Surface Hardening Research Articles

Content and Dispersion of Ferroalloys in the Coating During Microarc Alloying of Steel

Introduction. The main disadvantage of traditional processes of diffusion surface hardening of steel products is its long duration. Therefore, the problem of intensification of such processes is relevant. To solve it, the use of high-energy effects on the material is proposed, which allows us to obtain a hardened surface layer from a coating composed of ferroalloy powders containing alloying elements. There is no data in the literature on the required content and dispersion of such powders in the composition of the coating. The aim of this study was to select the particle size of ferroalloys and their concentration in the coating to achieve the most effective hardening of the processed product.Materials and Methods. For experimental studies, cylindrical samples made of steel 20 with a diameter of 12 mm and a length of 35 mm were used. On the surface of these samples, an alloying coating containing ferroalloy powders and an electrically conductive gel as a binder was applied. After that, the samples were immersed vertically for half their length into a metal container, which was then filled with carbon powder with a particle size of 0.4–0.6 mm. Then an electric current of 2.5 to 3.0 A was passed in the circuit power source — container — carbon powder — sample. The duration of the process was 2–8 minutes.Results. The calculated estimation of the electrical conductivity of coal powder was performed, and the thermophysical parameters of microarc heating of steel were calculated. These include the power released by electric current on the surface of the steel product, the density of the heat flux, and the energy of a single microarc discharge. The expressions for calculating the particle size of ferroalloy powder were obtained, as well as the experimental dependencies of the diffusion layer thickness on the particle size of ferroalloys and their content in the coating.Discussion and Conclusion. The results of this study have allowed us to determine the size range of ferroalloys and their content in the coating. This information is essential for optimizing the alloying process and ensuring the most efficient surface hardening treatment for steel products. The data collected will be used to develop improved technological processes for the surface hardening process, leading to improved product quality and performance.

Analyzing PEO anodization time to monitor coatings phases, composition, morphology, thickness, and microhardness during the growth of TiO2 pores on the CP-Ti surface

The objective of this study was to develop an oxide coating on commercially pure titanium using the plasma electrolytic oxidation (PEO) technique. During the surface treatment process, the time value was varied for 1, 10, 15, 30, 45, and 60 min. The PEO treatment was carried out at a limited current of 2.5 A and a voltage of 300 V. The coatings exhibit the anatase and rutile crystalline structures of TiO2. The coating produced for longer treatment times has higher concentrations of rutile, resulting in surface hardening. The thickness and the roughness of the coatings increased with the increase in treatment time, but there was a reduction in the size of the pores per unit area.

Influence of oxygen ingress on microstructure and phase formation during two-step oxidation surface hardening of TiZrNbHfTa high entropy alloy

Aiming for an increased surface hardness and a better wear resistance of TiZrNbHfTa, we investigate a two-step process combining oxidation of rolled, ultrafine-grained, single-phase bcc TiZrNbHfTa in air at 550 °C with a vacuum heat treatment process at 1200 °C, including subsequent quenching. The first process step is associated with the formation of a surface oxide layer, a phase decomposition of the bulk, and oxygen ingress into the bulk, leading to an oxygen-enriched subsurface region containing internal oxides. The second process step is capable of restoring the single-phase nature of the bulk TiZrNbHfTa. At the same time, the presence of a compact surface oxide layer of 1–2 μm and an oxygen-enriched subsurface region underneath is preserved. The oxygen present in the subsurface region stabilizes a two-phase regime consisting of a Hf- and Zr-rich hcp phase and an Nb- and Ta-rich bcc phase, with the oxygen being interstitially dissolved predominantly in the hcp phase.

Indentation fracture of 4H-SiC single crystal

Understanding the deformation and fracture behavior of single crystal silicon carbide (SiC) under a single particle is of scientific and practical importance for the micromachining of single crystal SiC. In this work, we investigate the indentation fracture of a 4H-SiC single crystal wafer with the indentation direction perpendicular to (0001) plane, using Berkovich, Vickers, and Knoop indenters. All the indentations create radial cracks for the normal loads used in this work. Both the Vickers and Knoop hardness tests produce lateral cracks. The fracture toughness calculated from the Vickers hardness tests is smaller than the ones calculated from the Knoop hardness tests and the Berkovich indentations under large indentation loads. The fracture toughness of 4H-SiC single crystal decreases with the increase of the indentation load under small indentation loads for the Berkovich indentations, revealing the phenomenon of surface hardening. The surface energy calculated from the radial cracks is comparable to the results reported in the literature. We establish an analytical expression of the total energy dissipation of a single indentation cycle, including the contribution of indentation-induced cracking, which offers an approach to calculate the ratio of the energy dissipation due to cracking to the energy dissipation due to plastic deformation and determine the dominant deformation process controlling the indentation deformation. The analysis of the energy dissipation for the indentations of the 4H-SiC single crystal by the Berkovich indenter reveals that the energy dissipation from the indentation-induced cracking is significantly larger than (more than eight times) that from plastic deformation for the indentation loads larger than 75 mN.

Effect of laser shock peening on fretting wear behaviour of AISI 304 stainless alloy

Unlike many other surface treatment techniques, such as shot peening (SP), low plasticity burnishing (LPB), ultrasonic surface rolling process (USRP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP) is a non-contact process. This means that LSP achieves surface modification without direct physical contact, thereby eliminating the risk of media contamination and undesired wear on the peening equipment. As a surface hardening technology, LSP tends to produce a hardened layer with a high gradient of residual stress (RS) in the near-surface, significantly enhancing wear resistance. The well-known wear theories applied for numerical prediction, whether Archard model or dissipated frictional-energy model, contain a multiplier for contact pressure and relative slip amplitude p·ds or shear stress and relative slip amplitude q·ds, respectively. These multipliers are sensitive to the mechanical properties near the surface. Additionally, the wear profile is governed not only by the wear effect but also by the deformation of materials. Therefore, to accurately evaluate the wear performance for surface-hardened materials, the influence of RS is hard to be overlooked. In this work, the finite element method (FEM) is utilised to construct a 3D numerical model, which ignores and considers RS, for both as-received and LSP-treated samples. Two distinct RS distributions induced by different scanning strategies (one- and five-time), are introduced in the finite element (FE) model. The numerical simulation results are then compared with the experimental data to verify the accuracy of the fretting wear model built in this study. On this basis, the impact of different RS distributions on fretting wear characteristics, including wear profile and volume, is extensively investigated. The findings reveal that higher amplitude RS can reduce the degree of fretting wear to a greater extent, highlighting the beneficial role of RS in enhancing wear resistance. Furthermore, the numerical models incorporating RS demonstrate superior predictive accuracy compared to those that omit RS. This naturally underscores the importance of integrating RS in numerical simulations of LSP and other surface-hardened materials.

Mathematical modelling of thermal stresses of induction surface hardening in axi-symmetric formulation

The paper presents the original general model of induction surface hardening based upon analysis of coupled electromagnetic, thermal, mechanical and metallurgical phenomena. The distribution of mechanical strains and stresses in surface layers of steel materials subjected to induction hardening is determined. This distribution is not caused only by the thermoelastic processes, but often, it is also influenced by plastic deformations of the exposed layers and transformation of particular levels of steel. An illustrative example shows the methodology of solution for an axi-symmetric configuration.

Enhanced Microstructure and Wear Resistance of Ti-6Al-4V Alloy with Vanadium Carbide Coating via Directed Energy Deposition.

Ti-6Al-4V alloys are known for their suboptimal tribological properties and are often challenged by durability issues under severe wear conditions. This study was conducted to enhance the alloy's wear resistance by forming a hardened surface layer. Utilizing directed energy deposition (DED) additive manufacturing with a diode laser, vanadium carbide particles were successfully integrated onto a Ti-6Al-4V substrate. This approach deviates from traditional surface enhancement techniques like surface hardening and cladding, as it employs DED additive manufacturing under parameters akin to those used in standard Ti-6Al-4V production. The formed vanadium carbide layer achieved a remarkable thickness of over 400 µm and a Vickers hardness surpassing 1500 HV. Pin-on-disk test results further corroborated the enhanced surface wear properties of the Ti-6Al-4V alloy following the additive-manufacturing process. These findings suggest that employing vanadium carbide additive manufacturing, under conditions similar to the conventional DED process with a diode laser, significantly improves the surface wear properties of Ti-6Al-4V in metal 3D-printing applications.

In-situ formation of ultra-hard titanium-based composite coatings on carbon steel through electro-spark deposition in different gas media

In the current study, ultra-hard TiC, TiN, and Ti(C,N) layers were in-situ formed on carbon steel substrate using pure titanium electrode via electro-spark deposition (ESD) in argon, nitrogen, argon/nitrogen, and air atmospheres. The synthesized coatings were characterized using various techniques, including FE-SEM/EDS, X-ray diffractometry, Raman spectroscopy, microhardness and nanoindentation tests, and surface roughness measurement. Also, a thermodynamic simulation was executed to estimate the phase-stability. Fe5C2, TiN, Fe3N, and Ti2O3 were determined as the major phases formed under the argon, nitrogen, Ar/N2, and air atmospheres, respectively. The formation of martensite at the interface of the coating and substrate in all atmospheres indicates the capability of the ESD process for surface hardening. The observed discrepancies between the empirically formed phases and the thermodynamics prediction can be related to the non-equilibrium conditions of the ESD process. It was revealed that gaseous media such as argon and nitrogen serve as a protective/active environment in the titanium/steel system. It is proposed that the electro-sparking of titanium under the active nitrogen medium follows an avalanche plasma regime. Under the argon flow, FeTi intermetallic layer is formed. Whilst, electro-sparking in ambient air leads to the formation of various Fe-Ti-O compounds, as well as different TiOn oxides. On the other hand, the utilization of nitrogen gas during the ESD increases the surface roughness and the thickness of the coating, rather than the deposition under the argon flow, due to the extra heat of reactions. The dynamic reactions occur between pure titanium, nitrogen, carbon, and oxygen, leading to the initial formation of Ti(C,N) at the top surface, followed by the production of titanium oxides in the middle layer. The coexistence of the super-hard Ti(C,N) with a hardness of 3130 HV at the top surface and titanium nitrides beneath it in a gradient mode effectively impedes the crack propagation.

THE EFFECT OF HARDENING TECHNIQUES ON WEAR RESISTANCE AND FATIGUE LIFE OF DUCTILE CAST IRON

Many hardening methods have been developed and proposed as an effective technology to produce microstructural modification and improvement of mechanical properties of variety metallic materials. In this experimental study, the effects of applying laser peening (LP) and friction stir processing (FSP) methods on wear resistance and fatigue properties of selected cast iron ASTM A536, grade (80-55-06) with ferrite/pearlite microstructure were investigated. Microscopic study revealed evident refinement and crashing of graphite nodules as 50% of the basic size with FSP and 32% with LP within the processed surfaces hence improving average microhardness by 100% and 48% respectively. The wear resistance and fatigue life were increased by 33% and 122% after FSP whereas, the corresponding increments were 15% and 22% after LP in comparison with the basic ductile iron. These improvements were linked to surface hardening, compressive stresses and structural modification by the employed processes.

Simulation of thermal processes in a half-space under heating by a moving source with a uniformly distributed heat flow

Using the method of applying instantaneous point sources, a solution was obtained to the problem of heat conduction during surface heating of a body in the form of a half-space by a uniformly distributed highly concentrated heat flux moving at a constant speed along a rectilinear trajectory with a different shape of the heating spot at constant thermophysical characteristics of the material. The effect of temperature loading modes and the shape of the heating spot on thermal processes in the heat-affected zone is studied. The surfaces and lines of the temperature level are constructed for different moments of time and speed loading modes in different planes of the heating zone. Time dependences of temperatures, heating and cooling rates for body points are given. The shortcomings of the methods used for linear thermal conductivity, the lack of direct consideration in the design scheme of the surface melt zone of the material do not allow one to reliably assess the effect of heat treatment modes on changes in material properties, focusing only on the level of the maximum design temperature. In this regard, the structure formation of metal in the zone of thermal action is proposed to be associated with a thermal impulse, i.e. the total thermal energy perceived by the material at a given point of the body, as well as with the effective structurization impulse introduced into consideration, which characterizes the energy spent on the process of structural transformations of the material, and the structurization time at a point and some volume of the body. The dependencies of these values on the speed of movement and the shape of the heating spot are presented. The considered approaches can be applied to various metals and alloys. The research results can be used to develop more effective methods for determining the optimal modes of surface hardening of metal products with a high-energy source.

Surface hardening of Ti-Al-V superalloy spinal implant by using the boronization method.

We compared the raw Ti-Al-V super alloy transpedicular implant screws with boronized and surface-hardened transpedicular implant screws. To improve patients' postoperative prognosis with the production of harder and less fragile screws. Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti-Al-V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of ∼15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure. Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools. Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use.

Improving surface hardness of AISI 1045 steels using melamine derived from urea

ABSTRACT AISI 1045 steels are medium carbon steels used in applications that require greater strength and hardness such as gears, railway wheels and tracks, crankshafts, rolls, axles and other structural components. Although AISI 1045 steels are highly demanded engineering materials, they suffer from deformation and wear resistance when these applications are used. The hardness and wear resistance of the material are improved using a surface hardening method. Pack nitriding is the cheapest and easiest method of surface hardening method implemented in this work. The surface hardness of AISI 1045 steel is improved by the diffusion of nitrogen from the nitrogen-bearing material (melamine) to the surface of the steel and forms a metal nitride compound, which has strong hardness and wear resistance. This work reports that substantial surface hardening of AISI 1045 steel was achieved by the pack nitriding method using melamine obtained by in situ reaction of urea. The surface hardness increases manifold with the amount of melamine used, soaking time and temperature. The microscopic investigations of the nitrided surfaces of the metal show the formation of two distinct layers. The microstructural properties and hardness of the samples before and after nitriding were thoroughly investigated and interpreted.

Electrolyte-plasma surface hardening of hollow steel applicator needles for point injection of liquid mineral fertilizers

<abstract> <p>This paper presents the results of research on the effect of electrolyte-plasma hardening on tribological and mechanical properties of hollow needles of 12Kh18N10Т steel applicators for liquid fertilizer application. For the application of liquid fertilizers for processing and testing, the hollow needles of the applicator are made of 12Kh18N10Т steel of cylindrical shape with a diameter of 20 mm. To ensure uniformity of the hardening process, the part was rotated clockwise during the entire procedural cycle. To reveal the influence of the sample rotation speed on the uniform surface hardening, an experiment was conducted for three applicators with rotation speeds of 4, 6, and 8 rev/min. As a result of electrolyte-plasma surface hardening (EPSH), the phase composition of the specimen's surface is characterized by the presence of austenite (γ-Fe) and ferrite (α-Fe). It is revealed that the maximum value of microhardness after EPSH is 2 times higher than the initial value. According to the results of the performed works, the contract on application of tests in field conditions and revealing of perspectivity of needle applicators for liquid fertilizers application was concluded.</p> </abstract>

Vplyv technológie tepelného spracovania na tribologické vlastnosti vybraných oceľových materiálov

The heat treatment technology changes all sorts of materials properties. We examined the change of tribological properties of selected powder metallurgy materials and conventional steels, in this article. We used special testing equipment, for measuring the changes of friction coefficient of individual tested materials, before application of the heat treatment and after application of the heat treatment. We tested two types of powder metallurgy steels and two types of conventional steels. The changes in friction coefficient are shown in the table and charts. We used boronising, nitriding and surface hardening as procedures of heat treatment.

Fatigue life prediction of the nitrided steel by multiaxial high cycle fatigue criteria

The present study aims to predict the fatigue strength of ion-nitrided 42CrMo4 steel, using multiaxial high cycle fatigue (HCF) criteria and considering the effects of stabilized residual stresses and surface hardening. The predicted fatigue strength was compared to experimental data obtained after three-points bending fatigue tests at two stress ratios (0.1 and 0.5) and for notched (Kt = 1.6) nitrided and untreated specimens. A 3D finite element (FE) model of a three-point bending fatigue test was developed under ABAQUS software in order to determine the actual applied cyclic stress state at the notch. The results show that ion-nitriding treatment led to 32% improvement in the fatigue strength at 106 cycles compared to the untreated material. This improvement is explained by the advantageous effect of ion-nitriding treatment in terms of compressive residual stresses and surface layer hardening. Both stabilized residual stress state and hardening effects were successfully implemented into various multi-axial HCF criteria, including Sines, Crossland, Dang Van and Matake criteria. A sensitivity analysis has shown that Crossland criterion has permitted to predict the fatigue limits in accordance with the experimental results.

Surface hardening of MIM porous metals by ultrasonic vibration assisted pressing

Micro MIM is one of the manufacturing methods for medical devices, which has seen a rapid increase in demand in recent years, but due to the porous structure of the product, there are concerns about insufficient strength due to low density. Ultrasonic-assisted surface reinforcement was proposed to supplement the strength by hardening the surface and improving bending stiffness in this study. Ultrasonic-assisted pressing was performed to verify mechanism for the surface hardening by comparing MIM and rolled specimen. The materials used are pure copper MIM. It was found that MIM specimen have a characteristic in which strain is concentrated near the surface compared to rolled specimen. This suggests that the cause of the concentration of strain on the surface may be the absorption of ultrasonic energy by the pores inside the material due to sound and shock absorption properties of the porous structure.

Assessment of possibility of surface hardening of rail welding joint using surfacing of wear-resistant layer

The article considers the possibility of leveling the consequences of the welding process by applying a hardening wear-resistant layer with the study of the microstructure of the resulting layer and testing the resulting compounds.

Surface hardening of structural steels ShKh15 and 40KhN2MA by pulsed plasma flows

The article is devoted to an innovative method of surface hardening of steels 40KhN2МА and ShKh15 by pulsed plasma flows. The treatment was carried out in a wide range of absorbed energy density from 20 to 100 J/cm2, with a plasma exposure duration of 1 ms. The results of a study of the structure, phase composition and morphology of the modified surface layer, as well as such characteristics as thickness, microhardness, surface roughness, and level of residual stresses are presented. The modified layer of steel contains several structural components with distinctive characteristics. The maximum thickness of the modified hardened layer was 125 µm. The conducted research made it possible to establish optimal treatment modes, characterized by an increase in surface microhardness by 3—4 times, a decrease in roughness by up to 35 % and the presence of compressive residual stresses, which opens up prospects for the development of highly effective technology for strengthening critical products.

ВОССТАНОВИТЕЛЬНАЯ НАПЛАВКА И ЭЛЕКТРОМЕХАНИЧЕСКАЯ ПОВЕРХНОСТНАЯ ЗАКАЛКА ЗАМКОВ БУРИЛЬНЫХ ТРУБ

The main reason for the wear of the drill pipe locks when rotating in an open borehole is the presence of a solid layer in aggressive geological formations. (Research purpose) The research purpose is increasing the physical and mechanical properties of the surface layer by researching and developing a technology for hardening the outer surfaces of drill pipe locks restored by electromechanical surface hardening. (Materials and methods) Surfacing was performed on the coupling parts of drill pipes with thread Z-147 in the strength group G105. They were fused with a powder wire of various chemical composition back-to-back with three belts on each sample. Wear tests of surfacing were carried out on a test bench using a special technique (resistance to abrasive wear). The chemical composition of the surfacing indicates a carbon content in the surface layer of 0.28 to 0.40 percent. Methods of restoration of locks by surfacing were examined and the physical and mechanical properties of the surface layer of the restored drill pipes were evaluated, the microstructural state of the base and deposited metal was analyzed. (Results and discussion) It was noted that despite the large number of technologies for surfacing drill pipe locks, the special equipment used, the high labor intensity and cost of surfacing processes and subsequent turning on pipe-cutting machines, it is not possible to increase their wear resistance. This is due to the insufficient hardness of the surface layer of the deposited locks (no more than 28-32 on the Rockwell scale), which does not exceed the surface hardness of the new drill pipe. An experimental increase in the hardness of the surface layer of the deposited samples after electromechanical surface hardening was confirmed. (Conclusions) The results of wear tests of deposited materials indicate the effectiveness of electromechanical surface hardening of reducing surfacing.

ернативна технологія поверхневого зміцнення внутрішніх поверхонь довгомірних деталей

Barrel survivability is the main indicator of tank guns. In order to ensure the competitiveness of Ukrainian armored vehicles on the foreign arms market, there was a need to ensure the survivability of the barrels of domestic tank guns at the level of the best world samples. Solving the problem of strengthening, restoring and increasing the service life of long-dimension parts is associated with the complexity of preparing and processing the inner surface (bore) along its entire length and eliminating possible residual deformations. The problem of increasing the survivability of tank gun barrels by applying protective coatings is considered. Their brief characteristics and limits of application are given. An alternative technology for surface hardening by electrical contact sintering of powder materials is proposed. This technology makes it possible to apply coatings up to 3 mm thick, with a density approaching that of a compact material and an adhesive strength of up to 220 MPa. Electrocontact sintering refers to impulse technologies and can exclude further mechanical processing of coatings The electrical contact method is the most promising method of strengthening and restoration, as it refers to the methods with the minimum necessary heating, thereby excluding thermal deformation of the parts being strengthened (this technology will allow to eliminate the most characteristic defect of the barrel, such as its swelling and distortion). For cauterization, a specially developed electrode-tool made of a copper alloy, dispersed-reinforced with solid particles, was used, which allows combining in one operation the application of coatings and the finishing treatment by the method of plastic surface deformation to the limit size, surface cleanliness and density.