Additive manufacturing of multi-principal element alloys is a promising approach for fabricating functional materials. A medium-entropy alloy (MEA) composite was fabricated using micro-scale laser powder bed fusion (mu -LPBF) with nano-ceramic particle doping, exhibiting a notable strength-ductility synergy. The microstructural evolution, mechanical properties, and deformation mechanisms of the composite were systematically investigated. The unique mu -LPBF process and subsequent aging treatment enabled the composite to exhibit good properties, including high hardness (557.5-789.1 HV), excellent tensile strength (1675 MPa), and uniform elongation (28%). Furthermore, the tensile strength was increased to 1817 MPa via ceramic particle doping, without compromising the ductility at 18%. Ultra-high temperature gradients and cooling rate in mu -LPBF are conducive to grain refinement and the simultaneous activation of multiple strengthening mechanisms, thereby enhancing strain-hardening and ductility. The enhanced performance of the MEA, including tensile strength, corrosion resistance, and wear resistance arise mainly from synergistic multi-level microstructures, featuring segregation-induced dislocation banding, ultrafine gamma ' precipitates, Cr-rich sigma-phase precipitates with controlled fraction and morphology, dense 9R phase, high-density dislocations, dense nanotwin/microband networks, Lomer-Cottrell locks, and related crystallographic defects. The novel alloy design, combined with a streamlined, optimized processing strategy, plays a crucial role in developing multi-component alloys and composites with outstanding mechanical properties.

To provide a greater competitive advantage for dual-property turbine disks in advanced aeroengines, this study proposes a strategy for preparing enhanced dual-grain structures in which the coarse-grained regions possess serrated grain boundaries. A series of designed serration heat treatments is applied to prefabricate serrated grain boundaries, followed by deformation on samples subjected to an optimized serration heat treatment to fabricate dual-grain structures. This processing route successfully achieved pronounced microstructural gradients across the structures, optimal serrated grain boundaries in the coarse-grained regions, and effective microstructure control in the fine-grained regions. The results indicate that the amplitude and wavelength of serrated grain boundaries are negatively correlated with the cooling rate of serration heat treatment. These serrations primarily form at 1170–1050 °C and require cooling rates below 10 °C/min. Two mechanisms govern the formation of serrations, both of which are correlated with γ’gb particle precipitation at grain boundaries. Owing to impeded grain boundary sliding and additional energy dissipation, the sample with serrated grain boundaries produced at a cooling rate of 4 °C/min shows a 49.08% increase in creep life compared to the sample with flat grain boundaries. The grain-size gradient can be effectively tailored by controlling the deformation conditions to obtain the desired dual-grain structures. The serration amplitudes in the coarse-grained regions decrease slightly during this process. Dynamic recrystallization governs microstructural evolution and completely changes the grain boundary morphology in the transition and fine-grained regions, involving multiple nucleation mechanisms. These findings offer a promising pathway for the development of advanced dual-property turbine disks.

Laser additively manufactured microscale metallic lattices show great potential for high-performance applications, yet trade-offs among geometric precision, structural integrity, and computational efficiency still persist. Here, we introduce a stereolithography file format-free (STL-free) hybrid toolpath generation method for laser-based powder bed fusion (PBF-LB) that synergizes implicit geometric modeling with optimized laser scanning strategy, overcoming these limitations. By circumventing traditional mesh-based workflows, our method directly translates implicit lattice geometries into laser toolpaths while precisely regulating energy deposition trajectories. This mesh-free process enables the fabrication of complex shell lattices with ultra-thin walls and enhanced surface quality. In addition to reducing memory usage and processing time by up to 90%, the method yields a synergistic enhancement in mechanical performance, notably improving both strength and toughness. By bridging computational design and fabrication, this framework enables the scalable production of high-performance microscale lattices and unlocks their potential for industrial applications.

High strength and good ductility are essential for the engineering applications of structural materials, yet these two attributes often do not coexist. In the present study, a composite heterostructuring designed with multi-scale, lamellar, and bimodal was developed to deal with the trade-off between strength and ductility. This heterostructuring includes coarse-grain soft domains arranged in a lamellar structure within a matrix characterized by both fine and ultrafine grains arranged in a bimodal structure created through a straightforward thermo-mechanical process. The gradient in strength among various grain structures generates a gradient in strain during deformation. This promotes the generation of additional geometrically necessary dislocations (GNDs) in the soft domain, favouring strength enhancement. The ongoing and efficient accumulation and evolution of GNDs within the soft domains are further developed into the dislocation cells and subgrain boundaries, which, on the other hand, increase the strain hardening and, hence, the ductility.

In this research, a unified damage indication considering the intragranular and intergranular damage initiation and evolution was developed for studying the damage and fracture behaviours of the excellent ductile alloys represented by TWIP steels, and a cohesive zone model-crystal plasticity finite element method (CZM-CPFEM) approach was developed, where the crystal plasticity with coupled slip and twinning and the strain energy-based damage criterion was employed to reveal the plastic deformation and damage in grain interior (GI), while the quadratic nominal stress (QUADS) and the power law of the CZM were selected to describe the damage and cracking at the grain boundaries (GBs). The stress-strain responses, twin evolutions, damage nucleation and cracking of fine-grained (FG) and fine-/ultrafine-grained (F/UFG) TWIP steels were validated by in-situ SEM/EBSD tensile experiments. The effects of grain size, misorientation angle, grain orientation and initial microvoids on the GI and GB damage and fracture were studied and analysed by combining micromechanical tests and the CZM-CPFEM approach. The results demonstrated that the interaction of deformation mechanisms promoted the preferential initiation of microcracks at GBs and their junctions, while slip bands and twin bundles in GI induced the rapid growth and extension of the localized microcracks, eventually resulting in the mixed fracture mode of intergranular and intragranular cracks. In addition, GB damage was dominant for F/UFG TWIP steels. Increasing grain size can effectively suppress GB damage and increase the proportion of GI damage. Larger misorientation angles can weaken GB properties, while smaller misorientation angles effectively promote strain/stress coordination and delay GI and GB damage. Larger Schmid factors for slip and twinning are favourable for activating dislocations and twins, promoting strain/stress coordination to retard microcrack initiation and improving uniform elongation. Moreover, both initial microvoids can effectively reduce uniform tensile strength (UTS) and fracture strain. Specifically, the microvoids located at GBs and their junctions increase the percentage of GB damage and the possibility of intergranular cracking, especially at the quadruple junctions of GBs.

The research on 3D printing of metallic microlattice structures for biological bone scaffolds has attracted more and more attention. Still, the mechanism by which 3D printing processes constraints such as manufacturing deviations and pore defects affect the mechanical, transport, and biological properties of microlattice scaffolds is unclear. This work involved constructing diamond-type microlattice structures with different spatial orientations and forming them using laser powder bed fusion additive manufacturing (LPBF-AM). The LPBF-printing defect formation mechanism of LPBF-printed diamond microlattices was studied, and the influences of different orientations on mechanical-transport-biological performances were systematically evaluated. The results show that the number and angle of the inclined struts in the microlattice structure are proportional to the manufacturing accuracy. The mechanical and transport properties of the CT-reconstructed 3D-printed microlattice structure are higher than those of the as-designed ones. In vitro cell experiments show that the [111]-oriented microlattice has the best stem cell proliferation and differentiation properties. This work provides guidance and reference for applying LPBF-manufactured microlattice bone scaffolds and can inspire research on designing and manufacturing next-generation 3D-printed bone scaffolds.

Since the as-cast microstructure benefits dynamic recrystallization (DRX) nucleation, the present research is focused on the microstructure evolution associated with the dendrites and precipitates during the thermal deformation of an ingot without homogenization treatment aiming at exploring a new efficient strategy of ingot cogging for superalloys. The as-cast samples were deformed at the sub-solvus temperature, and the DRX evolution from dendritic arms (DAs) to inter-dendritic regions (IDRs) was discussed based on the observation of the fishnet-like DRX microstructures and the gradient of DRX grain size at IDRs. The difference in the precipitates at DAs and IDRs played an essential role during the deformation and DRX process, which finally resulted in very different microstructures in the two areas. A selective strain-induced grain boundary bulging (SIGBB) mechanism was found to function well and dominate the DRX nucleation at DAs. The grain boundary was able to migrate and bulge to nucleate on the condition that the boundary was located at DAs and had a great difference in dislocation density between its opposite sides at the same time. As for DRX nucleation at IDRs, the particle-stimulated nucleation (PSN) mechanism played a leading role, and the progressive subgrain rotation (PSR) and geometric DRX were two important supplementary mechanisms. The dislocation accumulation around the coarse precipitates at IDR resulted in progressive orientation rotation, which would generate DRX nuclei once the maximum misorientation there was sufficient to form a high-angle boundary with the matrix. The PSR or geometric DRX functioned at the severely elongated IDRs at the later stage of deformation, depending on the thickness of the elongated IDRs. The uniform microstructure was obtained by the deformation without homogenization and the subsequent annealing treatment. The smaller strain, the lower annealing temperature, and the much shorter soaking time requested in the above process lead to a smaller risk of cracking and a lower consumption of energy during the ingot-cogging process.

Trimodal microstructure, consisting of equiaxed alpha (alpha p), lamellar alpha (alpha l), and transformed beta (beta t), has become an ideal target microstructure of titanium alloys. However, the complex microstructure morphologies and the differences in mechanical property among the three constituent phases of the trimodal microstructure significantly influence its microscopic crack propagation behaviour and further affect its fracture toughness. To address this issue, a multiscale finite element (FE) model, including a microscopic crack propagation (micro-CP) model and a macroscopic fracture toughness (macro-FT) model, was established for analysis and prediction of the damage fracture behaviour and property of the trimodal microstructure. In this model, the deformation, damage and fracture behaviours of the trimodal microstructure at both micro and macro scales were described by bridging the constitutive laws of constituent phases and deformation responses. In tandem with this, the micro-CP model adopted a macro-micro nested structure, and the macro-FT model was developed based on a virtual fracture toughness test. Using the established multiscale FE model, the dependence of microscopic crack propagation and macroscopic fracture behaviours on the constituent phases of the trimodal microstructure was revealed. It is found that both alpha p and alpha l improved the path tortuosity and energy consumption of microscopic crack propagation, and alpha l decreased the microscopic crack propagation rate simultaneously. In addition, alpha p and alpha l contributed to the fracture toughness of the trimodal microstructure from both the intrinsic toughening mechanism (suppressing the heterogeneous deformation and damage and then decreasing the strength and increasing the plasticity) and the extrinsic toughening mechanism (increasing the tortuosity and energy consumption of crack propagation). The research provided an in-depth understanding of the damage and fracture behaviours of TA15 titanium alloy with the trimodal microstructure.

Concerning the micro-scale deformation of titanium metal sheets, the number of grains in the sheet thickness direction decreases, and their formability exhibits a strong grain size sensitivity. Meanwhile, the twinning-induced dynamic recrystallization (TDRX) associated with grain size significantly affects the fracture behavior in the microforming of titanium sheets. Therefore, an accurate prediction of formability to improve manufacturing reliability remains challenging in the microforming of miniaturized titanium components. To address this issue, an in-depth understanding of the grain size-dependent TDRX behavior and its role in damage and fracture development in the microforming of alpha-titanium sheets is critical, and a coupled cellular automata-crystal plasticity (CA-CP) modeling framework was thus developed as an approach providing efficient solutions and insightful comprehensions of the issue. For the proposed modeling framework, a kinematic model for TDRX was established and integrated into the CP model by the CA algorithm. As a result, the microstructure evolution caused by TDRX was regarded as an intrinsic part of the constitutive behavior to connect heterogeneous plastic deformation and damage evolution through data transmission between the CP model and the CA algorithm. Additionally, the coupled CA-CP modeling framework was validated with the internal defect morphologies and deformation microstructures characterized by X-ray computed tomography (X-CT) and electron backscattered diffraction (EBSD). Experiment and simulation results demonstrated that the fine recrystallized (DRXed) grains were generated after the twin fragmentation when the dislocation density at twin boundaries reached a threshold of 9.2 x 10(13) /m(2). After TDRX, the dislocation density and the stress concentration intensity in recrystallization regions were revealed to decrease, accounting for the ductility improvement. Nevertheless, the dislocation density at twin boundaries was determined to decrease with the increase of grain size, leading to less twin fragmentation and the absence of TDRX. The uncoordinated deformation between fine DRXed grains motivated defects to grow spherically into microvoids, thereby preventing premature intergranular cracks along twins/grain boundaries. Ultimately, the deformation microstructures resulting from TDRX with the decrease of grain size were confirmed to control the brittle to ductile fracture transition of alpha-titanium sheets. The presented modeling framework and simulation procedure were validated to be able to predict the material integrity affected by crystalline microstructure in the deformation of titanium metal sheets.

Advances in micro-laser powder bed fusion (mu LPBF) have enabled the utilisation of pure copper in low-density triply periodic minimal surface (TPMS) structures, which are mostly characterised by thin walls. Although coarser-grained pure copper components enhance the conductivity, there are only a limited number of grains along the wall in the thickness direction in the low-density TPMS structures, leading to an unpredictable mechanical performance owing to size effect (SE). In this study, pure copper sheet-based TPMS structures (specifically, gyroid structures) were fabricated via mu LPBF followed by different annealing conditions to achieve distinct grain sizes. Compression tests were conducted to investigate SE on the mechanical behaviours of the structures. A constitutive model considering both wall thickness and grain size was developed to explore the uncertain mechanical response induced by SE via finite element (FE) simulations. An optimised FE modelling strategy considering roughness was developed to describe the interactive effect of SE and the surface powderinduced roughness on the deformation behaviours of the TPMS structures. The results show that the mechanical performances of the structures, such as plateau stress and energy absorption, are improved with the refinement of grains and are also highly related to the deformation behaviours influenced by SE. SE offers the potential to achieve the desired multifunctional performance of TPMS structures with acceptable mechanical properties and enhanced electrical conductivity. This study enhances the understanding of SE on the mechanical behaviours of the TPMS structures.

Cr-rich stainless steel sheets exhibit superior corrosion resistance but low ductility, which presents a trade-off between fabrication complexity and performance of the materials in multiple industrial applications, such as marine equipment and microreactors. By transitioning the Cr-rich (30 wt.% Cr) stainless steel component to SS 316 L with a smooth composition gradient in the thickness direction, the intrinsic homogeneous elongation of the Cr-rich layer was increased by 260 % while maintaining the naturally high corrosion resistance (100 %) and retaining most of the strength (more than 80 %). By employing in-situ tensile testing and electron backscatter diffraction analysis, it was revealed that the Cr-rich layer in the gradient structure underwent a profound deformation mechanism, including significant heterogeneous deformation-induced hardening and grain reorientation induced by multiplication and accumulation of geometrically necessary dislocations, in such a way to enable a substantial plastic strain and thereby retarding the occurrence of fracture. The proportion of the Cr-rich layer makes a significant impact on the magnitude of the strain gradient in the gradient specimens, therefore affecting the increment of density of geometrically necessary dislocations. The critical proportion value of the Cr-rich layer is found to be around 22 %. Before and after the critical value the gradient specimens showed different sensitivities to the proportion. This discovery underlines the significance of intrinsic plasticity in low-ductility metals and the role of compositional gradient materials in enhancing strength and ductility.

To illustrate the microstructural factors of grain refinement for enhancing mechanical properties, the fine-/ultrafine-grained TWIP steels with a product of strength and elongation of similar to 71 GPa center dot% were first prepared by combining rolling and stress relief annealing. Subsequently, the evolution of dislocations, stacking faults, and associated substructures of the fine-/ultrafine-grained TWIP steels was analysed by using in-situ EBSD tensile tests and TEM characterisation of the interrupted strain experiments. The results reveal that the excellent mechanical properties of the TWIP steels are attributed to dislocations and associated dislocation cells, dislocation walls, dislocation tangles, stacking faults and associated Lomer-Cottrell locks (LCs), nano-twins, primary and secondary twins and their interactions during plastic deformation. The density of geometrically necessary dislocations (GNDs) was evaluated based on the modified Ashby's model and compared with experimental results, indicating that grain size heterogeneity can promote the accumulation of GNDs, which facilitates the generation of subgrains and new boundaries to reduce the mean free path (MFP) of dislocations, thus enhancing strain hardening. Meanwhile, the interaction of lamellar primary and secondary twins in fine grains and the generation of stacking faults and nano-twins in ultrafine grains at higher strains can further promote strain hardening to elevate strength. Furthermore, the effects of grain orientation and grain size on the activation and evolution of dislocations and twins were elucidated. In ultrafine grains, twinning is strongly inhibited due to the elevated critical shear stress for twinning, resulting in more stacking faults and nano-twins, but fewer dislocation cells. The present work contributes to an in-depth understanding of the mechanical properties of fine-/ultrafine-grained materials to exploit their potential for industrial applications.

Wire and arc additive manufacturing (WAAM) has been developed to be a highly efficient technique for making large Ti-alloy products. However, the deposition of metal by this method causes coarse texture, which limits its application. To address this, the study utilizes a wire and pulsed arc additive manufacturing (WPAAM) process for making TA15 alloy. Compared with the WAAM method, this WPAAM method inducts several current/voltage-impulse cycles under different pulse frequencies, which makes grains tiny and improves tensile strength. The study then uses a VOF model to discuss the effect of impulse cycles on the solidification process. The findings suggested that the impulse cycles deform the molten pool and influence the vibration in the solid/liquid interface. This makes the coarse columnar grains tiny and forms diminutive α laths. This paper further discusses the correlation between the microstructure and the mechanical properties. The results show that the CBGs and the α laths play a joint contribution to yield strength in the WAAMed TA15 alloy. This study provides a reference for optimizing the microstructure of WAAM titanium alloys by adjusting pulse frequencies and provides a theoretical basis for strengthening WAAMed Ti-alloy.

Buckling failure is a major concern in lightweight lattice core sandwich structures (LCSSs). This study proposes an efficient method for designing LCSSs with superior buckling strength under uniaxial compression. In this approach, the buckling-resistant non-uniform shapes of single struts with different slenderness and inclination are first identified, and then they are directly used to replace uniform struts in LCSSs. This method can save considerable design time compared to conventional methods, which require conducting optimizations on entire LCSSs. Numerical results demonstrate that four designed representative non-uniform LCSSs can gain over 15% improvement in buckling strength compared to their counterpart uniform LCSSs. This improvement is even comparable to the solutions from optimizations on entire LCSSs. Two LCSSs with non-uniform struts are 3D printed, and the test results validate at least 10% improvement in compressive strength. Based on the proposed method, various LCSSs with superior buckling strength could be designed for different loadings.

Progressive microforming is widely recognized as one of the most efficient and desirable methods of mass production in micromanufacturing arena. To predict the deformation behaviour and size effects of materials induced in progressive microforming, the finite element method (FEM) employed for modelling the microforming process needs to account for microstructure details and deformation/failure mechanisms of the materials. This led to the development of the novel crystal plasticity finite element method (CPFEM) and cohesive zone model (CZM). Previous research and application of CPFEM have been mainly limited to simple deformations such as uniaxial tension and compression, whereas the new method can provide physical insights into how the grain size affects the interplay between crystallographic slip and mechanical twinning in complex microforming, and further material deformation during sheet blanking. A case study was conducted to manufacture a hexagonal socket part using a three-step progressive microforming system, with the comparison between experiments and CPFEM simulations focusing on microstructure evolution, deformation load, and product quality. The CPFEM was found to be more reliable than the conventional FEM in predicting complex deformation, particularly in microstructure and texture evolution, dimensional accuracy and irregular geometries. Results showed that the total height of the part increases with the decreasing grain size, while the head diameter rises with grain size. Simulations successfully anticipated the distributions of dead metal zones and shear bands and identified hole and rollover geometries and corresponding grain size effects. In conclusion, this research facilitates the understanding of grain size effects on the deformation behaviour in progressive microforming and presents a novel approach and strategy for modelling, prediction, and product quality assurance in complex micro deformation and forming processes.

In recent years, there has been tremendous growth in the use of Al matrix composites (AMCs) in various engineering applications. The aerospace and automotive industries are using more and more AMC parts. It has been widely recognized that the comprehensive properties of AMCs are significantly affected and determined by the structural design and the evolution of the microstructure of AMCs in the deformation process. Based on the current research status of the design of AMC structure and the evolution of microstructure, this paper presents a panorama of the design of the structure and the evolution of microstructure with respect to the reinforcements, the interface between Al matrix and reinforcements, and the Al matrix in AMCs, respectively. The overall properties or performance of AMCs are examined in this review, which emphasizes their advantages and limitations as compared to their traditional or unreinforced counterparts. The experimental and theoretical analysis and prediction to aid the design of the spatial distribution of reinforcements and the optimization of structural parameters, as well as the study of the evolution of microstructures, are critically analyzed, discussed, and elucidated. Finally, the research gap, the key challenges in research and the promising application potentials in future are also discussed and articulated.

TA15 titanium alloy components produced via wire-arc direct energy deposition (WA-DED) face challenges related to grain coarsening, suboptimal mechanical properties, and pronounced anisotropy. To address these issues, the current study employed a dual-wire-arc directed energy deposition (DWA-DED) approach to fabricating the alloys by introducing LaF3 quantitatively into the deposition metal using a metal cored wire. The incorporation of LaF3 was predicated on the in situ reaction: 6[O] + 6[H] + 2 LaF3 = La2O3 + 6HF. This reaction effectively removed [H] and [O] from the molten pool, diminishing the presence of the brittle intermetallic compounds and concurrently enhancing toughness. The addition of LaF3 resulted in a notable 56.8% increase in elongation and a 33.1% boost in impact toughness. Moreover, the DWA-DED quantitatively introduced [La], facilitating the precipitation of La2O3 particles. This precipitation reduced the size of primary columnar grains (PCGs) and promoted heterogeneous nucleation of alpha-laths. As a result, the elongation of the PCGs' boundaries diversified the alpha phase transformation, resulting in the reduced multiple of uniform density (MUD) along the building direction. As a result, the isotropy ratio between vertical and horizontal directions also increased, underscoring the efficacy of LaF3 in mitigating anisotropic behaviour in WA-DEDed titanium alloys.