Condition Of Surface Layer Research Articles

Fine evaluation of surface integrity of hardened 1.4418 stainless steel after finish dry turning

1.4418 hardened stainless steel (SS) is widely used in mechanical engineering because of its high functional properties. They can also be enhanced by procuring improvements in the state of the surface layer (SL) and, above all, in the factors of its strengthening, among others the average size of coherent scattering regions (ASCSR), dislocation density (DD), residual stresses (RS) of first and second orders, and relative micro-deformations of the crystal lattice (RMCL). This study investigates the effect of cutting speed (vc) ranging from 100 to 250 m/min and feed rate (f) ranging from 0.005 to 0.25 mm/rev on the indicators of SL condition after finish turning the steel tested. A reduction in ASCSR values below 8 nm was obtained for vc = 100–135 m/min, while an increase of ~ 20% was obtained for 180–250 m/min and with the f ranging from 0.2 to 0.25 mm/rev. An increase in RMCL of ~ 90% was registered for vc = 170–230 m/min and f = 0.2–0.25 mm/rev. A decrease in DD below 109 cm−2 was obtained for vc = 180–250 m/min and its ~ 25% increase for vc = 100–135 m/min. A high correlation between ASCSR and DD was shown. In the deformed material, the dislocation’s resistance to motion increases in proportion to the increase in its density. A high linear correlation coefficient in the range of 0.8–0.9 is found between ASCSR, DD, and first-order RS on the one hand, and Sa and Sz surface texture parameters, which are used in the industry to assess product quality, on the other. Additionally, the effect of plastic side flow (PSF) was observed and described. When machining with vc = 119 m/min and f = 0.22 mm/rev, the intense plastic deformation of the material causes outflow and shearing of the surface micro-hills. Favorable compressive stresses (below − 100 MPa) were registered in the range of vc = 225–250 m/min at f = 0.005–0.05 m/rev and 0.2–0.25 mm/rev, as well as vc = 115–180 m/min and f = 0.05–0.17 mm/rev. The study proved the existence of a relationship between the cutting parameters and indicators of the thin crystalline structure of SL. This means that by proper controlling of these parameters, it is possible to obtain such a state of the SL workpiece, which will ensure its long-term use.

Large Deflection and Post-Buckling Analysis of Cantilever Nanorods Including Effects of Couple and Surface Stresses by Intrinsic Coordinate Finite Elements

This paper presents a novel approach to the analysis of large deflection and post-buckling behavior of cantilever nanorods under different load conditions. The proposed approach utilizes a variational method, incorporating the Gurtin–Murdoch surface elasticity theory and the consistent couple stress theory to account for size-dependency effects. By accounting for the strain energy contributions of the bulk material, surface layer, and load conditions, this approach expresses the behavior of the nanorods in terms of their intrinsic coordinates. A finite element method was used to solve this numerical problem, generating a system of non-linear equations that were iteratively solved using the Newton–Raphson method. The results obtained from the finite element method were confirmed by those from the shooting method. Also, it highlights the effectiveness of the variational model in predicting the large deflection and post-buckling behavior of cantilever nanorods while considering both surface stress and couple stress effects. Furthermore, the study investigated the influence of surface stress and couple stress on the response of the nanorods to point and uniform loads. The results showed that incorporating both effects enhanced the stiffness of the nanorods compared to scenarios in which these effects were neglected. In addition, the couple stress effect was found to have a greater influence on the stiffening of nanorods for the same value of unitless parameters compared to surface stress effects. These findings offer valuable insights into the large deflection and post-buckling behavior of cantilever nanorods and highlight the importance of surface stress and couple stress effects. The model proposed in this study has potential applications in advanced technological device designs by providing a comprehensive understanding of the mechanical response of nanorods, allowing for more accurate predictions and enhanced device performance.

Многокритериальная оптимизация операционных режимов технологических процессов

The issues that are rarely combined in one small study are viewed. First of all, this is a well-known problem of engineering support of a specified quality of hardened steels surface layer using a blade tool made of superhard materials and the state of microclimate of operating areas of metal-cutting machines. It had a shot at creating a mathematical model that combines these two objective functions. As a mathematical tool that allows optimizing the modes of finishing and fine turning, the linear- programming technique was applied, which visualises through its graphic image, a picture of the influence of the engineering constraints included in the model on the optimal values of the cutting speed and feed. On the basis of analytical studies, the dependences of the formation of hydrogen sulfide vapors in the operating areas of metal-cutting machines using sulfofresols of various brands as lubricating and cooling fluids were obtained. Theoretically, it has been established that the maximal influence on the intensity of hydrogen sulfide vapor formation is exerted by the temperature in the cutting zone, which is more effected by the lathe turning speed. The paper presents empirical dependencies ratios that allows finding an average temperature in the cutting zone in the process of various steels treatment, as well as high-strength alloys and non-ferrous alloys. The roughness and the degree of cold work coefficient were taken as parameters of the surface layer condition for cylindrical surfaces, which decisively determine the durability of the products under conditions of friction and cyclic loads. Testing of the obtained mathematical models made it possible to obtain optimal values of feed and cutting speed for finishing and fine turning of hardened steels 45 and 65G.

Effect of grinding conditions of gears made of 20MnCr5 steel after single-piece flow heat treatment on the condition of the surface layer of the tooth working surface

The paper investigated the effect of selected processing conditions during gear grinding on the value and distribution of microhardness and residual stress formed in the technological surface layer of gears after thermochemical treatment (TCT) conducted by a continuous single-piece flow method.The gears were carburised with LPC at 920C, then quenched in a 4D Quenching chamber at 7 bar and tempered at 190C for 3 hours. In the next step, the working surfaces of the gear teeth were ground by supplying grinding fluid (GF) to the grinding zone using the WET method and the MQL method with a minimum amount. Measurements were made on the distribution of microhardness and residual stress formed in the technological surface layer of gears after thermochemical treatment and after the grinding process.The results of the study showed the influence of workpiece speed vw and the method of delivery to the grinding zone GF on selected parameters describing the condition of the technological surface layer of the teeth of gears made of 20MnCr5 steel. The grinding process with a white aluminium oxide grinding wheel causes deterioration in the material's residual stress state. For each of the three analysed workpiece speeds vw, smaller changes in microhardness with respect to the microhardness of the material before grinding occur in the surface layer of samples ground with GF fed with the MQL method. Similarly, residual stress values are in the area of favourable compressive stresses.Environmental considerations and the need to comply with increasingly stringent environmental protection and worker safety regulations are pushing researchers and entrepreneurs to completely eliminate or reduce the consumption of grinding fluids in the grinding process. Based on the research and analysis carried out in this study, it was concluded that applying minimum GF by the MQL method could be an alternative to the conventional WET method.In sustainable manufacturing, it is extremely important to produce high-quality items while reducing the cost of manufacturing and taking care of the environment and workers' health. This includes the manufacture of gears, a basic component used in gear transmissions in the automotive industry, for example. The research has established that it is possible to use the MQL method, which reduces the amount of GF used when grinding the working surfaces of gear teeth, as an alternative to the conventional WET method.The conducted research was the first to determine the most favourable conditions, in terms of the obtained residual stresses and microhardness, for grinding the working surface of gear teeth using the MQL method.

Investigation of Surface Layer Condition of SiAlON Ceramic Inserts and Its Influence on Tool Durability When Turning Nickel-Based Superalloy

SiAlON is one of the problematic and least previously studied but prospective cutting ceramics suitable for most responsible machining tasks, such as cutting sophisticated shapes of aircraft gas turbine engine parts made of chrome–nickel alloys (Inconel 718 type) with increased mechanical and thermal loads (semi-finishing). Industrially produced SiAlON cutting inserts are replete with numerous defects (stress concentrators). When external loads are applied, the wear pattern is difficult to predict. The destruction of the cutting edge, such as the tearing out of entire conglomerates, can occur at any time. The complex approach of additional diamond grinding, lapping, and polishing combined with an advanced double-layer (CrAlSi)N/DLC coating was proposed here for the first time to minimize it. The criterion of failure was chosen to be 0.4 mm. The developed tri-nitride coating sub-layer plays a role of improving the main DLC coating adhesion. The microhardness of the DLC coating was 28 ± 2 GPa, and the average coefficient of friction during high-temperature heating (up to 800 °C) was ~0.4. The average durability of the insert after additional diamond grinding, lapping, polishing, and coating was 12.5 min. That is superior to industrial cutting inserts and those subjected to (CrAlSi)N/DLC coating by 1.8 and 1.25 times, respectively.

Influence of Surface Layer Condition of Al2O3+TiC Ceramic Inserts on Quality of Deposited Coatings and Reliability during Hardened Steel Milling

The specific features of the destruction of tool ceramics, associated with structural heterogeneity and defects formed during diamond grinding, largely determine their reduced reliability (dispersion of resistance). This is most pronounced at increased heat and power loads on the contact surfaces and limits the industrial application of ceramic cutting tools. The surface layer of industrially produced Al2O3+TiC cutting inserts contains numerous defects, such as deep grooves and torn grains. During the milling of hardened steels of the 100CrMn type with increased cutting parameters, the “wear–cutting time” curves have a fan-shaped character with different wear rates. The resistance of the tool that was taken from one batch before reaching the accepted failure criterion has a significant variation in values (VarT is 30%). The study is aimed to evaluate the influence of the condition of the surface layer of Al2O3+TiC inserts processed by various types of abrasive treatments, such as diamond grinding, lapping and polishing, on the quality of the (TiAl)N and (TiZr)N coatings and the reliability of prefabricated end mills. The obtained “wear–cutting time” curves are characterized as closely intertwined bundles. The coefficient of resistance variation (the tool’s reliability) decreases by more than two times (14%). This can be used further in coating development to improve the performance of CCT.

Calculation model of the stressed state of the tooth contact zone of surface-hardened gears

Stress state of the surface layer in the contact zone of mating teeth of cylindrical gears has been studied. It is established that stressed state of contact surfaces in the meshing pole of mating teeth is characterized not only by surface contact stresses, but also by deep equivalent stresses. It is shown that under contact loading the stressed state of surface layer is heterogeneous and changes with distance from the surface. Analysis and substantiation of calculation model for stressed state of diffusion layer in contact zone of mating teeth of surface-hardened gears are performed. Value of coefficient, which takes into account influence of normal stresses on efficiency of tangential ones, is specified. Reliability and validity of model of calculation of stressed condition of surface layer in contact zone of mating teeth of surface-hardened gears were estimated according to results of full-scale bench tests of the gears made of cemented steel 20ХГНР. The values of contact stresses in tooth meshing pole were corrected considering the load concentration across the width of cogged ring gear. Spalling depth of damaged teeth was determined by measuring impressions taken from the teeth of each examined gear with methacrylic resin. It is established that the nucleation zone of deep contact pitting for gears with 6.5 mm module is on the depth of occurrence of calculated maximum equivalent shear stresses. The consistency of the calculation results with the experimental data shows the validity of the calculated stress-strain model for involute gears.

Mechanical surface treatment of EBM Ti6Al4V components: Effects of the resulting surface layer state on fatigue mechanisms and service life

Although additive manufacturing of the titanium alloy Ti6Al4V has been an established process for years, problems still exist with regard to the design of components subjected to cyclic loads. In this context, process-related defects play an important role, such as surface roughness and pores. Typically, AM Ti6Al4V components are machined and subjected to a hot isostatic pressure (HIP) treatment, which, however, strongly limits the cost advantage. Mechanical surface treatment processes can be used locally where high loads are expected and thus make a cost-effective contribution to the service life of additively manufactured components. In the present work, the influence of the mechanical surface treatment process of deep rolling (DR) on the surface state of electron beam melted (EBM) and EBM+HIP components is investigated. In addition, rotating bending tests are presented in SN curves and these are evaluated in the context of the surface layer condition and the failure mechanisms. The fatigue strength could be improved from RAB=157MPa in the as built state (AB) to RAB+DR=251MPa in the deep rolled state (AB+DR). Through the deep rolling treatment, the surface could be strengthened to the extent that the location of the failure shifts into the component volume. The comparison of the fracture surfaces analysis of deep rolled samples shows that pores below the surface are the cause of failure, in a depth that is not influenced by the mechanical surface treatment. In an additional series of tests, the fatigue strength of the HIP and deep-rolled (HIP+DR) state was determined. Since HIP EBM specimens are nearly pore-free, the failure mechanism switches back to the strengthened surface, resulting in an increased fatigue limit of RHIP+DR=413MPa.

Influence of deep rolling on surface layer condition and fatigue life of steel welded joints

Deep rolling is an established mechanical surface treatment method to modify surface and subsurface properties and increase the wear- and fatigue strength of metallic parts and components. However, until now, deep rolling has not been considered for use as a post treatment method of welded joints to extend fatigue life of steel constructions. In this study, butt joints made of construction steels S355J2+N and S355G10+M were treated by means of hydrostatic deep rolling with tool diameter. The surface and subsurface properties after treatment were quantified by roughness-, hardness and residual stress measurements. Reduced roughness of 50–80%, increase of surface near hardness of up to 45% and compressive residual stresses of up to -1,000MPa were determined after deep rolling. Furthermore, the stress concentration factor of the weld toe was evaluated for each specimen based on surface scans. Due to the comparable low contact force of the deep rolling tool-process parameter combinations investigated, the stress concentration of the weld toe was mostly unaffected by deep rolling. However, a significant fatigue life improvement by deep rolling was determined for all test series, showing a maximum increase of FAT-class of approximately 60%. A tendency is shown that a higher tool diameter leads to higher fatigue life improvement.

The Influence of the Depth of Grinding on the Condition of the Surface Layer of 20MnCr5 Steel Ground with the Minimum Quantity Lubrication (MQL) Method.

This paper describes the research on abrasive machining conditions and their influence on microhardness and residual stresses distribution in the technological surface layer of 20MnCr5 steel. The roughness of ground samples was also measured. Samples underwent a vacuum carburizing process (LPC) followed by high-pressure gas quenching (HPGQ) in a 4D quenching chamber. Processes were realized with a single-piece flow method. Then, the flat surfaces of samples were ground with a Vortex type IPA60EH20VTX alumina grinding wheel using a flat-surface grinder. The samples were ground to three depths of grinding (ae = 0.01; 0.02; 0.03 mm) with grinding fluid supply using either flood method (WET) or minimum quantity lubrication (MQL) method. The condition of the technological surface layer was described using microhardness and residual stresses, as well as some selected parameters of surface roughness. The results obtained revealed that changes in microhardness as compared to microhardness of the material before grinding were lower in samples ground with grinding fluid supplied with MQL method. At the same time, the values of residual stresses were also better for samples ground using MQL method. Furthermore, the use of grinding fluid fed with MQL method produced lower values of surface roughness compared to the parameters obtained with WET method. It was concluded that for the tested scope of machining conditions, the MQL method can be a favourable alternative to the flood method of supplying grinding fluid into the grinding zone.

ОПТИМІЗАЦІЯ РЕЖИМІВ РІЗАННЯ НА ВЕРСТАТАХ ГНУЧКИХ ВИРОБНИЧИХ СИСТЕМ

The main problem of manufacturing products in conditions of flexible automated production is the achievement of high quality indicators of parts, such as accuracy characteristics, surface roughness and surface layer condition. Obtaining of high quality parts in modern technological systems requires the study of specific features of flexible production. Frequent readjustment of equipment, replacement of tools, redistribution of characteristics of the elastic system of machine tools, the production of parts from materials of different workability determine the variablenature of the accuracy parameters of products manufactured in flexible manufacturing systems (FMS). In addition, the difficulties associated with the full automation of the technological process are added: automatic basing and fixing of workpieces and tools, transfer and reorientation of parts for processing on various machine modules, accumulation of errors when basing blanks on satellites, branching of dimensional connections of multipurpose machines, inaccuracies of automatic adjustment and positioning of the tool, the need for active control of the treated surface and the condition of the cutting tools, providing feedback between real and specified accuracy, automatic maintenance of thermal characteristics of machine equipment, ensuring optimal cuttingmodes for all FMS machines. The solution of most of these problems is achieved through adaptive management of the processes in order to obtainspecified indicators of processing quality. Designing the optimal technological process under changing conditions of flexible production is a very difficult task, due to the multivariate technology of processing parts included in the group. Meanwhile,in the theory of group production there are methods to optimize the process of choosing the right technological solution. With the optimization of group technologies, it is necessary to be able to specialize in real production. On the first stage on the basis of advanced technological processes, it is necessary to create a type for the development of technological processes. The cost of developing such processes is insignificant, so that the technology is widely implemented. In the process of developing group technological processes of machining complex parts or a complex combination of surface elements of a part in order to ensure the efficiency of the process, it is necessary to solve the problem of optimizing machining parameters in accordance with accepted optimality criteria and taking into account the main technical limitations. At the same time, it is considered as the optimization of constantly set, for a specific instrumental group adjustment, processing modes using the methods of mathematical modeling and automated information processing, and continuous optimization with the help of control systems for technological equipment, which are part of the FMS. Therefore, the problem of calculating and optimizing cutting modes on interconnected FMS machines is extremely urgent. At the same time, not the most intense modes are considered optimal, but just those that ensure the stable operation of the FMS for a long time.

Transformation Plasticity in Carbonitrided PM-Steels: Quantification of Plasticity Effects in Dependence of the Part Density*

Abstract To optimize heat treatment processes of case hardened components, heat treatment simulations are used to predict surface layer conditions. Only a precise knowledge and modelling of the transformation processes allows a trustworthy prediction of the hardness and residual stresses in the surface zone. The transformation plasticity mechanism plays an essential role in the heat treatment process and its correct simulation has a significant influence on the resulting calculated residual stress profiles and component distortion. Without considering transformation plasticity, simulative residual stresses are significantly overestimated [1]. In this work, powder metallurgical components are pressed and sintered and subsequently carbonitrided for a dilatometric investigation to characterize the correlation between transformation plasticity effect and the density. The results show a dependence of the austenite-martensite volume change that led to a significant difference of 0.5 Vol-%. A model describing the martensite volume change with respect to density is proposed. This also affects the description of the transformation plasticity constants (K) between K = 5 – 6 × 10–5 MPa–1 in dependence of density. With currently available data, the effect of chemical composition and density cannot be separated and quantified and further studies are therefore necessary to allow such a refinement.

Influence of structure formation and properties of bimetal produced by ultrasound-assisted explosive welding

The aim of this paper was to study how ultrasonic vibrations during explosive welding influence the formation of the structure and properties of bimetal plate. The effect of changes in joint formation kinetics and in the structure and properties of the bimetal plate formed by explosive welding assisted by ultrasonic vibrations was determined. Ultrasound-assisted explosive welding resulted in improved strength and microhardness and decreased wave parameters and molten metal amount in the wave vortex areas compared to explosive welding without ultrasound. The influence of the propagation scheme, frequency and amplitude of the ultrasonic vibrations on the structure and property formation of the bimetal plate during explosive welding was demonstrated. The results of the influence of ultrasound on the weldable zone of dissimilar metals are discussed. Ultrasonic treatment of metal produces a decrease in yield stress, which results in modified metal surface layer properties and conditions for joint formation of collided plates during explosive welding.

Experimental and Numerical Investigation of the Surface Layer Conditions after Carbonitriding of Powder Metallurgical Steels. Part 2: Surface Layer States in Components of Graded Porosity

Abstract Case hardening processes such as carbonitriding can be used to improve the performance of powder metallurgical (PM) structural components. The partially open porosity of these components leads to a significant increase in diffusion, which in turn leads to a change in the element gradient in the surface layer (and consequently the surface layer state) compared to melting metallurgic materials. Within the scope of a two-part work, the surface layer states in common densities are investigated after the case hardening process. The present part 2 comprises the characterisation of the resulting surface layer states depending on the carbon and nitrogen profile and the tempering heat treatment. Through the deep rolling and the subsequent carbonitriding treatment, hardness of up to 850 HV0.1, retained austenite contents of up to 25 vol-% and residual stresses of up to –300 MPa are determined across densities. The extensions to the numerical models described in this paper enable the FE model to predict the surface layer states in a wide range of process combinations and densities with an error tolerance of ±20 %.

The Present State of Surface Conditioning in Cutting and Grinding

All manufacturing processes have an impact on the surface layer state of a component, which in turn significantly determines the properties of parts in service. Although these effects should certainly be exploited, knowledge on the conditioning of the surfaces during the final cutting and abrasive process of metal components is still only extremely limited today. The key challenges in regard comprise the process-oriented acquisition of suitable measurement signals and their use in robust process control with regard to the surface layer conditions. By mastering these challenges, the present demands for sustainability in production on the one hand and the material requirements in terms of lightweight construction strength on the other hand can be successfully met. In this review article completely new surface conditioning approaches are presented, which originate from the Priority Program 2086 of the Deutsche Forschungsgemeinschaft (DFG).

Wear Model of Sliding Rough Surfaces

Purpose of research.To develop a wear model that takes into account the quality parameters of the surface layer and friction conditions, which will allow, through controlled technological action, providing the required wear intensity of friction surfaces.Methods.Electromechanical processing, in particular, can provide the required intensity of friction surfaces wear being carried out in finishing and strengthening modes.An increase in wear resistance, endurance limit and other operational properties, and at the same time a change in the physical, mechanical and geometric parameters of the surface layer of parts is achieved by a combination of thermal and force influences on the surface of the processed part. To achieve this effect, an original installation has been developed, which includes a device for machining based on a universal machine with a set of necessary tools and devices for fixing a workpiece and supplying coolant and electric current of high power and low voltage, as well as an industrial electric current converter and control units for processing modes, switching devices and computers.Results.An approach to the representation of the nature of friction and wear has been proposed. Based on the proposed wear model, which takes into account the quality parameters of the surface layer and friction conditions, it is possible to provide the required wear intensity of friction surfaces through controlled technological action.The developed wear model, which takes into account the quality parameters of the surface layer and friction conditions, makes it possible to provide the required wear intensity of friction surfaces through controlled technological action.Conclusion.The calculated data obtained with the help of the developed model and the data obtained experimentally will find practical application in creating resource-saving processes for processing metal alloys and composite materials.

High-cycle fatigue and surface layer stability of case-hardened PM-steels with graded porosity

ABSTRACT In order to increase the fatigue performance of mechanically loaded PM-components, case hardening procedures can be used to improve the surface layer states in terms of hardness and residual stress. In this work, the effects of carbonitriding treatment on two typical PM-steels with multiple densities are investigated in terms of their surface layer state (hardness, residual stress and retained austenite) before and after fatigue testing and their resulting pulsating fatigue performance. The results confirm fatigue strengths that can be formulated linearly as a function of porosity as well as a cyclic stability of the surface layer condition at loads below the fatigue strength. Further optimisation of the fatigue strength can be expected by tailoring the surface layer with respect to residual stresses. Comparisons to other studies are difficult due to many process parameters, different load cases and limited data, but indicate comparable fatigue strengths.

Experimental and Numerical Investigation of the Surface Layer Conditions after Carbonitriding of Powder Metallurgical Steels. Part 1: Diffusion in Components of Graded Porosity

Abstract Case hardening processes such as carbonitriding can be used to improve the performance of powder metallurgical structural components. Due to the amount of carbon and nitrogen introduced, it is possible to adjust the hardness and residual stress of the surface layer. Due to their porosity, powder metallurgical components show a significantly increased diffusivity and therefore increased demands on the process control. In order to be able to make a quantitative statement about the effects of diffusivity as a function of porosity, common densities of 6.9 g/cm3, 7.2 g/cm3and 7.35 g/cm3for PM-steel are examined in a total of ten process sequences. By means of simulative approaches, the resulting element depth profiles can be calculated and the surface layer condition can be predicted by a subsequent heat treatment simulation. In a two-part work, the mass transport during carbonitriding is investigated in the first part and the resulting surface layer conditions after heat treatment in the second part. By considering different process combinations and porosities, model approaches of volume and pore diffusion can be formulated and quantitative element depth profiles can be predicted and validated depending on the process parameters. ◼

The Accuracy of Finishing WEDM of Inconel 718 Turbine Disc Fir Tree Slots.

Servicing aircraft engines sometimes requires manufacturing only a single piece of a given part. Manufacturing a turbine disc using traditional methods is uneconomical. It is necessary to use a different machining method recommended for small lot production. One of the proposed methods is WEDM (wire electrical discharge machining). The article presents the results of the research on finishing WEDM of Inconel 718 turbine disc fir tree slots. The influence of infeed, mean gap voltage, peak current, pulse off-time, and discharge energy on the shape accuracy, surface roughness, microcracks, and the white layer thickness were determined. Mathematical models were developed based on the DoE (Design of Experiment) analysis. The statistical significance of the models was verified with the ANOVA (Analysis of Variance) test. The machining parameters control methods that allow achieving the required shape accuracy, surface roughness, and surface layer condition were presented. The obtained surface roughness was Ra = 0.84 μm, the shape accuracy of the slot in the normal-to-feed direction was Δd = 0.009 μm, the profile shape accuracy was Δr = 0.033 μm, and the thickness of recast (white) layer was approximately 5 μm.

Interannual variability of parameters of the Arctic Ocean surface layer and halocline

As the area of the sea ice cover has considerably reduced in the recent years, the Arctic Ocean surface layer has become more exposed to the effect of atmospheric processes. In order to evaluate the influence of the new conditions on the surface layer state, a large array of winter oceanographic data was used to calculate the Arctic Ocean mixed layer thickness and salinity along with the thickness and salinity of the halocline layer for the 1950-2013 period. Analysis of the interannual variability of the surface layer parameters listed has shown that the mixed layer thickness has increased in recent years, from 30-35 m in 1950-70s to 40-44m in 1980-2000s. The halocline thickness, conversely, has decreased from 65m in 1950-90s to 50 in the 2000s. At the same time, mixed layer salinity and the salinity of the halocline layer has become lower in the 2000s by about 0,5 % compared with 1950-90s. Three periods with distinctive configurations of the fields of the surface layer parameters have been identified. These quasi-20-year periods correspond to different climatic stages with different regimes of the atmospheric circulation. However, this is certainly not the only cause of the changes that occur in the surface layer condition. To reveal other causes of these changes, statistical methods were used to analyze the time series of the Arctic Ocean surface layer parameters. Linear regression equations allowed us to find out that the variability of the mixed layer thickness and salinity is almost equally determined by changes of the atmospheric circulation and fluctuations of the water exchange with the neighboring oceans along with river runoff and ice processes. At the same time, the thickness and salinity of the halocline layer strongly correlate with mixed layer parameters and, as there is no direct contact with the atmosphere, their variability is determined mostly by the mixed layer condition and the underlying Atlantic waters.