Search Results (73)

This work demonstrates the possibility of creating effective composite coatings with a complex structure and phase composition on carbon steel C45 via electrospark deposition (ESD) with multicomponent electrodes with a bonding mass composition of Co-Ni-Cr-B-Si semi-self-fluxing alloys and superhard compounds WC, B₄C and TiB₂. The variation in the roughness, thickness, composition, structure, microhardness and wear at the friction of the coatings as a function of the ratios between the bonding mass and the high-hardness components in the composition of the electrode and of the pulse energy for ESD has been studied. It has been established that with a content of the bonding mass in the electrode of 25–35%, coatings with improved adhesion and simultaneously higher hardness and toughness are obtained. Suitable electrode compositions and optimal pulse energy have been defined, which provide dense and uniform coatings with an increased amount of crystalline-amorphous structures, as well as intermetallic and wear-resistant phases, with thickness, roughness and microhardness that can be changed by the ESD modes in the ranges of δ = 8–65 µm, Ra = 1.5–7 µm, and HV 8.5–15.0 GPa, respectively, and minimal wear of the coated surfaces that is up to 5 times lower than that of the substrate and up to 1.5 times lower than that obtained with conventional WC-Co electrodes. Full article

In this study, NiCrBSi composite coatings reinforced with 5–15 wt.% TiC particles were prepared using laser cladding to investigate the influence of the TiC content and laser beam power on the coatings’ quality, structure, and properties. Penetrant tests revealed the presence of cracks in the composite coatings, which were reduced with the higher laser power due to a decrease in cooling rate. A macroscopic analysis showed that pure NiCrBSi coatings exhibited a high quality and were free of defects, while the addition of TiC particles led to the formation of large pores, particularly in coatings produced with a lower laser power. Microstructural characterization was conducted using Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). The microstructure of the pure NiCrBSi coatings consisted of an austenitic matrix with chromium-based precipitates (carbides and borides). Variations in structural morphology across different regions of the coatings and under varying laser powers were described. When TiC particles were added, partial dissolution occurred in the molten pool, enriching it with titanium and carbon, which subsequently led to the precipitation of titanium carbides. The average microhardness of the composite coatings increased by 28%–40% compared to the pure NiCrBSi coating, while the erosion resistance remained comparable. Solid particle erosion tests in accordance with the ASTM G76-18 standard resulted in average erosion values of the pure NiCrBSi coating of 0.0056 and 0.0025 mm³/g for the 30° and 90° impingement angles, respectively. Full article

In sealing, sliding, and power transmission operations, surface quality and contact tolerances have high impacts on material system efficiency. Although the boriding process improves the wear resistance of metallic surfaces, it increases surface roughness, affecting the tribological efficiency of material systems. This study presents the tribological results of AISI 4140 boriding surfaces tested using a dehydrated paste pack boriding method with and without a finishing polish process to reduce the roughness. The duration of the boriding process was 1 h at 1123, 1173, 1223, and 1273 K using boron paste obtained from a commercial source and using a pot-polishing process with Al₂O₃ with a particle size of 0.5 μm for 25 min. The samples with and without the finishing polish process were structurally characterized using X-ray diffraction, and the boride coating adhesion was determined using Rockwell C indentation. The tribological properties of the boride surface with and without the finishing polish process were determined using a reciprocating sliding test, with a ZrO₂ ball as a counter body. The boride surfaces’ crystalline structure changed with polishing, which revealed the FeB phase and reduced the roughness value. These modifications in the surface characteristics altered the adhesion and tribological performance of the coating, resulting in a more stable tribological performance on the polished boride surfaces, with a reduction in the coefficient of friction (Cof) value from 0.75 ± 0.02 for the tribological test on the 1123 K-P sample to 0.59 ± 0.002 for the 1273 K-P sample surface at 20 N of applied load. Full article

Metal and metalloid powders are widely used in high-energy compositions (HECs) and solid propellants (SPs), increasing their energetic characteristics in the combustion chamber. The particle size distribution, protective coatings of the particles and heat of combustion of the metal powders influence the ignition and combustion parameters of the HECs as well as the characteristics of the propulsion systems. Boron-based metallic fuels achieve high-energy potentials during their combustion. The effect of Al-B, Fe-B and Ti-B (Me-B) mixture ultrafine powders (UFPs) on the ignition and combustion characteristics of a model HEC based on a solid oxidizer and a polymer combustible binder was investigated. The Me-B mass ratios in the mixture UFPs corresponded to the phase composition of the borides AlB₂, FeB and TiB₂. It was found that replacing the aluminum UFP with Al-B, Fe-B and Ti-B UFPs in the HECs changed the exponent (n) in the correlations of the ignition delay time t_ign(q) and burning rate u(p). The maximum burning rate and n over the pressure range of 0.5–5.0 MPa were obtained for the HEC with Al-B UFPs due to the increase in the heat release rate near the sample surface during the joint combustion of the Al and B particles. Full article

In this study, a comprehensive machine learning (ML) model was developed to predict and optimize boride coating thickness on steel surfaces based on boriding parameters such as temperature, time, boriding media, method, and alloy composition. In a dataset of 375 published experimental results, 19 features were applied as inputs to predict the boride layer thickness in various steel alloys. ML algorithms were evaluated using performance metrics like Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and R². Among the ML algorithms tested, XGBoost exhibited the highest accuracy. XGBoost achieved an R² of 0.9152, RMSE of 29.57, and MAE of 18.44. Incorporating feature selection and categorical variables enhanced model precision. Additionally, a deep neural network (DNN) architecture demonstrated robust predictive performance, achieving an R² of 0.93. Experimental validation was conducted using 316L stainless steel (SS), borided at 900 °C and 950 °C for 2 h and 4 h. The DNN model effectively predicted the boride thickness under these conditions, aligning closely with the observed values and confirming the models’ reliability. The findings underscore the potential of ML to optimize boriding processes, offering valuable insights into the relationships between boriding parameters and coating outcomes, thereby advancing surface modification technologies. Full article

Laser cladding technology is an effective method for producing wear-resistant coatings on damaged substrates, improving both wear and corrosion resistance, which extends the service life of components. However, the fabrication of hard and brittle materials is highly susceptible to the problem of cracking. Using gradient transition layers is an effective strategy to mitigate the challenge of achieving crack-free laser-melted wear-resistant coatings. This study presents the cracking issue of laser cladding Ni60B (NiCrBSi) coatings on 38CrMoAl (18CrNiMo7-6) steel by designing a gradient transition layer infused with varying amounts of Ni powder. We examine how different levels of Ni doping in the transition layer influence the fabrication of the Ni60B coating. The results indicate that the cracking mechanism of Ni60B is primarily due to the brittleness and hardness of the fusion cladding layer, which can result in cold cracks under residual tensile stress. Increasing the nickel content in the transition layer reduces the difference in thermal expansion coefficients between the cladding layer and the substrate. Additionally, the nickel in the transition layer permeates the cladding layer due to the laser remelting effect. The physical phase within the cladding layer transitions from the initial CrB, M₇C₃, and γ-Ni solid solution to γ-Ni solid solution and Ni-B-Si eutectic, with a small amount of boride and carbide hard phases. As the nickel doping in the transition layer increases, the proportion of the toughness phase dominated by Ni elements significantly rises, leading to a decrease in the hardness of the fused cladding layer. However, the average hardness of the fusion cladding layer in crack-free samples was measured at 397.5 ± 5.7 HV_0.2, which is 91% higher than that of the substrate. Full article

This study investigates the optimization of boron coating parameters for medium-carbon steels, specifically AISI 1137, and their subsequent effects on mechanical properties, which are crucial for industrial applications. Despite extensive research on boronizing processes, an understanding of the optimal conditions that enhance wear resistance and hardness while maintaining structural integrity is still lacking. To address this gap, we systematically examined the impact of boronizing temperatures (850 °C and 950 °C) and durations (2, 4, and 8 h) on the structural and mechanical properties of AISI 1137 steel. Our findings indicate the need for improved surface properties in medium-carbon steels used in demanding environments, such as automotive and machinery components. The boronizing process was carried out using Ekabor 1 powder, with characterization performed through optical microscopy, pin-on-disk wear tests, and Vickers hardness analysis. Results showed that the thickness of the boronized layer ranged from 50.6 μm to 64.8 μm, with wear resistance increasing by 1.8 to 3.9 times at 950 °C compared to at 850 °C. The measured hardness of the boronized surface layers varied between 1963.7 HV and 219.3 HV, decreasing from the boronized layer toward the base material. The optimal parameters for wear resistance and hardness were found to be a temperature of 950 °C and a duration of 8 h, facilitating the formation of FeB and Fe₂B phases, which significantly enhanced the steel’s mechanical properties. This research provides valuable insights into the boronizing process and establishes a foundation for the optimizing of surface treatments to extend the lifespan and performance of medium-carbon steels in industrial use. Full article

High-entropy ceramics (HECs) represent an emerging class of materials composed of at least five different cations or anions in near-equiatomic proportions, garnering significant attention due to their extraordinary functional and structural properties. While multi-component ceramics have played a crucial role for many years, the concept of high-entropy materials was first introduced eighteen years ago with the synthesis of high-entropy alloys, and the first high-entropy nitride films were reported in 2014. These newly developed materials exhibit superior properties over traditional ceramics, such as enhanced thermal stability, hardness, and chemical resistance, making them suitable for a wide range of applications. High-entropy carbides, borides, oxides, oxi-carbides, oxi-borides, and other systems fall within the HEC category, typically occupying unique positions within phase diagrams that lead to novel properties. HECs are particularly well suited for high-temperature coatings, for tribological applications where low thermal conductivity and similar heat coefficients are critical, as well as for energy storage and dielectric uses. Computational tools like CALPHAD streamline the element selection process for designing HECs, while innovative, energy-efficient synthesis methods are being explored for producing dense specimens. This paper provides an in-depth analysis of the current state of the compositional design, the fabrication techniques, and the diverse applications of HECs, emphasizing their transformative potential in various industrial domains. Full article

To improve the wear resistance of the Ti60 alloy, laser cladding was used to obtain a composite coating containing a high-entropy (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ boride phase, with Ti, Zr, Mo, Ta, Nb, and B powders as the raw materials. The microstructure and wear characteristics of the coating were studied using XRD, SEM, EDS, and the pin-on-disc friction wear technique. The results show that the coating mainly consists of six phases: (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂, ZrB₂, TiB, TiZr, Ti_1.83 Zr_0.17, and Ti_0.67Zr_0.67Nb_0.67. The average microhardness of the coating was 1062.9 HV_0.1 due to the occurrence of the high-entropy, high-hardness (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ boride phase, which was about 2.9 times that of the Ti60 alloy substrate. The coating significantly improved the wear resistance of the Ti60 alloy substrate, and the mass wear rate was about 1/11 that of the Ti60 alloy substrate. The main types of wear affecting the coating were abrasive, adhesive, and oxidation wear, while the main wear affecting the Ti60 alloy matrix was abrasive wear, accompanied by a small amount of adhesive and oxidation wear. Full article

Molten salt electrophoretic deposition is a novel method for preparing coatings of transition metal borides such as TiB₂, which has emerged in recent years. To broaden the applications of transition metal boride coatings prepared by this method, this paper investigates the corrosion resistance of TiB₂ coatings, produced through molten salt electrophoretic deposition, to liquid zinc. By applying a cell voltage of 1.2 V (corresponding to an electric field of 0.6 V/cm) for 1 h in molten NaF-AlF₃, the nanoscale TiB₂ particles migrated to the cathode and were deposited on the graphite substrate, forming a smooth and dense TiB₂ coating with a thickness of 43 μm. Subsequently, after subjecting the TiB₂-coated graphite to corrosion resistance tested in molten zinc for 120 h of continuous immersion, no cracks were observed on the surface or within the coating. The produced TiB₂ coating demonstrated excellent corrosion resistance. These research results suggest that the fully dense TiB₂ coating on the graphite substrate, produced through molten salt electrophoretic deposition, exhibits excellent corrosion resistance to liquid zinc. Full article

The surface of 17-4PH martensitic stainless steel was laser-cladded with Ni60 and Ni60+nano-WC composites and a comprehensive investigation was conducted of the microstructure and wear mechanism. The findings demonstrate that despite the added nano-WC particles being fused and dissolved during laser cladding, they still lead to a reduction in grain size and a decrease in crystallographic orientation strength. Furthermore, the dissolution of nano-WC makes the lamellar M₂₃C₆ carbides transform into a rod or block morphology, and leads to the CrB borides becoming finer and more evenly dispersed. This microstructural evolution resulted in a uniform increase in hardness and wear resistance, effectively preventing crack formation. When the nano-WC addition increased to 20 wt.%, there was a 27.12% increase in microhardness and an 85.19% decrease in volume wear rate compared to that of the pure Ni60 coating. Through analysis of the microstructure and topography of wear traces, it can be inferred that as the nano-WC addition increased from 0 wt.% up to 20 wt.%, there was a gradual transition from two-body abrasive wear to three-body abrasive wear, ultimately resulting in adherent wear. Full article

Earlier studies have shown that 30 L steel, used for the manufacture of hydraulic machinery equipment elements, has greater resistance to cavitation wear than 20 GL steel. This paper presents the results of experimental studies of the solid particle erosion resistance of 30 L structural steel samples with different surface modifications based on nitriding and boriding processes. The characteristics of the modified near-surface layers were determined. The results of the solid particle erosion resistance tests carried out according to the ASTM G76-13 standard are presented. The research results demonstrated that boriding processes worsen the solid particle erosion resistance of 30 L steel at flow impact angles of 30° and 90°. All the considered variants of surface nitriding at an impact angle of 90° do not worsen the solid particle erosion resistance of 30 L steel samples, while at an impact angle of 30°, they increase the solid particle erosion resistance by at least 10–20%. Full article

This study shows the possibility of the fabrication of titanium borides by an alloying of a titanium substrate with boron powder via a scanning electron beam. During the electron beam alloying experiments, the speed movement of the specimens was varied, where it was 4 and 6 mm/s. The thickness of the alloyed zone formed by the lower velocity of the movement of the workpiece is greater than that of the coating obtained by the higher speed movement. The phase composition of the coatings is in the form of the TiB₂ phase, as well as some amount of undissolved boron in both considered cases. In the case of the lower speed of the movement of the sample, the undissolved boron is within the whole volume of the alloyed zone, while at the higher speed movement, it is on the top of the specimen. The hardness of the obtained coatings by the higher speed of the specimen movement reached values of about 4500 HV. Considering the values of the surface alloy fabricated via the lower velocity movement of 4 mm/s, it is about 2600 HV, which is lower than that of the one obtained by the 6 mm/s speed of the sample movement. The result obtained for the friction coefficient (COF) for the specimen alloyed by the speed of the specimen motion of 4 mm/s is 0.40; the value for the coating obtained at a speed movement of 6 mm/s is 0.34. In both cases, these values are lower than that of the titanium substrate. Full article

We report a new industrial application of aluminum magnesium boride AlMgB₁₄ (BAM) coatings to enhance the hardness of tungsten carbide ceramic (WC-Co) and high-speed steel tools. BAM films were deposited by RF magnetron sputtering of a single dense stoichiometric ceramic target onto commercial WC-Co turning inserts and R6M5 steel drill bits. High target sputtering power and sufficiently short target-to-substrate distance were found to be critical processing conditions. Very smooth (6.6 nm RMS surface roughness onto Si wafers) and hard AlMgB₁₄ coatings enhance the hardness of WC-Co inserts and high-speed R6M5 steel by a factor of two and three, respectively. Complete coating spallation failure occurred at a scratch adhesion strength of 18 N. High work of adhesion and low friction coefficient, estimated for BAM onto drill bits, was as high as 64 J/m² and as low as 0.07, respectively, more than twice the surpass characteristics of N-doped diamond-like carbon (DLC) films deposited onto nitride high-speed W6Mo5Cr4V2 steel. Full article

Three groups of spherical WB-reinforced Co-based coatings (Co coating, Co + 15%WB coating, Co + 45%WB coating) were fabricated by laser-cladded technology. The microstructure and constituent phase of spherical WB-reinforced Co-based coatings were examined through scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The low-temperature tribological properties were analyzed by coefficient of friction, 2D and 3D profiles across the wear track, and wear surface morphology, respectively. The results showed that the phases in the WB-reinforced Co-based coatings are mainly γ-Co, carbides Cr₂₃C₆ and Cr₇C₃, WB, and WO₃. Under dry sliding friction at −20 °C, the more spherical WB, the lower the friction coefficient. The wear rate of Co + 45%WB coating was as low as 3.567 × 10⁻⁴ mm³/N·m⁻¹, indicating the outstanding wear resistance. Abrasive wear was observed on the rough surface of the WB-added coatings. Compared with dry sliding, due to the plastic deformation of micro-convexes and lubrication function in the 3.5 wt.% NaCl solution, the wear tracks on the surfaces of the three tested coatings were shallower, exhibiting distinct elongated plough grooves. Full article