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• A novel dual-nanoprecipitation of intragranular "B2+κ′-carbides" strengthened austenitic lightweight steel is designed by coupling the pre-cold rolling and two-step aging process. • Typical K-S and N-W orientation relationships between the austenite matrix and intragranular B2 particles are confirmed. • Pre-cold rolling process effectively promotes the heterogeneous nucleation of B2 particles by introducing dislocations. • The balance of strength-ductility is enhanced via the nanoscale "planar slip and dislocation bow-out" multiple deformation mechanisms. Strength-ductility trade-off is usually an inevitable scenario in κ′-carbides strengthened austenitic lightweight steel. The reduction of ductility is primarily attributed to the shearing of coherent κ′-carbides by dislocations, resulting in strain localization and ultimately leading to a low work hardening rate. Semi-coherent B2 particles, on the other hand, effectively enhance the work hardening capability due to the non-shearable feature. However, achieving a large volume fraction and uniform distribution of B2 particles within the austenite matrix, as well as optimizing their morphology as fine particles, remains a challenge for austenitic lightweight steel. In this study, we have addressed the above challenges by implementing the two-step aging process combined with pre-cold rolling process. The pre-cold rolling treatment, performed prior to the initial aging treatment at 900 °C, effectively promotes the heterogeneous nucleation of B2 particles by introducing dislocations, resulting in a more uniform distribution of B2 particles and a refinement in size (with an average length of 200–500 nm and a width of 50–80 nm). Furthermore, these intragranular B2 particles exhibit the typical K-S and N-W orientation relationships with the austenite matrix. Subsequently, after the second-step aging process at 450 °C, spherical nano-sized κ′-carbides (5 nm) are homogeneously dispersed within the austenite matrix. The above dual nanoparticles provide an approximate precipitation hardening effect of 400 MPa. Concurrently, the nanoscale "planar slip and dislocation bow-out" multiple deformation mechanisms contribute to an efficient source of work hardening capability, leading to a beneficial synergy of strength-ductility. This promising strategy is expected to expand the applications of dual-nanoprecipitation austenitic low-density steel in various lightweight structural materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• In-situ EBSD investigation at cryogenic temperature was first performed during the uniaxial tension of metallic material. • An Al1Mg0.4Si alloy that displayed superior strength-ductility synergy and strain hardening capacity during deformation at cryogenic temperature was investigated by a combination of experimental and simulation study. • The excellent strength-ductility synergy and extraordinary strain hardening capacity observed at 77 K can be attributed to the presence of multiple slip systems and reduced dynamic recovery. • The GBH effect significantly enhances the SSD density and screw dislocation proportion, which are advantageous for promoting homogeneous deformation and enhancing strain hardening capacity at 77 K. In this work, we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy, which exhibited significantly higher strength and outstanding strain hardening capacity at 77 K compared to its counterparts at 298 K. The deformation mechanisms responsible for the excellent strength-ductility synergy and extraordinary strain hardening capacity at cryogenic temperature were elucidated through a combined experimental and simulation study. The results reveal the presence of numerous slip traces and microbands throughout grain surfaces during deformation at 298 K, whereas at 77 K, vague grain surfaces dominate, indicating the simultaneous operation of multiple slip systems. Transmission electron microscopy (TEM) analysis using the two-beam diffraction technique demonstrates the presence of dislocations with several different Burgers vectors inside a grain at cryogenic temperature, confirming the activation of multiple slip systems. The accumulation of dislocations facilitated by these multiple slip systems, combined with the high dislocation density, contributes to strain hardening and remarkable uniform elongation at 77 K. A modified dislocation density-based crystal plasticity model, incorporating the effect of grain boundary hardening (GBH) and temperature, was developed to gain a better understanding of the underlying mechanisms governing alloy's strength and plasticity. The GBH effect significantly enhances statistically stored dislocation (SSD) density and screw dislocation proportion, which promote homogeneous deformation and enhance strain hardening capacity at cryogenic temperature. These findings deepen the understanding of plastic deformation at cryogenic temperatures and pave the way for the development of ultrahigh-performance metallic materials for cryogenic applications. [Display omitted] [ABSTRACT FROM AUTHOR]

• Oxygen gradient Ti-15Mo alloy is fabricated via compositional gradient design. • It exhibits optimal strength-ductility balance along with high work hardening rate. • Coupling deformation of twinning and slip is achieved due to oxygen gradient. • The crack tips is blunted by twins and GNDs, avoiding the premature necking. The low work hardening is a prominent deficiency for high-strength titanium (Ti) alloys. The gradient design of oxygen content was adopted to realize the coupling deformation of {332}<113> twinning and dislocation slip in the Ti-15Mo alloy. This oxygen gradient alloy exhibited an optimal balance of yield/tensile strength (700 and 848 MPa) and elongation (25 %), with remarkable work hardening behavior. The dominated dislocation slip deformation and the solution strengthening of oxygen atoms in the oxygen-rich region resulted in a remarkable increase in yield strength. The successive formation of {332}<113> twins and piled-up geometrically necessary dislocations around the twin boundaries in the oxygen-free region induced remarkable back stress strengthening, maintaining the high work hardening rate, which resulted in a stable increase in strength. The twins and dislocations formed at the crack tips effectively hindered the cracking behavior, avoiding premature necking. The present study provides a novel idea for designing oxygen layer-distributed Ti alloys, which further improves the strength–ductility tradeoff. [Display omitted] [ABSTRACT FROM AUTHOR]

• A Co 42 Cr 20 Ni 30 Ti 4 Al 4 quinary medium entropy alloy (MEA) with excellent mechanical properties over a wide temperature ranging from 77 to 873 K. • Post heat treatment leads to refinement of grains and heterogeneous precipitation of L1 2 phase. • Stacking faults mediated deformation behavior of the SLMed Co 42 Cr 20 Ni 30 Ti 4 Al 4 MEA. Modern engineering has long been in demand for high-performance additive manufactured materials for harsh working conditions. The idea of high entropy alloy (HEA), medium entropy alloy (MEA), and multi-principal-element alloy (MPEA) provides a new way for alloy design. In this work, we develop a Co 42 Cr 20 Ni 30 Ti 4 Al 4 quinary MEA which exhibits a superiority of mechanical properties over a wide temperature ranging from 77 to 873 K via selective laser melting (SLM) and post-heat treatment. The present MEA achieves an excellent ultimate tensile strength (UTS) of 1586 MPa with a total elongation (TE) of 22.7 % at 298 K, a UTS of 1944 MPa with a TE of 22.6 % at 77 K, and a UTS of 1147 MPa with a TE of 9.1 % at 873 K. The excellent mechanical properties stem from the microstructures composed of partially refined grains and heterogeneously precipitated L1 2 phase due to the concurrence of recrystallization and precipitation. The grain boundary hardening, precipitation hardening, and dislocation hardening contribute to the high YS at 298 and 77 K. Interactions of nano-spaced stacking faults (SFs) including SFs networks, Lomer–Cottrell locks (L–C locks), and anti-phase boundaries (APBs) induced by the shearing of L1 2 phase are responsible for the high strain hardening rate and plasticity at 77 K. Our work provides a new insight for the incorporation of precipitation hardening and additive manufacturing technology, paving the avenue for the development of high-performance structural materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• The stress and strain partitions of Al and Si phases have been measured. • The Al matrix contains the supersaturated solute Si. • The solute Si enhances yield strength and work hardening. • The cellular structure generates significant back stresses during deformation. • The deformation mechanism of alloys is closely reliant on cellular structure. Compared to a cast AlSi10Mg alloy, a laser powder bed fused (LPBF) AlSi10Mg alloy shows superior yield strength and strain hardening capability. However, the underlying microstructure origin has not been comprehensively understood. In this work, the microstructural evolution of an LPBF AlSi10Mg alloy during tensile deformation was investigated. Synchrotron X-ray diffraction characterization shows that both stress and strain exhibit significant partition between an Al phase and a Si phase upon tensile deformation. This leads to a significant strain gradient between those two phases, which is evident by the high density of dislocations in the cell boundaries of the deformed alloy. The strain gradient results in long-range internal stress, also known as back stress, in the cell boundaries, and in turn leads to enhanced strength and strain hardening in the LPBF AlSi10Mg alloy. Quantitatively analyses via loading-unloading-reloading tests show that during the tensile deformation, the back stress contributes 135 MPa to the yield strength of the alloy, which continuously increases with increasing the strain beyond the yielding point. This work illuminates the microstructural origin of the back stress in the LPBF AlSi10Mg alloy, i.e. the back stress arises from the stress/strain partition between the Al and Si phases in the cellular structures, and the back stress leads to significant strengthening of the alloy upon tensile deformation. This work may also provide guidance for manipulating the mechanical properties of additively manufactured Al-Si alloys for specific application needs. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel gradient pseudo-precipitates heterostructure (GPHS) is designed and fabricated for non-heat treatable 5xxx aluminum alloy. • The proposed GPHS achieves enhanced strength-ductility synergy for Al-2.5%Mg alloy. • The formation mechanism of the GPHS is revealed as an inter-diffusion mechanism activated and promoted by various sub-structures. • HDI strengthening and strain hardening of GPHS are demonstrated as dominant effects in deformation mechanism. Heterostructures of alloyed composites, comprising heterogeneous domains with dramatically different constitutive properties, hold remarkable potential to expand the realm of material design systems and resolve the trade-off between strength and ductility. This study introduces an innovative materials design method for synthesizing gradient pseudo-precipitates heterostructure (GPHS) in non-heat-treatable Al-2.5%Mg alloys. Utilizing cost-effective mild steel as both the diffusion source and protective layer, this heterostructure is achieved through pin-less friction stir-assisted cyclic localized deformation process. Exogenous Fe atoms diffuse across the interface by friction stir-induced heat conduction, forming Fe-Al second-phase particles in the Al alloy matrix. A rapid inter-diffusion mechanism is activated in conjunction with dense dislocation walls, grain boundaries, and sub-structures, resulting in the formation of pseudo-precipitates. These pseudo-precipitates are ultimately dispersed in a gradient distribution throughout the entire thickness of the Al alloy matrix induced by localized incremental deformation. The GPHSed Al-2.5%Mg alloy exhibits an enhanced synergy of strength and ductility, with a uniform elongation increase from 11 % to 21.2 %, while maintaining the strength. Multiple strengthening and hardening mechanisms, such as solid solution strengthening, dislocation hardening, and second phase strengthening, work synergistically to promote mechanical performance. Notably, the hetero-deformation between hard pseudo-precipitates and soft Al alloy matrix induces additional strain hardening, leading to high ductility. This work provides a fresh perspective on the design and fabrication of high-performance alloys with advanced heterostructures, especially for non-heat-treatable alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

• Origin and evolution of HDI stress were assessed by loading-unloading-reloading tension tests, nanoindentation results, KAM map and slip trace analysis. • Contribution of HDI stress to strength of the dual-phase alloy was quantified by EVPSC model. • Correlation between deformation micro-features and tension properties were recognized. The Mg-Li dual-phase alloys, comprised of hexagonal (HCP) and body-centered cubic (BCC) phases, exhibit a better combination of strength and ductility than Mg single-phase alloys. In this work, the deformation behaviors of Mg-6Li-2Gd and Mg-2Gd alloys, representatives of dual-phase and single-phase alloys, have been studied at both microscale and mesoscale to elucidate the underlying mechanisms. Nanoindentation results show that the α-Mg phase in the Mg-6Li-2Gd alloy is harder than the β-Li phase. The intergranular deformation incompatibility, which arises from the elastic-plastic interactions, different strain accommodation behaviors, and strain hardening behaviors between the hard α-Mg phase and the soft β-Li phase, leads to pronounced hetero-deformation induced (HDI) stress of the Mg-6Li-2Gd alloy. The HDI stress strengthens the two phases simultaneously, so that the yield strength of the dual-phase Mg-6Li-2Gd alloy is higher than the Mg-2Gd alloy as well as the harder α-Mg phase in the Mg-6Li-2Gd alloy. Due to the decreased strength difference between the two phases caused by the HDI stress strengthening, the dual-phase alloy exhibits homogeneous plasticity at the mesoscale, which benefits the elongation of the Mg-6Li-2Gd alloy. The HDI strengthening magnitude in the Mg-6Li-2Gd alloy is further quantified. Based on the equal strain upper bound and equal stress lower bound approximations, the yield strength improved by the HDI stress is estimated to be 18–37 MPa, which is in the same range as the elastic visco-plastic self-consistent (EVPSC) simulation results. As the tensile strain is larger than ∼3 %, the HDI strengthening magnitude for the Mg-6Li-2Gd alloy reaches 50–65 MPa, accounting for 35 % of the corresponding flow stress. [Display omitted] [ABSTRACT FROM AUTHOR]

• in-situ observation of deformation-induced grain reorientation in 718 Ni alloy microlattices. • Additively manufactured of unique high temperature resistant 718 ODS microlattices. • Significant extrinsic control of mechanical properties via altering the design. • Shear induced crystallographic reorientation observed via intermittent EBSD scans. • Utilization of in-situ videos to compare snap shots to finite element model. Microlattices pose ample opportunity for constructing light weight structures for the automotive and aerospace industries. Laser powder bed fusion is an appealing technique to fabricate these structures because of its capabilities to process high-resolution complex architectured structures. In this work we explore the use of a 718 oxide dispersion strengthened alloy to create three microlattice structures designed in nTop, a straight bar, honeycomb and body-centered cubic (BCC) microlattice and investigate the effects of architectures on tensile behavior of the microlattices in a scanning electron microscope. The straight bar configurations deliver high strength but low ductility. The BCC lattices are highly deformable but soft. The honeycomb has an attractive combination of high strength and pronounced work hardening. Furthermore, electron backscattered diffraction studies revealed substantial crystallographic reorientation and grain refinement in the honeycomb lattice during deformation, in contrast to little crystal orientation change in the straight bar specimens. This study suggests that architectures play a significant role in the tensile behavior and deformation mechanisms in metallic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel (TaMoZrTi) 92 Al 8 refractory high-entropy alloy with in-situ forming heterogeneous structure was prepared, which is featured by hard disordered BCC phase embedded into soft intermetallic B2 matrix. • Suah a heterogeneous structure endows the alloy a promising strength-plasticity synergy at room temperature. • Based on the strain partitioning effect, the strengthening and toughening mechanism of the alloy were revealed. • The present study provides a possibility for the construction of heterogeneous structure in brittle refractory high-entropy alloys. Although refractory high-entropy alloys (RHEAs) possess excellent softening resistance and thermal stability at high temperatures, their practical application is often limited due to room temperature (RT) brittleness. In this work, we successfully achieved RT plasticization in a brittle (TaMoTi) 92 Al 8 RHEA via in situ forming heterogeneous structure (HS) with the doping of Zr. Different from the mainstream design concept of "soft solid solution matrices with hard intermetallic phases" proposed in the literature, the newly developed TaMoZrTiAl RHEA is featured by a hard disordered BCC phase embedded into a soft intermetallic B2 matrix. Such an HS leads to the remarkable strength–plasticity synergy in this alloy at RT, showing a large plasticity of > 20 %, associated with a high strength of > 2380 MPa. It was found that solid solution strengthening and heterodeformation-induced strengthening caused by dislocation pile-ups at phase boundaries are responsible for the enhancement in the yield strength, while deformation-induced strain partition and the frequent operation of dislocation cross-slip substantially improve the work hardening capacity of alloy, thus enabling the high strength and good RT plasticity. In short, the current work not only reveals the micromechanisms of the influence of heterogeneous dual-phase structure on the RT mechanical behaviour in RHEAs but also provides a useful strategy for plasticizing brittle RHEAs. [Display omitted] [ABSTRACT FROM AUTHOR]

Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti 2 Cu and α-Ti after additive manufacturing, they are potential candidates for high-performance materials. To reveal the deformation and strengthening mechanisms, the molecular dynamics (MD) simulations and experimental analysis were carried out upon Ti-Ti 2 Cu lamellae. In this work, we focused on revealing the interface dislocations (IDs) pattern and its effects on the dynamic evolution of the lattice dislocations (LDs) at the Ti/Ti 2 Cu interface with (0001) α / / (0 1 ‾ 3) Ti 2 Cu orientation relationship. Atomistic simulations depicted that the equilibrium Ti/Ti 2 Cu interface contains three groups of partial dislocations which dictate two interfacial coherent structures with low stacking fault energy. Each ID consists of several segments, connected by atomic steps with identical direction. The nucleation sites of LDs under external loading locate at the intersection between the dislocation segment and the atomic step, which is related to the local high atom strain. Under compression deformation, the 〈 100 〉 { 011 } and 〈 331 〉 { 103 } slip systems in Ti 2 Cu, and the 〈 11 2 ¯ 3 〉 { 10 1 ¯ 1 } slip system in α-Ti are activated, achieving a co-deformation mechanism in the Ti-Ti 2 Cu multilayers. The dislocation-interface interactions are responsible for the deformation plasticity and in turn governs the mechanical strengthening. During nanoindentation tests, larger hardness (∼6.2 GPa) and smaller activation volume (∼12 b 3) were found in the Ti-Ti 2 Cu lamellae, which is mainly ascribed to the presence of high-density lamellae interface and confined layer slip, resulting in interface-mediated dislocation annihilation/deposition and consequent high strain hardening. The MD simulations, nanoindentation tests and TEM investigations of interlayer dislocation activity support the strengthening mechanism of dislocation-interface interactions. [ABSTRACT FROM AUTHOR]

• The CR95 RHEA forms heterogeneous structure by severe plastic deformation. • The CR95 RHEA possesses the highest tensile strength among RHEAs. • HDI hardening accounts for ultra-high strength in the CR95 RHEA. • The MBIP effect contribute the CR95–850 alloy an excellent tensile ductility. Refractory high-entropy alloys (RHEAs) are potential materials for high-temperature structural applications due to their excellent high-temperature performance. However, the early onset of plastic instability in RHEAs is a critical issue to be addressed. In this study, a novel Zr 35 Ti 30 Nb 20 Al 10 V 5 RHEA was subjected to 95% cold rolling and annealing, achieving outstanding mechanical properties. Notably, the cold-rolled alloy exhibited the highest reported tensile strength (∼2.0 GPa) among RHEAs with a moderate ductility of ∼8.5%. Moreover, Additionally, the subsequent annealing process enabled the alloy to achieve an outstanding combination of yield strength (1.1 GPa) and fracture elongation (20%). The cold-rolled alloy has a heterogeneous lamella structure with high-density dislocation cells and dislocation pile-ups, and lattice distortion in the locally chemically ordered structure. The high work hardening behavior originates from the heterogeneous deformation-induced (HDI) hardening, which makes the HDI stress and hardening rate increase with increasing strain. In the annealed alloy, lattice distortion increases significantly with increasing strain, promoting dislocation cross-slip. The dislocation pile-ups and interactions facilitate the transition of microbands, and the relatively stable work-hardening behavior of the alloy is mainly attributed to the microband-induced plasticity effect. This study provides novel insights into the design and optimization of highly formable RHEAs with excellent mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

• Forged HfNbTaTiZr refractory high-entropy alloy (RHEA) demonstrates significant strain hardening at elevated temperatures, showcasing a clear distinction from the strain softening observed at room temperature. • Defects introduced through the forging process act as a driving force for the initiation of slip bands in high-temperature tensile deformation, thereby promoting dynamic recrystallization. • The bimodal distribution of grain sizes, attributed to factors such as dynamic recrystallization and initial grains, impedes dislocation movement, consequently enhancing strain hardening. Refractory high-entropy alloys (RHEAs) exhibit outstanding strength at room temperature, but their high-temperature applications are hindered by severe strain-softening. Here, we report slip-band-driven dynamic recrystallization to enhance the high-temperature strain hardening of HfNbTaTiZr RHEA. By introducing partial lattice defects through hot forging, we increase the nucleation sites for dynamic recrystallization during subsequent thermomechanical deformation, thus suppressing the strain-softening behavior. We reveal that the high-temperature deformation is governed by the formation of heterogeneous bimodal grains along slip bands, which effectively constrain dislocation motion and improve strength, while microbands prevent premature failure. The fracture mode also changes from ductile to mixed to cleavage-dominated with increasing temperature. Our results demonstrate a simple and effective method for overcoming high-temperature strain-softening for BCC high entropy alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

• Addition of P element reduces the stacking-fault energy and enhances the tensile plasticity of CrCoNi medium-entropy alloy. • Deformation faulting-induced strain hardening, coupled with solution strengthening leads to an extraordinary strength-ductility synergy in P-doped CrCoNi MEA. • P-segregation at grain boundaries intensifies the hetero-deformation-induced (HDI) hardening effect in P-doped CrCoNi MEA. A newly developed P-doped CrCoNi medium-entropy alloy (MEA) provides both higher yield strength and larger uniform elongation than the conventional CrCoNi MEA, even superior tensile ductility to the other-element-doped CrCoNi MEAs at similar yield strength levels. P segregation at grain boundaries (GBs) and dissolution inside grain interiors, together with the related lower stacking fault energy (SFE) are found in the P-doped CrCoNi MEA. Higher hetero-deformation-induced (HDI) hardening rate is observed in the P-doped CrCoNi MEA due to the grain-to-grain plastic deformation and the dynamic structural refinement by high-density stacking fault-walls (SFWs). The enhanced yield strength in the P-doped CoCrNi MEA can be attributed to the strong substitutional solid-solution strengthening by severer lattice distortion and the GB strengthening by phosphorus segregation at GBs. During the tensile deformation, the multiple SFW frames inundated with massive multi-orientational tiny planar stacking faults (SFs) between them, rather than deformation twins, are observed to induce dynamic structural refinement for forming parallelepiped domains in the P-doped CoCrNi MEA, due to the lower SFE and even lower atomically-local SFE. These nano-sized domains with domain boundary spacing at tens of nanometers can block dislocation movement for strengthening on one hand, and can accumulate defects in the interiors of domains for exceptionally high hardening rate on the other hand. [Display omitted] [ABSTRACT FROM AUTHOR]

• By manipulating the cold-welding of composite powders during the segmented ball milling, two-level heterogeneity in microstructures including MgO-rich FG regions and heterogeneous lamellar structure composed of band-like CG regions embedded within FG regions were successfully developed, which exacerbates the mechanical property mismatch among distinct domains and consequently contributes to high HDI strengthening. • The absence of movable dislocations in the FG region necessitates higher stress for yielding, which is responsible for the "yield drop" of the bulk composite. During the subsequent deformation process, the significant interaction between MgO and dislocations within the FG regions maintains sustainable strain hardening. • The initial deformation of the CGs results in the accumulation of high strain, leading to the formation of dislocation walls that facilitates the aggregation and recovery of dislocations. This process promotes the transformation of CGs into primary equiaxed grains or substructures in the subsequent strain deformation, thereby significantly contributing to the work hardening. Constructing heterostructures is essential for tailoring the mechanical properties of Al matrix composites (AMCs). In this work, multi-level heterostructures were achieved in AMCs by manipulating the cold welding of initial composite powders and in-situ solid-state reaction. The resulting microstructure features band-like coarse grain (CG) regions embedded within fine grain (FG) regions, demonstrating a heterogeneous lamella (HL) grain structure. Moreover, the in-situ solid-state reaction between Al, Mg and CuO gives rise to the generation of intragranular nano-sized MgO particles, which are primarily distributed in FGs. This unique microstructure activates hetero-deformation induced (HDI) strengthening by exacerbating the mechanical property mismatch between distinct domains. Notably, the FG regions necessitate high stress for activating dislocations, causing a "yield drop" in the bulk composite. It was also elucidated that CGs experience higher stress in the early stages of deformation compared to FG domains, leading to the formation of dislocation walls. The aggregation and recovery of these dislocations facilitate the transformation of CGs into primary equiaxed grains or substructures during subsequent plastic deformation, thereby contributing to the exceptional strain hardening of the composite. Furthermore, the intragranular distribution of MgO reinforcement promotes significant dislocation proliferation and achieves stress redistribution, which rationalizes the considerable ductility of the composite. This work offers insights into the achievement of multi-level heterogeneous composites with superior mechanical properties by synergistically regulating grain structure and reinforcement distribution configuration. [Display omitted] [ABSTRACT FROM AUTHOR]

• The twin roll-cast Mg-2Al-1Zn-1Ca plates exhibit a distinct rare earth (RE)-like texture, with exceptional mechanical properties and notable in-plane anisotropy. • Substructure formation during pre-stretching enhances yield strength (YS) but reduces work hardening. • Activation of {0002} 〈11–20〉 basal slip transforms the RE-like texture to basal texture, optimizing in-plane anisotropy. • Dislocation activity is more intense along TD during pre-stretching than along RD. Pre-stretching and annealing treatments were conducted on twin roll cast Mg-2Al-1Zn-1Ca (AZX211, in wt.%) plates with a rare earth-like texture. Varying amounts of deformation were applied along the rolling direction (RD) and transverse direction (TD) of AZX211 alloy in order to modify its mechanical properties at room temperature. The results demonstrate that pre-stretching treatment effectively enhances the yield strength (YS), especially along the RD. The strengthening mechanism is attributed to the production of a large number of dislocations and sub-grain boundaries, but the work-hardening ability of the plate will be greatly weakened. Additionally, annealing treatment substantially improves the plasticity and in-plane anisotropy and restores the work-hardening ability. The notable distinction in the pre-stretching process between different directions lies in the underlying deformation mechanism. In case of RD, deformation is predominantly governed by the slip mechanism of {0002} 〈11−20〉 basal slip and {10−10} 〈11−20〉 prismatic slip, while along the TD, deformation is primarily controlled by {0002} 〈11−20〉 basal slip without significant twinning deformation. When a 6 % pre-stretching is conducted, the initial rare earth-like texture of the sample transforms into a symmetrically distributed double-peak basal texture, accompanied by grain refinement. This texture transformation is chiefly due to the dominance of {0002} 〈11−20〉 basal slip-driven deformation. Moreover, the annealed sample maintains a strong basal texture, owing to strain-induced recrystallization. [Display omitted] [ABSTRACT FROM AUTHOR]

• Explored microstructure evolution & bonding link in particle impact via multiscale analysis. • FEM modeling examined the effect of deformation variables on microstructure evolution. • Complex interplay of DRX & twinning results in 4 distinct deformation microstructures. • DRX induced softening in highly strained interface areas fosters atomic bonding. • Gradual orientation change, misfit dislocations & vacancies observed in atomic bonding. Large interfacial strains in particles are crucial for promoting bonding in cold spraying (CS), initiated either by adiabatic shear instability (ASI) due to softening prevailing over strain hardening or by hydrostatic plasticity, which is claimed to promote bonding even without ASI. A thorough microstructural analysis is vital to fully understand the bonding mechanisms at play during microparticle impacts and throughout the CS process. In this study, the HEA CoCrFeMnNi, known for its relatively high strain hardening and resistance to softening, was selected to investigate the microstructure characteristics and bonding mechanisms in CS. This study used characterization techniques covering a range of length scales, including electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and high-resolution transmission microscopy (HR-TEM), to explore the microstructure characteristics of bonding and overall structure development of CoCrFeMnNi microparticles after impact in CS. HR-TEM lamellae were prepared using focused ion beam milling. Additionally, the effects of deformation field variables on microstructure development were determined through finite element modeling (FEM) of microparticle impacts. The ECCI, EBSD, and HR-TEM analyses revealed an interplay between dislocation-driven processes and twinning, leading to the development of four distinct deformation microstructures. Significant grain refinement occurs at the interface through continuous dynamic recrystallization (CDRX) due to high strain and temperature rise from adiabatic deformation, signs of softening, and ASI. Near the interface, a necklace-like structure of refined grains forms around grain boundaries, along with elongated grains, resulting from the coexistence of dynamic recovery and discontinuous dynamic recrystallization (DDRX) due to lower temperature rise and strain. Towards the particle or substrate interior, concurrent twinning and dislocation-mediated mechanisms refine the structure, forming straight, curved, and intersected twins. At the top of the particles, only deformed grains with a low dislocation density are observed. Our results showed that DRX induces microstructure softening in highly strained interface areas, facilitating atomic bonding in CoCrFeMnNi. HR-TEM investigation confirms the formation of atomic bonds between particles and substrate, with a gradual change in crystal lattice orientation from the particle to the substrate and the occurrence of some misfit dislocations and vacancies at the interface. Finally, the findings of this research suggest that softening and ASI, even in materials resistant to softening, are required to establish bonding in CS. [Display omitted] [ABSTRACT FROM AUTHOR]

• An exceptional strength-ductility synergy was achieved in a solid solution 6063 aluminum alloy at cryogenic temperature. • In-situ EBSD experiments were carried out at both 298 K and 77 K to reveal temperature-mediated dislocation activation and orientation rotation behaviors. • The activation of multiple slip systems at 77 K contributed to the increased dislocation density and thus the superior strain hardening capacity of the alloy. A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K. Here, the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by in-situ electron backscatter diffraction (EBSD) observations coupled with transmission electron microscopy (TEM) characterization and fracture morphologies at both 298 and 77 K. It is found that kernel average misorientation (KAM) mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations (GNDs) at 77 K. The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems, which is consistent with the results of potential slip systems calculated by Taylor axes. Furthermore, dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K. This temperature-mediated activation of dislocations facilitates the increased dislocations, thus enhancing the strain hardening capacity and ductility of the alloy. This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications. [Display omitted] [ABSTRACT FROM AUTHOR]

• An oxide-dispersion-strengthened Fe-Cr-Al alloy with a bimodal grain size distribution is fabricated. • The heterogeneous microstructure improves the strength and ductility of Fe-Cr-Al alloy simultaneously. • Through selecting appropriate powder size and sintering processes, the microstructure of Fe-Cr-Al alloy towards a heterogeneous grain size distribution can be tailored. An oxide-dispersion-strengthened (ODS) Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy with a bimodal grain size distribution was developed via a simple process of internal oxidation and powder forging. The intentionally promoted heterogeneous microstructure consists of coarse-grained "core" regions enclosed by mutually connected fine-grained "shell" zones, facilitated by unevenly distributed oxide particles. The sample sintered and then forged at 1150 °C exhibited a yield strength of 598 MPa, a tensile strength of 734 MPa, and a fracture elongation of 25.1 %. Such simultaneously enhanced strength and ductility are significantly above those of cast or previous powder-consolidated counterparts. During tensile deformation, a strain gradient is built up across the inhomogeneous grains and a high density of geometrically necessary dislocations was observed near the interfaces of matrix/oxide particles, both contributing to heterogeneous deformation-induced strengthening. This elevates the work hardening rate and consequently the tensile elongation. Quantitative analysis indicates that the dislocation build-up during forging makes the dominant contribution to the high yield strength of Ox-1150. The present study offers a new route to the preparation of heterogeneously structured ODS Fe-Cr-Al alloys and provides guidance for optimizing the mechanical properties of such alloys in terms of strength-ductility synergy. [Display omitted] [ABSTRACT FROM AUTHOR]

• After high-temperature annealing, the compressive strength of the NiTiNb scaffolds with 85.9 % porosity was more than doubled. • There was an element diffusion zone in several nanometers surrounding the β-Nb particle, where the substitution of Nb with Ti led to a higher Ni: Ti atomic ratio, lowering transformation temperatures. • The β-Nb particles can store dislocations and coordinate the deformation, while internal dislocations will be gradually entangled and act as reinforcement. Metallic scaffolds with lightweight, low elastic modulus, and high energy-absorbing capacity are widely utilized in industrial applications but usually require post-heat treatment to enhance their comprehensive mechanical properties. However, it is unclear how to utilize the impact of β -Nb on the surrounding matrix for NiTiNb ternary alloys to achieve strength-ductility-superelasticity enhancement. Here, we prepared rhomboidal dodecahedral NiTiNb porous scaffolds with a porosity of 85.9% by additive manufacturing. Subsequently, annealing treatment was employed to drastically reduce the phase transformation temperatures and expand the thermal hysteresis. Interestingly, the 850 °C annealed scaffold exhibited exceeding double compressive strength of the as-built sample, with a remarkable improvement in ductility and superelasticity. From the microstructure perspective, high-temperature annealing caused a further eutectic reaction of the unmelted Nb particles with the NiTi matrix and the transformation of mesh-like β -Nb into dispersedly distributed spherical β -Nb particles. The microstructure evolution after deformation indicated that stress-induced martensitic transformation occurred in the matrix away from the NiTi-Nb eutectic region whereas almost no martensite formed nearby β -Nb particles. Atom probe tomography characterization revealed an element diffusion zone in several nanometers surrounding the β -Nb particle, where the substitution of Nb with Ti led to a higher Ni: Ti atomic ratio, lowering transformation temperatures. Molecular dynamics simulations illustrated that β -Nb particles can not only entangle dislocations internally, acting as reinforcements but also hinder the twin growth, contributing to strain hardening. This work elucidates the influence of β -Nb particles on the deformation mechanism of the NiTi-Nb eutectic region through in-depth atomic-scale investigation, which can provide inspiration for the improvement of comprehensive mechanical properties of NiTiNb alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

• Tungsten alloy with a CoCrFeNi high entropy alloy binder was deposited via the laser metal deposition method. • Typical solidification microstructures were elucidated via the CALPHAD method. • The nano precipitate and intermetallic compound layer were characterized. • The alloy exhibits a rarely high compressive stress of 2047 MPa and strain of 32 % at room temperature. Tungsten heavy alloys (WHAs) prepared using laser additive manufacturing (AM) exhibit intricate geometries, albeit with limited mechanical properties. Here we designed a high-strength WHA featuring a FeCrCoNi high entropy alloy (HEA) binder via the laser metal deposition (LMD) technique. Due to the distinctive thermal cycle and rapid cooling rate, the as-deposited alloys exhibit microstructures with hypoeutectic, eutectic-like, and spot-like characteristics. To elucidate this phenomenon, the solidification paths were delineated and analyzed by combining microstructural characterization and phase equilibrium simulation. The μ phase precipitated out from the supersaturated solid solution, thereby nucleating massive dislocations on the FeCrCoNi matrix to increase the work hardening rate. Furthermore, the μ phase formed an ultrafine intermetallic compound (IMC) layer around the W grain, reducing the hole or crack between the W grain and FeCrCoNi matrix. Attributed to the precipitation strengthening, the solid solution of the FeCrCoNi binder, along with the load-bearing strength of W, the developed alloy achieved ultrahigh compressive stress and strain of 2047 MPa and 32 % respectively at room temperature. These findings contribute valuable insights to the advancement of additive manufacturing for tungsten alloys, leveraging their excellent properties. [Display omitted] [ABSTRACT FROM AUTHOR]

• A special heterostructure with an alternating distribution of coarse and fine α lamella is achieved in bimodal Ti6242 alloy. • Such heterostructure can significantly inhibit strain localization and generate an extra HDI hardening. • High-density 〈 c + a 〉 dislocations are activated in the heterostructure to accommodate strain. • HDI strengthening and Hall-Petch strengthening are the dominant strengthening mechanisms for the heterostructure. In this work, a heterogeneous structure (HS) with an alternating distribution of coarse and fine α lamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heating treatment. Instead of a distinct interface between the primary α phase (α p) and β transformation microstructure (β t) in the equiaxed microstructure (EM), all α p /β t interfaces are eliminated in the HS, and the large α p phases are replaced by coarse α lamella. Compared to the EM alloy, the heterostructured alloy exhibits a superior strength-ductility combination. The enhanced strength is predominantly attributed to the increased interfaces of α/β plates and hetero-deformation induced (HDI) strengthening caused by back stress. Meanwhile, good ductility is ascribed to its uniform distribution of coarse and fine α lamella, which effectively inhibits strain localization and generates an extra HDI hardening. This can be evidenced by the accumulated geometrically necessary dislocations (GNDs) induced by strain partitioning of the heterostructure. Significantly, the HDI causes extra 〈 c + a 〉 dislocations piling up in the coarse α lamella, which generates an extra strain hardening to further improve the ductility. Such hetero-interface coordinated deformation mechanism sheds light on a new perspective for tailoring bimodal titanium alloys with excellent mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nanoprecipitates of Al–Zn–Mg–Cu alloys peak-aged at 80–220 °C were examined. • GP zones and η'/η precipitates contain ∼11Zn–9Mg–1Cu and ∼44Al–28Zn–24Mg–3Cu (at.%). • A shearable to non-shearable transition of nanoprecipitates occurred above 180 °C. • Both tensile strength and ductility decreased with increasing aging temperature. We investigate the effect of aging temperature on precipitation behavior and mechanical properties of an Al–7.6Zn–2.7Mg–2.0Cu–0.1Zr–0.07Ti (wt.%) alloy by evaluating the matrix's microhardness, electrical resistivity, and tensile properties: additionally, employing X-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and atom-probe tomography (APT) to characterize this alloy. The nanoprecipitates forming under peak-aging conditions vary with aging temperature, forming coherent GPI zones at 80 °C, GPII zones with minor η' at 120–150 °C, and η'/η with minor GP zones at 180–220 °C. GPI and GPII zones forming at 80–150 °C contain similar concentrations of solute atoms (11Zn–9Mg–(<1.0)Cu (at.%)), whereas the η'/η nanoprecipitates forming at 180 °C contain larger concentrations of solute atoms (28Zn–24Mg–3.4Cu (at.%)). The strength of the peak-aged alloy decreases with increasing aging temperature owing to the increasing size and decreasing number density of the nanoprecipitates. Under peak-aging conditions, precipitation strengthening originates mainly from dislocation shearing at 80–150 °C and from Orowan bypassing at temperatures above 180 °C. The shearable to non-shearable transition of the nanoprecipitates at 180 °C reduces the strain hardening rate, thereby decreasing the alloy's ductility. [Display omitted] [ABSTRACT FROM AUTHOR]

• With increasing Si content from 0 at.% to 0.8 at.%, the hardness, strength and strain hardening rate increase two to four times, while the uniform elongation only reduces a 50 %. This relatively small reduction in the strain to failure is not normal for solute hardening. • After testing, the stored intragranular dislocation structures change from complex, entangled dislocation patterns in pure Nb to long, parallel, and straight screw-dominate arrays in the Nb-Si alloys. We propose that these differences arise because the Si solute lowered the propensity for cross-slip. • During in-situ indentation, the edge dislocation velocity decreases proportionally with increasing Si content, whereas the screw dislocation velocity abruptly decreases and reaches a plateau. We rationalize that the reductions in the mobility of both types of dislocations and in the cross-slip propensity of the screw dislocations are the origins of the remarkable strengthening and strain hardening in Nb-Si alloy. • The pre-existing high density of superjogs and loops from the rolled and heat-treated material induced by Si solutes-dislocation interactions provide internal sources for dislocations. Easy activation of numerous dislocation sources enabled ductile deformation of the nb-si alloys. The segregation of Al on superjogs and loops stabilizes these structures, thus enhancing the content of Al could serve as a way to introduce more superjogs and loops in Nb alloys. Niobium (Nb) is sensitive to even minute quantities of silicon (Si) solutes, which are known to induce pronounced hardening. However, the underlying mechanism for hardening remains elusive since the effect of Si solutes on dislocation behavior is unclear. Here, using tensile testing, in-situ microscopy and nanomechanical testing, the behavior of dislocations in dilute Nb-Si alloys, containing from 0 at.% to 0.8 at.% Si, is investigated. We show that the hardness, strength and strain hardening rate increase from two to four times, while the uniform elongation in tension only reduces 50 % as the Si content increases. Dislocations evolve from complex entangled patterns in Nb to parallel long-straight screw dislocation-dominated structures in Nb-Si alloys. In-situ indentation reveals that the origins of the marked hardening in Nb-Si alloy are the reduction of dislocation mobility and cross-slip propensity. Large densities of dislocation debris-superjogs and loops introduced throughout the sample during warm rolling and annealing are found to provide active internal dislocation sources, which explain the minimal ductility loss seen in these Nb-Si alloys. These findings can help guide the alloy design of high-performance refractory materials for extreme temperature applications. [Display omitted] [ABSTRACT FROM AUTHOR]

• LSP-induced gradient microstructure was tailored through following annealing. • The defect-free zone and compressive residual stress with LSP were maintained after annealing. • LSP-induced combining annealing-regulated defect-free zone and gradient microstructure simultaneously improved strength and elongation. Wire arc-directed energy deposition (WADED) has shown great advantages and potential in fabricating large-scale aluminum (Al) alloy components. However, WADED Al alloys typically exhibit low strength and reliability due to pore defects and lack of work hardening or precipitation strengthening. This study utilized a combination of laser shock peening (LSP) and annealing to regulate the microstructure of WADED Al-Mg4.5Mn alloy and enhance mechanical properties. The effects of LSP and annealing on phase composition, pore distribution, and microstructures at multiple scales were systematically investigated to reveal the mechanical property improving mechanism. The results demonstrated that LSP-induced plastic deformation formed a defect-free zone by closing near-surface pore defects. LSP created the hardened layer with gradient mechanical properties by inducing gradient changes in grain size, the number of low-angle grain boundaries (LAGBs), and dislocation density along the depth direction. The annealing process promoted grain coarsening and reduced excessive dislocations and LAGBs, weakening the work hardening effect caused by LSP. Furthermore, the high-density dislocations and high stored energy generated by LSP accelerated the recrystallization, facilitating growth of near-surface grains. The defect-free zone, dislocation strengthening, and LAGBs strengthening were responsible for the increase in strength, while the synergistic deformation between hardened layers and soft core facilitated maintaining excellent elongation. The strength and elongation of WADED Al alloy can be synergistically improved by balancing the effects of LSP and heat treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

• The Fe-Cr-Ni-Mn-N austenitic stainless steel exhibits an exceptional mechanical property at 4.2 K with a high yield strength of 1.5 GPa. • The deformation nanotwinning, HCP ε-martensite transformation, dislocation slip with L -C locks and stacking fault formation which provided a marked contribution to the Fe-Cr-Ni-Mn-N alloy's ultrahigh strain hardening rate and outstanding strength at liquid helium temperature 4.2 K. • The Fe-Cr-Ni-Mn-N austenitic stainless steel displays outstanding cryogenic mechanical properties through a progressive synergy of deformation mechanisms leading to exceptional strength which provides a new insight into the commercialized development of high-performance alloys for cryogenic applications. We report the mechanical performance and microstructural characteristics of a Fe-Cr-Ni-Mn-N alloy at cryogenic temperatures. The exceptionally high yield strength of 1.5 GPa combined with a high strain-hardening rate and no deterioration in ductility at 4.2 K was displayed. The evolution of deformation microstructure was examined using electron backscatter diffraction (EBSD), the transmission Kikuchi diffraction (TKD), high-resolution transmission electron microscopy (HRTEM), and aberration-corrected scanning TEM (STEM). The deformation microstructure mainly consisted of dislocation slip with L -C locks, {111} stacking fault formation, {111} deformation nanotwinning, and FCC → HCP shear transformation at 4.2 K. The occurrence of FCC-HCP shear transformation inside/near {111} twins to form γ-γ tw -ε dual-phase structure induces a dynamic Hall-Petch effect that promotes the strain-hardening rate and enhances the strength-ductility combination. We believe that this alloy displays outstanding damage tolerance through a progressive synergy of deformation mechanisms leading to exceptional strength which provides a new insight into the commercialized development of high-performance alloys for cryogenic applications. [Display omitted] [ABSTRACT FROM AUTHOR]

• Correlation between SMAT processing parameters and surface integrity of Ti-6Al-7Nb alloy was revealed. • The optimal SMAT parameters for treating Ti-6Al-7Nb alloy were determined. • Synergistic effect of twin intersections and twin-dislocation interactions contributed to the grain refinement during SMAT. • SMATed Ti-6Al-7Nb with optimal processing showed an obvious improvement in fatigue strength. Current Ti-based orthopedic implants often suffer from fatigue damage, therefore shortening their service lifespan. To solve this issue, in this study, mechanically polished Ti-6Al-7Nb (P-Ti6Al7Nb) was subjected to surface mechanical attrition treatment (SMAT). Effects of various SMAT process parameters, including ball diameter and treatment duration, on the surface integrity of P-Ti6Al7Nb were investigated, specifically in terms of surface quality, surface nanocrystalline layer, and residual stress. Subsequently, the microstructure, in-depth residual stress and microhardness distributions, surface roughness, and fatigue behavior in simulated body fluids of optimally SMATed Ti-6Al-7Nb (S-Ti6Al7Nb) were examined and compared to those of P-Ti6Al7Nb. Results showed that based on the experimental conditions established in the present research, the optimal parameters were determined to be a 3 mm ball diameter and a 15 min treatment duration, which resulted in excellent surface integrity; S-Ti6Al7Nb showed a 300 μm-thick gradient nanostructured layer comprising the thickest nanocrystalline layer of about 20 μm, a 1000 μm-deep residual compressive stress field with the maximum surface residual compressive stress, and a micro-concave topography but free of any defects or cracks. The microstructural evolution mechanism was also elucidated, revealing that the combination of multidirectional primary and secondary twins' intersections and twin-dislocation interactions contributed to grain refinement. Compared to P-Ti6Al7Nb, S-Ti6Al7Nb exhibited a 40 % improvement in fatigue strength, owing to synergistic effects of the gradient nanostructured layer, surface work hardening, high amplitude of residual compressive stress, and improved surface integrity. These factors effectively prevented the initiation of fatigue crack at the surface and shifted it to the sublayer, and inhibited the subsequent crack propagation. [Display omitted] [ABSTRACT FROM AUTHOR]

• Twinning-induced plasticity (TWIP) is activated in TiZrHfNb high entropy alloys. • Metastable BCC and cryogenic temperature are two prerequisites for triggering TWIP. • Hierarchical {332}<113> twinning networks dominate the deformation process. • {112}<111> twins tend to be activated inside primary {332}<113> twin bands. • The strength-ductility can be regulated by adjusting the niobium content at 77 K. The twinning-induced plasticity (TWIP) effect has been widely utilized in austenite steels, β-Ti alloys, and recently developed face-centered-cubic (FCC) high-entropy alloys (HEAs) to simultaneously enhance the tensile strength and ductility. In this study, for the first time, the TWIP effect through hierarchical {332<113> mechanical twinning has been successfully engineered into the TiZrHfNb refractory HEAs by decreasing temperature and tailoring the content of Nb to destabilize the BCC phase. At cryogenic temperature, the comprehensive hierarchical {332}<113> mechanical twins are activated in TiZrHfNb 0.5 alloy from micro- to nanoscale and progressively segment the BCC grains into nano-scale islands during deformation, ensuring sustainable strain hardening capability and eventually achieving a substantial 35 % uniform tensile elongation. In addition, at 77 K, the tensile strength and uniform elongation of TiZrHfNb x alloys can further be adjusted by a moderate increase of Nb. The results above shed new light on the development of high-performance refractory HEAs with a high and adjustable strength and ductility combination down to the cryogenic temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

• A feasible strategy was suggested to produce "finer grains + high-density TBs + precipitates" architectures in LPBF-fabricated Inconel 718. • A favorable strength and excellent plasticity (1088 MPa, 1369 MPa, 30 %) was obtained. • The intensive interactions between GBs/TBs/precipitates and dislocations under finer grain scale offers a strong strain hardening effect. • Deformation modes of SFs, L-C locks, primary DTs, and secondary twins sustaining an additional and higher strain hardening rate. Tailoring high-density annealing twins in laser powder bed fusion (LPBF)-fabricated alloys based on their intrinsic residual stress requires high annealing temperatures and/or long-term annealing, resulting in the abnormal growth of large recrystallized grains, which is detrimental to mechanical properties. This work proposes a new strategy for achieving a favorable strength–plasticity synergy of the LPBF-fabricated Inconel 718 superalloy by performing a deep cryogenic treatment (DCT) with the subsequent heat treatment (including annealing and double aging) to tailor fine grains with "high-density annealing twins + precipitates" architectures and compares the obtained material with an alloy subjected to a direct heat treatment without a prior DCT. The obtained results reveal that the additional internal stress generated during DCT increases the stored energy and dislocation density, which provide a sufficient driving force for activating high-density annealing twin boundaries (63.2 %) with fine grains (31.6 μm) within a short annealing time. The more homogeneous tailored microstructure with the "finer grains + high-density twins + precipitates" architectures decreases the mean free path of slipping dislocations, promoting intensive interactions with dislocations and inducing a strong strain hardening effect. The multiple deformation modes of stacking faults coupled with Lomer–Cottrell locks, thin primary deformation twins, and secondary twins activated during tensile loading, sustaining a strong work hardening ability and delaying the plastic instability, which exhibits a high strength (yield strength of 1088 MPa and tensile strength of 1369 MPa) and excellent plasticity (elongation of 30 %). This work not only describes a feasible method for simultaneously enhancing the strength and plasticity in additively manufactured (AM) alloys but also provides new insights into increasing the fraction of twins at a small grain size to improve the grain boundary-related properties without destroying the AM alloy shape. [Display omitted] [ABSTRACT FROM AUTHOR]

• The preheating was introduced into the friction stir welded 7Mn steel to tailor austenitic stability. • The unprecedented the product of strength and elongation was obtained in the as-preheated NZ. • The deformation behavior of austenite in the NZ was systematically studied. • Multiple strain hardening mechanisms in the NZ were revealed. The martensite often appears in the nugget zone (NZ) of friction stir welding (FSW) 7 wt.% Mn steel due to low austenite stability, deteriorating ductility and toughness. In this work, a 7 wt.% Mn steel was subjected to FSW, and preheating was used to tailor the austenitic stability to greatly improve the strength–ductility combination of the NZ. The austenitic deformation behavior and strain hardening mechanism in the NZ were systematically investigated. The microstructure of the as-welded NZ was composed of ultrafine blocky ferrite, austenite, and small amounts of martensite, whereas the as-preheated NZ contained ultrafine blocky ferrite and austenite, and the concentration of Mn in austenite was increased from 8.4 wt.% to 10.7 wt.%. This enhanced the austenitic stability, resulting in a significant increase in the volume fraction of austenite in the as-preheated NZ from 37.3% to 66.4%. The product of strength and elongation (PSE) in the as-preheated NZ increased dramatically from 42.6 GPa% to 67.1 GPa%, depending on a persistent high strain hardening rate (SHR). Multiple strain-hardening mechanisms were revealed. The austenite with enhanced stability can provoke sustained transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects, and massive dislocation multiplication occurs during tension, resulting in strong strain hardening. [Display omitted] [ABSTRACT FROM AUTHOR]

• A well-bonded Ti/Mg laminate with heterostructures was produced via vertical extrusion and annealing. • The interface between Mg layer and Ti layer had a semi-coherent relationship. • Microstructural heterogeneities between Ti layer and Mg layer induced significant strain gradient near the layer interface. • The introduction of Ti layer effectively hindered the propagation of the cracks. • The well-designed AZ31 laminated composite exhibited excellent strength-ductility synergy. In this work, we introduced pure Ti into AZ31 Mg alloy by extrusion process followed by annealing at 350 °C for 1 h to significantly improve the mechanical properties of AZ31 laminate, with a yield strength of 243 MPa, an ultimate tensile strength of 338 MPa and a uniform elongation of 17.7%. Microstructural characterizations showed that there was slight diffusion of elements (Al, Zn, and Mn) across the layer interface, and the interface between the constituent layers maintained semi-coherent. Moreover, significant microstructure heterogeneities appeared across the hetero-interface, where the Mg layer possessed large equiaxed grains with lower dislocation density, while the Ti layer formed ultrafine grains (UFG) and unrecrystallized block grains with extensive dislocation cells and dislocation walls. Combining the digital image correlation (DIC) technique and in-situ electron backscatter diffraction (EBSD), it was found that the microstructural heterogeneities induced significant strain gradients near the layer interface during plastic deformation, which needed to be accommodated by geometrically necessary dislocations (GNDs). This resulted in hetero-deformation-induced (HDI) strengthening and HDI strain hardening to strengthen and toughen the AZ31 laminated composite. Additionally, the introduction of the Ti layer effectively hindered the propagation of the cracks and consequently improved the ductility of the laminate. [Display omitted] [ABSTRACT FROM AUTHOR]

• Axial grain size is a robust descriptor for representing complex states of grain morphology. • The introduced grain size anisotropy function can effectively represent anisotropic grain morphologies. • Uniaxial strain hardening is a suitable measure to represent anisotropic mechanical response. • A crystallographically textureless microstructure with strong morphological texture is instantiated. • Strain hardening anisotropy due to grain size anisotropy can be described by an inverse square relation. Additively manufactured (AM) metals exhibit highly complex microstructures, particularly in terms of grain morphology which typically features heterogeneous grain size distribution, irregular and anisotropic grain shapes, and the so-called columnar grains. The conventional morphological descriptors based on grain shape idealization are generally inadequate for representing complex and anisotropic grain morphology of AM microstructures. The primary aspect of microstructural grain morphology is the state of grain boundary spacing or grain size whose effect on the mechanical response is known to be crucial. In this paper, we formally introduce the notion of axial grain size from which we derive mean axial grain size, effective grain size, and grain size anisotropy as robust morphological descriptors capable of effectively representing highly complex grain morphologies. We instantiated a discrete sample of polycrystalline aggregate as a representative volume element (RVE) featuring random crystallographic orientation and misorientation distributions. However, the instantiated RVE incorporates the typical morphological features of AM microstructures including distinctive grain size heterogeneity and anisotropic grain size owing to its pronounced columnar grain morphology. We ensured that any anisotropy observed in the macroscopic mechanical response of the instantiated sample primarily originates from its underlying anisotropic grain size. The RVE was then employed for mesoscale full-field crystal plasticity simulations corresponding to uniaxial tensile deformation along various axes via a spectral solver and a physics-based crystal plasticity constitutive model which was developed, calibrated, and validated in earlier studies. Through the numerical analyses, we isolated the contribution of anisotropic grain size to the anisotropy in the mechanical response of polycrystalline aggregates, particularly those with the characteristic complex grain morphology of AM metals. This contribution can be described by an inverse square relation. [Display omitted] [ABSTRACT FROM AUTHOR]

• The laminates composing of alternating coarse-grained Cu layers and elongated nano-grained Fe layers exhibited considerable synergy of strength and ductility. • Mutual constraint between adjacent layers lead to geometrically necessary dislocations accumulation near interface, promoting extra strain hardening. • Strain partitioning and interfacial strain gradient efficiently prevented strain localization in laminated materials. • Increasing interface affected zone fraction can increase the strength-ductility synergy in laminated materials. The hetero-zone boundary affected region (HBAR) significantly influences the mechanical behaviors of layered materials, where the deformation mechanisms differ from those in the bulk layers. In this study, three kinds of heterogeneous Cu-Fe layered materials with different interface spacing but identical total thicknesses were prepared. The effects of HBAR and strain partitioning on the tensile behavior of the layered materials were investigated. The results showed that layered materials had enhanced yield strength and uniform elongation with decreasing interface spacing. During tensile deformation, geometrically necessary dislocations (GNDs) were generated at hetero-zone boundaries and piled up near them, resulting in hetero-deformation induced (HDI) strengthening and HDI work hardening. Surface profilometry measurements showed that the Cu and Fe layers exhibited obvious strain partitioning and mutual constraint. With decreasing interface spacing, strain partitioning is enhanced by interlayer constraint, which prevented strain localization at interfaces and thus improved the synergetic deformation of layers. A higher fraction of HBAR can improve the mechanical performance of heterogeneous layered materials. This study deepens our understanding of the relationship between HBAR and strength-ductility synergy and provides some insight into the design of layered materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• In-situ synchrotron X-ray diffraction in tensile deformation was performed using Al–Si alloy manufactured by laser powder bed fusion. • At the early stage of deformation, the stress was dominantly partitioned into the α-Al matrix, rather than the Si phase. • Highly concentrated solute Si served as a driving force for the dynamic precipitation in loading for contributing high strength. • The partitioned stress in the Si phase monotonically increased under the strain-hardening regime. • Si-phase particles localized in the cellular microstructure played a significant role in dislocation obstacles for strain hardening. The microstructural factors contributing to the high strength of additive-manufactured Al–Si alloys using laser-beam powder bed fusion (PBF-LB) were identified by in-situ synchrotron X-ray diffraction in tensile deformation and transmission electron microscopy. PBF-LB and heat treatment were employed to manufacture Al–12%Si binary alloy specimens with different microstructures. At an early stage of deformation prior to macroscopic yielding, stress was dominantly partitioned into the α-Al matrix, rather than the Si phase in all specimens. Highly concentrated Si solute (∼3%) in the α-Al matrix promoted the dynamic precipitation of nanoscale Si phase during loading, thereby increasing the yield strength. After macroscopic yielding, the partitioned stress in the Si phase monotonically increased in the strain-hardening regime with an increase in the dislocation density in the α-Al matrix. At a later stage of strain hardening, the flow curves of the partitioned stress in the Si phase yielded stress relaxation owing to plastic deformation. Therefore, Si-phase particles localized along the cell walls in the cellular-solidified microstructure play a significant role in dislocation obstacles for strain hardening. Compared with the results of the heat-treated specimens with different microstructural factors, the dominant strengthening factors of PBF-LB manufactured Al–Si alloys were discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

• TiN is a highly effective grain refiner for additive manufacture (AM) of 316 steel. • δ-ferrite is the primary solid phase during AM of the 316 steel. • Grain refinement in the TiN-inoculated 316 steel was inherited from the refinement of δ-ferrite. • Grain refinement led to dislocation-based deformation mechanism in the TiN-inoculated 316 steel. • TiN inoculation led to the superior strength-ductility synergy in the 316 steel. As a potent grain refiner for steel casting, TiN is now widely used to refine γ-austenite in steel additive manufacturing (AM). However, the refining mechanism of TiN during AM remains unclear despite intensive research in recent years. This work aims to boost our understanding on the mechanism of TiN in refining the γ-austenite in AM-fabricated 316 stainless steel and its corresponding effect on the mechanical behaviour. Experimental results show that addition of 1 wt.% TiN nanoparticles led to complete columnar-to-equiaxed transition and significant refinement of the austenite grains to ∼2 µm in the 316 steel. Thermodynamic and kinetic simulations confirmed that, despite the rapid AM solidification, δ-ferrite is the primary solid phase during AM of the 316 steel and γ-austenite forms through subsequent peritectic reaction or direct transformation from the δ-ferrite. This implies that the TiN nanoparticles actually refined the δ-ferrite through promoting its heterogenous nucleation, which in turn refined the γ-austenite. This assumption is verified by the high grain refining efficiency of TiN nanoparticles in an AM-fabricated Fe-4 wt.%Si δ-ferrite alloy, in which δ-ferrite forms directly from the melt and is retained at room temperature. The grain refinement is attributed to the good atomic matching between δ-ferrite and TiN. Grain refinement in the 316 steel through 1 wt.% TiN inoculation not only eliminated the property anisotropy but also led to a high strain-hardening rate upon plastic deformation and thereby a superior strength-ductility synergy with yield strength of 561 MPa, tensile strength of 860 MPa and elongation of 48%. [Display omitted] [ABSTRACT FROM AUTHOR]

• The detailed precipitation sequence of κ′-carbides and B2 particles in Fe–28Mn–11Al–1C–5Ni (wt%) austenite low-density steel at different isothermal aging temperatures was investigated. • The enrichment of ni element at the phase boundaries among the austenite matrix and κ′-carbides is in favor of the B2 subsequent precipitates. • The homogenously distributed B2 nanoparticles within austenite lead to a significant improvement in the work hardening rate. Precipitation strengthening has been widely adopted in austenitic low-density steel owing to excellent hardened effects. This approach generally employs the coherent κ′-carbides and non-coherent B2 particles. Revealing the precipitation transformation pathway is decisive for further optimizing the microstructures under specific engineering applications. Herein, the detailed precipitation sequence of Fe–28Mn–11Al–1C–5Ni (wt%) austenitic low-density steel as well as its influence on mechanical properties during aging process is systematically investigated. Our results reveal that nano-sized κ′-carbides domains (2 nm) exist in the solution-treated specimen. During aging at 500 °C for 1 h, the cuboidal κ′-carbides (15–20 nm) uniformly disperse in austenite matrix. However, after aging at 700 °C for 15 min, the coarsen κ′-carbides (30–35 nm) inhomogeneously distribute and align preferentially along the 〈1 0 0〉 directions. Further, extending the aging time to 60 min, the needle-type B2 particles replace the κ′-carbides due to the enrichment of Ni elements at the phase boundaries among the austenite and κ′-carbides. After aging at 900 °C, κ′-carbides entirely dissolve into the austenite matrix, and the intragranular B2 particles are the sole precipitates in the austenite matrix and follow the K-S orientation relationship with austenite. The work hardening capability seriously deteriorates due to the shearing of κ′-carbides by gliding dislocations. While the intragranular B2 particles preserve excellent work hardening rate by dislocations bow-out mechanism. The present work is meaningful for guiding the design of new generation dual-nano precipitation austenitic lightweight steel. [Display omitted] [ABSTRACT FROM AUTHOR]