Search Results (439)

In this study, we examine an ex-service, Ni-base single-crystal blade made of alloy PWA1483, which was in service for 6000 h. Using light optical, scanning, and transmission electron microscopy, we analyzed the microstructure at the blade’s tip, middle, and root. Key focus areas included surface features, dendrite spacings, γ’-particle sizes, and dislocation densities. The findings reveal that the bulk microstructure hardly evolved. Dendrite spacings exhibited a consistent microstructure across all locations and there were no significant differences between the local alloy chemistries of dendritic and interdendritic regions, indicating high-quality processing. A bimodal γ’-particle distribution was observed. Variations in γ’-sizes and γ-channel widths were noted, with the tip showing rounded γ’-particles. Small spherical particles occurred only in the root and middle of the blade. The middle location exhibited the highest hardness. Dislocation densities were low and uniform, with the highest density correlating with the highest hardness. Full article

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

Thermal barrier coatings (TBCs) are an effective means of providing thermal insulation and protecting the hot-section components of gas turbine engines. Their quality and performance characteristics largely depend on the microstructural features and the bond strength between the bonding layer and the substrate. The present study aims to determine the optimal plasma spraying parameters that ensure the formation of NiCrAlY coatings with superior microstructural integrity and adhesion strength. The objective of the study is a thermally sprayed nickel–chromium–aluminum–yttrium (NiCrAlY) bond coat deposited onto an Inconel 718 nickel-based superalloy, which is widely used in aircraft gas turbine engines due to its high strength and excellent oxidation resistance at elevated temperatures. It was found that the coating produced under the optimized conditions exhibited a significantly higher adhesion strength compared with the samples obtained under other spraying regimes. The results confirm that a precise adjustment of the atmospheric plasma spraying (APS) process parameters, taking into account the equipment configuration, allows for a substantial improvement in coating quality and performance. Full article

Increased alloying content in advanced Ni-based superalloys for large disc forgings intensifies microsegregation and promotes the formation of detrimental secondary phases, challenging the cast-and-wrought processing route. This study investigates the effects of Ta addition on the solidification and homogenization behaviors of a high-alloyed GH4065A superalloy by comparing the base alloy with a variant containing 5 wt.% Ta (5Ta alloy). As-cast and homogenized microstructures were characterized using SEM and EPMA, solidification behavior was analyzed via DSC, and homogenization kinetics were modeled. Results demonstrate that Ta addition stabilizes the η phase, increasing its solidification temperature and fraction in the as-cast microstructure, but does not alter the solidification sequence. During homogenization, Nb remained the most segregated element and governed the homogenization kinetics, whereas Ta preferentially partitioned into MC carbides and the η phase. The diffusion activation energy for Nb in the 5Ta alloy was determined, and a diffusion model was established to describe the elimination of microsegregation. Optimum homogenization parameters were determined to completely dissolve the η phase and eliminate microsegregation. The results indicate that strategic Ta addition for enhanced performance does not compromise ingot manufacturability, providing valuable guidance for the processing and composition design of advanced disc superalloys. Full article

This study takes the commercial JG4246A cast Ni₃Al-based superalloy as the research object, under the conditions of preheating the mold shell at 1020 °C and a pouring temperature of 1520 °C, characteristic simulation castings were poured. The microstructure and room temperature mechanical properties of different modulus sections of the castings were systematically investigated. It was found that, except for the edge towards the middle section of the larger modulus, the cooling rates at the edge were greater than those at the middle sections. The cooling rate was the fastest at the upper-right corner section (referring to the castings position during pouring, the same below), and the grain is the finest (approximately 0.46 mm), with the highest strength (tensile strength approximately 698 MPa, yield strength approximately 581 MPa), while the cooling rate at the lower-middle section was the slowest, and the grain was the largest (approximately 1.55 mm), with the lowest strength (tensile strength approximately 612.5 MPa, yield strength approximately t 524.5 MPa); the difference in grain size between the two is nearly 237%. The MC carbides at the lower-edge middle section have the smallest size (approximately 3.0 μm) and the elongation rate in this area is the highest (approximately 8.7%), while the MC carbides at the lower-middle section have the largest size (approximately 5.8 μm) and the elongation rate in this area is the lowest (approximately 4.9%); the size difference in the MC carbides between two is nearly 94%. This study clarifies the quantitative correlation between cooling rate, microstructure and properties, providing clear guidelines for optimizing the casting process of high-temperature alloys and subsequent studies on the uniformity of microstructure. Full article

Cavitation erosion is a critical problem for many engineering components, such as ship propellers, diesel engine exhaust valves, cylinder liners, pump impeller blades, hydraulic turbines, and bearings, which are exposed to high-velocity flowing fluids or to vibratory fluid motion. It represents a mechanical degradation of the surface caused by the continuous collapse of bubbles in the surrounding liquid, which seriously affects flow efficiency and component service life, increasing maintenance frequency and refurbishment costs. The intensity and evolution of the cavitation erosion phenomenon depend on the hydrodynamic conditions to which the component surface is exposed, the properties of the liquid, and the judicious selection of the most suitable material. This paper aims to modify the microstructure of a Ni-based superalloy by applying recrystallization annealing heat treatment in order to obtain surfaces resistant to cavitation erosion for components that handle fluids under local pressure fluctuations. Experimental tests are carried out using a vibratory apparatus with piezoceramic crystals operating at a frequency of 20 kHz and an amplitude of 50 µm. The cavitation erosion performance of the Ni-based superalloy INCONEL 625, heat treated by recrystallization annealing, are compared with that of austenitic stainless steel AISI 316L subjected to solution treatment. For both metallic alloys, based on mass loss measurements, the characteristic time-dependent curves of the mean cumulative erosion penetration depth, MDE(t), and the mean erosion rate, MDER(t), are determined. The comparison of these curves and of the parameters defined and recommended by the ASTM G32 standard demonstrates that, for the Inconel 625 superalloy, resistance to cavitation erosion increases by 77–81% compared to that of AISI 316L austenitic stainless steel. X-ray diffraction analyses (XRD) show that, in the microstructure of the Inconel 625 superalloy, in addition to austenite, MC-type carbides, M₂₃C₆ carbides, and intermetallic phases γ″ = Ni₃(Nb, Al, Ti) and δ = Ni₃(Nb, Mo) are also present. Full article

During the extrusion of novel nickel-based powder superalloy bars, the die is subjected to elevated temperatures, high pressures, and severe friction, which readily lead to abrasive wear and thermal-fatigue damage. These failures deteriorate the quality of the extruded products and significantly shorten the service life of the die. Frequent repair and replacement of the tooling ultimately increase the overall manufacturing cost. This study investigates the friction and wear behavior of H13 and 5CrNiMo hot-work tool steels under extreme transient high-temperature conditions by combining finite element simulation with tribological testing. The temperature and stress distributions of the billet and key tooling components during extrusion were analyzed using DEFORM-3D. In addition, pin-on-disk friction and wear tests were conducted at 1000 °C to examine the friction coefficient, wear morphology, and subsurface grain structural evolution under various loading conditions. The results show that the extrusion die and die holder experience the highest loads and most severe wear during the extrusion process. For 5CrNiMo tool steel, the wear mechanism under low loads is dominated by mild abrasive wear and oxidative wear, whereas increasing the load causes a transition toward adhesive wear and severe oxidative wear. In contrast, H13 tool steel exhibits a transition from abrasive wear to severe oxidative wear. In 5CrNiMo steel, friction-induced recrystallization, grain refinement, and softening lead to the formation of a mechanically mixed layer, which, together with a stable third-body layer, markedly reduces and stabilizes the friction coefficient. H13 steel, however, undergoes surface strain localization and spalling, resulting in persistent fluctuations in the friction coefficient. The toughness and adhesion of the oxide film govern the differences in wear mechanisms between the two steels. Owing to its higher Cr, V, and Mo contents, H13 forms a dense but highly brittle oxide scale dominated by Cr and Fe oxides at 1000 °C. This oxide layer readily cracks and delaminates under frictional shear and thermal cycling. The repeated spalling exposes the fresh surface to further oxidation, accompanied by recurrent adhesion–delamination cycles. Consequently, the subsurface undergoes alternating intense shear and transient load variations, leading to localized dislocation accumulation and cracking, which suppresses the progression of continuous recrystallization. Full article

Metal additive manufacturing (AM) generates complex microstructures through extreme thermal gradients and rapid solidification, critically influencing mechanical performance and industrial qualification. This review synthesizes recent advances in cellular automata (CA) and phase-field (PF) modeling to predict grain-scale microstructure evolution during AM. CA methods provide computational efficiency, enabling large-domain simulations and excelling in texture prediction and multi-layer builds. PF approaches deliver superior thermodynamic fidelity for interface dynamics, solute partitioning, and nonequilibrium rapid solidification through CALPHAD coupling. Hybrid CA–PF frameworks strategically balance efficiency and accuracy by allocating PF to solidification fronts and CA to bulk grain competition. Recent algorithmic innovations—discrete event-inspired CA, GPU acceleration, and machine learning—extend scalability while maintaining predictive capability. Validated applications across Ni-based superalloys, Ti-6Al-4V, tool steels, and Al alloys demonstrate robust process–microstructure–property predictions through EBSD and mechanical testing. Persistent challenges include computational scalability for full-scale components, standardized calibration protocols, limited in situ validation, and incomplete multi-physics coupling. Emerging solutions leverage physics-informed machine learning, digital twin architectures, and open-source platforms to enable predictive microstructure control for first-time-right manufacturing in aerospace, biomedical, and energy applications. Full article

In the framework of high temperature components, the need to evaluate the accumulated creep damage during service life is fundamental to extend the life of components which are currently deemed as scrap as per design intent. Thus, the life assessment of Ni-based superalloys could be performed in relation to the accumulated creep deformation which represents the limiting factor for serviced components. Despite the different microstructural changes that occur in service life, this work focuses on the possibility to evaluate the material strain by means of electron backscattered diffraction (EBSD). The key point is the identification of the correlation between geometrically necessary dislocation (GND) density derived from EBSD analyses and the reached creep strain for a single crystal Ni-based superalloy. However, the results of GND density are affected by the settings’ parameters adopted to perform the analysis by the magnification level and the step size. These two parameters have been optimized by analyzing specimens from interrupted creep tests at strain levels between 0.5% and 10%, in the temperature range between 850 °C and 1000 °C. Full article

The bonding behavior of the Ni-based superalloy CM247LC during transient liquid phase (TLP) bonding is strongly governed by filler metal chemistry, particularly boron activity. In this study, the time-dependent bonding mechanisms of CM247LC joints fabricated using a high-boron MBF-80 filler and a low-boron MBF-20 filler are systematically compared to clarifying the transition between reaction-dominated brazing and diffusion-assisted TLP bonding. Microstructural analyses reveal that MBF-80 promotes the formation of a persistent, reaction-stabilized interlayer characterized by strong boron localization and the development of boron-rich intermetallic reaction products. These features kinetically suppress diffusion-assisted homogenization and prevent isothermal solidification, resulting in pronounced chemical and mechanical discontinuities across the joint. In contrast, MBF-20 enables progressive boron depletion, suppression of stable intermetallic accumulation, and interfacial smoothing, leading to diffusion-assisted chemical redistribution and partial isothermal solidification. This evolution is accompanied by gradual convergence of hardness profiles toward that of the CM247LC base metal, indicating improved mechanical continuity. These results demonstrate that joint hardness alone is insufficient for evaluating bonding quality in CM247LC. Instead, controlled microstructural evolution governed by low-boron filler chemistry is essential for achieving chemically and mechanically compatible joints. The present work establishes a clear mechanistic link between filler metal composition and bonding behavior, providing guidance for the design of reliable TLP bonding strategies in Ni-based superalloys. Full article

The thermodynamic instability and relatively low mechanical strength of γ/γ′ phase boundaries in Ni-based single-crystal superalloys compromise the service safety of these materials. The interfacial segregation behavior of alloying elements is expected to enhance the thermodynamic stability and mechanical strength of γ/γ′ phase boundaries. In the present research, first-principles computations grounded in density functional theory were performed to examine the unclarified cosegregation characteristics of W-Re/Cr solutes at the γ-Ni/γ′-Ni₃Al phase boundary, as well as the impacts of such cosegregation on interfacial formation heat and Griffith fracture work. The results indicated that Re and Cr atoms tend to segregate preferentially at the γ-L₁-3.52-cp site within the W-alloyed phase boundary. This phenomenon can be attributed to the attractive interactions between W and Re/Cr, along with the fact that this site exhibits the most negative segregation energy. The thermodynamic stability of W-Re and W-Cr cosegregated phase boundaries is significantly enhanced, being much higher than that of clean or W-segregated phase boundaries, which is ascribed to deeper pseudogaps at the Fermi level. Notably, the preferred fracture path remains in region-1 after cosegregation, as directly evidenced by its lower Griffith fracture work compared to region-2. This disparity is rationalized by charge density analysis, which reveals a pronounced charge accumulation and consequently stronger bonding in region-2. Our results may provide atomistic insights into the solute cosegregation behaviors and their interfacial strengthening and stabilizing effects, and also the interfacial composition manipulation of Ni-based single-crystal superalloys. 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

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

The oxidation behavior and microstructures of the GTD-111 Ni-based superalloy were investigated following heat treatment at 850 °C and 1000 °C for up to 5000 h, using Optical Microscopy (OM), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Transmission Electron Microscopy (TEM). SEM/EDS analysis showed that the microstructure of the samples mainly consisted of γ′ precipitates in the matrix, eutectic phases, and several types of carbides. Cross-sectional analysis revealed that the oxidation region was composed of three layers: a top layer (NiO, TiO₂, Cr₂O₃), a sublayer (Ta₂O₅, TiO₂), and an inner layer (Al₂O₃), followed by a needle-like Ti-containing phase. The oxidation kinetics followed the parabolic law as a function of time at each temperature. After the heat treatments, the dendritic regions of all specimens consisted of cuboidal primary γ′ precipitates and spherical secondary γ′ precipitates. Chinese-script-like and blocky-shaped MC carbides, as well as three types of M₂₃C₆ carbides, were found in the interdendritic region. The fracture mode of the tensile specimens transformed from cleavage (brittle) fracture to ductile fracture as the temperature increased. Cracks were observed inside the MC carbides on the fracture surface, which may serve as significant crack initiation sites. Full article

The present study systematically investigated the hot deformation behavior of GH2787 superalloy within the temperature range of 1060–1120 °C and strain rates of 0.1–10 s⁻¹. An Arrhenius-type constitutive equation was developed that accurately predicts the flow behavior, and the calculated thermal deformation activation energy Q is 364,401.19 J/mol. The hot working map was constructed based on the dynamic material model, which identified two preferred processing regions with power dissipation efficiency exceeding 0.3, and no flow instability was observed across the entire parameter range. Microstructural analysis reveals that the extent of dynamic recrystallization significantly increases with rising temperature and strain rate. Discontinuous dynamic recrystallization (via grain boundary bulging nucleation) serves as the dominant recrystallization mechanism in GH2787 superalloy during hot deformation, while continuous dynamic recrystallization (via subgrain rotation and coalescence) acts as a synergistic auxiliary mechanism, jointly driving microstructural evolution. This study provides important theoretical foundations for optimizing the hot working processes of GH2787 superalloy. Full article