Search Results (65)

During the vapor phase aluminizing process, protecting the joint regions of turbine blades remains a critical challenge, as the formation of the aluminide coating can significantly increase the brittleness of these areas. To address this issue, a novel double-layer anti-seepage coating was designed for the K4125 nickel-based superalloy. The coating employs a self-sealing mechanism, transforming from a porous structure into a dense NiAl/Al₂O₃ composite barrier at elevated temperatures, thereby suppressing aluminum penetration. Optimal anti-seepage performance is achieved at 1080 °C, reducing the transition zone width to 42 μm, which is a reduction of more than 70% compared to that of 880 °C. These results are attributed to the synergistic action of multiple mechanisms, including high-temperature densification, the formation of NiAl phase, and the growth of an oxide film on the substrate surface. Additionally, the thermal expansion mismatch enables easy mechanical removal of the coating after aluminizing without substrate damage. The coating system offers an effective and practical solution for high-temperature protection during vapor phase aluminizing in aerospace applications. Full article

In this work, iron aluminide coatings (FeAl and Fe₃Al) were developed on carbon steel substrates using the laser cladding process with mixtures of elemental iron and aluminum powders, aiming at protecting anodic pins in Soderberg electrolytic cells against oxidation and corrosion at high temperatures. These components operate under atmospheres rich in CO₂, alumina dust, and intense thermal cycles. The influence of processing parameters on the microstructure, phase formation, and mechanical properties of the coatings was investigated. X-ray diffraction confirmed the formation of the FeAl phase with a B2 ordered structure, while the expected D0₃ ordering in Fe₃Al was not detected, likely due to crystallographic texture effects. Microstructural analysis, optical and scanning electron microscopy, revealed dense coatings with good metallurgical bonding to the substrate and low porosity, being the conditions of 3.5 kW with 3 mm/s resulted in the best quality coatings. The FeAl coatings exhibited microhardness values of approximately 400 HV, whereas the Fe₃Al coatings showed values around 350 HV, indicating a significant improvement compared to the carbon steel substrate. These results demonstrate that laser cladding is an effective technique for producing iron aluminide coatings with potential application for corrosion and wear protection of anodic pins in Soderberg electrolytic cells. Full article

Nickel-based superalloys require protective low-activity aluminide coatings to withstand high-temperature oxidation and corrosion in turbine applications. As opposed to conventional gas processes, this study investigates the mechanisms of formation of alternative low-activity nickel aluminide coatings on the René N5 superalloy through electroless nickel pre-deposition followed by slurry aluminizing. Different thicknesses of electroless nickel layers (5, 10, 25 μm) were deposited and subsequently aluminized with varying slurry amounts (5–16 mg/cm²) under controlled heat treatments at 700–1080 °C with heating rates of 5 and 20 °C/min. Without electroless pre-deposition, high-activity coatings with refractory element precipitates formed. With electroless nickel, a precipitate-free low-activity coating developed, with thickness increasing linearly from 15 to 40 μm proportional to the initial electroless layer. An increasing slurry amount raised the overall coating thickness from 27 to 67 μm. Kirkendall porosity formed exclusively during the δ-Ni₂Al₃ to β-NiAl phase transformation at elevated temperature. Reducing the heating rate from 20 to 5 °C/min significantly decreased void formation by promoting more balanced Ni-Al interdiffusion. This work demonstrates that combining electroless nickel with slurry aluminizing provides an efficient route for producing low-activity coatings with controlled microstructure and minimal porosity. Full article

This study explores a novel approach to enhance the surface properties of Ti-Al alloys for biomedical applications by creating a compositional gradient layer through aluminum deposition using Electrical Discharge Machining (EDM). The primary goal was to develop a metallurgically bonded intermetallic zone that supports strong adhesion and improved compatibility for subsequent hydroxyapatite (HA) deposition. Aluminum was deposited onto a Ti6Al4V substrate via EDM under controlled conditions, followed by thermal and thermochemical treatments to induce diffusion and intermetallic phase formation. Comprehensive analyses using optical and electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) revealed the formation of well-adhered layers composed of complex Ti-Al intermetallics such as TiAl₂ and TiAl₃, along with oxide phases including TiO₂ and Al₂O₃. Thermal and thermochemical treatments further improved surface hardness, reaching up to 1057 HV, and influenced the diffusion behavior of aluminum, titanium, and vanadium. Adhesion tests confirmed that the untreated and thermochemically treated layers exhibited superior mechanical stability, while thermal treatment alone led to brittleness and delamination. These findings demonstrate that a properly engineered intermediate aluminide layer can significantly improve the performance of bioceramic coatings, particularly HA, by providing enhanced structural integrity and biocompatibility. Full article

This study investigates TNM-type titanium aluminide alloys, representing the third generation of β-stabilized γ-TiAl heat-resistant materials. The aim of this work is to study the combustion characteristics and to produce compact materials via the free SHS compaction method from initial powder reagents taken in the following ratio (wt%): 51.85Ti–43Al–4Nb–1Mo–0.15B, as well as to determine the effect of high-temperature isothermal annealing at 1000 °C on the structure and properties of the obtained materials. Using free SHS compression (self-propagating high-temperature synthesis), we synthesized compact materials from a 51.85Ti–43Al–4Nb–1Mo–0.15B (wt%) powder blend. Key combustion parameters were optimized to maximize the synthesis temperature, employing a chemical ignition system. The as-fabricated materials exhibit a layered macrostructure with wavy interfaces, aligned parallel to material flow during compression. Post-synthesis isothermal annealing at 1000 °C for 3 h promoted further phase transformations, enhancing mechanical properties including microhardness (up to 7.4 GPa), Young’s modulus (up to 200 GPa) and elastic recovery (up to 31.8%). X-ray powder diffraction, SEM, and EDS analyses confirmed solid-state diffusion as the primary mechanism for element interaction during synthesis and annealing. The developed materials show promise as PVD targets for depositing heat-resistant coatings. Full article

Ultrasonic-assisted machining (UAM) has emerged as a transformative technology for increasing material removal efficiency, improving surface quality and extending tool life in precision manufacturing. This review specifically focuses on the application of it to titanium aluminide (TiAl) alloys. These alloys are widely used in aerospace and automotive sectors due to their low density, high strength and poor machinability. This review covers various aspects of UAM, including ultrasonic vibration-assisted turning (UVAT), milling (UVAM) and grinding (UVAG), with emphasis on their influence on the machinability, tool wear behavior and surface integrity. It also highlights the limitations of single-energy field UAM, such as inconsistent energy transmission and tool fatigue, leading to the increasing demand for multi-field techniques. Therefore, the advanced machining strategies, i.e., ultrasonic plasma oxidation-assisted grinding (UPOAG), protective coating-assisted cutting, and dual-field ultrasonic integration (e.g., ultrasonic-magnetic or ultrasonic-laser machining), were discussed in terms of their potential to further improve TiAl alloys processing. In addition, the importance of predictive force models in optimizing UAM processes was also highlighted, emphasizing the role of analytical and AI-driven simulations for better process control. Overall, this review underscores the ongoing evolution of UAM as a cornerstone of high-efficiency and precision manufacturing, while providing a comprehensive outlook on its current applications and future potential in machining TiAl alloys. Full article

To ensure the mechanical performance of gas turbine hollow blades under high-temperature conditions, the application of aluminide high-temperature protective coatings on the inner gas flow channel surfaces of hollow blades via chemical vapor deposition (CVD) has become a critical measure for enhancing blade safety. This study employs computational fluid dynamics (CFD) to investigate the flow field within CVD reactors and the influences of deposition processes on the chemical reaction rates at sample surfaces, thereby guiding the optimization of CVD reactor design and deposition parameters. Three distinct CVD reactor configurations are examined to analyze the flow characteristics of precursor gases and the internal flow field distributions. The results demonstrate that Model A, featuring a bottom-positioned outlet and an extended inlet, exhibits a larger stable deposition zone with more uniform flow velocities near the sample surface, thereby indicating the formation of higher-quality aluminide coatings. Based on Model A, CFD simulations are conducted to evaluate the effects of process parameters, including inflow velocity, pressure, and temperature, on aluminide coating deposition. The results show that the surface chemical reaction rate increases with inflow velocity (0.0065–6.5 m/s), but the relative change rate (ratio of reaction rate to flow rate) shows a declining trend. Temperature variations (653–1453 K) induce a trapezoidal-shaped trend in deposition rates: an initial increase (653–1053 K), followed by stabilization (1053–1303 K), and a subsequent decline (>1303 K). The underlying mechanisms for this trend are discussed. Pressure variations (0.5–2 atm) reveal that both excessively low and high pressures reduce surface reaction rates, with optimal performance observed near 1 atm. This study provides a methodology and insights for optimizing CVD reactor designs and process parameters to enhance aluminide coating quality on turbine blades. Full article

An approach for the formation of intermetallic coatings on the titanium surface based on titanium aluminides is proposed. The approach involves producing a layered steel-aluminum-titanium metal composite via explosive welding, followed by heat treatment to form a diffusion zone at the steel–aluminum interface with a thickness of more than 30 μm, sufficient for the spontaneous separation of the steel layer. As a result, an aluminum layer approximately 0.3 mm thick remains on the titanium surface. Subsequent heating at temperatures of 700–850 °C, below the allotropic transformation temperature of titanium, results in the transformation of the aluminum layer into titanium aluminides. The formation of the intermetallic coating structure occurs as a result of the upward transportation of TiAl₃ fragments separated from the reaction zone by circulating melt flows. With increasing heat treatment time, these fragments become separated by the Al₂O₃ oxide phase. Full article

The slurry aluminizing process is widely employed to enhance the oxidation and corrosion resistance of nickel-based superalloys used in high-temperature environments such as gas turbines and aerospace engines. This study investigates the effects of the concentration of Al vapors in the reactor chamber and the initial slurry layer thickness on the microstructure, chemical composition, and phase composition of aluminide coatings. Coatings were manufactured on Ni-based superalloy substrates using CrAl powders as an aluminum source and chloride- and fluoride-based activator salts. The effect of the initial thickness of the slurry layer was studied by varying the amount of deposited slurry in terms of mg_slurry/cm²_sample (with constant mg_slurry/cm³_chamber). The microstructure and phase composition of the produced aluminide coatings were evaluated by SEM, EDS, and XRD analysis. Slurry thickness can affect concentration gradients during diffusion, and the best results were obtained with an initial slurry amount of 100 mg_slurry/cm²_sample. The effect of the Al vapor phase in the reaction chamber was then investigated by varying the mg_slurry/cm³_chamber ratio while keeping the slurry layer thickness constant at 100 mg_slurry/cm²_sample. This parameter influences the amount of Al at the substrate surface before the onset of solid-state diffusion, and the best results were obtained for a 6.50 mg_slurry/cm³_chamber ratio with the formation of 80 µm coatings (excluding the interdiffusion zone) with a β-NiAl phase throughout the thickness. To validate process flexibility, the same parameters were successfully applied to produce platinum-modified aluminides with a bi-phasic ζ-PtAl2 and β-(Ni,Pt)Al microstructure. Full article

The development of power engineering requires the introduction of new materials and technologies to improve the quality and durability of products. One promising direction is the creation of heat-protective coatings for the protection of working surfaces of turbine blades of gas turbine engines operating at temperatures up to 1000–1200 °C. Intermetallic coatings based on iron aluminides (Fe₃Al, FeAl) have high resistance to oxidation due to the formation of an oxide layer: Al₂O₃. However, their application is limited by brittleness due to the so-called third element effect, which can be reduced through alloying with chromium. In this study the processes of formation of Fe–Al–Cr intermetallic coatings produced by air plasma spraying and the mechanisms affecting their stability at high temperatures were investigated. Experimental studies included the analysis of the microhardness, wear resistance, and corrosion resistance of coatings, as well as their phase composition and microstructure. The results showed that the optimization of sputtering parameters, especially in the FrCrAl (30_33) mode, promotes the formation of a coating with improved tribological and anticorrosion characteristics, which is associated with its dense and uniform structure. These data have an important practical significance for the creation of wear-resistant and corrosion-resistant coatings applicable in power engineering. Full article

Aluminide coatings on nickel-based superalloys were synthesized via a high-temperature “clean” low-activity vapor-phase process. This process is environmentally friendly and meets manufacturers’ environmental protection requirements. Hence, it fulfils the Industry 4.0 requirements, where the reduction of environmental impact in the industrial sector is a key issue. Surface morphology, cross-section microstructure, and phase composition of the coatings were studied and compared by using an optical microscope and a scanning electron microscope (SEM) equipped with an energy dispersive spectroscope (EDS) and X-ray diffraction (XRD). Bare and coated superalloys’ lifetime was evaluated and compared via air exposure at 1100 °C. High-temperature low-activity aluminizing of the IN713, IN625, and CMSX4 superalloys enabled the obtainment of the desirable β-NiAl phase. The highest nickel content in the chemical composition of the IN713 superalloy among the investigated superalloys resulted in the highest aluminide coatings’ thickness. Moreover, the higher refractory elements concentration in the IN625 and CMSX4 superalloys than that in the IN713 superalloy may contribute to a thinner aluminide coatings’ thickness. Refractory elements diffused to the surface of the superalloy and formed carbides or intermetallic phases, which impeded outward nickel diffusion from the substrate to the surface and thereby inhibited coating growth. The obtained coatings fulfilled the requirements of ASTM B 875. Despite the fact that the coating formed on IN713 was thicker than that formed on IN625, the lifetime of both coated superalloys was comparable. Oxidation resistance of the aluminide coatings formed on the IN713 and IN625 superalloys makes them the favored choice for gas turbine applications. Full article

Intermetallic compounds from the Fe-Al system are attracting increasing attention due to their outstanding properties, including excellent mechanical performance, low density, corrosion, and oxidation resistance, as well as resistance to sulfidation, carburization, and wear at elevated temperatures. These unique characteristics make Fe-Al intermetallics promising candidates for high-temperature and harsh environmental applications. However, challenges such as brittleness and low plasticity have hindered their broader use. By exploring the impact of spray conditions on coating properties, this study contributes to enhancing the performance and functionality of Fe-Al coatings in industrial applications, where durability and resistance to extreme conditions are essential. This article presents the results of research on the production of composite coatings from the Fe-Al system with in situ fabricated intermetallic phases. For this purpose, arc spraying in an inert gas was used. The coating manufacturing process was carried out by simultaneously melting two different electrode filler wires, aluminum and steel, in a stream of argon. The obtained coatings were subjected to tests of roughness, adhesion to the substrate, and microstructure. It was shown that both the roughness and adhesion to the substrate of coatings sprayed in air are higher than those sprayed in argon. The increase in roughness results from the greater oxidation of coatings sprayed in air, while better adhesion is the result of the formation of coatings at a higher temperature. Metallographic studies have shown that during the spraying process, the in situ synthesis of intermetallic phases occurred. The results showed the local occurrence of intermetallic phases from the Fe-Al system. Among the two dominant phases, i.e., Al and the Fe alloy, there are also the following phases: FeAl₃, FeAl₂, and Fe₂Al₅. Furthermore, in layers sprayed in an inert atmosphere, the share of oxides is small. Full article

In this work, the oxidation behavior of an aluminide coating at 900, 1000, and 1100 °C was investigated. The aluminide coating was prepared on a cobalt-based superalloy using a vapor phase aluminizing process, which is composed of a β-(Co,Ni)Al phase outer layer and a Cr-rich phase diffusion layer. The experimental results showed that the oxidation of the coating at 900–1100 °C all obey the parabolic law. The oxidation rate constants of the coating were between 2.19 × 10⁻⁷ and 47.56 × 10⁻⁷ mg²·cm⁻⁴·s⁻¹. The coating produced metastable θ-Al₂O₃ at 900 °C and stable α-Al₂O₃ at 1000 and 1100 °C. As the oxidation temperature increases, the formation of Al₂O₃ is promoted, consuming large amount of Al in the coating, resulting in the transformation from β-(Co,Ni)Al phase to α-(Co,Ni,Cr) phase. And the decrease in the β phase in the coating led to the dissolution of the diffusion layer. Full article

In order to enhance the resistance of superalloys to high-temperature molten chloride salt corrosion, Fe-Al coatings were prepared on 310S and 347H stainless-steel surfaces via pack aluminizing. Then, the coatings were annealed at different temperatures to explore the influence of temperature on their phase constitution, microstructure, microhardness, and corrosion resistance. The results showed that the annealing temperature had a considerable effect on the corrosion resistance of the Fe-Al coatings, which was related to the change in the phase composition of the coatings that occurred due to the annealing treatment. The growth rate of the coating on 347H steel was higher than that on 310S steel, and their thicknesses from aluminizing at 800 °C for 20 h were 209.6 and 153.5 µm, respectively. When annealing at 900 °C for 30 h, the phase composition of the coatings was completely transformed into (Fe, Cr, Ni) Al. The corrosion loss rate of the annealed coating was clearly reduced, the loss rate of the 310 coating was 6.0 and −0.25 mg/cm² before and after annealing at 900 °C and that of the 347 coating was 4.89 and −0.7 mg/cm² before and after annealing at 750 °C, respectively. The two coatings showed good corrosion resistance to molten chloride salts, as demonstrated by the oxide scale (Al₂O₃) that formed on the surface, which had a thickness of about 30~40 µm. Full article

The present study focused on demonstrating the versatility of the slurry deposition technique to produce aluminide coatings to protect components from high-temperature corrosion in a broad temperature range, from 400 to 1400 °C. This is a simpler and low-cost coating technology used as an alternative to CVD and pack cementation, which also allows the coating of complex geometries and offers improved and simple repairability for a lot of industrial applications, along with avoiding the use of non-hazardous components. Slurry aluminide coatings from a proprietary water-based-Cr6+ free slurry were produced onto four different substrates: A516 carbon steel, 310H AC austenitic steel, Ti6246 Ti-based alloy and TZM, a Mo-based alloy. The resulting coatings were thoroughly characterised by FESEM and XRD, mainly so that the identification of microstructures and appropriate phases was reported for each coating. The importance of surface preparation and heat treatment as key parameters for the coating final microstructures was also evidenced, and how those parameters can be optimised to obtain stable intermetallic phases rich in Al to sustain the formation of a protective Al₂O₃ oxide scale. These coating systems have applications in diverse industrial environments in which high-temperature corrosion limits the lifetime of the components. Full article