reason for hardening or destruction of metal surface layers. The proposed approach was also applied to assess the compatibility of various elements consisting of iron and to relate this compatibility to the tribological characteristics. Comparative tests on friction and wear were aimed at investigating initial 38Х2МЮА-Ш nitrated steel, 38Х2МЮА-Ш nitrated steel with a diamond-like coating, and Nb- and Hf-alloyed 38Х2МЮА-Ш nitrated steel with a diamond-like coating. The tribospectral identification method proposed by the authors was used to study the friction processes in heavily loaded friction units using the example of Mi-26 helicopter spline joints.

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 %.

Расчет нагрева стального стержня, используемого при рафинировании технического алюминия

The purpose of the paper is to calculate heating of a steel rod (a crystallizer), determine its heating time up to the predetermined temperature and estimate the temperature to which the metal heats up if it is partially submerged in the aluminum melt. The heating of the steel rod immersed in the molten aluminum is calculated in the temperature range from 670 to 810°С. Based on the conducted calculations of the crystallizer heating, a new method of technical aluminum refining is proposed and its efficiency is substantiated. The presented method involves iron and silicon impurities extraction from the aluminum melt through its rapid cooling by the introduction of a massive steel body (a crystallizer) into the surface layer of metal. It is found out that the difference between the temperature of the rod end immersed in the melt (hot end) and the temperature of molten aluminum (rod holding time in the melt is 30s; immersion depth - 5 cm) is in the range of 226-260°C. Significant temperature head between the crystallizer and aluminum melt provides the possibility to use the proposed method for deep refining of technical aluminum.

Salisbury Screen Terahertz Absorber Formed with an Insulator: 4-N,N-Dimethylamino-4'-N'-methyl-stilbazolium Tosylate (DAST).

A novel Salisbury screen absorber (SSA) based on a 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystalline film was designed and fabricated. Different from the conventional SSA, an insulating organic DAST film replaced the normally highly conductive top surface metal layer. The absorption spectra and the structure of this SSA were optimized with a transmission line model to correspond to the DAST absorption peak at 1.1 THz, whose results were further verified by numerical simulations. If the thickness of the DAST film is 4 μm, a nearly perfect terahertz (THz) absorption is possible with this strategy, whereas the absorption of a bare 4 μm thick DAST film would be 4 times lower. The design allows the terahertz response of this DAST system to be tuned by adjusting either the thickness of the DAST film or the spacer, both of which remain in deep sub-wavelength to broaden the range of applications.

Impact of a High-Power Pulsed Plasma Flow with a Surface of High-Temperature Materials

The objective of this work is to study the behavior of surface layers of high-temperature metals in their interaction with a powerful pulsed plasma flow produced by a high-power ablative pulsed plasma thruster. This plasma generator produces plasma flows with a directed velocity of (7–9) × 106 cm/s, an initial diameter of 1.5–2 cm, and a maximum number density of about 1018 cm–3, as well as a maximum power of 5 GW. The main measured values are the residual temperature of the tungsten specimens and the evaporated mass. Also, metallographic analysis of the specimens was performed. The basis of the research method is to analyze the experimental data with the help of a numerical model describing the heating and evaporation of the material upon absorption of pulsed energy fluxes taking into account the evaporation kinetics based on the Hertz–Knudsen expression. Based on the developed numerical model and the obtained experimental data, the kinetics of evaporation of tungsten at high power fluxes to the surface (up to 1 GW/cm2) is investigated.

Microscale Surface Nanostructuration and Catalysis of Metallic Electrodes through Electrochemical Deposition and Dissolution in Ionic Liquids

Incorporation of highly active nanostructures into metallic electrode surface layers is of particular interest for a wide range of potential applications, such as electrochemical sensing and energy storage-conversion systems, because the nanostructures not only can increase the active area accessible to reactant molecules but can also improve electron mobility in the solid ligaments. However, controlling the nano-architecture of electrode surface layers faces great challenges since metals at nanoscale favor low surface areas in order to minimize the surface energy. In the past two decades, several strategies such as template synthesis, surfactant mediated synthesis and dealloying, have been developed to design and fabricate nanostructured electrodes with highly ordered networks and high surface area. We have developed a green-chemistry method based on in-situ electrochemical deposition-dissolution (ECDD) of an active metal on a target metal substrate in ionic liquids to achieve the nanostructuration of metallic electrodes.1-4 As shown in Figure 1A, during electrochemical deposition, a highly reactive metal component such as Zn is introduced via electrodeposition to interact with a less active electrode substrate such as Au to form an alloy phase. During subsequent electrochemical dissolution, the reactive component is selectively removed from the alloy phase leading to the formation of nanostructured surface layers. The nanostructured layers can grow deeper by repeating the process. The most obvious advantage of the ECDD method over other arts is that no net chemicals are consumed and it is a green-chemistry process. This method has been employed to successfully create different nanostructures on single-element metal and alloy electrodes at tens-to-hundreds micrometer scales, which are shown in Figure 1B to E. In this presentation, we will introduce the green-chemistry method based on the electrochemical alloying-dealloying in ionic liquids, the characterization and polarization behavior of resulting surface nanostructures, further catalysis of the nanostructures, and their applications to electrochemical sensing and energy storage conversion.

Structure and micromechanical properties of bimetal VT1-0 + AMg6 obtained by explosion welding

The weldability range of a VT1-0 + AMg6 bimetal without the traditional use of an intermediate layer of AD1 is determined. The phase composition of the melts on the interlayer boundary obtained by explosion welding of a titanium and an aluminum alloy at different values of the kinetic energy expended on the plastic deformation of the surface layers of metal was investigated. In the vortex zones, areas of melted metal with a hardness of 10-14 GPa were measured.

Rolling contact fatigue of hot-deformed powder steels with calcium microadditives

Fatigue damage of the surface layers of metal is a characteristic cause of failure of rolling bearings, gears and a number of other machine parts operating under cyclically repeated contact loads. Resistivity to the development of contact damage of steels obtained by hot forging porous blanks is determined by the presence of cohesive bonds between the particles of the base powder, as well as by the presence of non-metallic inclusions and grain size. The possibility of increasing the contact endurance of hot-deformed powder steels due to micro-doping with calcium has been studied. Iron powders with various content of impurities, as well as atomized powder of low-alloyed chromium-molybdenum steel were used as the basis for preparation of the blends. Calcium was doped as calcium carbonate. Mixing was performed in a planetary centrifugal mill. Samples for mechanical testing were obtained by hot forging porous blanks. After hot forging the samples were carburized to compensate for the loss of carbon in the surface layer. It has been established that doping calcium microadditives is favourable for increasing the energy content of damage under the conditions of exposure to contact-fatigue and bending loads. This is due to a decrease in the size of austenite grains at the expense of inhibition of their growth during the adsorption of calcium at the grain boundaries. Microalloying with calcium changes the localization of seats of contact fatigue damage. In samples-witnesses without microadditives of calcium cracks originate near non-metallic inclusions of sharp-angled shape in the near-surface zone. In microalloyed specimens the cracks are located in the subsurface layer in the area of Hertz maximum shear stresses.

Numerical Simulation of Metal Surface Layer Modification Using High-Frequency Induction Heating

Thermal processes of modifying the surface layer of a metal in a moving substrate with continuous induction heating of a rectangular substrate region by a high-frequency electromagnetic field have been studied using numerical simulation. The distribution of electromagnetic energy over the substrate surface is considered uniform, and over its volume, it is described by empirical formulas. It is assumed that, during the melting of the metal, the nanosized particles of the refractory compound inside of it are evenly distributed over the volume of the liquid metal and act as crystallization centers during its cooling. The boundary of the melting region is determined in the Stefan approximation, and the boundaries of the solid phase growth region are computed within the framework of the Kolmogorov theory of the metal crystallization. In the quasi-stationary distribution of the temperature field approximation, the size of the melting and crystallization zones was estimated and the growth kinetics of the solid phase was calculated. The characteristics of induction heating that make it possible to reduce the surface treatment time were determined. Calculated estimates of the specific power of the electromagnetic field were obtained that ensures that the melting region remains unchanged at the substrate velocity in the range of 1–3 cm/s.

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

Experiment for Determination of Residual Stresses in Pipes

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