Nickel-based superalloys for heavy-duty gas turbines usually have a high Cr content, but the high Cr content makes it difficult to optimize the composition design of the alloy. In particular, in order to avoid the precipitation of harmful topologically close-packed (TCP) phases, the content of solution-strengthening elements W and Mo is limited. In this work, the effects of W and Mo content changes on the γ/γ' two-phase state and TCP phase precipitation of nickel-based directional superalloy DZ409 for gas turbines aged at 900 ℃ for 1000 h were studied by multi-component diffusion multi-junction technique. The results show that when the Mo content remains unchanged, the volume fraction of the γ' phase decreases slightly as the W content increases from 3.8wt% to 4.3wt%, the size of the γ' phase decreases, and its morphology remains spherical. When the W content exceeds 4.3wt%, σ and P phases begin to precipitate in the alloy. When the Mo content increases from 1.4wt% to 1.6wt%, and the W content decreases from 4.0wt% to 3.3wt%, the volume fraction of the γ' phase increases slightly, the size of the γ' phase decreases, and the morphology remains square. After the Mo content exceeds 1.6wt%, the σ phase and P phase are precipitated in the alloy. According to the APT tip reconstruction diagram and the ion distribution map of each major element, it can be seen that the increase in W content will promote the precipitation of TCP phase, and the addition of Mo while reducing W content will also promote the precipitation of TCP phase of the alloy, mainly because the enrichment of W, Cr, and other elements in the γ matrix makes the total amount of refractory elements in the γ phase exceed the solid solution limit of γ matrix.

Large-scale and complex thick-walled titanium alloy casings produced by investment casting are key components in heavy-duty gas turbine. Characterized by their large contour size, substantial wall thicknesses, and complex shapes, these castings often face challenges such as difficult monolithic molding, numerous shrinkage pore and shrinkage cavity defects, and low dimensional accuracy, limiting the assembly and use of high-power gas turbines. The solidification temperature field and flow field during centrifugal investment casting process were investigated using the ProCAST software. Results show that the potential isolated liquid phase regions are identified. According to the characteristics of centrifugal casting, the mathematical models for designing spiral runner and inclined riser are derived. Based on this, an integrated gating system is developed, which combines exhaust gas and slag collection, flow regulation, and temperature field optimization, thereby significantly reducing solidification defects in castings. Furthermore, a wax mold splicing scheme is designed, and a wax mold tree for the gating system is constructed, featuring a straight runner, cross runner, and inner runner with cross-sectional area ratios of 1∶2.5∶6. Additionally, through the integration of dimensional calibration and shell reinforcement tooling, high-quality castings with complete filling, good metallurgical quality, and precise dimensional accuracy are achieved. This work provides effective technical guidance for the manufacturing of titanium alloy casings in heavy-duty gas turbines, and the gating system configuration offers reference value for other large-scale and complex thick-walled titanium alloy castings.

The effect of speed ratio factor of friction stir processing on microstructure, microhardness and superplasticity of Al-3Mg-0.1Sc-0.1Zr alloy was investigated. The results show that with the increase in speed ratio factor and heat input, the area of stir zone and the grain size are increased, the dynamic recrystallization is more complete, while the peak hardness in stir zone is decreased. All alloys processed at different speed ratio factors show high-strain-rate superplasticity when they are tensile-tested at 475 ℃ with strain rate of 10^-2 s^-1. Three types of true stress-true strain curves are observed during tensile tests. The optimal elongation of 2500% is achieved in the alloy processed with a speed ratio factor of 4, and significant strain hardening occurs before tensile fracture, which improves the common softening loss of stress at the later stage of superplastic forming, implying high engineering application value. The outstanding superplasticity is mainly attributed to equiaxed fine grains with excellent thermal stability and a high proportion of high angle grain boundaries. Based on the analysis of grain aspect ratio, cavity evolution, and morphology of fracture profile, the dominant mechanism of superplastic deformation under all speed ratio factors is grain boundary sliding.

Inconel617 alloy has significant application potential in Generation IV nuclear energy systems. The effects of Mo content on carbide precipitation at grain boundaries (GBs) and high-temperature tensile properties of Inconel617 alloy were studied by mechanical testing and advanced techniques such as scanning electron microscope, transmission electron microscope, and electron backscatter diffractometer. The results show that there are only fine granular M₂₃C₆ carbide at GBs when the Mo content ranges from 8wt% to 9wt%. However, as Mo content increases from 9.3wt% to 9.6wt%, massive M₂₃C₆ and M₆C carbides could be predominantly observed at GBs. As Mo content increases from 8.0wt% to 9.6wt%, the elongation increases initially and then decreases, and the alloys with the Mo content of 8.5wt%-9.3wt% achieve optimal strength-ductility balance. The fractographic analysis reveals that the precipitation of granular M₂₃C₆ at GBs effectively strengthens grain boundaries, resulting in the transgranular fracture features on the high-temperature tensile fracture surface. When massive M₂₃C₆ and M₆C carbides precipitate at GBs, the initiation of intergranular crack is promoted and the intergranular fracture features are observed on the high-temperature tensile fracture surface. The Mo content of Inconel617 alloy for high-temperature components in Generation IV nuclear systems cannot exceed 9.3wt% and it should be controlled with in the range of 8.5wt%-9wt%

Diverse heat treatment schedules were designed and their effects on microstructural evolution and tensile properties at 750 ℃ were investigated by SEM, EDS, TEM, and mechanical testing. The results demonstrate that multi-stage heat treatment schedules lead to a multi-modal size distribution of γ' precipitates within the alloy, where fine γ' precipitates contribute to strength, while coarse γ' phases enhance ductility. At 750 ℃, the alloy subjected to the heat treatment of 1030 ℃/4 h, AC+1000 ℃/4 h, AC+875 ℃/16 h, AC+725 ℃/16 h, AC develops a trimodal γ' phase distribution. This microstructure balances the strength between intragranular and grain boundary regions, facilitating the transfer of dislocation slip and enhancing the ductility of the alloy. The alloy exhibits the best overall mechanical properties, with a tensile strength of 706 MPa and an elongation after fracture of 9.3%.

The effects of different heat treatment processes, alloy states, and stress relief annealing processes on recrystallization defects in 4777DS superalloy were studied using SEM and EBSD. SEM observation shows that the γ' phase near the surface of the sandblasted sample undergoes deformation, changing from an initial butterfly shape to a long strip distribution on the alloy surface. The observation of recrystallization of the alloy after insulation at different heat treatment temperatures shows that the temperature at which recrystallization occurs is 1055 ℃. When the heat treatment temperature is higher than the dissolution temperature of the γ' phase, recrystallization presents an equiaxed morphology, while when the heat treatment temperature is lower than the dissolution temperature of the γ' phase, it presents a cellular recrystallization morphology. With the prolongation of heat treatment time, the proportion of large angle grain boundaries decreases, and the resulting annealing twins help to reduce distortion energy. A comparison of recrystallization behavior under different initial alloy states reveals that the as-cast alloy exhibits the highest tendency for recrystallization. In line with practical engineering requirements, a shorter annealing time can effectively reduce the recrystallization degree of alloys.

To design a porous titanium alloy structure suitable for cervical spine implants, according to different stress conditions of cervical spine, such as compression, compression-shear, compression-torsion, and compression-bending, four types of unit cell structures, TO-C, TO-CS, TO-CT, and TO-CB, were constructed by combining topology optimization and computer-aided design. The mechanical properties were analyzed by compression simulation. Finally, the quasi-static compression test of porous samples with porosity of 60% prepared by laser powder bed fusion technique was conducted. The results of finite element simulation and compression test show that the compressive properties and elastic moduli of the four porous structures meet the requirements of human bone implants. Among them, the TO-CB structure has the best compressive performance and is suitable for porous titanium alloy cervical spine implants.

Through controlling forging and heat treatment processes of nickel-based wrought superalloy, the microstructures with coarse grain volume fractions ranging continuously from 0% to 100% were prepared, and the stress rupture properties of different mixed-grain structures were tested under the condition of 730 ℃/530 MPa to explore the influence regularity and mechanism of mixed-grain structures on the stress rupture properties. The research results show that the mixed-grain structures with coarse grain volume fractions from 0% to 100% exhibit significantly different stress rupture properties. The mixed-grains structure with coarse grain volume fraction of 15% presents the shortest stress rupture life, while the coarse-grained structure with coarse grain volume fraction of 100% possesses the longest stress rupture life. The high-temperature stress rupture fracture surfaces of the mixed-grain structure specimens with low coarse grain volume fraction from 0% to 15% show typical ductile fracture characteristics, whereas those of the specimens with high coarse grain volume fraction from 50% to 100% present intergranular fracture characteristics. The high-temperature stress rupture deformation mechanisms of all mixed-grain structure specimens take the form of intragranular deformation governed by dislocation motion and grain boundary sliding. However, with the increase in coarse grain volume fraction, the high-temperature stress rupture properties of the superalloy are improved as the strong textures on the {111} crystal planes is changed, the internal dislocation distribution in coarse and fine grains is inhomogeneous, and the tendencies of stress concentration and cavity nucleation induced by dislocation pile-up and grain boundary sliding are significantly changed.

Al-Ga-Mg-Sn soluble aluminum alloy was selected for a one-step hydrometallurgical technique. Acid leaching agents, including organic acid solutions (e. g., oxalic, malic, and acetic solutions) and inorganic acid solutions (e. g., nitric acid) were used. The type of leaching agent, pH value, temperature, and solution concentration are key factors influencing the recovery of Ga during hydrogen production. Recovery results show that under the temperature of 70 ℃ and the agent concentration of 0.2 mol·L^-1, the organic acid solution successfully recovers gallium, with oxalic acid exhibiting the highest recovery efficiency (86.88%), followed by malic acid (73.40%) and acetic acid (13.17%). In contrast, the inorganic acid (nitric acid) solution fails to recover gallium. Oxalic acid, with an initial pH value of approximately 3.8, achieves a recovery efficiency of 94.38% under 70 ℃/0.3 mol·L^-1 and 93.78% under 90 ℃/0.2 mol·L^-1. The leaching behavior of gallium was then tested and analyzed based on changes in pH value, shape of the recovered gallium, solid particle size and Zeta potential of the product during the hydrolysis process. The results show that the recovery of gallium from oxalic acid leachate increases with the decrease in particle size of the product and increase in absolute value of Zeta potential. The highest recovery efficiency (94.38%) is achieved with a product particle size of 155 nm and a Zeta potential value of -31.29 mV.

The effects of adding 1at% early transition metals (M=Ti, V, Cr, Zr, Nb, Mo) on the melt-spun structure, crystallized microstructure, and magnetic properties of Fe_84.5B₁₃Cu_1.5M₁ alloys were investigated. The mechanisms of different M elements in regulating the alloy structure and magnetic performance were also discussed. Results show that except for the M=Zr alloy presenting fully amorphous state in the as-spun condition, other alloys all contain pre-existing α -Fe grains dispersed in amorphous matrix with average grain sizes (d_α-Fe) smaller than 10 nm and high numerical density (N_d). M doping can reduce both N_d and d_α-Fe of pre-existing α -Fe phases to varying degrees, with reduction effectiveness following the sequence: Cr<V<Mo<Nb<Ti<Zr. This trend positively correlates with the enhanced amorphous-forming ability derived from increased atomic size mismatch and negative mixing enthalpy induced by M elements. M doping significantly influences the α -Fe phase/amorphous-nanocrystalline composite structure and magnetic properties after heat treatment. Compared with Fe_85.5B₁₃Cu_1.5 alloy, alloys with M=V/Cr/Nb/Mo exhibit reduced average grain size (D_α-Fe) and coercivity (H_c) of α-Fe, while alloy counterparts with M=Ti/Zr show increased D_α-Fe and H_c. All doped alloys demonstrate slightly decreased saturation magnetic induction (B_s). Notably, the Mo-doped alloy achieves optimal nanocrystalline structure and soft magnetic properties, showing D_α-Fe=14.9 nm, H_c=8.3 A/m and B_s =1.84 T, which significantly outperforms the results as 17.9 nm, 22.1 A/m and 1.90 T of reference alloy, respectively. Mo doping attains optimized matching between N_d and d_α-Fe of pre-existing α-Fe grains in melt-spun alloys, which enhances the coordinated intergranular competitive growth effects during thermal crystallization. This mechanism effectively refines the nanocrystalline structure, reduces magnetocrystalline anisotropy, and consequently improves soft magnetic properties.