Second-generation single-crystal superalloys, developed through the incorporation of approximately 3%Re into first-generation alloys, demonstrate substantially enhanced high-temperature capabilities and have become critical materials for modern aero-engine turbine blades. However, as a strategic rare element, the addition of merely 1%Re doubles the casting cost of single-crystal superalloys while excessive Re content readily induces precipitation of topologically close-packed (TCP) phases that compromise microstructural stability. Therefore, it has become a critical challenge in the present to not only reduce production costs, but also maintain the microstructure stability, while avoiding sacrificing high-temperature mechanical properties. To address this challenge, therefore, a ramp-step heat treatment procedure for low-Re second-generation nickel-based single-crystal superalloys was proposed. Then the effect of long-term aging at 900 ^oC for different durations on the evolution of microstructure and the high-temperature durability performance of the alloy was assessed by means of differential scanning calorimetry (DSC) combined with metallographic analysis. Results revealed that after being aged for 3000 h at 900 ^oC, the γ′-precipitates were coarsened and coalesced with progressive size enlargement, along with precipitation of M₆C carbides in the absence of TCP phase formation or γ′ rafting phenomena, indicating excellent structural stability. Observations for the fractured alloy after durable strength performance tests revealed that a dense γ/γ′ dislocation network was formed in the alloy and shearing super-dislocations a<101> and a<010> emerged within the γ′-phase. Notably, stress rupture properties after 500 h and 1000 h aging at 900 ^oC remain equivalent to the as heat-treated ones. Based on these findings, this work establishes a novel heat treatment procedure for second-generation superalloys while elucidating microstructural stabilization mechanisms and revealing competitive precipitation behavior between M₆C carbides and TCP phases.

FeSiBCuNbZr@SiO₂ amorphous composite was prepared by single roller melt-spinning, mechanical ball milling and sol-gel method. The microstructure, phase composition, morphology, and electromagnetic properties of the composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and vector network analysis. The influence of the matching thickness of SiO₂ dielectric layer on the wave absorption performance of FeSiBCuNbZr amorphous composite powder was studied. The results indicate that the optimal reflection loss of the amorphous composite powder, obtained from FeSiBCuNbZr amorphous powder and the SiO₂ dielectric layer generated by the hydrolysis and polycondensation of 5 mL tetraethyl orthosilicate is -58.19 dB at 11.2 GHz with a matching thickness of 2.18 mm. When the matching thickness is reduced to 1.85 mm, the maximum effective absorption bandwidth reaches 7.7 GHz. The excellent microwave absorption properties may be attributed to the synergistic effect between the magnetic loss from the Fe-based amorphous core and the dielectric loss from the SiO₂ shell, which collectively optimize the impedance matching.

The effect of hot stamping process parameters on the microstructure and mechanical properties of 24Mn2CrNb automotive steel was studied, focusing on austenitizing temperatures at 860 ^oC, 890 ^oC, 910 ^oC, 930 ^oC, 860 ^oC, 890 ^oC, 910 ^oC, 930 ^oC and step quenching at 250 ^oC,450 ^oC. Results showed that with the increasing austenitizing temperature, the austenite grain size coarsened slowly. Optimal comprehensive mechanical properties that tensile strength of 1815 MPa, yield strength of 1377 MPa, elongation of 11.13%, and strength-ductility product of 20.20 GPa·% were achieved for the steel austenitizing at 930 ^oC. Step quenching simulations of hot stamping revealed the microstructural evolution of the steel that quenching at 250 ^oC produced refined lath martensite, while isothermal treatment at 450 ^oC produced bainite and martensite. The excellent properties of 24Mn2CrNb steel may originate from synergistic strengthening mechanisms involving grain refinement, dislocation and precipitates hardening. The steel demonstrated superior high-temperature oxidation resistance compared to 22MnB5 steel, with decarburization depth below 5 μm, it suitable for coating-free hot stamping applications.

25Cr3Mo3NiNb steel is an outstanding material for special pressure vessels, in which thermal fatigue cracking is a critical factor limiting its service life. The strength of this steel is primarily derived from secondary hardening induced by dispersed carbides, whose size strongly depends on the diffusion rate of key alloying elements at different temperatures. Herein, the effect of thermal fatigue temperature on the crack propagation behavior of 25Cr3Mo3NiNb steels, being subjected to quenching and tempering treatments respectively was studied. The thermal fatigue test was conducted via helding the steel at 600 ^oC or 700 ^oC for 5 min and then quick cooling in room temperature water as one cycle. The variation of microstructures and crack propagation behavior along with the thermal cyclic testing up to 300 cycles was characterized using scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The results show that after thermal fatigue at 600 ^oC, the M₂C carbides coarsened slightly while still maintaining a high number density, which effectively retarded the microstructure recovery and preserved the tempered martensite structure, accompanied by a slight decrease in hardness. In contrast, after thermal fatigue at 700 ^oC, the M₂C carbides coarsened significantly, resulting in the transformation of the microstructure into tempered sorbite and a remarkable drop in hardness. The difference in microstructural state directly governed the crack propagation mode: at 600 ^oC, both the main and secondary cracks propagated primarily along pre-austenite grain boundaries where severe dislocation pile-ups occurred; at 700 ^oC, microstructural recovery eliminated local inhomogeneity, leading to transgranular propagation of the main crack, while the secondary cracks tended to nucleate and extend along inclusions.

35MnB steel, a low-alloy high-strength steel, is used for making track shoes, yet its properties fail to meet the requirements of new-generation track steels due to detrimental inclusions (BN, MnS, etc.) formed during smelting and solidification processes. To mitigate the detrimental effect of inclusions, herein, the influence of Ti microalloying on the formation and distribution of secondary phase particles and mechanical properties of 35MnB steel was systematically investigated by means of techniques such as XRD, SEM, EBSD, and TEM, as well as Aspex inclusion analysis system and universal testing machine, etc. The results demonstrate that Ti addition effectively optimizes inclusion distribution, remarkably refines grains, and enhances the mechanical properties of the alloy steel. Notably, with the addition of 0.045% (mass fraction) Ti, the Ti-micro-alloyed steel exhibits > 50% improvement in impact toughness compared to that of the Ti-free steel, therewith, an optimal regulation of secondary phase particles may be acquired for simultaneous enhancement in strength-toughness. The strengthening mechanisms may involve Ti reacting with C and N to form secondary phase particles that pin grain boundaries and dislocations, while inhibiting the high-temperature coarsening of austenite grains, thereby refining grains, stabilizing grain boundaries, increasing dislocation density, and ultimately improving the performance of the 35MnB steel.

An austenitic oxide dispersion strengthened (ODS) alloy with the composition of Fe-15Ni-15Cr-2.0Mo-1.0Mn-(0.2, 0.8, 1.5) Ti-0.4Y₂O₃ was fabricated using mechanical alloying and hot isostatic pressing (HIP). The effect of Ti content on the microstructure and microhardness of austenitic 15Cr-ODS alloy was studied through SEM, EBSD, TEM, and microhardness tester. The results show that the increase of Ti content significantly facilitates the formation of Y-Ti-O complex oxide particles. When the Ti content approaches 0.8% (mass fraction), the size of oxide particles in the matrix is mainly concentrated in the range from 2 nm to 7 nm. These nano oxideparticles nanoparticles are mainly composed of Y₂Ti₂O₇ with pyrochlore structure and Y₂TiO₅ with orthogonal structure. Due to the strong pinning effect of nano oxide-particles to grain boundaries, the grain refinement is achieved in the ODS alloy with 0.8% addition of Ti. At the same time, the microhardness of the alloy is increased from 302.7HV_0.5(0.2%Ti) to 401.3HV_0.5 (0.8%Ti). However, when Ti increases to 1.5%, the excessive Ti leads to the formation of coarse TiO₂ particles in addition to Y₂Ti₂O₇ and Y₂TiO₅, which leads to increased grain size and decreased hardness of the alloy. It is proven that the nano oxideparticles with homogenous distribution and fine size can be obtained in the 15Cr-FeCrNi ODS alloy when the contents of Ti and Y₂O₃ are about 0.8% and 0.4% (mass fraction), respectively, thus providing better mechanical properties.

In this study, two symmetric organic molecules with α,β-unsaturated ketone configuration, i.e., COP and CNP, were designed and synthesized with phenothiazine as an electron donor, and their photophysical and third-order nonlinear optical properties were investigated. Due to the introduction of the electron-withdrawing dicyanoethene group in the CNP molecule, its maximum absorption peak red-shifted by approximately 60 nm, in comparison to that of the COP. Furthermore, under the irradiation of a 532 nm laser, both CNP and COP exhibited reverse-saturable two-photon absorption characteristics. However, CNP showed a significantly higher absorption coefficient (COP: 1.2 × 10^-11 m/W and CNP: 4.0 × 10^-11 m/W), indicating a stronger nonlinear optical response. To determine the origin of this performance discrepancy, the nonlinear absorption of CNP molecules was first identified to primarily arise from the charge transfer process in the excited state through transient absorption spectroscopy. Subsequently, theoretical calculations were employed to analyze the charge and hole distribution of CNP molecules in the excited state. The results revealed that the introduction of a stronger electron-withdrawing receptor group led to a smaller energy gap in the frontier molecular orbitals, a longer charge transfer distance, and enhanced electron delocalization ability in CNP molecules. These findings provide a meaningful reference for designing organic molecular materials with superior nonlinear optical properties.

Regarding the structural instability and poor cycling performance of vanadium-based oxide cathode materials during the charge-discharge processes in aqueous zinc-ion batteries, a series of La³⁺-doped VO₂ materials (La³⁺-VO₂) have been synthesized via a simple hydrothermal method. The results of electrochemical measurement indicate that an appropriate amount of rare-earth La³⁺-doping could enhance the rate capability and cycling stability of VO₂ electrodes. When the V:La molar ratio is 2:0.3, the prepared La³⁺-VO₂ electrode exhibits a specific capacity of 160.2 mAh·g^-1 at a current density of 0.1 A·g^-1 and a discharge specific capacity of 131.9 mAh·g^-1 with a capacity retention rate of 82% after 100 cycles. The rate capability tests reveal the electrode with a maximum specific capacity of 209.8 mAh·g^-1 at a current density of 0.1 A·g^-1 and with a capacity of 60.8 mAh·g^-1 at a high current density of 5.0 A·g^-1, and with a maximum specific capacity of 217.6 mAh·g^-1 when the current density returned 0.1 A·g^-1, showing good reversibility and structural stability of the La³⁺-VO₂ electrodes. The electrode maintains a specific capacity of 52.2 mAh·g^-1 after 1000 cycles at 1.0 A·g^-1 demonstrating good cycling performance even at high current densities. The electrochemical kinetic analysis indicates that the charge-discharge process of the La³⁺-VO₂ electrode is simultaneously governed by both capacitive and diffusion-controlled reactions with the pseudocapacitive contribution percentages of 77% and 88% at scan rates of 0.2 mV·s^-1 and 1.0 mV·s^-1, respectively showing its fast kinetic behavior. The contribution of the capacitive charge storage mechanism ensures the excellent cycling stability of the La³⁺-VO₂ electrode at high capacity and high-rate conditions.