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.

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.

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.

Fe-Al alloys exhibit excellent mechanical properties, low cost, and moderate magnetostriction, making it a promising magnetostrictive material. The polycrystalline (Fe₈₁Al₁₉)_100-xCe_x (x=0, 0.05, 0.10, 0.20, 0.30, 0.40, at%) alloys were prepared by arc melting. The effect of trace doping rare earth elements Ce on the microstructure, texture, and magnetostrictive behavior of Fe₈₁Al₁₉ alloys was investigated. Results show that the trace doping of the Ce element transforms the equiaxed crystals into columnar crystals, thus significantly improving the volume fraction of favorable η texture. The columnar crystal characteristics gradually weaken with the increase in Ce content, leading to weakening of η texture and an increase in the volume fraction of α and γ texture. With the increase in Ce content, a large amount of Ce-rich phases form at grain boundaries and within the grains. Among them, the phases at grain boundaries are mainly composed of Ce-Al-rich phases, while the phases within the grains is a composite secondary phase of Ce-Al wrapped around the Fe-Ce-rich phase. The magnetostriction of Fe₈₁Al₁₉ alloy is significantly enhanced by trace doping of Ce element. The peak magnetostriction of 153 ppm is obtained at the Ce element of 0.05at%, with an enhancement of 89% compared to the magnetostriction of a binary alloy. This improvement in magnetostriction is attributed to more columnar crystals containing ηtextures and the formation of more nanoheterogeneous phases owing to solid solution of trace Ce element.

Taking β-Ti as the research object, the first-principles calculations based on density functional theory were performed to construct a model of Ti-V system with different V contents by substituting Ti atoms with V atoms and to calculate the mechanical properties and electronic structures. The calculation results indicate that the addition of V atoms decreases the elastic constant and elastic modulus of β-Ti and improves the plasticity and toughness of the system. This is because during the formation of the Ti-V system, both atoms lose electrons. Therefore, the electronic mobility of the system increases, the bonding strength of the metallic bond is enhanced, and the plasticity and toughness of the system are improved. In addition, the 3d-orbitals of Ti and V atoms are mainly involved in bonding, which is the key reason for the improvement of plasticity and toughness. Meanwhile, there are also some electrons with directivity gathered around the two atoms, which indicates that there is also a covalent bond within the system. The existence of covalent bond is the key to enhancing the mechanical stability of the system.

The surface composition and microstructure evolution of a second-generation Ni-based single crystal superalloy were investigated during vacuum solution heat treatment. The effects of adding argon partial pressure and not adding argon partial pressure on the surface layer of casting were studied. Results show that during the high-temperature vacuum heat treatment of the test bars, when argon partial pressure is applied during solution heat treatment, a Cr-depleted layer forms on the surface, exhibiting three-layer structure: transition layer (adjacent to the substrate) composed of γ' phase and topologically close-packed (TCP) phase; sub-surface layer composed of γ' phase, TCP phase, and β phase; surface layer composed of γ' phase and β phases. In this case, Al and Ni are deposited on the surface. Conversely, when heat treatment is conducted without argon partial pressure, a Cr-depleted layer still forms, but with a two-layer structure: transition layer composed of γ' phase and TCP phase and surface layer composed of γ' phase, TCP phase, and β phase. During vacuum heat treatment, reactions such as volatilization, deposition, oxidation, and diffusion of surface elements occur simultaneously. Depending on the temperature, vacuum level, and argon partial pressure, condensation layer, depletion layer, and interdiffusion layer may be formed on the surface. This study analyzed these phenomena in detail based on the thermodynamics and kinetics of relevant reactions.

The connections of dissimilar materials LA103Z magnesium-lithium alloy and 1060Al alloy were achieved by electromagnetic pulse welding (EMPW). The effects of discharge energy on interface morphology, wave formation mechanisms, and element diffusion were systematically investigated through numerical simulations and experiments. The results indicate that the induced magnetic field and current are determined by the welding current's magnitude and rate of change, respectively. The increase in discharge energy enhances the Lorentz force experienced by 1060Al, thereby increasing the impact velocity, while the impact angle almost remains unaffected. The rebound phenomenon, which alters the contact state between the flyer plate and the target plate, is identified as the key factor in forming the annular weld seam. Both the simulated and actual interface morphologies are sinusoidal, with the amplitude increasing from 3.02 μm at 32 kJ to 6.48 μm at 38 kJ. The wave formation is attributed to shear-induced instability and metal-plastic flow triggered by high-speed collision. No melting is observed at the interface. The maximum shear strength of the joint reaches 90.38% of that of the aluminum base material. Numerical simulations confirm that the interface temperature remains below the melting points of both base materials, which is critical for improving the mechanical performance of the joint.

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%.

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.