Temporary Resistance Research Articles

Аналіз відповідності дослідних сталей для залізничних рейок сучасним стандартам України та ЄС

The process of operating vehicles determines the interaction of the wheel and rail. Traffic safety and the main technical and economic indicators of track management and rolling stock largely depend on these parameters. The result of this interaction are changes in the metal, which arise from rolling friction and especially from the friction of the wheel sliding on the rail during braking, due to these changes, the wheels of the rolling stock wear out. The purpose od the work is to research of the microstructure and mechanical properties of steels of promising chemical compositions to meet modern requirements for railway rails. Methods of metallographic analysis, determination of mechanical properties, and chemical analysis were used. Samples made from laboratory melts of steels with a promising chemical composition served as material for detailed microstructure studies. When comparing prospective chemical compositions, it was established that steel 1 meets the requirements of DSTU EN 13674:2018 for basic chemical elements and has differences according to DSTU 4344:2004, namely: increased carbon content. When comparing the experimental chemical composition of steel 2, it was found that this steel does not meet the requirements of DSTU EN 13674:2018 and DSTU 4344:2004, namely: a reduced amount of carbon and an increased content of silicon, chromium and molybdenum. According to the results of the analysis of the values of mechanical properties, it was established that steel 1 and 2 meets the requirements of DSTU EN 13674:2018. Steel 1 does not meet the requirements of DSTU 4344:2004 in terms of yield strength and relative narrowing, and steel 2 does not meet the requirements of DSTU 4344:2004 for the highest category of rails in terms of temporary resistance values. Based on the results of the microstructure studies, it was established that the test steel 1 after heat treatment has a structure of highly dispersed pearlite with a small amount of coarse-plate pearlite. When analyzing the microstructure of steel with a promising chemical composition 2, it was established that the structure consists of carbide-free bainite.

Friction stir welding of aluminum Al—Zn—Mg and Al—Zn—Mg—Cu alloys

The results of the effect of the parameters of the friction stir welding mode on the structure and mechanical properties of Al—Zn—Mg and Al—Zn—Mg—Cu aluminum alloys are presented. It is shown that the artificial ageing of welded joints allows to increase the level of their strength to 0.93...0.96 of the temporary resistance of the base metal in the T1 state.

Механические свойства соединений алюминиевых сплавов, выполненных сваркой трением с перемешиванием, при статическом и динамическом нагружении

On the basis of metallographic analysis and test results of samples of welded junctions of aluminum alloys AMg6 and D16T, made by friction stir welding, for static stretching, it is shown that destruction occurs in the zone of thermo-mechanical action for the AMg6 alloy and in the zone of thermal influence for the D16T alloy. At the same time, the dependence of the temporary resistance value of the welded junction on the state of the seam weld face has not been revealed. Tests for low-cycle fatigue have shown that the endurance limit is clearly dependent on the amount of seam weld face roughness. The value of the roughness of the seam weld face for the studied alloys has been determined, in which the nature of the fracture during the low-cycle fatigue test changes from multi-stage to single-stage.

РАЗРАБОТКА ТЕХНОЛОГИЧЕСКОГО ПРОЦЕССА ИЗГОТОВЛЕНИЯ СВАРНЫХ КОНСТРУКЦИЙ

the main goal of this article is to obtain welded permanent joints of modern thermally hardened aluminum and aluminum-lithium alloys made by laser welding, having mechanical characteristics (temporary tensile resistance, yield strength, elongation at break) and structural-phase composition close to or equal to the base alloy. It is shown for the first time that by controlling the parameters of heat treatment of samples with a welded joint of all studied aluminum-lithium alloys, it is possible to purposefully influence the formation of the specified mechanical properties of the weld by changing the structural and phase composition of the weld. The evolution of the struc-tural and phase composition of welded joints of thermally hardened aluminum and aluminum-lithium alloys has been investigated using modern independent diagnostic methods: for the first time, the use of synchrotron radia-tion diffractometry in combination with high-resolution transmission, scanning electron and optical microscopy. The dependences of the increment of deformation under cyclic loading with amplitudes exceeding the elastic limit on temperature are established. For untreated welded joints, it was found that at +85 C, the inhomogeneity of the deformation increment increases, and its speed increases by 8 times for alloy 1461, 5 times for alloy 1420 and 1.5 times for alloy 1441. At a temperature of -60 0C, alloys 1420 and 1461 have hardening stages, during which the value of deformation decreases at given boundary stress values. At +20 0C, there is a uniform increment of defor-mation and an increase in the amplitude of deformation with an increase in the amplitude of stress. At +85 0C, the strain amplitude does not change with increasing stress amplitude, its value is 0.55-0.5 of the strain amplitude at +20 0C. Based on the research results, technological techniques have been developed that allow obtaining me-chanical characteristics and structural-phase compositions of welded joints close to the main alloy during laser welding of aviation thermally hardened aluminum and aluminum-lithium alloys of the Al-Mg-Cu. Al-Mg-Li, Al-Cu-Mg-Li, Al-Cu-Li systems.

Influence of titanium and zirconium on structure and heat-resistance of low-carbon iron-aluminium alloys

The paper considers the effect of introducing ferroalloys containing titanium and zirconium on the structure and heat-resistance of low-carbon ferroalloys. Theoretically and experimentally, it has been proven that addition of 1.0 mass. % of titanium and 0.1 mass. % of zirconium to a low-carbon iron-aluminum melt containing 12 – 14 mass. % of aluminum, grinds its structure increasing temporary resistance and heat-melting. Titanium and zirconium are strong carbide-forming elements. When introduced into a low-carbon iron-aluminium alloy, they form a large number of crystallization centers, thus affecting its microstructure, allowing to get shredded and more equal grain compared to an alloy without additive. This in turn increases the strength limit of processed alloy. In addition, the use of titanium as a modifying additive in a low-carbon ferroalloy allows increasing its heatresistance, which exceeds several times the heat-resistance of famous chrome-nickel steel of 20Kh23N18 grade. As a result, a new technology for obtaining titanium and zirconium was developed based on research of the effect of their modifying additives on the structure and heat-resistance of low-carbon iron-aluminum alloys.

Features of the formation of structure and mechanical properties in rolled products of various thicknesses from low-carbon microalloyed steel produced by casting and rolling complex

The article considers results of the study of microstructure parameters effect on the impact strength in temperature range from 0 to –80 °C in 20 °C increments of Charpy samples with a sharp stress concentrator and Mesnager test pieces with a circular stress concentrator from rolled coils of low-carbon microalloyed steel with various thicknesses. The used roll products were produced in conditions of JSC “Vyksa Metallurgical Plant”. The tests were performed using optical and scanning electron microscopy. It is shown that with the same chemical composition and thermomechanical treatment modes, the metal of smaller thickness (6, 8 mm) is characterized by higher strength properties (on average, by 10 MPa for temporary resistance, by 30 MPa for yield strength) and a margin for viscous properties at negative temperatures at close values of grain score and average grain size corresponding to 10 – 11 numbers according to the State standard GOST 5639. The metal with a thickness of 12 mm has the lowest level of cold resistance, and the temperature of brittle transition is minus 50 °C. Structure of rolled products of various thicknesses has a variation in grain size. Rolled metal of smaller thicknesses have a smaller grains corresponding to number 14, rolled metal of larger thicknesses has a larger grains corresponding to number 8. By conducting electron microscopic studies using the backscattered electron method, it was found that a greater number of large-angle boundaries, which are barriers for brittle cracks propagation, are observed in the 6, 8 mm thick rolled products. The constructed orientation maps of the microstructure showed the presence of pronounced deformation texture corresponding to the orientations <110>||RD (rolling direction) and (<113>...<112>)||RD for rolled products with a thickness of 6 mm.

Effect of Pt electrodes in cerium oxide semiconductor-type oxygen sensors evaluated using alternating current

We developed a cerium oxide thick film semiconducting sensor for measuring the oxygen concentration in simulated exhaled gas. The oxygen sensor characteristics were investigated using simulated exhaled gas containing 15 % oxygen, 5 % carbon dioxide, and 80 % nitrogen. The sensor is required to accurately measure oxygen concentrations in the 15 % (typical of exhaled breath) to 21 % (atmospheric oxygen concentration) range. Since temporary resistance is widely known to drift when a direct current (DC) voltage is applied during sensing, we used alternating current (AC) in this study. The results suggest that changes in sensor resistance in response to simulated exhaled gas depend on the frequency of the AC signal. Furthermore, change in resistance depends on the morphology of the platinum electrode at a given frequency.

Metal inclusions in the seams and fracture of the tool during friction stir welding of aluminium alloys

ABSTRACT It is shown that the appearance of foreign metal inclusions in the seams of aluminium alloys created by friction stir welding is a consequence of the interaction of the working tool with the metal being welded, as well as the tool wears itself. Working tool fracture occurs when a tribological layer is formed on the tool surface as a result of the welded metal diffusion interaction and the tool material. The formation of the tribological layer is accompanied by the formation of aluminium penetration tongues along the grain boundaries into the steel from which the tool is made. Foreign metal inclusions are an intermetallic iron-aluminium particles of the FeAl3 type, which are detached from the tool surface and get mixed in the weld metal. It was found that tool wears increases with an increase in the temporary resistance of the welded aluminium alloy and with the presence of reinforcing ceramic particles SiC in its structure.

Investigation of plastic properties of AISI 316l steel by method of registration of macrolocalization fields

Selective laser melting is one of the modern methods of manufacturing parts in the production of machine-building equipment, a special place is occupied by complex technological processes used in the manufacture of high-load units of pneumatic-hydraulic system from heat-resistant alloys. The research was carried out on samples made of powder material - stainless steel AISI 316L martensite class. Metallographic studies showed that the density of the sample is 99.83%, the structure of the samples is a martensitic structure of equilibrium constructed tracks. Tests to determine the mechanical properties were performed in accordance with ISO 6892 on an INSTRON test machine. From the tensile diagram it was found that the yield strength was 376.56 MPa, the maximum point of temporary resistance of the sample - 615, 40 MPa 319 seconds after the start of the test. The control of the surface roughness was performed using a BioBase device. The working area of the tensile sample consisted of two areas: a roughness area of 5 μm, which accounted for 80% of the working part of the sample (zones A and Б) and 20% of the working part of the sample (zone Б), the roughness was 17 μm. According to the results of microstructure studies and studies by the method of registration of macrolocalization fields of the working zone of the samples, it was found that the destruction began from the surface of the samples from microconcentrators due to different roughness. It is established that the surface and subsurface layer with increased roughness in comparison with the main body has a smaller elongation by 10.84%. From microstructural studies of the working zone in the area of the gap, it was found that the destruction began from the surface of the samples between zones A and Б. During the research in zone A and Б, one of the concentrators of the gap was detected. As a result of the study, it was found that the destruction began with the surface of the samples and the place of change of its roughness. The mechanism of deformation of the sample from AISI 316L steel is shown, the scheme of extraction of tail sections of tracks and crack propagation in the conditions of tensile testing of the sample is constructed.

Дослідження неметалевої композитної базальтової арматури періодичного профілю та перспективи її застосування

Дослідження неметалевої композитної базальтової арматури періодичного профілю та перспективи її застосування

Инженерная оценка минимальной циклической долговечности при заданном уровне вероятности ее реализации

Object and purpose of research. This paper discusses structural materials under cyclic load. The purpose is to determine the minimum fatigue life corresponding to a certain non-exceedance probability of this value. Materials and methods. The study was performed on three structural materials: steel 15ХМ, steel 08Kh18N10Т and titanium alloy PТ-7М. Initial estimate of fatigue life distribution parameters relied on the data about guaranteed maximum and minimum values of temporary resistance and relative cross-section tapering. The assessment was performed as per a common curve “conditionally elastic stress amplitude versus number of cycles to failure” taking into account the mechanical prop-erties of given material. The values of minimum fatigue life were obtained as per two different methods: statistical simulation of the random values following the Weibull distribution law and the analytical expression for probability density of the lows for given distribution function of random value and fixed scope of sampling. Main results. The lows yielded by statistical simulation are more conservative than those yielded by the analytical formula. The margin in terms of the number of cycles to failure stipulated as 10 in several regulatory documents seems to be somewhat unsubstantiated. This margin is too great in the low-cycle domain and too small in the high-cycle one. Conclusion. This paper postulates the existence of guaranteed maximum and minimum values for mechanical properties of structural materials, namely temporary resistance and relative cross-section tapering. These values were applied to well-known analytical curves of fatigue, which finally yielded possible variation ranges for fatigue life at various amplitudes of conditionally elastic reduced stresses, assuming the existence of a certain shift in the sensitivity limit of fatigue life distribution. These data were further used to establish standard deviations and mathematical expectations for the number of cycles to failure.

Features of structure and properties formation in welded joints made of A500C and B500C strength classes reinforcing steels

In the manufacture of welded reinforcing mesh, rolled products of various strength classes are used. High requirements for mechanical properties and structural condition are imposed on welded joints. Connections must provide a set of operational properties. This article presents the results of studies of the structure and mechanical properties of welded joints of reinforced rolled products of strength classes A500C and B500C, performed by spot welding. It is established that the weld (core) of A500C strength class steel is characterized by the presence of a layer of cast metal (hardness 180–190 HV) with slag inclusions. In the heat-affected zone, widmanstett ferrite and bainite — like structures with a hardness of 251–268 HV are observed. The temporary breaking resistance of A500C steel joints is 322–350 MPa. It is shown that the welded joint of steel of strength class B500C does not have a clear division into structural zones. Similar bainite structures in the form of batch formations are observed in the seam and the heat-affected zone. The hardness of the metal of the welded joint is in the range from 205 to 241 HV, and the level of temporary resistance is 510–525 MPa. It is established that the probable cause of premature failure of welded joints of A500C steel is the presence of large slag formations in the metal seam (core). This may be due to insufficient cleaning and preparation of the weld site. Particles of scale and other contaminants fall into the molten metal of the core and "freeze" in it, forming slag inclusions. Cavities filled with slag reduce the cross-section of the seam and as a result significantly weaken it. In addition, slag inclusions are additional stress concentrators and act as a source of destruction when an external load is applied. For the manufacturer of reinforcing nets, it is proposed, as a technological recommendation, to use additional tools for cleaning the welding site in the form of metal brushes or abrasive tools with additional surface degreasing.

Polycythaemia vera: molecular genetics, diagnostics and therapeutics.

Polycythaemia vera is one of several classical myeloproliferative neoplasms that may occur in a juvenile onset or late-onset adult forms. It is linked to specific genetic mutations that cause a deleterious elevation in the patient's red cell mass. The discourse on genetics includes an exposé on the molecular biology of the disease and how a shared JAK2 V617F mutation can co-exist among three distinct neoplasms. Concepts of genetics and immunology help define the origin and behaviour of the disease: the tracking of allele burdens of mutations (genetic dosage), the timing or order of acquired mutations, the import of bystander mutations and the onco-inflammatory response; all theories are invoked to explain the progression of disease severity and potential transformational leukaemia. The World Health Organization's diagnostic criteria are accessed to focus on the subtleties of the Hb laboratories and sifting through the challenging listing of differential diagnoses that mimic PV, and our report includes an overview of manual and automated phlebotomy (erythrocytapheresis) procedures, enumerating their clinical indications, significance of temporary phlebotomy resistance and optimizing safety/ efficacy, quality and cost. Stratification of low and high-risk disease distinguishes when to commence chemo-cytoreductive therapy in the high-risk patient to prevent thrombotic complications. Drug resistance is circumvented by artfully switching drugs or using novel drug designs.

Wind Resistant Analysis of 5000m Hyperbolic Parabolic Spatial Mixed Cable Suspension Bridge

Combined with the engineering background of a 5000-meter Strait Suspension Bridge, the configuration study of the hyperbolic parabolic space cable suspension bridge was carried out, and the ANSYS finite element analysis model was established to analyze and study the structural internal force and dynamic modal characteristics. The research shows that the hyperbolic parabolic space mixed cable suspension bridge has excellent spatial stiffness and wind stability performance, its torsional frequency and torsional frequency ratio are significantly improved, the critical wind speed of flutter is greatly improved. In order to further improve the wind stability of the hyperbolic parabolic space mixed cable suspension bridge, temporary wind resistance cable measures adopted during strong typhoons are proposed. This method can ensure that the 5000-meter-level hyperbolic parabolic space mixed cable suspension bridge has the ability to withstand 120 m / s rare extreme typhoons.

СТРОЕНИЕ СНЕЖНОЙ ТОЛЩИ НА КОЛЬСКОМ ПОЛУОСТРОВЕ

In 2016–2019, the structure of the snow thickness in the northern and central parts of the Kola Peninsula (from the Barents Sea to the Khibiny Mountains) was studied in tundra, forest-tundra, taiga, high–altitude Arctic and other landscapes during the periods of maximum recrystallization of the snow (February–April) and initial snow accumulation (October). 37 borings were made in the snow thicknesses. 399 snow layers of different ages and genesis were examined. In the total, 399 measurements of the density, porosity, structure of snow (size and shape of ice crystals) and texture (orientation of crystals and pores) of snow layers, 413 measurements of temperature at the contacts between snow layers, 46 measurements of the temporary resistance of the layer to rupture, 27 measurements of the time resistance to compression, 119 measurements of the resistance of the snow layer to horizontal sounding (with a cross-shaped tip that allows taking into account the anisotropy of the snow layer) were performed. The percentage of crystals of different classes of shapes in the layer was determined. It was found that the Kola Peninsula has a high rate of evolution of the snow thickness. Even in multi-snow winters (including the landscapes of high-altitude Arctic deserts in Khibiny and Monche-tundra) in March, up to 90% of the snow thickness is made up of snow layers with a columnar and fibrous texture, composed of ice crystals of semi-skeletal and skeletal classes of shapes with a diameters of up to 4 mm. These patterns of the evolution are typical for the Arctic and Subarctic (confirmed by studies on the Yamal Peninsula, in the lower reaches of the Northern Dvina River and in Karelia). Values of the strength characteristics of the snow layer (time resistance to rupture, resistance to compression, and to horizontal sounding with regard for the anisotropy of the snow layer texture) are the lower, the higher the content of crystals in the layer of the highest stages of evolution (skeletal) and the more developed the texture of the layer. The lowest values of strength characteristics were observed in snow layers with a fibrous texture.

ПРО МОЖЛИВІСТЬ ПРОГНОЗУВАННЯ МЕХАНІЧНИХ ВЛАСТИВОСТЕЙ ХОЛОДНОДЕФОРМОВАНИХ МЕТАЛОВИРОБІВ ЗІ СТАЛЕЙ ПЕРЛІТНОГО КЛАСУ

In accordance with the latest global trends and modern needs of hardware factories, the demand for wire rod made of pearlitic steels has significantly increased, which can undergo cold plastic deformation with large degrees of reduction and is intended for the manufacture of various commercial products (cold-worked reinforcement, reinforcing ropes, spring wire, steel cord, wire for high pressure hoses, construction fiber, etc.). The most promising direction for increasing the strength class of hot-rolled steels is strain hardening during cold plastic deformation. The structure of cold-worked steels has a more uniform distribution over the cross-section, in contrast to thermally hardened ones, which in the latter case are characterized by annular structural zones formed due to different mechanisms of austenite decomposition. In a number of cases, structural heterogeneity causes instability of the mechanical properties of rolled steel, therefore, there is currently no alternative way to strain hardening. The manufacture of high-strength cold-worked metal products is a complex process and depends on the quality of the wire rod. If the cold-worked hardware does not meet the requirements of the normative documentation for the strength class, then it is no longer possible to ensure the correction of this defect using heat treatment. In this regard, scientific and practical interest has arisen to determine the possibility of creating a method for predictive determination of the mechanical properties of cold-deformed metal products made of pearlitic steels. The features of the influence of cold plastic deformation by on the formation of the strength class of pearlite grade steels with a carbon content of 0.7…0.9 % are considered It is established that the temporary resistance to fracture, at the known parameters of structure and carbon content, lends itself well to mathematical calculations and allows to create predictive models. According to the results of the research, a computer program was created that allows to automatically calculate the energy parameters of drawing and determine the tensile strength of the wire after depending on the total relative compression, parameters of the structure of wire rod and the carbon content in the steel.

Environmental pollutants induce noninherited antibiotic resistance to polymyxin B in Escherichia coli.

Aim: The mechanisms behind antibiotic resistance by bacteria are important to create alternative molecules. Objective: This study focuses on the impact of environmental pollutants on bacterial resistance to antibiotics. Materials & methods: The effect of various environmental pollutants on noninherited bacterial resistance to antibiotics was examined. Results: The tolerance to the polymyxin-B antibiotic was shown to be conferred to Escherichia coli, by pretreatment with subinhibitory concentrations of environmental toxicants. The cell survival to a sublethal dosage of antibiotics was tested. Exposure to low concentrations of toxic compounds (500ppb copper, 2% [v/v] ethanol or 0.5μg/ml trimethoprim) stimulated the bacterial heat shock systems and led to increased tolerance to polymyxin B. Conclusion: Environmental pollutants induce a temporary bacterial noninheritable resistance to antibiotic.

The progress of type II persisters of Escherichia coli O157:H7 to a non-culturable state during prolonged exposure to antibiotic stress with revival being aided through acid-shock treatment and provision of methyl pyruvate.

Persisters are a form of dormancy in bacteria that provide temporary resistance to antibiotics. The following reports on the formation of Escherichia coli O157:H7 E318 type II persisters from a protracted (8days) challenge with ampicillin. Escherichiacoli O157:H7 followed a multiphasic die-off pattern with an initial rapid decline (Phase I) of susceptible cells that transitioned to a slower rate representing tolerant cells (Phase II). After 24h post-antibiotic challenge, the E.coli O157:H7 levels remained relatively constant at 2 log CFU/mL (Phase III), but became non-culturable within 8-days (Phase IV). The revival of persisters in Phase III could be achieved by the removal of antibiotic stress, although those in Phase IV required an extended incubation period or application of acid-shock. The carbon utilization profile of persister cells was less diverse compared with non-persisters, with only methyl pyruvate being utilized from the range tested. Inclusion of methyl pyruvate in tryptic soy agar revived non-cultural persisters, presumably by stimulating metabolism. The results suggest that persisters could be subdivided into culturable or non-culturable cells, with the former representing a transition state to the latter. The study provided insights into how to revive cells from dormancy to aid enumeration and control.

Аналіз та гармонізація національних до міжнародних стандартів якісних показників чавунів з вермикулярним графітом

Ensuring and coordination of high quality indicators of materials in the foundry industry is necessary in the development of Ukraine's economy. High quality products need to be enshrined in new national standards, harmonized with international and European standards. Thus, the purpose of this work is to analyze national and international standards for quality indicators of vermicular graphite iron and their harmonization with each other. The foundry industry of Ukraine has developed mainly with the use of interstate standards - GOST, which differ significantly from European and international and requires coordination and other approaches to the development of new standards. Today there are a number of international standards: ISO, SAE, CEN, VDG, ASTM, JIS, GB, STAS, which regulate the properties of cast iron with vermicular graphite. Most standards define the range of permissible content of spherical graphite (0… 20%) in the structure of cast iron with vermicular graphite, as well as determine the shape of samples to determine the properties and provide for the determination of graphite on surfaces formed after machining castings. In accordance with the needs of the automotive industry, the Society of Automotive Engineers (SAE) has created the standard SAEJ1887 JUL2002 for cast iron with vermicular graphite. The DSTU standard in force in Ukraine regulates only the temporary resistance to tensile and elongation laid down in the brand designation. Thus, the improvement, provision and harmonization of the national standard at the vermicular graphite iron by achieving high quality indicators of materials in the foundry industry, will ensure the stability of the technological production process, and further entry into international and European markets and a qualitatively new level of domestic engineering. An analysis of the current standards in Ukraine DSTU for cast iron with vermicular graphite is given, as well as its regulated mechanical properties and recommended chemical composition. The properties of similar international and European standards for cast iron with vermicular graphite according to ISO, SAE, CEN, VDG, ASTM, JIS, GB, STAS standardization are analyzed, as well as cross-references to ISO 16112 to other standard brands of the vermicular graphite iron. The conformity of brands of materials, depending on their chemical composition and mechanical properties given in GOST, international and European indicators is found out.

Pulse potential method-assisted construction and regulation of a trivalent chromium conversion coating on hot-dip coated steel sheet

A pulse potential method (PPM) was used to regulate the formation of Cr(III) conversion coating (TCC) on hot-dip Zn-55 % Al-1.6 % Si. The micromorphology analysis and the contact angel measurement showed that the application of PPM changed the micro-features and hydrophobicity on the surface of TCC. Surface XPS analysis indicated that PPM increased the proportion of hydroxides and greatly reduced the content of Cr(VI) on TCC. Better corrosion resistance of the TCC was measured using multiple electrochemical methods when the pulse square-wave potential Ep = −0.10 V. The results corroborated the positive role of PPM in improving the temporary corrosion resistance of hot-dip coating.