Laser-cladding repair of high-strength steels leaves porosity and oxide-covered interfaces that degrade mechanical performance. This study clarifies how interfacial strain and temperature control solid-state pressure bonding in EA4T axle steel, validates a physics-based bonding model, and applies the insights to heal voids in laser-clad material. Half-bar couples and laser-clad/wrought pairs were hot-compressed to engineering strains of 0.1–0.5 at 9001000and 1100 °C. EBSD/SEM-EDS characterised oxide fragmentation and grain continuity; tensile tests measured bond strength; finite-element (FE) simulations supplied local strain and normal-stress fields for model validation. A critical local strain of 0.25 initiates bonding, while 50

Additively manufactured materials typically contain undesired defects and microstructures. These defects reduce material performance and limit the adoption of the technique in production environments. In this work, we report a hybrid manufacturing strategy that integrates additive manufacturing with hot forging to achieve exceptional mechanical properties in Ti-6Al-4V. The resulting material exhibits improved tensile and fatigue properties compared to its purely additively manufactured and conventionally wrought counterparts. The control of thermal history and plastic flow is capable of healing defects and tailoring microstructure. A series of combined forging and heat treatment processes were undertaken to reveal correlations between fabrication parameters and the resulting microstructures and mechanical response. The underlying mechanisms of microstructure evolution were investigated through systematic and integrated experimental characterization, finite element modelling and mechanical tests. A generic component, representative of an aero-engine blade, was fabricated using this technology, demonstrating the huge promise of adopting this technique in practical applications.

In the hot metal forming processes, materials deform viscoplastically and the microstructure changes dynamically, and constitutive equations used to characterize the material flow and microstructure evolution can be complicated. Although different types of constitutive equations have been proposed by many researchers, due to the strong non-linear relationship and interconnectivity between the variables, determining the material constants could be complex, and it lacks a unified optimization method and program for these problems. This work will develop a groundbreaking step-by-step optimization methodology to determine the material constants in constitutive equations effectively and efficiently. Relationships between the variables will be analyzed, and the computational complexity and cost will be reduced by dividing the whole optimization process into several steps and considering only one or several variables in each step. Five different sets of experimental data for different materials and forming conditions will be considered in this work for demonstration, and different constitutive equations will be used to describe the material flow behaviors and microstructure evolution, where the material constants will be determined using the proposed optimization method. Instead of taking days, weeks or even months to accurately determine the large number of material constants, the proposed unified data-based optimization method only took less than 7 min even for the most complex case, using a conventional personal desktop computer. This transformative optimization method will significantly improve the accuracy and efficiency of viscoplastic constitutive models' development, enabling more complex microstructure behaviors e.g., phase transformation, void reduction, solid welding quality to be incorporated and reliably modelled.

Interface Grain Boundary (IGB) migration is a critical phenomenon in solid-state bonding, yet its direct effect on joint mechanical performance remains unclear due to its coexistence with processes such as dynamic recrystallization and oxide evolution. This study isolates the influence of IGB migration by minimizing other contributing factors. Forge welding and diffusion bonding were applied to high-purity nickel to fabricate joints with and without IGB migration while maintaining void- and impurity-free interfaces. Microstructural evolution was characterized using multiple analytical techniques. Furthermore, a Crystal Plasticity Finite Element (CPFE) model, combined with in situ tensile testing, was employed to clarify deformation mechanisms near the bond line. Results reveal that, in the absence of oxides and voids, IGB migration exerts minimal influence on overall mechanical behavior. Both experimental observations and CPFE simulations indicate that local stress concentrations are alleviated through grain orientation differences and reorientation during deformation, thereby reducing the impact of unmigrated boundaries. A four-grain CPFE model further illustrates the synergistic effects of IGB migration and grain reorientation when examined separately. These findings enhance understanding of the intrinsic role of IGB migration and provide guidance for designing high-performance bonded materials.

Heat treatable aluminium alloys have widespread applications in various industries owing to their significant strengthening capability through certain heating and cooling processes. However, these processes result in a trade-off between strength and ductility/formability, and the underlying fundamental mechanisms remain poorly understood. In this study, a multi-scale investigation was conducted on a heat treatable Al-Mg-Si alloy to explore the mechanisms underlying the trade-off between strength and ductility/formability. Three different tempers T6, T4, and O were produced, each leading to the formation of different second-phase precipitates. Uniaxial tensile tests and Nakajima punch tests were carried out to quantify the alloy’s ductility and formability, respectively. These mechanical properties were subsequently linked to the microstructure of the alloy by conducting micro uniaxial tensile tests alongside in-situ microstructural characterisations. The results indicate that the trade-off mechanisms arise from the competition between deformation occurring within the grain interiors and deformation near the grain boundaries. In the T6 temper alloy, precipitates significantly impede slip within the grain interiors, leading to strain concentration near the grain boundaries and the occurrence of intergranular fractures. Consequently, the T6 temper alloy exhibits the lowest ductility and formability. In contrast, slip occurs throughout all grains in the O temper alloy, thereby accommodating more deformation and resulting in the highest ductility and formability. Additionally, the precipitates in the alloy affect the dispersion of the geometrically necessary dislocation (GND) density. This study sheds light on the fundamental understanding of how precipitates influence the trade-off between the enhancement of strength and the simultaneous reduction of both ductility and formability.

Dynamic recrystallisation (DRX) is a significant restoration mechanism in the hot deformation of materials with high stacking fault energy (SFE), such as aluminium alloys. Both continuous DRX (CDRX) and geometric DRX (GDRX) have been observed concurrently during hot deformation of aluminium alloys. However, the kinetics of these DRX mechanisms during hot deformation remain considerably controversial in the literature, leading to the development of distinct constitutive models for CDRX and GDRX. To address this knowledge gap, the present study conducted hot compression tests on an aluminium alloy (AA6061) at varying strain levels up to 1.5. Crystallographic orientation and misorientation were characterised over a large area of the deformed samples using high-resolution electron backscatter diffraction (HR-EBSD) with a misorientation resolution of 0.05 degrees. A quantitative analysis was then performed on the characteristics of high-angle grain boundaries (HAGBs), low- angle grain boundaries (LAGBs) and geometrically necessary dislocations (GNDs). The results indicate that CDRX initiates in the early stages of deformation and reaches saturation as deformation progresses. This saturation of CDRX is attributed to a reduction in GNDs and LAGBs. GDRX occurs slightly before CDRX saturation, then accelerates as deformation continues, ultimately becoming the dominant mechanism at higher strain levels. In addition, hot deformation results in formation of Sigma 3 (60 degrees (111)) twin boundaries (TBs), initially in the original HAGBs and subsequently in new HAGBs produced through GDRX. In contrast, these TBs are not observed in the new HAGBs generated through CDRX. This research provides significant insights into the kinetics of CDRX and GDRX in high SFE materials, supporting the development of predictive models for these DRX mechanisms.

Predicting fracture toughness is an important part of developing an overall structural integrity methodology for components. This study therefore tries to establish a fracture toughness prediction model based on the concept of remaining multiaxial ductility exhaustion. Numerical simulation model which takes into account the level of constraint at the crack tip and the material’s inherent multiaxial ductility is established to research fracture initiation and propagation. The core of the model is based on increasing load to consume the remaining multiaxial ductility of metallic alloys until final fracture. The presence of grains (G) and grain boundaries (GB) in the simulation model is used to highlight a sensitivity analysis on the local interaction of microstructural at meso-scale with regards to crack initiation and growth. The model has been validated with fracture toughness tests by using additively manufactured Ti6Al4V alloy compact tension (CT) specimens. It is shown that the predicted plane strain KIC compares well with results from both wrought and heat-treated additively manufactured test specimens. Future tests on different other materials using low/high constraint cracked geometries should strengthen the model’s predictive capabilities for different fracture scenarios.

Solid-state bonding is paramount in joining dissimilar materials, often combined with metal forming, such as forging, rolling and extrusion, to fabricate composites with a designed structure. Owing to its superior mechanical properties and low density, the carbon steel/Ti composite structure is attractive in automotive and aerospace industries but is difficult to fabricate due to the decarburization of carbon steel's faying surface. In this work, a carbon steel/Ti6Al4V composite structure was first fabricated via a forge-bonding method with the assistance of a Ni coating layer. Results show that the Ni layer on the faying surfaces precludes the decarburization of the steel and the growth of the TiC phase so as to improve the bonding quality. Meanwhile, the in-situ eutectic reaction between the Ni layer and β-Ti was observed. As a result, a seamless bonded interface with the total elimination of the Ni layer can be obtained. The bonding strength was examined to establish the relationship between bonding windows, microstructure and the resulting mechanical properties. An experimentally validated thermal-mechanical finite element model was also developed to understand the process-dependent interface evolution. This work opens a new avenue for fabricating carbon steel/Ti6Al4V composite, extending the flexibility of achieving complex structures by combining solid-state bonding with other metal-forming technologies.

Volumetric defect is a significant factor that influences the fatigue life assessment accuracy in additive manufactured (AM) metals. In order to accurately assess the effects of volumetric defects on fatigue property of AM alloys, this study investigates the influence of geometric characteristics such as size, location, and shape of volumetric defects on low-cycle fatigue (LCF) properties. The results indicate that these factors have a significant influence on the fatigue life of material, and the volumetric defect location is found to be the most critical factor. In order to identify the critical volumetric defects on the fatigue fracture, a defect characteristic parameter " P" is proposed to characterize the influence of volumetric defect characteristics on the fatigue performance of material. Subsequently, a low-cycle fatigue life prediction model for AM metals that considers the geometrical characteristics of volumetric defects is established based on the relationship between P-parameter and low-cycle fatigue life. The accuracy of the prediction model is within 1.5x error band, which is significantly improved compared to the Manson-Coffin (M-C) model and Smith-Watson-Topper (SWT) model.

Thermally-induced cracking typically occurs during the cooling stage of various manufacturing processes, and is commonly seen in multiphase or the joints of dissimilar materials due to mismatch in their thermo-mechanical properties, such as thermal expansion, elastic-plastic deformation and, in some cases, phase transformation. However, the underlying cracking mechanism associated with local microstructure is still elusive. To improve the mechanistic understanding of thermal cracking, this work uses the diffusion-bonded 9Cr-1Mo steel as an example to study the key microstructural variables, such as interfacial phases, voids, grain boundary migration and crystallographic orientations. Meanwhile, a temperature-dependent crystal plasticity model coupled with a cohesive zone model is developed to provide more insights into the thermal-induced stress distribution at the grain scale. It is found that the stress at the void-free boundary of martensite and ferrite is dominated by shear, and its magnitude is insufficient to nucleate cracks. Whereas voids at phase boundaries can induce significant tensile stress, resulting in cracking at the phase boundaries as well as diffusion-bonded interfaces. Also, the occurrence of interfacial grain boundary migration plays an important role in local stress distribution. These microstructure features and their evolution are experimentally observed and used to verify the developed crystal plasticity models. These findings enhance the understanding of the influence of microstructure features on thermal cracking and provide a guide to designing and fabricating the microstructure with improved thermal crack resistance in various manufacturing processes.

Purpose To investigate the effects of accommodation on the geometrical parameters of human lens. Methods Eight databases from inception to November 2023 were used for the literature search: CNKI, CBM, VIP, Wan-Fang, PubMed, Web of Science, EMBASE, and the Cochrane Library. The Methodological Index for Non-randomized Studies was used to assess the risk of bias. The PRISMA were followed and the following outcomes were taken into consideration: lens diameter (LD), lens thickness (LT), anterior curvature radius (ACR), posterior curvature radius (PCR), lens center position (LCP), and total cross-sectional area (TCSA). This systematic review was registered on an international platform for registered systematic reviews and meta-analysis (INPLASY202260085). Results A total of 19 studies were included. LT increased by 0.04 mm/D (18 studies; 95 % confidence interval [CI], 0.03–0.06; I2 = 96.6 %; P < 0.001). At the same time, LD, ACR, and PCR decreased by 0.06 mm/D (6 studies; 95%CI, −0.07–0.05; I2 = 50.1 %; P < 0.001), 0.53 mm/D (8 studies; 95%CI, −0.64–0.41; I2 = 96.5 %; P < 0.001), and 0.14 mm/D (9 studies; 95%CI, −0.19–0.09; I2 = 94.7 %; P < 0.001) during accommodation, respectively. Moreover, LCP shifted forward by 0.01 mm/D (3 studies; 95%CI, −0.02–0.00; I2 = 0.0 %; P < 0.001), and TCSA by 0.58 mm2/D (2 studies; 95%CI, 0.41–1.57; I2 = 97.0 %; P = 0.457) during accommodation. Conclusions Changes in LT, LD, ACR, PCR and LCP supported Helmholtz's theory. Different apparatuses or measurement methods influenced the measurement of lens geometrical parameters.

The low-cycle fatigue properties of selective additively manufactured (AM) laser melt (SLM) Ti-6Al-4V alloys using different sintering rates, deposition direction and post-treatment are assessed. The results show that the shape difference among stable hysteresis loops is closely related to the fatigue life and energy dissipation critical value. Additionally, the relationship between the plastic strain energy and plastic strain shows a strong linear correlation in log-log coordinate. Based on the plastic strain energy dissipation process, an energy dissipation-based model is established to predict low cycle fatigue life in the candidate AM alloy. Fatigue life results from the proposed model shows an improvement in the accuracy of the predictions with the experiment and narrows the scatter/error band when compared to the Manson-Coffin, plastic strain energy and the total plastic strain energy models. The proposed model is applied to the AM TiAl alloy to overcome the drawback of the wider scatter in fatigue life predictions caused by dispersion of fatigue properties found in this mode of manufacture.

Dynamic recrystallisation (DRX) usually occurs during hot forming of metallic materials, significantly impacting the mechanical properties of the final parts. Although DRX has been studied for decades, the types of DRX that occurs in high stacking fault energy (SFE) materials like aluminium alloys are still controversial, and their dependence on both temperature and strain rate is surprisingly missing. To fill these gaps, in the present study, uniaxial compression tests on an aluminium alloy AA6061 were carried out at different temperatures from 250 to 475 °C and strain rates from 0.01 to 1 s-1. The grain orientation and misorientation before and after the hot deformation were quantitively characterised using high-resolution Electron Backscatter Diffraction (EBSD) with a misorientation resolution of 0.05°, enabling high-angle grain boundaries (HAGBs), low-angle grain boundaries (LAGBs) and geometrically necessary dislocations (GNDs) to be accurately quantified and correlated against temperature and strain rate. Results reveal that both continuous dynamic recrystallisation (CDRX) and geometric dynamic recrystallisation (GDRX) occurred concurrently, resulting in the formation of discontinuous HAGBs and fine equiaxed grains, respectively. The misorientation angle distributions of the discontinuous HAGBs exhibit an opposite trend compared to those of the fine grains’ HAGBs. Both temperature and strain rate significantly affect the density of HAGBs formed by DRX, but have little effect on their misorientation angle distributions. This study sheds light on the fundamental understanding of DRX and provides comprehensive experimental data for future modelling of DRX processes in high SFE materials.

Understanding the deformation mechanisms in magnesium alloys is critical to develop the next-generation high-performance magnesium alloys. In this work, the effects of grain size and temperature on slip and twinning activities in WE43 magnesium-rare earth alloy were investigated with the quasi-in-situ electron backscattering diffraction method and slip trace analysis. Compression tests were conducted for the samples with three different grain sizes at room temperature (RT) and liquid nitrogen temperature (LNT), respectively. More pyramidal slips were activated in the fine-grained sample to accommodate the plastic strain instead of more twins generated in the coarse-grained sample, which contributed to its higher strain to failure and strain hardening rate. Numerous individual twins with thin structures formed in the fine-grained sample, while thick twins were observed in the coarse-grained sample. The numerous thin twins and high activities of pyramidal slips in the fine-grained sample would be attributed to the high kernel average misorientation (KAM) value and local stress concentration around grain boundaries. Regarding temperature effects, more thin twins and twin-twin interactions were observed at LNT than at RT, and the KAM value was high around these twin boundaries, which contributed to enhancing the flow stress but reducing the strain to failure at LNT.

Compression tests were conducted at room and cryogenic temperatures to investigate the low-temperature plasticity in Mg–3Al–1Zn alloy. The strain to failure and fracture strength in Mg–3Al–1Zn alloy increase by 21.4% and 51.6% from room to cryogenic temperature. Using a quasi-in-situ EBSD method, it is found that {10 1¯ 2} tension twins dominate at room temperature, while abundant (10 1¯ 2)-(01 1¯ 2) twin-twin interactions are observed at cryogenic temperature. Multiple slips, including pyramidal and basal slips, occur in twin-twin interactions, enhancing the strain to failure and flow stress at cryogenic temperature. The high dislocation density near twin-twin interactions boundaries would contribute to the high hardening rate and flow stress at cryogenic temperature. This work would provide a novel way to enhance plasticity in magnesium alloys and gain an in-depth understanding of twin-twin interactions.

To solve the poor printability issue of high-performance aluminum alloys in additive manufacturing processes, a solid-state hybrid additive manufacturing (AM) technology, combining extrusion and roll bonding operations, is proposed, in which the extruded aluminum layers are soundly bonded through the hot-rolling operation. In this feasibility and early-stage research, a lab-scale extrusion-roll-bonding prototype machine is designed and built. Aluminum alloy, AA1060, owing to its relatively low loading requirements for the prototype, is used for the proof of the concept. The extrusion-roll-bonding tests have been undertaken at different temperatures and rolling reductions to identify optimal processing parameters. The corresponding bonding quality was estimated using an optical microscope (OM). Also, miniature AM tensile samples were tested to evaluate the tensile properties of the bonding interfaces. It is of great interest to see that the AM material did not fracture at the bonding interface and its stress-strain response is similar to that of the original material. In-depth analyses on the interfacial grain and oxide distribution and their effects on the interfacial strength were undertaken using a transmission electron microscope (TEM) and scanning electron microscope (SEM)/electron backscatter diffraction (EBSD). This study demonstrates the proposed solid-state AM technique can successfully manufacture aluminum alloys at their solid states, achieving comparable mechanical properties to their wrought states. This new solid state AM technique may enable a wide range of alloys with poor printability to be used in various industries to produce safety-critical and large, structural components with simple geometry.

Magnesium alloys are the lightest structural alloys and have attracted substantial research attention in the past two decades. However, their mechanical properties, including ductility and strength, are limited after forming due to the formation of coarse grains and strong texture. This study proposes and proves a new cryogenic-hot forming process concept. Cryogenic deformation is imposed before the hot deformation. The effect of the cryogenic step has been compared with a conventional direct hot deformation process. The mechanical properties, microstructure, and texture of both the novel and conventional process routes have been compared. The cryogenic-hot deformed sample exhibits the highest ductility and fracture strength (ultimate tensile strength: 321 MPa, ductility: 21 %) due to effective grain refinement and texture weakening by cryogenically formed twin-twin interaction induced recrystallisation. The proposed cryogenic-hot forming process can be a potential innovative manufacturing method for producing high-performance magnesium components.

Understanding the interaction of micro-voids and grain boundaries is critical to achieving superior mechanical properties for safety-critical parts. Micro-voids and grain boundaries may interact during advanced manufacturing processes such as sintering, additive manufacturing and diffusion bonding. Here, we show imparted benefits on mechanical properties by achieving grain boundary migration across voids. The micromechanisms and quantitative analysis of grain boundary migration on local deformation were studied by integrated in-situ EBSD/FSE and crystal plasticity finite element modelling. It is revealed that a migrated grain boundary does not alter the activated slip systems but precludes grain boundary-multislip interaction around interfacial voids to alleviate stress concentrations. The stress mitigation caused by grain boundary migration is almost the same as that caused by void closure under the example diffusion bonding thermal-mechanical process used in this study. This new understanding sheds light on the mechanistic link between GND hardening, grain boundary migration and the corresponding material tensile behaviour. It opens a new avenue for achieving superior mechanical properties for metallic parts with micro-defects such as those generated in diffusion-bonded, sintered and additive manufactured components.

Constraint uniaxial compression of magnesium single crystals along c-axis was carried out at room temperature and elevated temperatures of up to 500 ℃. The deformation structures were characterized by electron backscatter diffraction (EBSD). The results showed no evidence of pyramidal slip and twinning was responsible for plastic deformation in the range of temperatures tested. The atomic configurations and crystallographic features associated with pyramidal dislocations were revealed with the help of CrystalMaker software and a possible dislocation core structures was reconstructed. The crystallographic analysis suggested that pyramidal slip was difficult because dislocations would involve too many atoms on irrational lattice planes and directions.

The activation of non-basal pyramidal < c+a > slip has been perceived as key to enhance the ductility of magnesium and its alloys. However, there has never been convincing evidence to show the physical existence of < c+a > dislocations and their involvement in deformation has been a core issue in magnesium research. In the present work, the impossibility of < c+a > slip is analyzed based on fundamental concepts of dislocation and atomic interactions. The atomic configurations and crystallographic features in association with < c+a > dislocations are unambiguously revealed for the first time, demonstrating that any possible < c+a > dislocation core structures would involve too many atoms on multiple lattice planes and are physically impossible. Experiments of magnesium single crystal compression along its c-axis were conducted at temperatures from 20°C to 500°C and the results showed no evidence of the involvement of < c+a > dislocations in any form as a mechanism of deformation during either plastic flow or fracture. von Mises criterion for compatible deformation, which drives the pursuit of pyramidal < c+a > slip, is critically discussed.