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.

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.

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.

The effect of heat treatment on the microstructure and mechanical properties of a high-boron Ni₃Al-based superalloy was investigated by scanning electron microscope, tensile test and stress rupture test. The results show that when the solid solution temperature increases from 1080 ℃ to 1150 ℃, the volume fraction of γ' phase in dendrite trunk decreases gradually, the morphology changes from blocky to spherical, and fine tertiary γ' phases are precipitated inside the γ channel. When the temperature rises from 1080 ℃ to 1120 ℃, the skeleton-like primary borides are partially dissolved, and the granular secondary borides are precipitated. The precipitation tendency of secondary borides is increased with the increase in temperature, and the borides are completely dissolved when the temperature rises to 1150 ℃. After aging at 900 ℃ for 10 h, the alloy solid-solution-treated at 1080 ℃ achieves the ultimate tensile strength of 900 MPa during the tensile test at 800 ℃ and the stress rupture life of 144.5 h under the condition of 580 MPa/800 ℃, exhibiting the best comprehensive mechanical properties. Therefore, the optimal heat treatment process of the test alloy is 1080 ℃×4 h→air cooling+900 ℃×10 h→air cooling.

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 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.

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%.