Erosion-corrosion (EC)-induced damage is a primary contributor to premature failures in hydraulic transport structures involving sudden changes in flow patterns, especially the hydraulic pipeline (tee, reducer, pipe bend, etc.), pumps, and valves. A comprehensive exploration of EC behavior of steels subjected to high tensile stress was provided, as most engineering structures are operated under high stress. The stress-accelerated erosion (SAE) and stress-accelerated corrosion (SAC) behaviors of highly stressed steel and their synergistic effect were mainly focused. SAE, SAC, and their synergistic mechanisms, existing debate, and possible reasons, as well as available analytic models with their advantages and limitations, are thoroughly discussed. The multiphysics simulation methods for modeling EC interactions with both static and cyclic stresses are also summarized, and EC mitigation strategies, especially the bionics-based strategies, were also summarized in detail.

Microwave pre-oxidation and biomass reduction were adopted to enhance the separation of titanium and iron in vanadium-titanium magnetite. The effects of microwave pre-oxidation temperature and time, as well as biomass reduction temperature and time, were investigated. The results showed that the average particle size of vanadium-titanium magnetite decreased, and the specific surface area increased with the increase in pre-oxidation temperature and time. The reaction pathway (Fe_3-xTi_xO₄ → Fe_2-xTi_xO₃ → Fe₂TiO₅) was proved in microwave pre-oxidation process. The results of biomass reduction roasting showed that biomass reduction could effectively reduce ferric oxide to metallic iron while Ti was enriched in a solid solution of magnesium anosovite, which was beneficial to the subsequent grinding and acid leaching separation. The combined process of microwave pre-oxidation and biomass reduction achieved a high separation efficiency of titanium and iron in vanadium-titanium magnetite without forming complex titanium minerals. The titanium grade in the vanadium-titanium-rich material was 32.10%, and the recovery rate was 91.51%. The iron grade in the iron concentrate (metallic iron) was 90.90%, the recovery rate was 93.47%, and metallization rate was 93.87%.

Controlling the adhesion of potentially corrosive substances from flue gas on grate bar is crucial for extending the operational lifespan of the equipment. The adhesive behaviour and mechanism of ultrafine particulate matters (UPM) throughout the sintering process were elucidated, and measures to control adhesion on grate bars were developed. Research findings indicated that a small quantity of UPM were found on grate bar during the initial sintering stages (ignition stage and middle stage I and II). The main compositions of UPM were Fe_xO_y-rich, CaO-rich, and aluminium silicate-rich particles. In contrast, corrosive substances like alkali metal compounds were almost absent. These UPM adhered onto grate

To further enhance the recovery rate of low-temperature waste heat, the low-temperature flue gas in the sinter annular cooler was chosen as the heat source of an organic Rankine cycle (ORC) system, and the comprehensive evaluation of energy, exergy and economic performance of the ORC system was conducted deeply. The energy, exergy and economic performance models of the ORC system were established, and proper candidate organic working fluids (OWFs) were selected based on the thermo-physical properties of OWF and operating characteristics of ORC system. Then, the effects of ORC crucial parameters on the system energy, exergy and economic performances were evaluated in detail. Finally, the biobjective optimization based on the genetic algorithm was conducted to analyze the optimal performance of the ORC system under the designed ORC crucial parameters, and the exergy efficiency and electricity production cost were set as the evaluation indexes of parametric optimization. The results indicate that the ORC system with the higher evaporation temperature and lower condensation temperature can obtain the larger system exergy efficiency and smaller electricity production cost. The smaller the superheat degree of OWF and pinch-point temperature difference in the evaporator are, the better the energy and exergy performances of the ORC system are. Under the optimization results, R245fa has the best comprehensive performance with the exergy efficiency of 46.34% and electricity production cost of 0.12123 $/kWh among the selected candidate OWFs, which should be preferentially chosen as the OWF of the ORC system.

The hydrogen-enriched direct reduction shaft furnace addresses the high CO₂ emissions associated with the blast furnace process. A discrete element method (DEM) model was introduced to explore how the structure of the diversion cone affects particle descent behavior in a hydrogen-enriched shaft furnace. The results indicated that in the absence of a diversion cone, the descending velocity near the furnace wall zone is significantly lower than that at its center, resulting in a ‘V’- shaped burden flow pattern. The discharge velocity has a minor impact on the flow pattern in the shaft furnace. Upon installation of a diversion cone, burden descending velocity becomes more uniform, leading to a ‘-’-shaped burden flow pattern. As the bottom of the diversion cone ascends (i.e., the lower end of the diversion cone is progressively closer to the top), there is an increase in the volume fraction of the dead zone within the shaft furnace. This is particularly evident in the formation of a triangular dead zone at the base of the diversion cone. It is suggested that the lower cone of the bi-conical diversion cone should maintain a sufficient height.

The application of machine learning was investigated for predicting end-point temperature in the basic oxygen furnace steelmaking process, addressing gaps in the field, particularly large-scale dataset sizes and the underutilization of boosting algorithms. Utilizing a substantial dataset containing over 20,000 heats, significantly bigger than those in previous studies, a comprehensive evaluation of five advanced machine learning models was conducted. These include four ensemble learning algorithms: XGBoost, LightGBM, CatBoost (three boosting algorithms), along with random forest (a bagging algorithm), as well as a neural network model, namely the multilayer perceptron. Our comparative analysis reveals that Bayesian-optimized boosting models demonstrate exceptional robustness and accuracy, achieving the highest R-squared values, the lowest root mean square error, and lowest mean absolute error, along with the best hit ratio. CatBoost exhibited superior performance, with its test R-squared improving by 4.2% compared to that of the random forest and by 0.8% compared to that of the multilayer perceptron. This highlights the efficacy of boosting algorithms in refining complex industrial processes. Additionally, our investigation into the impact of varying dataset sizes, ranging from 500 to 20,000 heats, on model accuracy underscores the importance of leveraging larger-scale datasets to improve the accuracy and stability of predictive models.

A new flow control technology in continuous casting process named permanent magnet flow control-mold (PMFC-Mold) was proposed, in which the permanent magnets are arranged in Halbach array near the narrow region of the mold. The behavior of molten steel flow and the fluctuation of molten steel/slag interface in the PMFC-Mold under different continuous casting speeds were investigated. Firstly, a physical experiment of liquid Ga-In-Sn alloy circulating flow was carried out in Perspex mold with Halbach’s permanent magnets (HPMs) to investigate the magnetic field distribution of HPMs and its impactful electromagnetic braking effect. The numerical simulation of 1450 mm 9 230 mm slab shows that a stronger magnetic field over 0.3-0.625 T is formed at the wide surface and the narrow surface of the mold, which provides an effective electromagnetic braking for controlling the impingement of molten steel jet and suppressing the fluctuation of molten steel/slag interface. The numerical simulation results show that in the PMFC-Mold, the region with the turbulent kinetic energy greater than 0.01 and 0.04 m² s^-2 on the upper backflow zone and near the narrow surface of the mold are significantly reduced. The maximum turbulent kinetic energy of the submerged entry nozzle (SEN) jet in front of the narrow surface is significantly reduced, and the SEN jet moves downward before impacting the narrow surface of the mold. In the PMFC-Mold, the region with the surface velocity greater than 0.2 m s^-1 on the steel/slag interface is eliminated, the flow pattern and fluctuation profiles on the molten steel/slag interface become regular on both sides of SEN, and the vortex near SEN disappears. The maximum fluctuation height of molten steel/slag interface is controlled below 2.59 and 5.40 mm corresponding to the casting speed of 1.6 and 2.0 m min-1, respectively.

In order to examine the flow state of the steel-slag interface in a thin slab mold at high casting speed, a flexible thin slab casting mold and a novel five-hole nozzle were investigated. The maximum velocity and fluctuation height of the steel-slag interface in the mold served as the evaluation criteria. Numerical simulation techniques, including large eddy simulation and volume of fluid, were employed to develop a two-phase flow model of liquid steel and slag. This model facilitated the analysis of the fluctuation behavior of the steel-slag interface and the mechanisms of slag entrapment. The results indicated that maintaining the stability of the steel-slag interface could be achieved by ensuring that the maximum velocity did not exceed 0.30 m s^-1 or that the wave height remained below 30 mm. The relationship between the maximum velocity and wave height of the steel-slag interface was established by analyzing different casting speeds. Slag entrapment occurred when the maximum velocity exceeded the critical value. The critical velocity for shear slag entrapment was 0.485 m s^-1, while for vortex slag entrapment, it was when the velocity of the swirl center reached 0.235 m s^-1. Electromagnetic braking proved effective in controlling flow in the mold, reducing fluctuations in the steel-slag interface, preventing slag entrapment, and maintaining the position of the interface. Furthermore, it facilitated the control of the uniformity and stability of slag movement along the outer wall of the submerged entry nozzle and the copper wall of the mold.

During the continuous casting process of low carbon steel, the solidified hook formed in the mold has great effects on the surface quality of the cast slab. Some factory experiments have been conducted to investigate the microscopic characteristics and reveal the influence of process parameters on solidified hooks. The depth of the hooks showed a positive correlation with the deflection angle, length, and oscillation mark (OM) depth, which indicates that the OM depth can serve as an approximate indicator for evaluating the depth of the solidified hooks. On the wide and narrow faces of the cast slab, the depth of the solidified hooks and the temperature distribution in the mold show opposite trends, with lower depths of solidified hooks at positions with higher temperatures. In addition, the influence of process parameters on solidified hooks was analyzed. With the increase in superheat, not only the depth of solidified hooks gradually decreases, but also the ratio of depression-typed marks increases. Increasing casting speed and decreasing immersion depth of the submerged entry nozzle will both lead to a decrease in the depth of the solidified hook.

A secondary-cooling-segment electromagnetic stirring (S-EMS) experiment was performed at 150 A and 4 Hz to evaluate the effect of S-EMS on solidification characterization near the white band. The upper and lower parts of the white band exhibited average secondary dendritic arm spacing of 205.4 and 214.4 lm, respectively. The S-EMS operation resulted in large Lorentz forces and cooling intensity, which could produce additional dendritic arms with low carbon concentrations, leading to local negative segregation. Moreover, a 3D flow-temperature-magnetic coupling numerical model was established. The results revealed that the magnetic induction intensity and Lorentz force were symmetrically distributed along rollers S1 and S2. The average velocity magnitude increased by approximately 42.52%, 58.69%, and 64.11% for liquid fractions of 0.7, 0.8, and 0.9, respectively. During the S-EMS operation, the Lorentz force may alter the velocity of the solidification front and promote the dissipation of superheat. Additionally, the influence of S-EMS on grain nucleation and growth was investigated using Gibbs free energy theory and component undercooling. Furthermore, a formation model for the white band was established, and the mechanism of white band formation was elucidated according to the changes in the solute-enriched layer, solute precipitation, and diffusion.

Accurate crown control is paramount for ensuring the quality of hot-rolled strip products. Given the multitude of influencing parameters and the intricate coupling and genetic relationships among them, the conventional crown control method is no longer sufficient to meet the precision requirements of schedule-free rolling. To address this limitation, an optimization framework for hot-rolled strip crown control was developed based on model-driven digital twin (MDDT). This framework enhances the strip crown control precision by facilitating collaborative operations among physical entities, virtual models, and functional application layers. In virtual modeling, a data-driven approach that integrates the extreme gradient boosting and the improved Harris hawk optimization algorithm was firstly proposed to fit the relationship between key process parameters and strip crown, and a global-local collaborative training strategy was proposed to enhance the model adaptability to diverse working conditions. Subsequently, the influence of crucial process factors on the virtual model was examined through model responses. Furthermore, a novel optimization mode for crown control based on MDDT was established by aligning and reconstructing both the physical and virtual models, thereby enhancing the crown control precision. Finally, data trials were conducted to validate the effectiveness of the proposed framework. The results indicated that the proposed method exhibited satisfactory performance and could be effectively utilized to improve the crown control precision.

The interfacial structure and its effect on the resistivity of cross-layered silver-copper composite strip fabricated by hot-roll bonding and diffusion welding processes with the same specification were studied. Through optical and scanning electron microscope analysis of metallographic structure of the diffusion region of interface, it is found that the thickness of the interfacial diffusion layer is related to the composite conditions. Under the condition of sufficient diffusion, the interface of silver-copper composite strip produced by diffusion welding process has a wider interfacial transition region and fine grain area. Due to the higher diffusion rate of copper atoms than that of silver atoms, copper atoms tend to aggregate at the silver boundaries to form a copper-rich second solid solution, which has a fixing and expanding effect during annealing. The fine grain area at the interface of the composite strip produced by diffusion welding process still exists after annealing treatment and reaches a width of 55-97 lm. While the fine grain region at the interface of hot-rolled composite strips is mainly formed by crushing the surface under rolling pressure with less diffusion effect, it almost disappears after annealing. The resistivity of silver-copper composite strip increases with the extension of the interfacial diffusion region. The resistivity of hot-roll bonding composite strip is increased by about 4% higher than that of the theoretical calculation, while the resistivity of diffusion welding composite strip is increased by 6%.

To enhance the gelation activity of steel slag, a calcination process was employed to activate it. The activated steel slag was then utilized as the primary raw material, combined with sodium silicate as the activator, to prepare a gel material. The effect of calcination temperature on the physicochemical properties of steel slag and the resulting samples was examined. The chemical composition and microstructure of the steel slag, along with the derived samples, were meticulously examined using advanced analytical techniques such as X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscope analysis. The results show that calcination can significantly enhance the gelation activity of steel slag. The steel slag exhibits its highest gelation activity at the temperature of 600℃. At this temperature, the compressive strength of the material reaches its highest value of 11.7 MPa, while the porosity is at its lowest level of 12.6%. The microstructure of the samples reveals large continuous regions on the surface of the gel material, with minimal surface cracks.

Resource utilization of metallurgical solid waste is vital for the sustainable development of the steel industry in the context of ‘‘dual carbon.’’ The calcification-carbothermal reduction method was employed to extract zinc and iron from electric furnace dust effectively. In this process, calcium oxide reacts with zinc ferrite to form dicalcium ferrite and zinc oxide, which further promotes the effective separation of zinc and iron. However, the addition of pure calcium oxide increases production costs for steel companies. Herein, a new process for dust removal and zinc recovery in electric furnaces has been developed, using electric furnace slag as a calcium agent and mineral trough ash as a reducing agent. Large amounts of dicalcium ferrate phases were detected in the carbothermal reduction products by steel slag synergistic calcification. The reaction mechanism was determined as ZnFe₂O₄ + CaO → Ca₂Fe₂O₅ + ZnO → Ca₂Fe₂O₅ + Zn(g). Such a two-step reaction path indicated that steel slag can effectively promote the reduction and volatilization of zinc. The experimental optimal roasting parameters were determined as roasting temperature of 1150 _C, roasting time of 45 min, calcium to zinc molar ratio of 1.1, and carbon to oxygen molar ratio of 0.8. The mass percentage of added steel slag was recorded as 21.83%, while that of mineral trough ash was 21.85%. Under these conditions, the zinc removal rate above 99% and the metallization rate of pellets of about 75.31% were achieved. Overall, the proposed method looks promising for future efficient separation of zinc and iron in industrial steel slag.

The development and utilization of mineral resources are accompanied by the production of a large number of solid wastes such as tailings and smelting slag. Bayan Obo tailings and blast furnace slag were used as the main raw materials. Coal gangue was used as pore-forming agent to prepare ceramsite which can efficiently treat ammonia nitrogen wastewater. The optimum preparation process parameters were obtained. The mineral evolution process of ceramsite prepared by smelting solid waste during roasting was clarified. The effects of sintering process parameters on the properties of ceramsite and its removal of ammonia nitrogen wastewater were revealed. The results show that, the optimum proportion of raw materials for preparing ceramsite was: 25% Bayan Obo tailings, 65% blast furnace slag and 10% coal gangue. The reasonable process for preparing ceramsite was: temperature of 400℃, preheating for 20 min, heating rate of 10℃/min, calcination at 1090℃ for 15 min, and cooling with the furnace. With the increase in calcination temperature, the main crystal phase changes from dolomite, kaolinite, fluorite and calcite to melilite and Fe₂O₃. Finally, the ceramsite with porosity of 48.13%, specific surface area of 2.44 m2/g and soluble rate of hydrochloric acid of 1.88% was prepared. The removal rate of ammonia nitrogen wastewater by the ceramsite was 54.13%.

To recover the valuable elements in Bayan Obo tailings, Fe-Si bath smelting reduction was adopted to separate and enrich rare earth elements (REE), niobium and titanium from the REE-Nb-Ti-containing slag. The reduction reaction process of the Fe-Si bath and the migration behavior of valuable elements in the solidification and crystallization process of silicothermic reduction tailings were investigated, and a treatment method for efficiently separating and enriching REE, Nb and Ti was explored. Thermodynamic analysis indicated that at 1600℃, with a 6 wt.% addition of Si as the reducing agent, the niobium oxide in the REE-Nb-Ti-containing slag could be selectively reduced to metallic Nb. In the Fe-Si bath reduction process, the Nb mass fraction in the metal phase increased with prolonged reaction time, peaking at 2.77%, while the Ti mass fraction consistently stayed below 0.12%. Lowering the w(CaO)/w(SiO₂) enhanced the migration of Nb from slag to metal phase and reduced the Ti impurities. During solidification and crystallization, a significant quantity of perovskite precipitated from reduction tailings, with the REE dissolving into this perovskite. By adjusting the w(CaO)/w(SiO₂) in tailings to 1.2-1.9 and maintaining a temperature of 1100℃ for 4 h, the perovskite area fraction in the final slag could exceed 37%. Finally, a method was proposed to separate and enrich valuable elements in REE-Nb-Ticontaining slags via Fe-Si bath smelting reduction and crystallization control.

Laboratory experiments and thermodynamic calculations were performed to investigate the interfacial reactions between the MgO-C refractory and the steel with and without the lanthanum (La) addition. Following a reaction time of 50 min, a reaction layer comprised MgO and CaS with a thickness of 30 lm was observed at the interface between the La-free steel and refractory. The MgO layer was observed in La-bearing steel after just 10 min of reaction. The addition of La to the steel accelerated the formation of the MgO layer. As the reaction time increased, a La-containing layer was formed at the La-bearing steel/refractory interface. This La-containing layer progressed through stages from La₂O₂S +La₂O₃ → La-Ca-O-S → La-Ca-O → La-Ca-Al-O. Furthermore, the evolution of oxide inclusions in the La-free steel followed the sequence of MgO∙Al₂O₃, Ti-Ca-Al-O and Ti-Mg-Al-O → MgO ∙Al₂O₃ and MgO with increasing the reaction time. In contrast, the sequence for the La-bearing steel was: La₂O₂S and La₂O₃ → La₂O₂S and La-Ti-Al-Mg-O → La-Ti-Al-Mg-O, MgO and MgO∙Al₂O₃. The average penetration depth of the La-bearing steel into the refractory was notably lower than that of the La-free steel, revealing that the incorporation of rare earth element La in steel exhibits a significant inhibitory effect on the penetration of molten steel into the MgO-C refractory.

Nitrogen gas pressure sintering was successfully employed to achieve the in-situ formation of Si₃N₄-bonded MgO–C refractories. The primary objective was to investigate the influence of different gas pressures on the mechanical properties and microstructure of MgO–C refractories. The results indicate that higher nitrogen pressure promotes the transformation of silicon nitride from the a phase to the b phase. This phase transition positively impacts the mechanical properties of Si₃N₄-bonded MgO–C refractories, leading to an enhancement in their overall strength. Notably, when the nitrogen pressure was set at 3 MPa, exceptional compressive strength of 109.7 MPa and an elastic modulus of 142.4 GPa were achieved by these prepared refractories. These findings highlight the great potential for utilizing gas pressure sintered Si₃N₄–MgO–C refractories.

Interfacial evolution and bonding mechanism of reduced activation ferritic/martensitic (RAFM) steel were systematically investigated through a series of hot compression tests conducted at various strains (0.15-0.8), strain rates (0.001-1 s^-1), and temperatures (950-1050 ℃). Interfacial microstructural analysis revealed that plastic deformation of surface asperities effectively removes interfacial voids, and the evolution of dynamic recrystallization (DRX) aids in achieving a joint characterized by homogeneously refined microstructure and adequate interfacial grain boundary (IGB) migration. Electron backscattered diffraction analysis demonstrated that the continuous dynamic recrystallization, characterized by progressive subgrain rotation, is the prevailing DRX nucleation mechanism in RAFM steel during hot compression bonding. During DRX evolution, emerging DRX grains in the interfacial region expand into adjacent areas, transforming T-type triple junction grain boundaries into equal form, and resulting in a serrated and intricate interface. Elevated temperatures and strains, coupled with reduced strain rates, augment DRX grain nucleation and IGB migration, thus enhancing RAFM joint quality with regard to the interface bonding ratio and the interface migration ratio.

The correlation between the microstructure, properties, and strain partitioning behavior in a medium-carbon carbide-free bainitic steel was investigated through a combination of experiments and representative volume element simulations. The results reveal that as the austempering temperature increases from low to intermediate, the optimal balance of properties shifts from strength-toughness to plasticity-toughness. The formation of fine bainitic ferrite plates and bainite sheaves under low austempering temperature (270 ℃) enhances both strength and toughness. Conversely, the wide size and shape distribution of the retained austenite (RA) obtained through austempering at intermediate temperature (350 ℃) contribute to increased work-hardening capacity, resulting in enhanced plasticity. The volume fraction of the ductile film-like RA plays a crucial role in enhancing impact toughness under relatively higher austempering temperatures. In the simulations of tensile deformation, the concentration of equivalent plastic strain predominantly manifests in the bainitic ferrite neighboring the martensite, whereas the equivalent plastic strain evenly spreads between the thin film-like retained austenite and bainitic ferrite. It is predicted that the cracks will occur at the interface between martensite and bainitic ferrite where the strain is concentrated, and eventually propagate along the strain failure zone.

Abstract Different stress states have a significant influence on the magnitude of the microscopic plastic strain and result in the development of the microstructure evolution. As a result, a comprehensive understanding of the different scale variation on microstructure evolution during bending deformation is essential. The advanced high strength dual-phase (DP1180) steel was investigated using multiscale microstructure-based 3D representative volume element (RVE) modelling technology with emphasis on understanding the relationship between the microstructure, localised stress-strain evolution as well as the deformation characteristics in the bending process. It is demonstrated that the localised development in bending can be more accurately described by microscopic deformation when taking into account microstructural properties. Microstructure-based 3D RVEs from each chosen bending condition generally have comparable localisation properties, whilst the magnitudes and intensities differ. In addition, the most severe localised bands are predicted to occur close to the ferrite and martensite phase boundaries where the martensite grains are close together or have a somewhat sharp edge. The numerically predicted results for the microstructure evolution, shear bands development and stress and strain distribution after 3-point bending exhibit a good agreement with the relevant experimental observations.

The effects of prior austenite and primary carbides on the mechanical properties of a novel 2.5 GPa grade steel were investigated by treating at various solid-solution temperatures. The ultimate tensile strength and Charpy U-notch impact energy initially increased and subsequently decreased as the solid-solution temperature rose, while the yield strength consistently decreased. The size of prior austenite grain and martensite block always increased with rising the solidsolution temperature, and austenite grain growth activation energy is 274,969 J/mol. The growth of prior austenite was restricted by primary carbides M6C and MC. The dissolution of the primary carbides not only enhanced solid-solution strengthening and secondary hardening effects but also increased the volume fraction of retained austenite. The increase in the ultimate tensile strength and Charpy U-notch impact energy was primarily attributed to the dissolution of the primary carbides M6C and MC, while the decrease was due to the increase in the size of prior austenite grain and martensite block. Exceptional combination of strength, ductility and toughness with ultimate tensile strength of 2511 MPa, yield strength of 1920 MPa, elongation of 9.5%, reduction of area of 41% and Charpy U-notch impact energy of 19.5 J was obtained when experimental steel was solid-solution treated at 1020 ℃.

Selective laser melting (SLM) has become a critical technique for manufacturing molds with conformal cooling channels to achieve high cooling efficiencies. A novel selective laser-melted 718HH plastic mold steel with an excellent combination of strength and toughness was investigated. After SLM fabrication, quenching and tempering are conducted as postprinting heat treatment (PPHT) to improve the mechanical properties of the as-built samples. Both the microstructure and the corresponding mechanical properties were systematically studied. The results show that PPHT facilitates the complete martensite transformation. Meanwhile, the retained austenite (c) phase was still found in the as-built samples. And highdensity dislocations were dispersively distributed within the martensite matrix for both as-built and as-PPHTed samples. After PPHT, due to the recovery and recrystallization of martensite, reduced dislocation density and increased high-angle grain boundaries, the microhardness of the as-built samples decreased from 498.8 ± 16.7 to 382.1 ± 5.0 HV_0.3. Correspondingly, the strength, including the ultimate tensile strength and yield strength, of the as-built and as-PPHTed samples also decreased from 1411.3 ± 17.8 to 1208.7 ± 3.2 MPa and 1267.3 ± 11.7 to 1084.7 ± 5.1 MPa, respectively. On the contrary, the value of impact energy significantly increased from 15.3 ± 1.2 J (as-built) to 39.7 ± 1.2 J (as-PPHTed). Notably, the mechanical properties of SLMed 718HH samples are significantly better than those of corresponding wrought samples.

6061 aluminum alloy was successfully vacuum brazed to 304 stainless steel using Al-Si-Ge/Cu composite filler metal. The thermodynamic model was established to analyze the formation mechanism of microstructure in brazed joint and element diffusion behavior between filler metal and substrate. The findings indicated that the microstructure of 6061 aluminum alloy/304 stainless steel joint was a multilayer structure composed of three zones (Zone I, Zone II and Zone III). The free energy (∆G) calculation results indicated that Al-Si-M (M was Fe, Cr, Ni and Cu) ternary intermetallic compounds (IMCs) formed, when DG on M-Al side and M-Si/Ge side was similar. And only Al-M binary IMCs would be generated when there was large difference between ∆G on M-Al side and that on M-Si/Ge side. The calculation results of chemical potential of Si (∆μ_Si) and Ge (∆μ_Ge) indicated that there was continuous Si and Ge diffusion toward Zone I, forming (Ge, Si) layer. The segregation of Si and Ge hindered the diffusion of Cr toward Zone II and promoted its diffusion toward (Ge, Si) layer, leading to an upward trend of Cr distribution in Al₇(Fe, Cr)₂Si layer. Negative ∆μ_Ni and ∆μ_Fe were responsible for continuous diffusion of Fe and Ni toward Zone II. The small difference between DlCu in Zone I and Zone II contributed to distribution of CuAl₂ in Zone II. The formation mechanism of joint could be mainly divided into four steps.

Refill friction stir spot welding process is difficultly optimized by accurate modeling because of the high-order functional relationship between welding parameters and joint strength. A database of the welding process was first established with 6061-T6 aluminum alloy and DP780 galvanized steel as base materials. This dataset was then optimized using a backpropagation neural network. Analyses and mining of the experimental data confirmed the multidimensional mapping relationship between welding parameters and joint strength. Subsequently, intelligent optimization of the welding process and prediction of joint strength were achieved. At the predicted welding parameter (plunging rotation speed ω1=1733 r/min, refilling rotation speed ω2=1266 r/min, plunging depth p=1.9 mm, and welding speed v=0.5 mm/s), the tensile shear fracture load of the joint reached a maximum value of 10,172 N, while the experimental result was 9980 N, with an error of 1.92%. Furthermore, the correlation of welding parameters-microstructure-joint strength was established.

The high melting point element W and the rare earth element Ce were added to 18Cr-Mo (444-type) ferritic stainless steel to improve its high-temperature oxidation resistance in exhaust gas. A simulated exhaust gas was filled in the simultaneous thermal analyzer to simulate the service environment, and the oxidation behavior in high-temperature exhaust gas environment of 444-type ferritic stainless steel alloyed with W and Ce was investigated. The oxide structure and composition formed in this process were analyzed and characterized by scanning electron microscopy/energy-dispersive spectroscopy and electron probe analysis, and the mechanism of W and Ce in the oxidation process was revealed. The results show that 18Cr-Mo ferritic stainless steel containing W and Ce has better oxidation resistance in high-temperature exhaust gas. The element W can promote the precipitation of Laves phase at the matrix/interface, inhibit the interface diffusion of oxidizing elements and prevent the inward growth of the oxide film. The element Ce can suppress the volume of SiO₂ at the oxide film/interface, reducing the breakaway oxidation caused by cracking of the oxide film. The CeO₂ provides nucleation sites for oxide particles, promoting the healing of cracks and voids within the oxide film.

The transformation mechanism of the inclusions and microstructure in 316L stainless steel after post-isothermal heat treatment (IHT) was revealed, along with the pitting behavior of the inclusions in a chloride environment before and after the transformation. The effect of the inclusion transformation on the pitting corrosion behavior of 316L stainless steel and its intrinsic mechanism was also revealed. Results revealed a gradual transformation of MnO-SiO₂ inclusions into MnO-Cr₂O₃ within the temperature range of 1373 to 1573 K. MnO-Cr₂O₃ inclusions exhibited minimal dissolution in chloride ion corrosion environments, while MnO-SiO₂ oxides demonstrated higher electrochemical activity and were more prone to dissolve and form pits. Meanwhile, IHT significantly reduced the dislocation density of stainless steel, rendering it more stable in corrosive environments. X-ray photoelectron spectroscopy peak distributions of the passive films demonstrated that IHT increased the proportion of Cr and Fe oxides and hydroxides in the passive film which improved the stability and corrosion resistance of the steel.

Al_0.5CrFeNi_2.5 high-entropy alloy (HEA) was reinforced by the small-radius Si. Al_0.5CrFeNi_2.5Six (x = 0 and 0.25) HEAs were fabricated by laser melting deposition. The evolution of microstructure, nanohardness, and wear properties of Al0.5CrFeNi2.5Six (x=0 and 0.25) HEAs were systematically investigated. Al_0.5CrFeNi_2.5 HEA exhibits a face-centered cubic (FCC) matrix with Ni₃Al-type ordered nanoprecipitates. When Si was doped, δ phase and Cr-rich nanoprecipitates existed in the B2 matrix and L12 in the FCC matrix. The nanohardness was increased from 4.67 to 5.45 GPa with doping of Si, which is associated with forming the new phases and improved nanohardness of L12/FCC phases. The coefficient of friction (COF) value was reduced from 0.75 to 0.67 by adding Si.σ phase and Cr-rich nanoprecipitates in B2 matrix support a decreased wear rate from 7.87×10^-4 to 6.82×10^-4 mm³/(N m). Furthermore, the main wear mechanism of Al_0.5CrFeNi_2.5 and Al_0.5CrFeNi_2.5Si_0.25 HEAs is abrasive wear.

The GH4720Li alloy is one of the most widely used precipitation-strengthened nickel-based superalloy. However, sys-tematic study about effect of strain rate on the plastic deformation behavior of GH4720Li alloy at intermediate temperature is lacking. The evolution of the tensile properties and plastic deformation mechanism of GH4720Li alloy with the strain rate at 650 ℃ were systematically studied with the help of transmission electron microscopy analysis. The results show that the tensile strength of the alloy increases and the plasticity decreases with the increase in strain rate. When the strain rate is 5 min^-1, the tensile strength of the alloy is 1448 MPa and the tensile plasticity is 18%. As the strain rate increases from 0.05 to 0.5 min^-1, the size and morphology of the primary $\gamma^{\prime}$ phase of the alloy remain unchanged, with an average size of about 1.8 lm. However, when the strain rate further increases to 5 min^-1, the average size of the primary $\gamma^{\prime}$ phase increases to 2.5 lm. In addition, the increase in strain rate has no significant effect on the size and distribution of secondary and tertiary $\gamma^{\prime}$ phases. As the strain rate increases from 0.05 to 5 min^-1, the deformation mechanism of alloy gradually evolved from dislocation slip and twin to dislocation slip, indicating that the plastic deformation mechanism of the alloy presents a high strain rate sensitivity at 650 ℃.

The effect of ω_iso and α precipitation on microstructure, microhardness, tensile properties and impact toughness of Ti-25Nb-10Ta-1Zr-0.2Fe (TNTZF) alloy was investigated. The results showed that the solution treated TNTZF alloy with a small amount of nano-sized ω_ath particles in β matrix possesses tensile strength of 697 MPa, elongation of * 34%, Young’s modulus (YM) of 75 GPa, and impact toughness of 58.7 J/cm2. After aging at relatively lower temperatures of 400 ℃, the hardness and modulus of the alloy increased significantly, while the plasticity and toughness dropped sharply due to the precipitation ofω_iso phase.ω_iso phase displayed an ellipsoidal morphology with high volume fraction and a size of about 50 nm after aging at 400 ℃, leading to the highest hardness of 364 HV and YM of 108 GPa, along with completely embrittlement since elongation and toughness were almost zero. A brittle impact fracture morphology was observed in the alloy, which is dominated by intergranular fracture, with a mixed fracture characteristics of cleavage surfaces, terraces and tiny dimples. When aged at 550 ℃, plate-like a distributed in β matrix uniformly and in β grain boundaries in parallel, resulting in the high strength of 804 MPa, as well as lowest YM of 72 GPa, elongation of 9% and toughness of 35.8 J/cm². The fracture morphology of the alloy aged at 550 ℃ showed a ductile fracture mechanism with a large number of dimples.