Hydrogen atom incorporation into alloys can lead to hydrogen embrittlement, significantly affecting mechanical properties. However, the interaction between hydrogen and microstructure remains unclear for Ni-based polycrystalline superalloys intended for hydrogen-fueled gas turbines. Therefore, the hydrogen embrittlement behavior of Ni-based polycrystalline superalloy was systematically investigated through multi-scale characterization, identifying MC carbide as the primary factor influencing the hydrogen embrittlement behavior of the superalloy. Secondary ion mass spectroscopy and hydrogen microprint technique analysis revealed significant hydrogen segregation at the MC carbide/matrix interface and within MC carbide rather than the grain boundary and M6 C carbide. Besides, the first-principles calculation also identified that MC carbide in the superalloy acted as the hydrogen trapping site. After hydrogen charging and tensile testing, the number of cracks within MC carbide, kernel average misorientation values and the dislocation density at carbide/matrix interface increased significantly. Nanoindentation tests further confirmed that MC carbide exhibited superior hydrogen embrittlement susceptibility. This research provides new insight for the development of hydrogen-embrittlement-resistant Ni-based polycrystalline superalloys. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

In this work, the synergistic enhancement of strength and ductility in a high-Cr Ni-based polycrystalline superalloy was achieved through modulating the precipitation behavior. The optimized alloy with more irregular shape and higher linear density of M23C6 carbide along grain boundaries, higher absolute value of γ/γ’ lattice misfit and higher area fraction of γ’ phase exhibited the best strength and elongation. Firstly, M23C6 carbide along grain boundaries in the optimized alloy, which had more irregular morphology and higher linear density, can efficiently separate micro-voids, leading to the enhancement of pinning effect and improved elongation. Secondly, the stacking fault energy of γ’ phase in the optimized alloy increased, which made greater resistance of γ’ phase to deform. Additionally, the area fraction of γ’ phase and absolute value of γ/γ’ lattice misfit in the optimized alloy were both higher, resulting in a stronger strengthening effect. Therefore, the synergistic enhancement of the strength and ductility of the superalloy was achieved by regulating the precipitation behavior of the precipitates.

The design and application of high-tungsten (W) superalloys represent an effective strategy for enhancing the high-temperature performance of superalloys. However, the associated deterioration of mechanical properties caused by high refractory element content remains an urgent issue to be resolved. A model high-W superalloy with Al contents of 3, 4, 5, and 6 wt% was designed to study the optimization mechanism of Al content. The effects of Al content on the microstructure and stress rupture properties were investigated. The results of thermodynamic calculations and microstructural observation demonstrated that increasing the Al content promoted the precipitation of both the gamma ' and alpha-W phases. The peak stress rupture life was achieved at an Al content of approximately 5 wt%. This optimum is attributed to the competing strengthening mechanisms: increased Al content enhanced precipitation strengthening but concurrently reduced the solid solution strengthening of W as it partitioned into alpha-W precipitates. Thus, the optimized performance at 5 wt% Al resulted from a balance between these mechanisms. The regulation of Al content enabled control over the microstructural morphology, which in turn enhanced the stress rupture life at elevated temperatures. This work provides novel insights and theoretical support for the development and application of high-W superalloys.

The multi-blade casting technique used in fabricating blades by the superalloy K418B was investigated, which is more efficient and cost-saving in comparison with the traditional polycrystalline superalloy casting technique. In this work, the differences in microstructures and mechanical properties were analyzed by adjusting different thicknesses of the blades. The results of experimental studies and numerical simulations showed that the size of the γ' phase and the stress rupture property were positively correlated with the thickness of the blades and that the cooling rate and the residual stress were negatively correlated with it. Additionally, the residual stress decreased from 200 to 50 MPa as the thickness of the blades increased which followed the same trends as the geometrically necessary dislocation (GND) density. This study provides guidance in the optimization of microstructure in multi-blade casting technology.

The effect of Nb and Ti on the microstructure and stress rupture life of high tungsten superalloy was studied experimental characterization and theoretical calculation. Referring to the existing high-tungsten superalloys, the phase composition of different Nb as well as Ti contents was calculated and counted by Thermo-Calc calculation. Both the Nb and Ti contents were decided to be 1.8 wt % and 0.8 wt %, respectively, as the addition amount of Nb and Ti in this experiment. The experimental results revealed that the addition of Nb and Ti promoted the increase of MC carbides as well as gamma '-phase area fraction, and the stress rupture life (1100 degrees C/70 MPa) with1.8Nb0.8Ti is nearly 7.5 times higher than that of alloy with 0Nb0Ti. The crack of the alloy with 0Nb0Ti were found to initiate at MC carbides and extend along grain boundary, and eventually fractured. The addition of Nb and Ti reduced the W content in MC carbide and improved the coordinated deformation ability between MC carbide and gamma phase, the initiation of the crack was difficult to occur at gamma/gamma ' interface. Through the first-principles calculation, the elastic modulus of gamma '-Ni3 (Al0.5Nb0.25Ti0.25) phase with the addition of Nb and Ti is obviously increased, which obviously enhance the deformation resistance ability of gamma ' phase, and dislocations were not easy to shear into the interior of gamma ' phase and form dislocation network with high density at interface of gamma/gamma ' phases, substantially improving the stress rupture life. The experimental results and in-depth analysis provided theoretical reference and support for the future high tungsten superalloys design.

The interfacial reaction between CaO-Y2O3 system and superalloy melt was systematically studied, and the relationship between reaction temperature and interfacial reaction was revealed. Innovative experimental methods combined with XRD and SEM-EDS characterization techniques were applied in this paper. The reaction behavior of CaO-Y2O3 c9eramic system and typical high activity superalloy interface reaction products, including phase and element distribution, has been systematically studied. The interface reaction is in the form of CaOY2O3+Al+S -> CaS+Y+CaAlYO4. CaAlYO4 composite oxide plays a key role in the reaction as a dielectric layer between the melt and the refractory. CaAlYO4 acts as the medium layer to ensure the desulfurization and yttrium addition of the superalloy melt. Temperature affects the chemical composition and reaction rate of the dielectric layer, which in turn determines the interface reaction process. Temperature dependent relationship of the interface reaction between melt and ceramic is explained in detail. The increase of reaction temperature changes the oxide composition of the medium layer and promotes the desulfurization and yttrium reaction. CaO-Y2O3 is a refractory system with both desulfurization and rare earth effect.

The M23C6 phase is usually precipitated in high-Cr content Ni-based polycrystalline superalloys, which has significant effects on properties of the alloys. In this work, the role of Ti on the modification of M23C6 carbides was investigated. In the alloys without Ti (6.6Al-0Ti alloy), MC carbides decomposed and M23C6 carbides precipitated during primary aging treatment. In contrast, alloy containing Ti (3.8Al-3Ti alloy), MC carbides remained stable throughout aging process and M23C6 carbides precipitated during secondary aging treatment. Furthermore, M23C6 carbides distributed along grain boundaries in 6.6Al-0Ti alloy were larger and more regular. According to first-principle calculations, the formation energy of MC carbide in 3.8Al-3Ti alloy was lower, which indicated MC carbide was more stable, resulting in limited carbon available for M23C6 carbides precipitation. Therefore, the introduction of Ti would inhibit precipitation of M23C6 carbides due to more stable MC carbides in superalloy containing Ti.

The reaction mechanism at the interface between CaO-Y2O3 composite oxide refractories and superalloy melt during vacuum induction melting of Ni-based superalloys was investigated. Once the reaction occurred, the interfacial layer consisted of exterior CaS layer and interior CaYAlO4 layer. CaS was formed by the desulfurization reaction of CaO and S from alloy melt. While the CaYAlO4 was formed by the reaction of 12CaO.7Al2O3 or Al2O3 (CaO and Y2O3 were replaced by Al), CaO and Y2O3. The whole interfacial reaction was: CaO(s)+[S]Ni(l)+ [Al]Ni(l)+Y2O3(s)=CaYAlO4(s)+ CaS(s)+[Y]Ni(l).

To investigate the influence of W and Al on the microstructure and mechanical properties of a high-W superalloy, the Thermo-Calc calculation was utilized to simulate the microstructure with various W and Al contents. The results indicated that the concentration of W and Al exceeded 15.7 wt

The addition of Mg was intentionally applied in Ni-based superalloy and the effect of Mg on the mechanical and microstructural properties was systematically investigated in this study. It was found that adding small amount of Mg could be beneficial to the mechanical properties. However, the mechanical properties decreased with higher Mg addition, which was due to the variation in the morphology of MC carbides and the number of γ/γ’ eutectics. The spheroidized MC carbides resulted from the small amount of Mg addition could reduce stress concentration, while the increasing number of γ/γ’ eutectic caused by higher addition of Mg would generate more microcracks. The results of experiments and density-functional theory (DFT) calculations show that the addition of magnesium facilitated the nucleation of MC carbides and constrained the growth, resulting in spherical MC carbides. Overall, this study provided a new insight for designing and enhancing the properties of cast superalloys.

The formation of freckles in a novel central cooling and central heating (CCH) process and high-rate solidification (HRS) process were investigated. The CCH process improves the growth conditions for single crystals to reduce the scrap rate and has a structure with a cluster of large-caliber castings to improve production. The results of experiments and numerical simulations showed that the CCH process basically eliminates the shadow effect. The width of the mushy zone in the CCH process is 0.25 mm-0.31 mm, much narrower than that of the HRS process. It is not wide enough to form plume flow so reducing the freckles formation. In addition, by introducing the modified parameters, an improved Rayleigh number criterion is proposed. Compared to the original criterion, the improved Rayleigh number criterion has a higher accuracy of freckle formation prediction.

Eutectic high entropy alloy (EHEA) is the most promising high entropy alloy (HEA) system for large-scale industrial applications due to its excellent comprehensive properties. However, the strength-ductility matching ability of as-cast EHEAs is still slightly insufficient compared with advanced high-strength steels. Heterostructure design is an effective means to improve the mechanical properties of materials. Therefore, the thermomechanical treatment parameters of introducing the multi-level heterogeneous lamellar structure into the self-designed AlCrFe1.5Ni2.6 EHEA were determined, and the influence of the constructed structure on the mechanical properties, the strengthening mechanism, and the fracture behavior of the alloy were revealed in this work. The results showed that the AlCrFe1.5Ni2.6 EHEA underwent phase decomposition behavior and selective recrystallization behavior after cold rolling and isothermal annealing at 800 degrees C for 1 h, thus forming the heterogeneity of two-phase size and spatial distribution, and the heterogeneity of multi-scale grain size. Due to the heterodeformation-induced strengthening and hardening effect of the unique heterostructure, compared with as-cast alloy, the strength of the fabricated EHEA was increased significantly, and the elongation remained unchanged. At the same time, heterostructure design could effectively hinder the propagation process of microcracks in the alloy and improve the crack tolerance of the alloy, thus avoiding the premature failure of the material caused by the rapid propagation of microcracks. The findings of the current work will provide a simple and efficient way to strengthen the mechanical properties of EHEAs.

The utilization of revert cast superalloys presents significant advantages in environmental protection and production efficiency enhancement, which contain large amounts of nitrogen. This study comprehensively investigated the nitrogen-induced effects on microstructural characteristics and creep performance in Ni-based cast superalloys, with focus on microsegregation and inclusion evolution. Experimental results demonstrated that increasing nitrogen content from 4 ppm to 55 ppm led to progressive intensification of elemental segregation. A direct correlation between nitrogen concentration and nitride precipitation was revealed: higher nitrogen levels promote both increased number density and dimensional growth of nitride particles. First-principles calculations demonstrated that TiN inclusions preferentially form during solidification and serve as heterogeneous nucleation cores, thereby refining the grain structure. Increased nitrogen content reduced the volume fractions of MC carbides, gamma/gamma ' eutectics, and gamma ' precipitates. A MC carbide morphological transition from rod-like to blocky configurations was observed as N content rose, accompanied by increased number density and reduced particle dimensions. Creep tests demonstrated an inverse relationship between nitrogen content and mechanical properties, with average creep life decreasing from 49.63 h (4 ppm N) to 23.33 h (55 ppm N). These findings provide critical insights into the application of revert superalloys and sustainable manufacturing in high-temperature component production.

The heterostructure design has been extensively utilized in eutectic high entropy alloys (EHEAs) to further improve their comprehensive mechanical properties. Nevertheless, the impact of heterostructure construction on the corrosion resistance of EHEAs remains unclear. In this study, the corrosion behavior of a multi-level heterogeneous lamellar structure (MHLS) EHEA was studied, and the effect of heterostructure design on the corrosion mechanism of the alloy was clarified. The results showed that the MHLS EHEA exhibited significantly improved corrosion resistance in 3.5 wt% NaCl solution compared to the as-cast EHEA. The enhanced performance was attributed to a more compact, chemically stable passive film with higher concentrations of corrosionresistant elements and higher content of corrosion resistant oxides. These attributes arise from the numerous structural defects and the precipitation of fine FeCr-rich FCC phases within the B2 lamellae. The findings of the current work will provide a theoretical basis for the development and design of EHEAs with excellent strengthductility matching ability and superior corrosion resistance.

The microstructures and properties of DD32 nickel-based single-crystal superalloy with varying revert ratios were investigated by OM, SEM, EPMA, and XCT. The results indicated that as the increase in revert ratio, the content of Si and Zr increased. The primary dendrite arm spacing (PDAS), segregation between dendrite cores and interdendrite regions, the counts of γ/γ′ eutectic, and porosity all increased with increasing revert ratio. Chinese-script MC carbides displayed edge coarsening; a small number of refractory-rich strip-like precipitates and Zr-rich low melting precipitates were observed near γ/γ′ eutectic structures. After heat treatment, the morphology of MC carbides transformed from Chinese script into granular. The stress rupture life decreased with increasing revert ratio at 1000 °C/280 MPa, with carbides and porosities acting as the primary crack initiation, exhibiting ductile fracture characteristics dominated by porosity coalescence. According to the relationship between microstructure and performance, the proportion of revert addition should not exceed 50 percent.

Superalloys are the most important materials for hot components of aero-engines, and the continuous improvement of the control level of trace elements is the development trend of the field. Sulfur (S) and rare earth (RE) elements are harmful and beneficial trace elements that have the most significant impact on the properties of superalloys. The precise control of their contents has attracted increasing attention in the academic and engineering fields. The CaO-Y2O3 system is a promising composite oxide ceramic. It is expected to realize the comprehensive control of S and Y elements in superalloys by regulating the in-situ interface reaction between CaO-Y2O3 system and superalloy melt. At present, there is no effective report on its interaction behavior with superalloy melt. In this paper, XRD, SEM-EDS and other characterization methods combined with statistical methods were used to systematically study the phase and elemental distribution of the interfacial reaction products between CaO-Y2O3 system ceramics with different ratios and typical high-activity superalloys. The total chemical equation of melt-refractory interface reaction was obtained. The significance of CaO center dot Al2O3 center dot Y2O3 ternary oxide as the reaction medium layer has been confirmed. In the CaO-Y2O3 system, the initial ratio determines the interfacial reaction process by affecting the thermodynamic conditions of CaO and Y2O3 activities in the dielectric layer and the kinetic conditions of the generation rate of the dielectric layer. The CaO-Y2O3 system has been proved to have both desulfurization and rare earth addition capabilities.

Increasing the print quality is the critical requirement for the additive manufactured complex part of aero-engines of nickel-based superalloys. A study of the effects of Co and Nb on the crack is performed focusing on the selective laser melting (SLM) nickel-based superalloy. In this paper, the solvus temperature of γ', crack characteristics, microstructure, thermal expansion, and mechanical properties of SLM nickel-based superalloy are investigated by varying the content of Co and Nb. The alloy with 15Co/0Nb shows the highest comprehensive quality. Nb increases the crack risk and thermal deformation, and then Co accelerates the stress release. Therefore, Co is an extremely important alloying element for improving the quality of SLM nickel-based superalloy. Finally, the crack growth kinetics and the strain difference are discussed to reveal the SLM crack regular that is affected by time or temperature. The analysis work on the effect of alloying elements can obtain an effective foundational theory to guide the composition optimization of SLM nickel-based superalloys.

The formation and evolution of M6C carbides in high-W superalloy following solution treatment was investigated at different temperatures. Initially, during solid solution treatment, MC and M6C carbides was precipitated in the alloy. As the temperature increased, the morphology of M6C carbides transitioned from granular to needle-like. During the solution treatment at 1255 °C, the MC carbides degraded and transformed into M6C carbides, forming a symbiotic relationship between them. Nonetheless, no clear orientation relationship was observed between the two types of carbides. After further increasing the temperature to 1270 °C, the precipitation of needle-like M6C carbides in the dendrite arm was confirmed. This was supported by electron probe X-ray micro-analyzer and selected area electron diffraction patterns. Subsequently, a detailed examination of the three-dimensional morphology and orientation relationship of the needle-like phase with the matrix was carried out using focused-ion-beam and transmission electron microscopy techniques. The results indicated that the flat interface of the needle phase exhibited a specific orientation relationship with the matrix. However, in the three-dimensional plane, the interfaces between the needle-like phase and the matrix were not straight. Furthermore, no clear orientation relationship between the non-straight interfaces and the matrix was observed. As the solution temperature increased, the tensile properties at room temperature progressively decreased, while the stress rupture properties peaked at 1260 °C, suggesting that the alloy demonstrated its optimal comprehensive performance at this temperature. A subsequent analysis was conducted on the longitudinal section of the fracture using electron backscattered diffraction. The results showed a noticeable concentration of stress at the interface between MC and M6C carbides, which ultimately led to crack initiation at this interface. In addition, as the solid solution temperature increased, the quantity of symbiotic phases also increased. This phenomenon led to the initiation of cracks at multiple locations, which then propagated and interconnected. As a consequence, the tensile properties and stress rupture life of the alloy progressively deteriorated.

The effects of Al contents on the microstructures and mechanical properties of superalloy with high tungsten content were studied. During solidification, Al was found to be enriched in the residual liquid, which led to the transformation of eutectic morphology from reticular to bulk-like. When the Al content increased to 8 wt%, beta-NiAl phase formed in the inter-dendritic region, Thermo-Calc calculations confirms such the experimental phenomenon. The absolute value of the lattice misfit between the gamma/gamma' phases and the elastic strain energy increases, then the size of the gamma' phase increases when the Al concentration rises from 7 wt% to 8 wt%. When the Al content increased to 7 wt%, the tungsten-rich alpha-W phase is precipitated and the volume fraction is 1.20%. The volume fraction of the alpha-W phase increases to 7.84% when the Al content reached 8 wt%, which is consistent with the Thermo-Calc calculation results. After the room temperature tensile and stress rupture life test at 975 degrees C / 235 MPa, it revealed that the precipitation of hard and brittle alpha-W and beta-NiAl phases with high Al content, which resulted in the mechanical properties decreased due to the crack initiation at multiple locations and then interconnected. The higher density of gamma' phase with 6 wt% Al makes it difficult for dislocations to bypass. The site of crack initiation is decreased due to the absense of brittle phase. The stress rupture life can reach 49.21 h of the alloy.