Gradient nanostructures exhibit superior combination of strength and ductility compared with homogeneous counterparts. However, their practical performance is often limited by the poor thermal stability and restricted strain hardening capability of nanograined layers, as well as severe stress concentration at the fine-coarse grain transition zone, which typically leads to premature failure. Here, we overcome these limitations by introducing a thermomechanical-coupled incremental sheet forming strategy to engineer an oxide-mediated dual-gradient structure in a 316L austenitic stainless steel. During processing, the coupled high compressive stress and intense thermal exposure transform the inherent Cr-passivation film into dispersed nano-oxides penetrating ∼30 µm in depth. Detailed microstructural characterizations reveal a dual-gradient structure, consisting of a grain-size gradient (spanning from ∼40 nm at the surface to ∼20 µm in the core), and a “butterfly-like” dislocation-density gradient (with peak in the mid-layer), both driven by the cyclic thermomechanical gradients. Importantly, these dispersed nano-oxides play a dual and synergistic role: they stabilize the nanograined surface against thermal coarsening during processing, while counterintuitively acting as effective dislocation pinning sites upon plastic strain, thereby enabling sustained strain hardening in the strongest surface layer. In parallel, high-angular resolution EBSD (HR-EBSD) analyses suggest the presence of dense dislocation dipoles in the mid-layers, which mitigate strain concentration in the hard-soft transition regions. As a result, the engineered dual-gradient structure exhibits exceptional strain hardening capability that surpasses the conventional hetero-deformation-induced (HDI) strengthening regime, achieving an ultimate tensile strength approaching 1 GPa together with tensile ductility exceeding 40%. This work provides a new strategy for exploiting the intrinsic Cr-passivation film as a source for in-situ nano-oxide engineering, providing a simple yet powerful route toward simultaneously achieving ultra-high strength, sustained strain hardening, and large ductility without complex alloy design or external particle additions.

This study investigated the fatigue properties of diffusion-bonded TC4 titanium alloy under bending vibration loading, through experimental and computational methods. When interfacial atoms achieve complete metallurgical bonding, vibration fatigue crack initiates at the region of maximum stress concentration, rather than at the diffusion-bonded interface. To accurately model this behavior, a modified continuum damage mechanics model is developed to account for different damage evolution under tensile and compressive loading. Furthermore, an enhanced crack propagation rate model is proposed by modifying the Paris law to better characterize short-crack growth behavior after crack initiation. These models are integrated into a unified finite element framework that successfully predicts both crack initiation life and propagation life, as well as crack initiation site and propagation path. Numerical results obtained from a notched specimen demonstrate that damaged elements are distributed at the notch region, exhibiting pronounced damage localization. The damage evolutions of elements exhibit significant differences between tensile and compressive stress states. The total fatigue life prediction follows a two-stage computational process where crack initiation analysis first identifies critical damaged elements, which then serve as initial cracks for propagation analysis. Validation results, considering two stress amplitudes of 373 MPa and 400 MPa, confirm the framework's accuracy, showing relative errors of 1.4 % and 11.4 % for total fatigue lives.

Electrically-assisted forming (EAF) offers a promising solution for processing difficult-to-form metal foils. Nevertheless, how size effect and current interact during non-uniform plastic deformation is not fully clarified. This study investigates the influence of current on the strain gradient effect through experimental and computational methods. The forming angle decreases gradually with increasing current, as demonstrated by a series of electrically-assisted microbending tests on Ti65 titanium alloy foils. A mechanism-based strain gradient plasticity (SGP) model incorporating current effects is proposed. The model is further employed to quantify the current-induced variation of the material length scale. The strengthening contribution induced by geometrically necessary dislocations follows a non-monotonic trend with the increasing current. It rises initially but diminishes slightly beyond a critical thermal/current condition. The electrically-assisted roll forming process of the semi-hexagonal corrugated sheet is further investigated. Analyzing this process requires concurrently considering both the SGP effect and the non-uniform Joule heating induced by the current. Accordingly, an equivalent heat generation model is developed based on a simplified resistance framework. Coupling this thermal model with the current-dependent SGP theory enables accurate prediction of forming angles of the corrugated sheets. This modeling framework overcomes the oversimplified isothermal assumption in previous EAF simulations, and serves as a generalizable approach for EAF simulations of diverse thin-walled components.

By conducting adiabatic cyclic loading tests on three types of NiTi alloys with different martensite contents, dislocation densities, and grain sizes, the intrinsic influence mechanisms of different microstructures on the superelasticity, deformation modes, and elastocaloric cooling effect during the deformation process of NiTi alloys were investigated. The results show that the presence of a high dislocation density, high martensite content, and small grain size can reduce the degree of superelastic functional degradation and the possibility of local uneven deformation in NiTi alloys. However, the elastocaloric cooling ability is weak. A smaller strain value results in superior superelasticity (minimum epsilon(residual) =0.23%), but inferior elastocaloric cooling ability (maximum triangle T-cooling=0.63 K). Completely eliminating dislocations and martensite, as well epsilon residual as increasing grain size, can achieve a significant elastocaloric cooling capacity (triangle T-cooling=25 K), but induces severe functional degradation (a drop from 25 K to 9.6 K, a decrease of 61.6%). Annealing at 400 degrees C for 15 min to tailor the dislocation density, martensite content and grain size results in good superelasticity, uniform deformation ability and a considerable elastocaloric cooling ability (triangle T-cooling=7.2 K), along with improved resistance to functional degradation.

Catastrophic failures in engineering metallics frequently occur at high temperatures. A fundamental understanding of plastic deformation and the mechanisms governing the strength-ductility trade-off is essential for developing titanium alloys exhibiting superior properties at elevated temperatures. Herein, a metastable β titanium alloy (Ti-15.1Mo-3.1Nb-2.77Al-0.21Si, wt.%) exhibits unexpected mechanical properties, including an ultimate tensile strength of 863 MPa and a total elongation of 78.3% at 500 °C, accompanied by a continuous and strong work hardening rate (2000-3100 MPa). Dislocation slip and heating play pivotal roles in interlaced parallel α nucleation, and thermal activation promotes interlaced α nucleation. Finally, the dual-array nano configuration of dense (≈68%) and thin (≈10 nm in width) α phase forms. Hierarchical microstructural evolutions, including β to α phase transformation, nano α grains with dual-array configurations (interleaved and parallel), and dislocation interaction, contribute to the excellent mechanical properties. These findings reveal that dynamic nano α precipitation with unique dual-array nano configurations can unveil new prospects for the development of high-performance metastable titanium alloys at elevated temperatures.

Utilizing a vacuum environment to avoid high-temperature oxidation is regarded as an effective approach to improve the high-temperature formability of Ti-6Al-4V alloy, but hot forming in air remains widely employed in engineering practice. However, in-depth insights into the high-temperature deformation mechanisms of Ti-6Al4V alloy under these two distinct environments are still lacking. This study systematically investigated the hightemperature deformation behavior and microstructure evolution of Ti-6Al-4V sheet under vacuum and air environments. The interaction mechanisms between oxidation and high-temperature deformation were specifically examined. On the one hand, deformation inhibits the thickening of the oxide layer (OL) by accelerating the outward diffusion of aluminum atoms, while promoting the thickening of the oxygen-rich layer (ORL) by increasing the surface dislocation density and refining grains of the alpha-case. In addition, deformation-induced dynamic phase transformation (DT) can suppress the thickening of the alpha-case. On the other hand, under the coupling effect of oxygen diffusion and deformation, the alloy microstructure is divided into three distinct regions: the high-oxygen zone (HOZ), the low-oxygen zone (LOZ), and the substrate. Each zone shows unique hightemperature deformation mechanisms. Notably, elevated oxygen content inhibits grain boundary sliding (GBS) in the HOZ and LOZ, and a higher dislocation density facilitates the occurrence of softening mechanisms such as dynamic recovery (DRV) and dynamic recrystallization (DRX) in the HOZ. This study provides important theoretical support for revealing the mechanisms of oxidation affecting the high-temperature deformation of Ti6Al-4V alloy and optimizing its hot forming process.

During diffusion bonding of Al-Li alloys, the dense oxide layer limits joint quality. Using a nano-Cu interlayer can inhibit interfacial oxidation, but its mechanism is unclear. This study combines molecular dynamics simulation and experiment to investigate the diffusion-bonding behavior of 2A97 Al-Li alloy using a nano-Cu interlayer. Results show that the nano-Cu layer promotes element diffusion, with higher temperatures enhancing the effect. At 480–500 °C, oxides and continuous Cu intermetallics in the bonded interface hinder diffusion. At 520 °C, oxides and intermetallics decrease and disperse, allowing interfacial atoms to achieve sufficient diffusion. At 540 °C, coarsening of Cu-containing intermetallics reduces mechanical properties. Simulation matches experiments, providing a theoretical basis for nano-Cu interlayers in Al-Li alloy diffusion bonding.

The Mg-4Y-3RE (WE43) magnesium alloy possesses high specific strength, excellent shock absorption, strong electromagnetic shielding, and recyclability. However, the oxidation and defects often happen during conventional welding. Solid-state diffusion bonding in a near-vacuum environment enables high-reliability joints by minimizing these issues. It is difficult to obtain high bonding joint strength due to the limitation of various factors. This work systematically investigates the effects of temperature, time, pressure, and surface roughness on the diffusion-bonded joint quality of WE43 magnesium alloy through a phased optimization strategy. The optimal parameter combination is optimized. The results demonstrate that the joint interface achieves a shear strength of 179.9 ± 3.9 MPa and a bonding ratio of 94.14 % when the minimal plastic deformation is ensured. Microstructural characterization reveals that recrystallization, precipitates evolution and elemental diffusion effects collectively promote metallurgical bonding at the interface. Subsequent solution treatment at 525 °C for 8 h and aging at 250 °C for 16 h, the shear strength significantly increases to 229.5 ± 5.2 MPa, which represents the highest value in comparable reported studies. This research provides theoretical foundations and technical references for solid-state bonding processes of high-strength magnesium alloys.

Electrically assisted forming (EAF) technologies leverage electroplastic effects induced by electric current passage through metallic materials to enhance the deformation ability of difficult-to-form alloys, such as titanium alloys, which typically require elevated temperature (>700 degrees C) for high-precision forming due to their limited formability at lower temperature. However, microstructure evolution and mechanical response prediction of titanium alloy foils during EAF at elevated temperature remain insufficiently investigated owing to complex interplay between electroplasticity and size effect. In the present study, electrically assisted uniaxial tensile experiments were performed on Ti65 titanium alloy foils with a thickness of 0.1 mm and grain sizes ranging from 7.2 mu m to 22.3 mu m. Experimental results demonstrated that electric current-induced softening and strain rate strengthening exhibit a pronounced size effect. Initial grain size and critical recrystallization strain show an inverse correlation. Dynamic recrystallization (DRX) volume fraction increases significantly with electric current density for fine-grained specimens. But, the effect of current density on DRX process is limited and nonmonotonic for coarse-grained specimens. A physically based constitutive model that integrates size effects with multiple strengthening and softening mechanisms is developed. The proposed model accurately characterizes the flow softening behavior of Ti65 titanium alloy foils with different initial grain sizes across varying electric current densities and strain rates. It is revealed that grain coarsening significantly weakens the contributions of precipitation strengthening and DRX softening on dislocation density evolution. Furthermore, significant flow stress drop due to athermal electroplasticity is calculated based on the proposed model.

High-quality iron/nickel-based bonded joints can ensure long-term service of heat exchangers under high-temperature and cyclic thermal stress conditions. In this work, dissimilar diffusion bonding between IN617 nickel-based superalloy and P92 heat-resistant steel was realized via hot pressing (HP) and electric field-assisted (EFAS) diffusion bonding (DB) with pure nickel interlayer. The influences of process parameters, interlayer thickness and current on interfacial microstructure and mechanical properties were investigated by orthogonal experiments, mechanical tests and microscopic characterization. Results show that pure nickel interlayer effectively promotes interfacial void closure and metallurgical bonding via fine-grained diffusion layers induced grain boundary diffusion and migration, and ∑3 special grain boundaries in fine-grained layers enhance joint service performance. Under the optimal parameters (1000 °C, 20 MPa, 50 μm Ni interlayer, HP-DB), the joint exhibits a maximum shear strength of 581.13 MPa. The calculated activation energies (130.4 ± 7.7 kJ/mol for Ni/IN617 and 121.7 ± 37.1 kJ/mol for Ni/P92 with the 50-μm interlayer) support that interfacial diffusion is dominated by the grain-boundary diffusion mechanism. Electric current and nickel interlayer present a significant synergistic effect: current accelerates interfacial grain boundary migration and atomic interdiffusion. Interface grains grow under high-speed kinetic control without a specific crystallographic orientation relationship. The Fe-Ni solid solution layer near the Ni/P92 interface strengthens the joint by inhibiting brittle intermetallic compounds and by using its compositional gradient to ease thermal mismatch stresses. This study provides a robust experimental and mechanistic foundation for optimizing process parameters and selecting interlayer thickness in high-performance Fe/Ni-based alloy diffusion-bonded joints.

While Sc and Zr additions markedly improve the printability and mechanical properties of Al-Mg alloys fabricated via additive manufacturing (AM), the recyclability and sustainability of supersaturated Sc/Zr-containing alloys remain largely unexplored. Here, Al-Mg-Sc-Zr alloys with Sc/Zr contents spanning the AM-relevant compositional range, were prepared by conventional casting and tailored heat treatments to mimic the microstructure-property evolution in recycled Al scraps enriched with Sc and Zr. Dual-scale second phases are identified, comprising micrometer-scale primary Al3(Sc1-x, Zrx) particles and nanoscale L12-Al3(Sc1-x, Zrx) precipitates. Moreover, three distinct primary particles, i.e., Zr-dominated, Sc-dominated and Sc/Zr-enriched are revealed. The associated local strain/stress concentration and geometrically necessary dislocation densities are quantitatively resolved using high-resolution EBSD. A competitive interaction between dual-scale second phases is demonstrated to govern recrystallization, where particle-stimulated nucleation and Zener pinning act antagonistically, leading to non-monotonic dependence of recrystallization and room/high temperature mechanical properties on Sc/Zr contents. These findings establish a quantitative composition-precipitation-property framework for the sustainable design of high-performance Al alloys recycled from AM applications.

Oxide films in Al-Li alloy diffusion bonding joints hinder atomic diffusion, reducing bond strength. A new electrodeposition process applies a nano-Cu coating, achieving a peak shear strength of 102.8 MPa at 1 mu m and 520 degrees C. Cu atoms from the coating diffuse into the Al matrix, forming intermetallic compounds (IMCs) that enhance Al-Al mutual diffusion. However, thinner coatings (<0.5 mu m) fail to prevent oxide film formation, while thicker ones (>4 mu m) hinder Al diffusion due to continuous IMC structures. Low temperatures (<480 degrees C) result in coarse, non-diffusive IMCs, while high temperatures (>540 degrees C) promote IMC growth and increase void and crack risks. This study introduces a novel nano-coating concept for Al-Li alloy bonding, with practical engineering applications.

The production of aero engine casings requires forming Ti-6Al-4V cylinders with low aspect ratios. Compared to conventional thermal forming, electrically assisted forming demonstrates higher efficiency and leverages non-thermal effects to enhance the plastic deformation ability of Ti-6Al-4V titanium alloy. The electrically assisted differential thermal bulging, combining characteristics of thermal/electrically assisted forming, produces the cylinder components that maintain peak tensile strength among all experimental conditions across 25–350℃ under lower effective currents and forming temperatures. During bulging process design, the finite element methods were performed to optimize electrode quantity and spacing, which aims to alleviate thermal expansion and achieve uniform electrical/thermal distribution. The cylinder components produced via this novel approach exhibit only 40

In this work, a method to enhance the superelasticity and elastocaloric cooling effect of NiTi alloy by shot peening treatment was proposed. This work investigated the influence of shot peening on the microstructure of NiTi alloy, focusing on deformation modes (uniform and non-uniform), superelasticity and elastocaloric cooling effect during stress-cycling-induced phase transformation. The results demonstrated that shot peening significantly altered the microstructure of the samples, changing it from a fully austenitic state to a “sandwich” structure. This newly formed microstructure consists of needle-like martensite near the surface, austenite in the middle layer, and plate-like martensite at the core. Furthermore, shot peening effectively mitigated non-uniform deformation during phase transformation, resulting in reduced local strain concentrations and temperature inhomogeneity. This process also minimized the degradation of superelasticity and the elastocaloric cooling effect, thereby enhancing the cyclic stability of these properties.

Understanding the relationship between deformation behaviors and mechanisms is significant for the processing and application of metastable beta titanium alloys. Here we aim to investigate and evaluate the abnormal yield strength and strain softening of a Ti-15.1Mo-2.77Nb-3.1Al-0.21Si alloy at room temperature. This alloy exhibits a high yield strength of 970 MPa, followed by the continuous stress drop behavior in the entire engineering strains (or true strains of 0.018 similar to 0.056). Digital image correlation (DIC) reveals that the flow stress drop results from local strain softening associated with a local increase in strain rate, instead of L & uuml;ders strain. The pinning between dislocations and Si atoms as well as other interstitial atoms at and near grain boundaries is mainly responsible for the high yield strength. Subsequently, dislocations originating from grain boundaries can easily slip in a planar pattern along the {110} < 111 > slip systems, resulting in a continuous stress drop. In addition, both the low density of dislocations within beta grains and large grain size also provide favorable conditions for dislocation slip over a long distance. This study reveals the mechanisms of both high yield strength and strain softening in the metastable beta Ti alloys.

This study aims to predict the thickness variation of Al3003-H14 square lithium battery shells during multi-stage deep drawing and ironing processes. A modified material model, MAT122_3R_3D_CL_user, was developed by coupling the Hill'48 yield function and Cockcroft & Latham ductile damage criterion through secondary development in LS-DYNA. Anisotropic parameters for MAT122_3R_3D were determined using Lankford coefficients (r0, r45 , r90 ) obtained from uniaxial tensile tests. Numerical simulations with 3D solid elements accurately captured thickness changes and failure positions, which aligned well with experimental results. The causes of thickness deviations, including simplified assumptions for anisotropic coefficients and constant friction condition, were analysed. The proposed model enables optimization of process parameters to prevent excessive thinning or fracture during forming.

The superplastic forming (SPF) technique presents new potential for the near-alpha Ti6321 titanium alloy in the fabrication of critical ultra-thick components for the marine industry. This study investigates the effects of temperature and strain rate on the flow behavior, microstructural evolution, and deformation mechanisms of the Ti6321 alloy during superplastic deformation. Optimal SPF conditions are identified at 850 degrees C/0.0005-0.001 s(- 1) and 900 degrees C/0.0005-0.005 s(-1), under which elongations exceeding 370 % and a strain rate sensitivity above 0.3 are achieved, indicating excellent superplasticity. The enhanced alpha ->beta dynamic phase transformation with increasing temperature moderately contributes to superplastic performance. A maximum elongation of 824.4 % is attained at 900 degrees C/0.0005 s(- 1) with an alpha/beta phase ratio of 75/25, driven by synergistic interactions among grain boundary sliding, dynamic globularization, dynamic recrystallization, grain rotation, and active dislocation activity. However, at 950 degrees C, a significantly higher beta-phase content (similar to 50 %) induces dynamic grain coarsening and convergent evolution of microtexture in the alpha phase, which impedes grain rotation and leads to strain incompatibility between adjacent grains. Consequently, the macroscopic deformation is compromised due to the inability of existing mechanisms to effectively accommodate localized stress concentrations. At comparable beta-phase fractions, a higher initial strain rate is found to promote grain refinement and orientation divergence, but also intensify dislocation multiplication. Pyramidal slips, particularly the first-order slip, serve as the dominant slip mode in the primary alpha phase. These findings provide a mechanistic basis for optimizing SPF conditions in the Ti6321 alloy and offer novel insights into its marine applications.

The Mg-4Y-3RE (WE43) magnesium alloy possesses significant advantages such as high specific strength, excellent shock absorption, strong electromagnetic shielding capabilities and recyclability. However, its close-packed hexagonal structure leads to poor plasticity at room temperature, which limits its broader engineering applications. Therefore, superplastic forming at high temperatures is used to manufacture the components from this alloy. This study conducted tensile tests on hot-rolled WE43 rare-earth magnesium alloy with coarse grains at various temperatures and strain rates. The high-temperature superplastic properties were characterized, revealing the intrinsic mechanisms of thermal deformation behavior. The results indicate that the best superplasticity is achieved at 460 °C. This is attributed to the smallest grain size, the weakest texture, and the relatively uniform distribution of the second phase at this temperature. The influence of strain rate on elongation at temperatures among 440 °C∼500 °C is not significant as the impact of strain rate is multifaceted. Meanwhile, the elongation can reach up to 367.7 ± 3.7 % at a strain rate of 0.01s−1, which exhibits the high strain rate superplasticity (HSRS). Under these conditions, the deformation of coarse-grained WE43 rare-earth magnesium alloy is controlled by grain boundary sliding (GBS) and solute drag dislocation creep. Furthermore, the GBS involves deformation coordination mechanisms such as grain boundary diffusion, lattice diffusion, dislocation climbing, and dynamic recrystallization accommodation mechanisms.