Search Results (99)

Nickel-based superalloys are extensively used in fabricating high-temperature gas turbine components, owing to their superior high-temperature strength, excellent structural stability, and remarkable hot corrosion resistance. The influence of impurity sulfur content on their hot corrosion performance is a core scientific issue in hot-end component compositional design and smelting. This study investigated chromium (Cr)-rich nickel-based superalloys with sulfur (S) contents of 3 ppm, 16 ppm, and 42 ppm via XRD, SEM, and an EPMA, focusing on their hot corrosion behavior under a 100% Na₂SO₄ deposit at 900 °C. The results indicated that their hot corrosion products were basically identical, forming a Cr-dominated outer oxide layer rich in Ti, Co, and Ni, an Al₂O₃-based inner corrosion zone, and a CrS_x-dominated sulfide layer. With increasing sulfur content, the outer layer thickness decreased from approximately 30 μm to less than 20 μm, pores in the outer oxide layer increased in quantity and size, and internal sulfides and nitrides accumulated. The average depth of spallation increased from 55 μm for the S3 alloy to 80 μm for the S16 alloy, with the S42 alloy showing even more extensive spallation. The alloy’s hot corrosion performance deteriorated notably with increasing S content. The mechanism of sulfur’s effect on hot corrosion behavior is that sulfur in the alloy segregates at oxide film defects, enhancing defect stability and increasing their quantity and size. These defects serve as rapid diffusion channels for corrosive media, thereby accelerating the alloy’s hot corrosion rate. Full article

Thermodynamic calculations were performed in the Co-Nb-V ternary system on the isothermal sections at 1000 °C and 1200 °C, and several vertical sections at different compositional ranges were constructed using the CALPHAD methodology, drawing upon published experimental measurements. An internally consistent set of thermodynamic parameters describing the Gibbs free energies of the individual phases in the Co-Nb-V ternary system was established, yielding strong agreement between the calculated phase equilibria and reported experimental data. Furthermore, isothermal sections at other temperatures, along with the liquidus surface of the Co-Nb-V system, were subsequently calculated. Full article

An IN738 alloy with a high Al and Ti contents induces a significant cracking tendency during laser powder bed fusion (LPBF) processing, leading to a mismatch between printability and mechanical properties. Modification of alloy compositions is an effective strategy to enhance the printability and mechanical properties of nickel-based superalloys via LPBF. In this study, the effects of adding 5 wt.%Co on the printability and mechanical properties of LPBF-fabricated IN738 were investigated by using three-dimensional high-resolution micro-computed tomography (micro-CT), electron backscatter diffraction (EBSD), and quasi-static room-temperature tensile tests. The results show that adding 5 wt.%Co can significantly reduce the defect rate and defect size of the LPBF-fabricated IN738 alloy, remarkably improve alloy densification, and optimize printability. Meanwhile, compared with the LPBF-fabricated IN738 alloy, the 5 wt.%Co-IN738 alloy exhibits an excellent balance of strength and ductility in horizontal and vertical directions, both LPBF-fabricated and heat-treated. These results are anticipated to offer valuable guidance for the development of LPBF-fabricated Ni-based superalloys that achieve a favorable balance between printability and mechanical properties. Full article

Cobalt-based superalloy Co06A exhibits excellent high-temperature performance and is widely used in the repair and additive manufacturing of critical hot-end components via direct laser deposition (DLD). However, improper energy–mass input during direct laser deposition often leads to defects such as porosity, cracks, and poor surface quality, which seriously affect the performance of formed parts. In this study, a systematic experimental investigation based on an orthogonal design was carried out to examine the effects of laser power, scan speed, and powder feed rate on the dilution rate, surface roughness, and powder capture efficiency of a one-layer single Co06A track. Range analysis and multiple linear regression were employed to quantify the influence of each parameter. The results showed that the powder feed rate was the dominant factor affecting both η and Sa, while the laser power had the most significant impact on PE. Through multi-objective optimization, a balanced parameter set (u = 6.66 mm/s, f = 20.81 g/min, P = 2543 W) was recommended, which achieved a dilution rate of about 11.95%, a surface roughness of 4.64 um, and a powder capture efficiency of 79.6%. Through testing, it was found that the energy/mass input ratio was approximately 8. This work demonstrated that matching energy–mass input and adopting a constrained optimization strategy could effectively improve the forming quality and manufacturing efficiency of Co06A in the first-layer manufacturing process, providing a promising prospect in guidance for engineering applications. Full article

Dissimilar material welding enables the integration of the superior properties of different materials, thereby achieving optimal structural performance and economic efficiency while meeting specific service requirements. The presence of solid-solution strengthening elements such as Ti, Co, and Al, and trace elements such as P and S, in GH3030 nickel-based superalloy leads to their segregation and the formation of intermetallic compounds in the welded joint, resulting in deterioration of joint performance. High-entropy alloys (HEAs), with their high-entropy effect and delayed diffusion effect working synergistically, can effectively suppress compositional segregation caused by uneven elemental diffusion and the formation of intermetallic compounds at interfaces, thereby improving the quality of welded joints and demonstrating great potential for dissimilar material joining. Therefore, in this study, fiber laser welding was used to effectively join AlCoCrFeNi2.1 eutectic high-entropy alloy and GH3030 nickel-based superalloy, with the expectation to improve welded joint element segregation, suppressing the formation of intermetallic compounds, and enhance the welded joint quality and its performance. The AlCoCrFeNi2.1/GH3030 joint exhibits an average yield strength of 1.31 GPa, which is significantly higher than that of the GH3030/GH3030 joint (1.07 GPa). In addition, the AlCoCrFeNi2.1/GH3030 joint shows a higher average work-hardening exponent of 0.337 compared with 0.30 for the GH3030/GH3030 joint, indicating improved plasticity. The results showed that under appropriate welding process parameters, the hardness of the weld zone, transitioning from the nickel-based superalloy to the eutectic high-entropy alloy, exhibited a stable increasing trend, and the joint exhibits good plasticity, with brittle fracture being unlikely. Full article

Thermal barrier coatings (TBCs) extend gas-turbine blade lifetime by improving high-temperature oxidation resistance and mechanical performance. We investigated the microstructural evolution, TGO growth, and Al depletion in air-plasma-sprayed (APS) single-layer YSZ top coat over a NiCrCoAlY bond coat on Ni-based superalloy circular plates, heat treated isothermally at 850 °C and 1000 °C for 50–5000 h. Cross-sectional SEM/EDS analysis showed TGO quadratic thickening kinetics at both temperatures, reaching ~10 µm at 1000 °C/5000 h, the growth rate of which was ~5.8 times higher than at 850 °C. On top of the single-layer TGO of Al₂O₃ observed from the onset, a NiCrCo oxide layer appeared and grew from ≥500 h at 850 °C, with increasing growth rate and cracking. The layer configuration of the YSZ top coat, the TGO of Al₂O₃, and the bond coat (comprising β-NiAl and γ-NiCr) on top of GTD111, showed an Al concentration gradient in the bond coat starting at 850 °C for 250 h, which intensified with increased duration and temperature. The decrease in Al concentration in the bond coat and the growth of TGO are due to the dissolution of β-NiAl and subsequent Al diffusion to the Al₂O₃ TGO. Full article

In this study, 10% nitric acid was employed to remove the aluminum coating on the cobalt-based superalloy K6509, with a focus on elucidating the corrosion mechanism and evaluating the effect of ultrasonic on the removal process. The results shows that ultrasonic treatment (40 kHz) significantly improves coating removal efficiency, increasing the maximum corrosion rate by 46.49% from 2.5413 × 10⁻⁷ g·s⁻¹·mm⁻² to 4.7488 × 10⁻⁷ g·s⁻¹·mm⁻² and reducing removal time from 10 min to 6 min. This enhancement is attributed to cavitation effect of ultrasonic bubbles and the shockwave-accelerated ion diffusion, which together facilitate more efficient coating degradation and results in a smoother surface. In terms of corrosion behavior, the difference in phase composition between the outer layer and the interdiffusion zone (IDZ) plays a decisive role. The outer layer is primarily composed of β-(Co,Ni)Al phase, which is thermodynamically less stable in acidic environments and thus readily dissolves in 10% HNO₃. In contrast, the IDZ mainly consists of Cr₂₃C₆, which exhibit high chemical stability and a strong tendency to passivate. These characteristics render the IDZ highly resistant to nitric acid attack, thereby forming a protective barrier that limits acid penetration and helps maintain the integrity of the substrate. Full article

This article presents a review of the composition optimization progress of nickel-based single crystal (SC) superalloy design in recent years in order to obtain better high-temperature performance for the development of the aviation industry. The influence of alloying elements on the creep resistance, microstructure characteristics, oxidation resistance, castability, density, and cost of superalloys is analyzed and discussed. In order to obtain better high-temperature performance, the content of refractory elements (Ta + Re + W + Mo) and Co was increased gradually. The addition of Ru was added in the fourth-generation nickel-based SC superalloy to stabilize the microstructures and suppress the precipitation of the topologically close-packed (TCP) phase. However, the content of the antioxidant element Cr significantly decreased, while the synergistic effect of Al, Cr, and Ta received more attention. Therefore, synergistic effects should also receive more attention to meet the practical needs of reducing the content of refractory elements to reduce costs and density in future single crystal alloy designs without compromising critical performance. Full article

This study investigated how long-term aging (750 °C and 950 °C) affects the microstructure and room-temperature tensile properties of the Ni-Co-Cr superalloy GH3617. Characterization (SEM, EDS, EBSD) showed that initial aging (750 °C, 500 h) formed discontinuous M₂₃C₆ carbides, pinning grain boundaries and improving strength. Prolonged aging (750 °C, 5000 h) caused M₂₃C₆ to coarsen into brittle chain-like structures (width up to 1.244 μm) and precipitated M₆C carbides, degrading grain boundaries. Aging at 950 °C accelerated this coarsening via LSW kinetics (rate constant: 6.83 × 10⁻² μm³/s), with Mo segregation promoting M₆C formation. Tensile properties resulted from competing γ′ precipitation strengthening (post-aging strength increased up to 23.3%) and grain boundary degradation (elongation dropped from 70.1% to 43.3%). Fracture shifted from purely intergranular (cracks along M₂₃C₆/γ interfaces at 750 °C) to mixed mode (cracks initiated by M₆C fragmentation at 950 °C). These insights support superalloy microstructure optimization and lifetime prediction. Full article

This study presents a bibliometric analysis of the evolution and research trends in the additive manufacturing (AM) of superalloys over the last decade (2015–2025). The review follows a structured methodology based on the PRISMA 2020 protocol, utilizing data from the Scopus and Web of Science (WoS) databases. Particular attention is devoted to the intricate process–structure–property relationships and the specific behavioral trends associated with different superalloy families, namely Ni-based, Co-based, and Fe–Ni-based systems. The findings reveal a substantial growth in scientific output, with the United States and China leading contributions and an increasing trend in international collaboration. Key research areas include process optimization, microstructural evolution and control, mechanical property assessment, and defect minimization. The study highlights the pivotal role of technologies such as laser powder bed fusion, electron beam melting, and directed energy deposition in the fabrication of high-performance components. Additionally, emerging trends point to the integration of machine learning and artificial intelligence for real-time quality monitoring and manufacturing parameter optimization. Despite these advancements, challenges such as anisotropic properties, porosity issues, and process sustainability remain critical for both industrial applications and future academic research in superalloys. Full article

GH2097, a Fe-Ni-Co-based superalloy extensively employed in high-temperature critical components such as aircraft engines, was investigated to elucidate the influence of Si content on its precipitation behavior and mechanical properties. By systematically adjusting Si concentrations, it was demonstrated that Si significantly modulates the size, distribution, and stability of γ′ phase (Ni₃TiNb). As Si content increases, γ′ phase coarsening (mean size: 30.1→40.3 nm) results in a marginal increase in volume fraction of 2%. Mechanical testing revealed a direct correlation between Si content and yield strength enhancement, achieving a maximum increment of 97.1 MPa. Post solution-aging treatment, γ′ strengthening dominated the strengthening mechanisms in GH2097, contributing over 50% to the overall strength. Microstructural characterization (SEM/TEM) further confirmed that optimal Si addition balances precipitation kinetics and grain boundary stabilization without inducing detrimental phases. Therefore, it is important to consider the role of the Si element in the microstructure control of GH2907 alloy. Full article

This study comprehensively evaluates a non-weldable nickel-cobalt-based superalloy fabricated using laser powder bed fusion (LPBF) technology. The investigation systematically examined the impact of heat treatment, specifically solution treatment and solution treatment followed by aging treatment, on the microstructural characteristics and the evolution of residual stress within the alloy. The findings indicated that the as-built Ni-Co-based superalloy predominantly consists of equiaxed crystals and epitaxial columnar crystals, with no formation of the γ′ phase observed. After the solution treatment, the alloy experienced equiaxed columnar crystallization, recrystallization, and grain refinement. Additionally, a significant quantity of γ′ phases within the alloy exhibited a specific arrangement and precipitation. Following the aging treatment, there was an observed increase in the average dimensions of both the γ′ phase and the grains within the alloy. The evolution of residual stress distribution perpendicular to the construction direction in the alloy, both before and following heat treatment, was assessed using the contour method. The results showed that heat treatment progressively diminished the residual stress levels within the alloy. Furthermore, this study discusses the interrelationship between residual stress and the microstructural evolutions of nickel-cobalt-based superalloys throughout the heat treatment process. Full article

This study systematically explores and expands upon the research questions, revealing the scientific principles and engineering value of chromium–aluminum (Cr-Al) co-diffusion coatings in enhancing high-temperature friction performance. This study addresses the critical need for wear resistance in GH5188 cobalt-based alloy stator bushings operating in high-temperature environments. The high-temperature wear resistance mechanism of aluminized coatings modified with Cr elements on the GH5188 alloy, based on thermal diffusion technology, was investigated. The experimental results indicate that the high-temperature wear resistance of the samples was directly related to the type and content of oxides in the wear scars and debris. After friction at 700 °C, the aluminized coating on the GH5188 alloy showed the lowest oxide content in the wear scars, primarily composed of CoAl₂O₄. The oxides in the wear scars of the GH5188 alloy and Al-Cr co-aluminized coatings were mainly CoCr₂O₄ and Cr₂O₃, with the Al-Cr co-aluminized coating showing the highest amount of wear debris. The Cr-rich oxide debris not only has high thermodynamic stability but also exhibits relatively low high-temperature growth stress, making it difficult to spall. Additionally, the higher diffusion coefficient of Cr³⁺ accelerates the reoxidation of wear debris pits, resulting in excellent high-temperature wear resistance. The wear rate of the Al-Cr co-aluminized coating was reduced by 30% compared with the GH5188 substrate and by 69% compared with the aluminized coating. In summary, the key findings are not only applicable to cobalt-based alloys but can also be extended to a broader range of material systems and engineering applications. This provides new perspectives and methodologies for the design of high-temperature coatings, the development of materials for extreme conditions, and interdisciplinary applications. Full article

CoNiCrAlY coatings are widely used as typical high-temperature materials to enhance the surface performances of nickel-based superalloy materials, which can be used as bond coats in thermal barrier coatings and abradable seal coatings. In this study, high-pressure cold spray technology was used to deposit CoNiCrAlY coatings on nickel-based superalloy substrates. The microstructure characteristics and oxidation behaviors of CoNiCrAlY coatings prepared by different gas types and cold spray parameters were systematically investigated. EBSD analysis showed that the deformation of the helium coating was more distinct, and the grain size of the coating fabricated by helium was smaller than that by nitrogen as seen from the grain morphology. The high-temperature oxidation results showed that the coating oxide film thickness varied parabolically with time for both coatings after 500 h isothermal oxidation at 800 °C, 900 °C, and 1000 °C, and the oxidation rate of the coating after heat treatment was lower than that of the as-sprayed coating. In addition, the shrinkage of the aluminum reservoir inside the coating, the element diffusion rate, and the amount and type of oxide generation on the surface all affected the oxidation process. Additionally, the helium coating had a lower oxidation growth rate and better oxidation resistance. Therefore, cold spray can be an alternative way to fabricate high-quality CoNiCrAlY coatings. 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