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The short-chain forming process using rotary swaging (RS) is an important method of achieving the manufacturing of lightweight axles. Axle steel, like 42CrMo, is widely used in many types of axles and shafts; however, there is no existing research on rotary-swaged axle steel's mechanical properties. It makes sense to carry out a comprehensive study on the effect of RS on the mechanical behaviors of axle steel rods. In this study, a 42CrMo steel rod was processed by RS through ten passes. The tensile properties, torsion properties, compression properties, and fatigue properties were tested. There was an overall improvement in the torsional and fatigue performance after RS. Combined with a finite element analysis (FEM), the uneven distribution of the dislocations and existence of the elongation material were inferred to have caused the different modes of the mechanical behaviors. Fracture surfaces were analyzed and the results showed that the fracture pattern had changed. There existed a competitive relation between the internal fatigue cracks and external cracks, which could be attributed to uneven strain hardening. This research proved the advantages of RS in the processing of axle parts, which mainly benefitted the torsional working conditions, and provided evidence for a new processing route for lightweight axles with RS. [ABSTRACT FROM AUTHOR]

Laser Directed Energy Deposition (LDED) has gained significant attention as a promising additive manufacturing technology for the repair and restoration of worn parts. The objective of this study is to assess the feasibility and performance of repairing 42CrMo substrates using Inconel 718(IN718) powder. In this study, the LDED process was employed to investigate the influence of varying laser power, scanning speed, and feed rate on a single track study. The optimal process parameters for trapezoidal groove repair were determined by comparing and evaluating factors such as dilution, aspect ratio, track continuity, and molten pool shape. Furthermore, the effects of different repair strategies (X-, Y-, Cross-paths) on the microstructure and mechanical properties were investigated. The results indicate that by using suitable process parameters, successful deposition of IN718 on 42CrMo is achieved. The investigation reveals elemental diffusion between the two materials, quenching phase transition on the substrate surface, and the formation of intermetallic compounds in the fusion zone. The fusion zone(FZ) and heat-affected zone(HAZ) exhibited the highest microhardness compared to the substrate. Significant changes in molten pool shape and arrangement were observed using different repair strategies, while the effect on grain size was not significant. Due to the high directionality of the samples fabricated using the LDED process, the samples of the X-path demonstrated the highest ultimate tensile strength and elongation compared to the other two repair strategies. The ultimate tensile strength after repair is comparable to that of the substrate, while the elongation is reduced. • The optimal process parameters for trapezoidal groove repair were determined by comparing and evaluating factors such as dilution, aspect ratio, track continuity, and molten pool shape. • The DZ exhibited the presence of MC-type carbides at the bottom, while the FZ contained numerous intermetallic compounds. The HAZ experienced a quenching transformation into martensite. • Repairing the part in the direction of stress results in excellent mechanical properties. [ABSTRACT FROM AUTHOR]

25CrMo4 steel is widely used in the manufacturing of high-speed train axles due to its excellent mechanical properties. The purpose of this study is to develop an accurate modified constitutive model to describe the hot deformation behavior of the steel. Isothermal compression experiments were performed at different strain rates (0.01, 0.1, 0.5, and 1 s−1) and different temperatures (950, 1000, 1050, and 1100 °C) using a Gleeble-3800 thermal simulator. The microstructure after hot deformation was observed by the electron backscatter diffraction (EBSD), and the effects of temperature and strain rate were analyzed. The results showed that the coupling effect of temperature and strain rate on the dislocation density led to the change in the shape of the true stress–strain curve and that dynamic recovery (DRV) and dynamic recrystallization (DRX) caused the macroscopic softening phenomenon, with DRX being the main mechanism. Based on the true stress–strain curves, the strain-compensated Arrhenius constitutive model was calibrated. To improve prediction ability, a modified Arrhenius constitutive model was proposed, in which the temperature and strain rate coupling correction functions were incorporated. The original, modified Arrhenius models were evaluated according to the absolute relative error (ARE), the average absolute relative error (AARE), and the correlation coefficient (R2). Compared with the original model, the modified Arrhenius model has a higher prediction accuracy, with the ARE value mostly below 4%, the AARE value of 1.91%, and the R2 value of 0.9958. [ABSTRACT FROM AUTHOR]

Rotary swaging (RS) with mandrel was performed on aeroengine high-temperature alloy steel tubes at room temperature. Annealing experiments were conducted on both the non-RS and RS sections at various temperatures. The evolution of microstructure and mechanical properties was analyzed. Mechanical testing results revealed that RS resulted in a greater increase in yield strength compared to tensile strength, with a less pronounced recovery of yield strength enhancement after annealing. Annealing at 700 °C showed the most effective recovery of elongation. Microstructural observations showed shortening and coarsening of martensite packets and blocks after annealing, along with the evolution of precipitates. The higher dislocation density introduced by the RS process led to recovery during annealing and extensive recrystallization at 900 °C. Both annealing temperature and dislocations jointly influenced microstructure evolution and the work-hardening behavior. The thickness of shear layers induced by the RS process on the surface could be reduced after annealing and the elongated grains underwent recovery and recrystallization. This study provides a comprehensive investigation into the mechanisms of mechanical performance and microstructure evolution. It holds practical insights for applying the RS-annealing process to aeroengine high-temperature alloy steel tubes and for developing advanced processing routes for aeroengine shafts. [ABSTRACT FROM AUTHOR]

• Failure analysis of a cold rotary swaging die which bears high-frequency impact loads is investigated. • A large amount of dislocations are believed to have accumulated in the near outer layer of the arc surface. • The common single circle design leads to the concentrated forming stress during rotary swaging process on the die surface. • Phase inhomogeneity caused in heat treatment process and internal damage accumulation are two other reasons for the failure. • Fillet and surface designs are proposed to improve the wear and stress distribution. Failure analysis was carried out on a cold rotary swaging die for batch production of small shafts and tubes. Characteristics of top and bottom surfaces were examined. Hardness distribution on the cross section and microstructure were analyzed. Stress distribution and wear on the die during rotary swaging were investigated by finite element analysis (FEA). The study showed that the internal damage, phase inhomogeneity, concentrated forming stress were the main three reasons for premature failure of the die. The internal damage caused the tensile strength to reduce by more than 55%. The content of 33.55% martensite near the arc surface was not high enough to prevent the cracks from propagating inward. The stress concentration at the bottom of the arc surface further decreased the bearing ability. Increasing the fillet angle can decrease the high stress by around 60% at the transition area and improving surface design can disperse the high stress area while reducing maximum stress by more than 35%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrasonic assisted rolling was introduced to laser metal wire deposition to eliminate dendrite and grain coarsening. • A multiple process microstructure evolution simulation for laser metal wire deposition was carried out. • The influence of ultrasonic amplitude, distance between laser focus point and ultrasonic roller on microstructure of deposition layer were explored. Directed energy deposition (DED) has a widely application prospect, but dendrite and component segregation are not easily controlled and predicted. In this study, the method of applying ultrasonic assisted rolling was introduced to the DED to eliminate above phenomenon. A multiple process microstructure evolution simulation (involved melting, solidification, dynamitic recrystallization and grain growth) was also carried out, which introduced ultrasonic effect in the form of energy. The influence of ultrasonic amplitude (A), distance between laser focus point and ultrasonic roller (d 0) on microstructure of Pb-Sn alloy deposition layer were explored. There is a good consistency between experiment and simulation with relative error of 4.33%. The results show that the roundness of grains is improved significantly after rolling, and the grain are refined with the increase of A and d 0. In all tests of this study, comprehensive effect of ultrasonic rolling achieves the best when d 0 is taken as 24 mm and A is taken as 20 μm, the average grain diameter (D 0) in grain size counted zone is 18.8 μm which is 23.23% lower than that without rolling. This study laid a foundation for the development of ultrasonic assisted rolling DED and provide a multiple process microstructure simulation method. [ABSTRACT FROM AUTHOR]

Inner-stepped shafts hold an important role in aero-engine design and manufacturing. The high strength of the aeronautical materials makes it difficult to process the shafts. Traditional machining methods especially the drilling processes usually take a lot of time, and manufacturing accuracy such as coaxiality and wall thickness error is hard to control, especially when the aero-engine shaft has a large length/depth-diameter ratio. In this study, a precision rotary swaging process was studied to form the inner-stepped hole. Based on the constructed constitutive model of nickel-based superalloy GH4169, die design analysis was carried out using the finite element method. Experimental results showed good size accuracy within 0.05 tolerance. The hardness increased by less than 16% and the developing compression residual stress could guarantee the mechanical properties of the shaft. The microstructure showed a slight texture after swaging. [ABSTRACT FROM AUTHOR]

Conductive structures determine the functions and actuation modes of electrically responsive soft actuators. The rewritability of conductive structures is highly desirable but has not been realized in electro‐driven actuators. Typically, once conductive pathways are established, they can hardly be modified; thus, the function of the actuator is permanently fixed. In this study, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is developed as a rewritable conductive coating for actuators composed of liquid crystalline elastomers (LCEs). This enables reconfigurable, adaptive, and precisely controllable electro‐driven motions and the repeated use of the same actuator for various purposes without disposal. Moreover, different PEDOT:PSS layers can be coated onto different regions, thus enabling the assembly of different actuation behaviors in a monolithic actuator under a single input voltage. Unlike all previously reported soft actuators that respond to electricity and light, opposite shape changes in an actuator with a series circuit can be performed under these two stimuli. Furthermore, when combining LCEs with dynamic covalent bonds, the PEDOT:PSS‐coated LCE (PEDOT:PSS‐LCE) actuator can be reprogrammed based on two different mechanisms: rewriting the conductive PEDOT:PSS patterns and re‐aligning the LCEs. This versatile method can be adapted to other types of actuators. [ABSTRACT FROM AUTHOR]

Aiming at the problems of a large amount of material cutting waste or large forming load when large gear profile forming adopts overall cutting or precision forging process, this paper proposed a three-roller bending process (TRBP) for large gear teeth profile, and analyzed the deformation mechanism of the rack bending, meanwhile the gear chain for roll forming was designed. Finite element analysis (FEA) was carried out to numerically simulate the load effects of both the precision forging process and the TRBP for the large gear teeth profile in 17CrNiMo6. The effects of deformation force and strain of TRBP for large gear teeth profile were analyzed. The results showed that as the deformation temperature and speed increase, the deformation force and strain required by the gear profile gradually change. And the reasonable parameter of TRBP is around 750 ∘ C of deformation temperature and 0.5 mm · s - 1 of speed. Compared with the precision forging process under the same boundary conditions, the deformation force of the gear profile TRBP has decreased by about 99 % which could significantly reduce the tonnage requirement of deforming equipment. [ABSTRACT FROM AUTHOR]

Silicon solar cells with cover glass irradiated by 1 MeV electron beams at various fluences were investigated using photocarrier radiometry (PCR) combined with lock-in carrierography (LIC, spectrally gated dynamic photoluminescence). The minority carrier transport properties (i.e., minority carrier lifetime τ, diffusion coefficient D, surface recombination velocities S) and the degradation of these properties were studied using PCR. The relative damage coefficient obtained by LIC was consistent with the PCR measurement. The local series resistance of the solar cell before and after irradiation was characterized by LIC. The results showed that the series resistance increased with electron fluences. [ABSTRACT FROM AUTHOR]

The distribution of minority carrier transport parameters (i.e., minority carrier lifetime, diffusion coefficient, and two surfaces recombination velocities) of multicrystalline silicon (mc-Si) solar cell was investigated using laser-induced photocarrier radiometry (PCR). Images of the amplitude and phase of the PCR measurements clearly showed the crystal boundaries of the mc-Si solar cell. The distribution of minority carrier transport parameters was obtained by best fitting the experimental results to the theoretical two-layer carrier density wave model of solar cells. The best-fitting results demonstrated that there was great difference in the minority carrier transport parameters among various grains. [ABSTRACT FROM AUTHOR]