Hardened Surface Layer Research Articles

Experimental Study on Friction Characteristics of Micro-Arc Oxidation Modified Layer on Titanium Alloy Surface

In order to study the effect of microarc oxidation modification treatment on the friction properties of titanium alloy surface, the surface treatment layer of Ti-6Al-4V ELI specimen modified by Microarc oxidation surface was sampled, the surface layer hardness, roughness and treatment layer thickness were tested, the microscopic morphology was analyzed, The friction tests of TC4 substrate and micro-arc oxidation treatment surface disc with 25% glass fiber, 15% fiberglass +5% graphite and 60% tin bronze reinforced PTFE pin were carried out, and the results showed that the thickness increased slightly and the surface layer hardness increased by about 75% after the micro-arc oxidation surface modification treatment. Compared with the substrate, the surface roughness is obviously improved, and the friction coefficient of the surface treatment specimen is similar to that of the TC4 titanium alloy substrate, but the wear amount is higher than that of the TC4 titanium alloy substrate.

Surface Structure of Grade-U8 Steel after Processing by Deforming Cutting

The structure of grade-U8 steel after high speed processing by deforming cutting is studied. The phase composition and structural features of a hardened surface layer comprised of separate areas (so called ribs) in close with each other are established. While applying the methods of optical and electron microscopy in the near-tool bit area of the rib, the following features are detected: nonequilibrium ferrite and coarse acicular martensite with crystal sizes of about 100 nm, parquet martensite-like structures with plate widths of tens of nanometers, as well as cementite crystals of various sizes from 10 to 100 nm. Such a heterogeneous structural state occurs in the rib area in contact with the tool bit during processing by deforming cutting. The structure of the opposite rib area is cardinally different and comprised of equiaxed ferrite grains with a size of ~500 nm and with fine boundary depositions (presumably carbides) with a size of 10–20 nm.

Study of the Effect of a Corrosive Medium on Medium-Carbon Steel Surface Layer Microhardness Subjected to Impact Electromechanical Treatment

The influence of a corrosive medium on the transformation of strength properties of a steel 45 surface layer subjected to impact electromechanical treatment is studied. Results are provided for a study of the effect of impact electromechanical treatment regimes on the corrosion activity of strengthened specimens, estimated by the change in hardened surface layer microhardness. The nature and degree of reduction in strengthened surface layer hardness in specimens strengthened with current density j = 100, 300, and 600 A/mm2 are established in relation to corrosion test duration.

Influence of plasma torch design on cutting quality during precision air-plasma cutting of metal

Optical interferometry and metallographic analysis were used to study structure of cutting seams obtained after 09G2S steel cutting by PMVR-5 plasma torch. These plasma torches have a number of design features in the system of gas-dynamic stabilization of plasma arc. It is shown that application of new plasma torch allows obtaining higher quality of cutting 09G2S steel of medium thickness with high productivity and lower energy costs. Metallographic analysis has shown that qualitative composition of the cut surface structure is almost the same, so priority criteria for comparative quality analysis are parameters of surface microgeometry. Evaluation of this parameter shows high quality of cutting almost along the entire length of a cut, since the influence of technological features of plasma arc cut into the metal affects at a distance of less than 0.3 mm from the edge of the sheet. The use of additional methods of gas-dynamic stabilization in PMVR -5.2 plasma torch (feed symmetry with a double swirl system of plasma-forming gas) allows to achieve additional advantages in terms of surface quality compared to PMVR -5.1. A number of features that affects quality of cut when cutting metals of different thicknesses for welding, is noted depending on the angle of inclination of plasma torch during cutting. Estimates of the surface layer hardness indicate minimal deviations from the requirements of GAZPROM Standard 2-2.4-083 (instructions on welding technologies in the construction and repair of field and main gas pipelines), which allows further use of cutting seams obtained by studied plasma torches for welding without removing zones of thermal influence. Thus, application of new plasma torches makes possible precision finishing plasma cutting of metals, including production of welded joints.

The resistance of S235JR steel to cavitation erosion

The erosion resistance of S235JR steel to flow cavitation was investigated. In order to understand an influence of steel properties and cavitation intensities on the degradation mechanisms, low-carbon S235JR steel was tested in the as-received state and after thermal treatment (annealing) under four different flow velocities. Annealing decreased steel hardness, which made S235JR steel less resistant to cavitation erosion. The performed investigations showed that the state of this steel affects the degradation process, e.g. erosion rate and development of surface roughness. An increase in flow velocity caused a linear increase in erosion rate of S235JR steel in as-received state, and an exponential increase in erosion rate of S235JR steel after thermal treatment. Regardless of the state of S235JR steel, an increase in the flow velocity caused a logarithmic increase in the area with increased roughness for Ra > 0.5 μm, where Ra parameter is the arithmetic average of all profile deviations from the mean line over the evaluation length. The increase in surface roughness and the Ra parameter depended on the flow velocity. However, for high flow rates, the Rp parameter, which is the mean of the five maximum profile peak heights from the mean line over the evaluation length, represented an effect of micro-jets impacts on the surface development better than the Ra parameter. A new parameter P, which combines elongation, impact energy and hardness, has been proposed. With increased value of this parameter, the resistance to cavitation erosion decreases. The performed investigations showed that the volume loss can be described by equation in the form of ΔV = C(t)∙(v-v0)n(t), where the function C(t) describes the development of cracks in the surface layer and the function n(t) describes the development of the hardened surface layer.

The Abrasion Behaviour of X40CrMoV5-1 Steel Under Various Surface Treatments

Abstract For evolving a surface layer on the X40CrMoV5-1 steel, a plasma-nitridation and PVD coating process was applied. In our experiments, the samples were heat-treated (high-temperature hardening, annealed three times) and surface treatments (plasma-nitridation, PVD coating by TiAlN, duplex surface treating by plasma nitridation and after that, PVD coating TiAlN). After the heat treatments, we performed hardness tests and surface abrasion wear tests. The abrasion wear resistance of the specimens was studied in order to understand the heat treatment effects on abrasion behaviour. It was observed that the heat treatment and surface treatment process greatly influence the tool steel surface hardness and abrasion resistance behaviour. By plasma-nitridation the surface hardness doubled compared to the quenched surface hardness while the PVD coated TiAlN surface layer hardness is more than five times that of the hardened one. There was no relevant difference between the PVD coated (TiAlN) surface hardness and the duplex surface-treated hardness. On the basis of the results of the comparative abrasive wear tests, it can be concluded that the duplex surface treatment resulted in the greatest wear resistance..

Quantitative Representation of Mechanical Behavior of the Surface Hardening Layer in Shot-Peened Nickel-Based Superalloy.

Surface hardening treatment can usually introduce severe grain distortion with a large gradient in the surface layer. It results in mechanical properties being difficult to accurately determine through macroscopic tests due to the non-uniformity of the shot-peened material. In this study, the mechanical behavior of uniformly pre-deformed nickel-based superalloy IN718 was investigated with monotonic tensile tests and instrumented indentation tests. For the shot-peened material, the hardness distribution of the surface hardening layer after shot peening was identified through the instrumented indentation method. According to the stress–strain results of pre-deformed materials, Ramberg–Osgood model parameters could be presented with plastic deformation. Assuming the power-law relationship between hardness and plastic deformation, the plastic deformation distribution along the depth of the surface hardening layer was clarified. Based on the results, a method to identify the stress–strain relationships of hardened material at different depths was established. Finally, the finite-element simulations of the instrumented indentation test considered residual stress and strain hardening were built to verify the method presented herein. The results show that the solution to evaluate the mechanical properties of hardening layer materials in the microscopic zone is feasible, which can provide the foundation for the failure analysis of shot-peened materials.

Properties of the surface layer after high-energy treatment by powder particles

Experiments were conducted on high-energy surface treatment of a structural steel substrate with a flow of tungsten, nickel, and titanium nitride powder particles. The impact pressure of the steel target and particles accelerated by explosion energy was estimated using the momentum conservation equation and the linear equation of the particle material shock adiabat. It was found that the impact pressure of the target and particles is 62 GPa for a tungsten particle, 48 GPa for a nickel particle, and 41 GPa for a titanium nitride particle. The heating temperature of particles during their collision with the steel target surface was calculated taking into account the conditions of mass and momentum conservation at the shock wave front. The maximum heating temperature of particles at the point of their collision with the substrate surface (at a particle velocity of 2000 m/s) is 1103 K for tungsten particles, 755 K for nickel particles, and 589 K for titanium nitride particles. It was shown that the steel target strength increases when it is subjected to high-energy treatment with a flow of particles. The maximum hardening of the steel target surface layer increases by 32–55 % compared to initial microhardness and is observed at a depth of 2–4 mm from the treatment surface. Then it decreases to the value of starting material microhardness (170 HV) at a distance of 15–20 mm from the treated surface.

Development of Inelastic Deformation upon Electromechanical Treatment and Surface Plastic Deformation of Grade 45 Steel

The effect of combined surface hardening such as electromechanical treatment and surface plastic deformation exerted on inelastic deformation processes occurring in grade 45 steel has been studied. The results of tensile tests and the analysis of the mechanical hysteresis loops for samples of grade 45 steel subjected to combined surface hardening are presented. The characteristic features of the inelastic properties and microinhomogeneous deformation of steel samples are considered, depending on a regularly inhomogeneous structure of the hardened surface layer.

Experimental investigation and effects of laser hardening process parameters on microhardness of En24 steel

In presented paper through experimental investigation is carried out with fiber laser system so as to evaluate the effects of laser surface hardening process parameters on the microhardness (width and depth) of the laser treated En24 steel using a Taguchi method. The optical microscope and microhardness tester is used to examine the microstructure, microhardness (width and depth) of the laser hardened samples across the heat affected zone. The selected process parameters were laser beam power (210, 225 and 300 W), laser scanning speed (1.0, 5.5 and 10.0 mm/s) and standoff distance (175, 200 and 225 mm) respectively. The laser treated hardened surface layer has a microhardness of 728.1 HV0.3 and reached a microhardness depth of 2471.44 µm, which is twice as high as untreated samples of En24 steel. From this study, it can be summarized that the microhardness of laser treated samples is maximized by controlling laser beam power, laser scanning speed and standoff distance, which improves the service life of laser-treated En24 steel components. The percentage error within the acceptable range was found to be small and was obtained by comparing the microhardness values obtained from the experimental results and predicted microhardness values obtained by using nonlinear regression equation.

Influence of Plasma Torch Design on Cutting Quality during Precision Air-Plasma Cutting of Metal

Optical interferometry and metallographic analysis were used to study the structure of cutting seams obtained after 09G2S steel cutting by a PMVR-5 plasma torch. These plasma torches have many design features in the gas-dynamic stabilization system of the plasma arc. The application of a new plasma torch can obtain higher quality and lower energy costs of cutting medium-thick 09G2S steel. Metallographic analysis has shown that the qualitative composition of the cut surface structure is almost the same, so priority criteria for comparative quality analysis are surface microgeometry parameters. The parameter evaluation shows high quality of cutting almost along the entire length of a cut, since the technological feature influence of plasma arc cut into the metal affects less than 0.3 mm from the sheet edge. The use of additional methods of gas-dynamic stabilization in PMVR-5.2 plasma torch (feed symmetry with a double swirl system of plasma-forming gas) makes it possible to achieve additional advantages in terms of surface quality compared to PMVR-5.1. A number of features that affects cut quality when cutting metals of different thicknesses for welding depends on the inclination angle of a plasma torch during cutting. Estimates of the surface layer hardness indicate minimal deviations from the requirements of GAZPROM Standard 2-2.4-083 (instructions on welding technologies in the construction and repair of field and main gas pipelines), which allows further use of cutting seams obtained by studied plasma torches for welding without removing thermal influence zones. Thus, the application of new plasma torches for precision-finishing plasma cutting of metals, including production of welded joints, is possible.

Effects of laser hardening process parameters on hardness depth of Ck45 steel using Taguchi’s optimization technique

Laser hardening is one of the reasonable procedures utilized to improve surface mechanical and wear resistance of target materials. This process is easy to use for improving surface properties of complex shape components with minimum time requirement. The beauty of this process is that it is possible to improve only selective surface properties without altering the remaining surface properties of bulk material. Ck45 steel has various important properties like hardness, superior wear resistance and frictional performance etc. These properties are useful in various industrial applications. The existing study is an attempt to analyse results on surface properties with the aid of process parameters of a laser hardening process on hardness depth and microstructure of laser hardened Ck45 steel the use of a design of experimental approach. From this analysis, it can be summarized that the depth of the surface layer hardness is maximized by controlling the laser beam power, laser scan speed and standoff distance, which improves the service life of Ck45 steel components hardened by laser. Comparing the experimental consequences with the effects of L9 orthogonal array approach, the proportion error was observed to be negligible with a higher co-relation coefficient (r2) of 0.905.

Formation of a hard surface layer during drying of a heated porous media

We report surface hardening or crust formation, like caking, during evaporation when a porous medium was heated from above using IR radiation. These crusts had higher strength than their closest counterparts such as sandcastles and mud-peels which essentially are clusters of a partially wet porous medium. Observed higher strength of the crusts was mostly due to surface tension between the solid particles, which are connected by liquid bridges (connate water). Qualitative (FTIR) and quantitative (TGA) measurements confirmed the presence of trapped water within the crust. Based on the weight measurements, the amount of water trapped in the crusts was ~1.5%; trapped water was also seen as liquid bridges in the SEM images. Further, in the fixed particle sizes case, the crust thickness varied slightly (only 10-20 particle diameters for cases with external heating) while with the natural sand whole porous column was crusted; surprisingly, the crust was also found with the hydrophobic glass beads. Fluorescein dye visualization technique was used to determine the crust thickness. We give a power-law relation between the crust thickness and the incident heat flux for various particle sizes. The strength of the crust decreased drastically with increasing hydrophilic spheres diameter while it increased with higher surface temperature.

The Influence of the Depth of Cut in Single-Pass Grinding on the Microstructure and Properties of the C45 Steel Surface Layer.

The paper contains the results of a metallographic examination and nanoindentation test conducted for the medium carbon structural steel with low content of Mn, Si, Cu, Cr, and Ni after its grinding to a depth ranging from 2 μm to 20 μm, at constant cutting speed (peripheral speed) of vs = 25 ms−1 and constant feed rate of vft = 1 m/min. Applied grinding parameters did not cause the surface layer hardening, which could generate an unfavorable stress distribution. The increase in the surface hardness was obtained due to the work hardening effect. Microstructure, phase composition, and chemical composition of the grinded surface layer were examined using an X-ray diffractometer, light microscope, and scanning microscope equipped with X-ray energy-dispersive spectroscopy, respectively. Hardness on the grinded surface and on the cross-section was also determined. It was shown that the grinding of C45 steel causes work hardening of its surface layer without phase transformation. What is more, only grinding to a depth of 20 μm caused the formation of an oxide scale on the work-hardened surface layer. Nanoindentation test on the cross-section, at a short distance from the grinded surface, has shown that ferrite grains were more susceptible to work hardening than pearlite grains due to the creation of an equiaxed cellular microstructure, and that different dislocation substructure was created in the work-hardened surface layer after grinding to different depths.

Stress analysis of specimen with a reinforced thin layer

The paper presents an analysis of the stress state in the tensile test sample. The test sample has a hardened surface layer with chemic heat treatment – cementation. The analysis was carried out for various thicknesses of the reinforced cemented layer. If the whole thickness of the material is not cemented, the fracture is near the grip section of the specimen. The analysis results explain the cause of this fracture.

Повышение твердости поверхностного слоя малоуглеродистой стали за счет плазменной обработки модифицирующей обмазки

Повышение твердости поверхностного слоя малоуглеродистой стали за счет плазменной обработки модифицирующей обмазки

Study on the rolling friction and wear properties of surface densified powder metallurgy Fe-2Cu-0.6C material

Rolling friction and wear behaviours of a surface densified Fe-2Cu-0.6C powder metallurgy material were investigated. Results indicated that friction coefficient and wear were significantly decreased after rolling. Wear rate tended to be steady as the rolling cycle increases. Under light load, wear was caused by delamination and ploughing. Delamination crack initiated on material surface. Under heavy load, wear was caused by delamination and pits. Cracks initiated at the surface and subsurface. However, due to the hardened surface layer and a lower porosity, probability of subsurface crack initiation was reduced and crack locations were closer to surface. Crack propagation distance also was shortened. The surface densified layer plays an important role in improving the rolling wear resistance of the material.

Electron Beam Cold Hearth Melted Titanium Alloys and the Possibility of Their Use as Anti-Ballistic Materials

Three commercial titanium alloys: two-phase α+β Ti-6Al-4V (low alloyed), and T110 (Ti-5.5Al-1.5V-1.5Mo-4Nb-0.5Fe, higher-alloyed), and β-metastable Ti-1.5Al-6.8Mo-4.5Fe were melted using EBCHM approach in the form of 100 mm in diameter ingots with the weight of about 20 kg each. After 3D hot pressing at single β-field temperatures ingots were rolled at temperatures below β-transus onto plates with thickness varying from 3 mm to 25 mm. Different heat treatments, including annealing at α+β or β-field temperatures, and special strengthening Surface Rapid Heat Treatment (SRHT) which after final aging provided special gradient microstructure with a hardened surface layer over ductile basic core, were employed. Mechanical properties were studied with tensile and 3-point flexure tests. It was established that the best combination of tensile strength and ductility in all alloys studied was obtained after SRHT, whereas at 3-point flexure better characteristics were obtained for the materials annealed at temperatures of (α+β)-field. At the same time, ballistic tests made at a certified laboratory with different kinds of ammunition showed essential superiority of plates having upper layers strengthened with SRHT. The effect of microstructure of the alloys, plate thickness and type of used ammunition on ballistic resistance is discussed.

STRENGTH CHARACTERISTICS OF HYPEREUTECTIC SILUMIN AFTER ELECTRON BEAM MODIFICATION

Irradiation (SOLO installation, Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences) of hypereutectic silumin specimens of Al-(22-24)Si composition with an intense pulsed electron beam was carried out. The formation of the structure of highspeed cellular crystallization of aluminum (cell size 250-600 nm) was revealed. It was shown that the cell boundaries are strengthened by globular-shaped silicon particles (particles of size 50-70 nm). It was found that the hardness of the silumin specimen surface layer increases by more than 5 times after modification. Tensile tests of plane proportional samples showed an increase in the ductility of irradiated samples while maintaining the tensile strength.

Исследование прочностных и пластических характеристик композиционных слоев в аустенитной нержавеющей стали, подвергнутой ионно-плазменной обработке, методом наноиндентирования

One of the main issues of austenitic stainless steel is low strength properties and low wear-resistance. It can be partially or fully eliminated by the product surface modification and the creation of hardened surface layers. The ion-plasma saturation of alloys with interstitials, which is carried out in a mixture of gases with different compositions is an available and effective method of surface hardening of complex structural parts. At the same time, the mechanical and plastic characteristics of the processed materials are determined by the complex of properties of the base alloy and the hardened surface, and it is not always possible to identify their influence on the mechanical and plastic properties of each component of the composite material. The nanoindentation method allows determining local mechanical and plastic characteristics in certain areas of hardened materials (base alloy and surface) by the dynamic loading of the local microscopic areas. In this paper, using the nanoindentation method, the authors identified the mechanical and plastic characteristics of hardened layers produced by the ion-plasma treatment of austenitic 01H17N13M3 stainless steel with the grain-subgrain and coarse-grain structures. The ion-plasma treatment of steel specimens facilitates surface hardening and the formation of a composite surface layer of ≈20-25 μm in thickness. High values of nano-hardness in a composite layer are caused by the complex hardening of specimens: solid-solution hardening of austenite with nitrogen and carbon, the dispersion hardening and the formation of different nitrides and carbonitrides and the ferrite low fraction. The experimental results show that the strength properties and plasticity characteristics of such a layer strongly depend on the base material initial microstructure - the formation of a highly-defective grain-subgrain structure promotes the formation of a more enforced surface layer compared to the coarse-grained specimens.