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Due to its characteristic of low stress brittle fracture, hydrogen embrittlement (HE) is a great challenge for the alloys exposed to hydrogen-containing environments, threatening the safety and integrity of structural components. The physical and chemical status of the interfaces, among which grain boundary (GB), twin boundary (TB), and matrix/nano-precipitate interfaces (coherent, semi-coherent, and incoherent) are the representative ones, play a crucial role in determining the HE susceptibility of materials. Hence, this study mainly reviews recent progress in the interaction between hydrogen and these interfaces, i.e., 1) hydrogen-GB interaction (dominant HE mechanisms, crystallographic features of hydrogen-assisted intergranular cracking, and the strategies for resisting HE through GB segregation and GB engineering); 2) hydrogen-TB interaction (the effect of deformation/pre-existing twins on HE susceptibility, four types of TB-related cracking mechanisms, and the improvement of HE-tolerance by the control of pre-twins, gradient-twins, and twin orientations); and 3) hydrogen-precipitate interaction (hydrogen capacity, hydrogen trapping sites, hydrogen activation energy, and the effect of nano-precipitates on HE of alloys). The correlation between HE susceptibility, active HE mechanisms and their synergy (HELP + HEDE model), and three types of interfaces have been comprehensively summarized and discussed. Also, the strategies for the improvement of HE resistance are proposed in terms of the control of these microstructural interfaces in metallic alloys. [Display omitted] • Effect of the interfaces on hydrogen embrittlement (HE) of alloys is reviewed. • Hydrogen-assisted interface cracking mechanisms of alloys is summarized. • Strategies for resisting HE are proposed through the control of the interfaces. • Semi-coherent precipitates are suggested to balance strength and HE-resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Twinning in Mg alloys arises due to challenges in slip along the c-axis, impacting orientations differently at varying CRSS. • Many factors like GBs, texture, and stress states influence the twinning nucleation, propagation, and growth in Mg alloys. • Dislocation interactions and thermal effects affect twinning activation in Mg alloys, while annealing treatments may stabilize TBs. • Anomalous behavior of ET in Mg-RE alloys suggests RE elements alter c/a ratio, favoring smaller Burger vector at TBs. • CT and DT in Mg alloys promote DRX but pose risks as sources of voids and cracks. Twinning is widely recognized as an effective and cost-efficient method for controlling the microstructure and properties of wrought magnesium (Mg) alloys. Specifically, twins play a crucial role in initiating dynamic recrystallization (DRX), while twin regions experience rapid recrystallization during static recrystallization (SRX). The activation of twinning can lead to changes in lattice orientation, significantly impacting the final texture in Mg alloys. The active roles of twinning are influenced by various factors during the activation process, and the mobility of twin boundaries (TB) can be amplified by stress effects, dislocation interactions, and thermal effects. Conversely, annealing treatments that involve proper segregation or precipitation on TBs serve to stabilize them, restraining their motion. Events such as segregation may also alter the twinning propensity in Magnesium-rare earth (Mg-RE) alloys. While {10–11} contraction twins (CT) and {10–11}-{10–12} double twins (DT) can promote dynamic recrystallization (DRX), they also pose a risk as potential sources of voids and cracks. Additionally, understanding the nucleation and growth mechanisms of twinning is crucial, and these aspects are briefly reviewed in this article. Considering the factors mentioned above, this article summarizes the recent research progress in this field, shedding light on advancements in recent eras. [ABSTRACT FROM AUTHOR]

This paper provided an effective method to further improve the mechanical properties of the AZ80+0.4%Ce magnesium alloy wheel spoke. The effect of high strength and ductility was obtained with a yield strength of 295.36 MPa, an elongation of 10%, by the combination of pre-deformation (7% deformation) and two-stage aging treatment (120 °C/9 h + 175 °C/24 h). The evolution of the microstructure and properties of the alloy was explored under the coupling conditions of different pre-deformation degrees and multi-stage aging. The results show that, pre-deformation introduced a large number of (10 1 ¯ 2) tensile twinning and dislocations, which greatly promoted the probability of continuous precipitates (CPs) appearing. On the contrary, the discontinuous precipitates (DPs) were limited by the vertical and horizontal twin structure. As a result, the pre-nucleation method of two-stage aging increased the proportion of CPs by 34%-38%. Owing to the DPs was effectively suppressed, the alloy's yield strength has been greatly improved. Besides, under multi-stage aging, the twin boundaries induce protruding nucleation to form static recrystallization by hindering the migration of dislocations, and the matrix swallows the twins, then the texture gradually tilts from the two poles to the basal plane. As an important supplement, the grain refinement and oblique texture promoted the improvement of the yield strength of the component. [ABSTRACT FROM AUTHOR]

It has been a common method to improve the mechanical properties of metals by manipulating their microstructures via static recrystallization, i.e., through heat treatment. Therefore, the knowledge of recrystallization and grain growth is critical to the success of the technique. In the present work, by using in-situ high temperature EBSD, the mechanisms that control recrystallization and grain growth of an extruded pure Mg were studied. The experimental results revealed that the grains of priority for dynamic recrystallization exhibit fading competitiveness under static recrystallization. It is also found that grain boundary movement or grain growth is likely to show an inverse energy gradient effect, i.e., low energy grains tend to swallow or grow into high energy grains, and grain boundaries of close to 30° exhibit superior growth advantage to others. Another finding is that {10–12} tensile twin boundaries are sites of hardly observed for recrystallization, and are finally swallowed by adjacent recrystallized grains. The above findings may give comprehensive insights of static recrystallization and grain growth of Mg, and may guide the design of advanced materials processing in microstructural engineering. [ABSTRACT FROM AUTHOR]

Hot torsion tests for AZ80 magnesium alloy were carried out in the temperature range of 380 °C-260 °C, with a constant decreasing temperature rate of 10 °C/s in order to weaken the basal texture and refine the grains. The results indicated that the average grain sizes were refined forming gradient structure with increasing specimen radial position from center (12.2–5.4 μm), and that the initial basal texture intensity of the extruded magnesium alloy was weakened from 46.2 to 8.3. Furthermore, the extension twins (ETs) could be disintegrated from the twins forming separated twins with smaller sizes. Interestingly, ETs with the same twin variant intersecting with each other could be coalesced forming grains with similar orientation, while ETs with different twin variants were separated by twins boundaries contributing to grain refinement. Moreover, in addition to the conventional continuous dynamic recrystallized (CDRX) grains with 30˚ orientation rotated around C-axis of the parent grains, CDRXed grains with 30˚ rotation around a-axis and random rotation axis were also discerned. Besides, the CDRX evolution induced twins were also elaborated, exhibiting the complex competition between CDRX and twining. Hot torsion deformation with constant decreasing temperatures rate is an effective way of grain refinement and texture modification. [ABSTRACT FROM AUTHOR]

Precipitation strengthening is a key strategy for improving the overall mechanical properties of Mg alloys. In Mg-Al alloys, basal precipitates are known to strengthen against twinning, resulting in an increase in the critical resolved shear stress (CRSS) necessary for continued deformation. Although several models have been proposed to quantify the influence of precipitate shape, size, and distribution on the CRSS, the accuracy, scope, and applicability of these models has not been fully assessed. Accordingly, the objectives of this study are: (i) to analyze the accuracy of analytical models proposed in the literature for precipitation strengthening against twin thickening and propagation (in Mg-Al alloys) using phase-field (PF) simulations, (ii) to propose modifications to these model forms to better capture the observed trends in the PF data, and (iii) to subsequently test the predictiveness of the extended models in extrapolating to experimental strengthening data. First, using an atomistically-informed phase-field method, the interactions between migrating twin boundaries (during the propagation and thickening stages) and basal plates are simulated for different precipitate sizes and arrangements. In general, comparison of the increase in CRSS determined from the PF simulations and the predictions from four precipitation strengthening models reveals that modifications are necessary to the model forms to extend their applicability to precipitation strengthening against both twin thickening and propagation. A subsequent comparison between predictions from the extended models and experimental strengthening data for peak age-hardened samples reveals that the (extended) single dislocation and dislocation wall models provide reasonably accurate values of the increase in CRSS. Ultimately, the results presented here help elucidate the fidelity and applicability of the various hardening models in predicting precipitation strenghtening effects in technologically important alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

A combined experimental and computational analysis is performed to investigate the less commonly studied embryo-to-lamella transition of deformation twins in magnesium. This work aims to understand the structural variables controlling the embryo-to-lamella transition from grain boundaries. Statistical analysis of hundreds of early-stage twins in the lightly deformed microstructure reveals a prevailing wedge shape, with a much thicker base along the grain boundary (GB) where they originate and a thinner tip terminating in the crystal. The analysis also shows that the GB base is super thick and identifies a minimum GB twin thickness among all early-stage twins that is about one micron. A crystal plasticity-based full-field model is employed to calculate the driving forces to migrate the boundary of a three-dimensional GB twin embryo. The stress analysis, considering a full range of embryo shapes and neighboring grain orientations, indicate that the twin embryo is most likely going to form a wedge shape when it first propagates. The calculations predict that the thickness of the embryo at the GB needs to be significantly larger than its length into the crystal in order to propagate into the crystal. The analysis finds that the more aligned the twin embryo variant is with basal slip in the neighboring grain, the thinner the twin embryo needed for propagation. [ABSTRACT FROM AUTHOR]

• The importance of grain refinement in improving strength of Mg alloys has been demonstrated. • The DRX models and DRX mechanisms and the related grain refinement ability are summarized. • The mechanical property enhancement by grain refinement strategy of newly developed low-RE containing Mg alloy and the RE-free Mg alloys are reviewed. • The perspectives and outstanding issues concerning high-performance Mg wrought alloys are proposed. Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth (RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization (DRX) plays a crucial role in refining grain size of Mg wrought alloys. Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized, including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy, are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing. [ABSTRACT FROM AUTHOR]

Magnesium alloys have received considerable research interest due to their lightweight, high specific strength and excellent castability. However, their plastic deformation is more complicated compared to cubic materials, primarily because their low-symmetry hexagonal close-packed (hcp) crystal structure. Deformation twinning is a crucial plastic deformation mechanism in magnesium, and twins can affect the evolution of microstructure by interacting with other lattice defects, thereby affecting the mechanical properties. This paper provides a review of the interactions between deformation twins and lattice defects, such as solute atoms, dislocations and twins, in magnesium and its alloys. This review starts with interactions between twin boundaries and substitutional solutes like yttrium, zinc, silver, as well as interstitial solutes like hydrogen and oxygen. This is followed by twin-dislocation interactions, which mainly involve those between { 10 1 ¯ 2 } tension or { 10 1 ¯ 1 } compression twins and 〈 a 〉, 〈 c 〉 or 〈 c + a 〉 type dislocations. The following section examines twin-twin interactions, which occur either among the six variants of the same { 10 1 ¯ 2 } or { 10 1 ¯ 1 } twin, or between different types of twins. The resulting structures, including twin-twin junctions or boundaries, tension-tension double twin, and compression-tension double twin, are discussed in detail. Lastly, this review highlights the remaining research issues concerning the interactions between twins and lattice defects in magnesium, and provides suggestions for future work in this area. [ABSTRACT FROM AUTHOR]

This study investigates the variations in the microstructural characteristics of a pre-twinned Mg alloy with the temperature of the subsequent annealing treatment. To this end, a rolled AZ31 alloy is compressed to 3% plastic strain along the rolling direction (RD) to activate {10-12} twinning and is subsequently annealed at 200, 250, 300, 350, and 400 °C. Numerous {10-12} twins are formed throughout the compressed material, leading to the formation of a RD-oriented texture. At an annealing temperature of 200 °C, no microstructural variations occur during annealing. As the annealing temperature increases from 250 to 400 °C, the residual strain energy and remaining twin boundaries of the annealed material decrease owing to the promoted static recovery and the increased area fraction of twin-free grown grains. Consequently, an increase in the annealing temperature results in a gradual microstructural transition from a fully twinned grain structure to a completely twin-free grain structure. The microstructural evolution during annealing is predominantly governed by the movement of high-angle grain boundaries via a strain-induced boundary migration mechanism, and a few twin boundaries migrate above 350 °C because of their lower boundary energy. The boundary migration behavior and resultant microstructural evolution are discussed in detail based on the variations in boundary mobility and driving force for boundary migration with annealing temperature. [ABSTRACT FROM AUTHOR]

An unusual F 3 basal stacking fault resulting from twin-dislocation interaction in magnesium is observed in molecular dynamics simulation. The F 3 fault is produced in the twin lattice from the interaction between a migrating (10 1 ¯ 2) twin boundary and a partial dislocation of either a prismatic 〈 c 〉 edge, or a prismatic 〈 c+a 〉 mixed dislocation in the matrix. The condition is that the partial dislocation needs to have a negative sign and lie on a plane intersecting a compression site of the twin boundary. The F 3 fault can also be generated when a positive basal 〈 a 〉 mixed dislocation in the twin lattice, with slip plane intersecting a compression site of the twin boundary, interacts with a basal-prismatic twinning disconnection. The F 3 fault comprises two I 1 faults that have the same character but are separated by two basal layers. It has one end connected to the twin boundary, and the other end bounded by a lattice defect with a Burgers vector identical to that of a 30° Shockley partial dislocation. The formation frequency of the F 3 fault is higher at a lower shear stress (below ∼400 MPa) and/or a lower temperature (100 K and 200 K). The F 3 fault can decompose into a glissile 30° Shockley and a T 2 fault at a temperature above ∼400 K. The relationships between the F 3 fault and other types of basal stacking faults such as I 2 , T 2 or paired I 1 faults that are separated by multiple basal layers are discussed. [ABSTRACT FROM AUTHOR]

Owing to the poor self-diffusion coefficient of TiC, the mechanical and tribological properties of the TiC matrix composites were difficult to improve simultaneously by adding reinforcements. In this paper, the degradation of Ti 3 SiC 2 was exploited as an advantage in obtaining the high-performance TiC matrix composites. The TiC matrix composites reinforced by SiC and Ti 3 SiC 2 were in-situ fabricated by spark plasma sintering at 1400–1600 °C for 10 min. SiC and Ti 3 SiC 2 were homogeneously distributed in the TiC matrix with well interfacial bonding with TiC matrix. The twin boundaries and stacking faults appeared in TiC particles. With the sintering temperature of 1500 °C, the TiC matrix composites exhibited excellent mechanical and tribological properties, which the bulk density, relative density, hardness, fracture toughness, and flexural strength reached the values of 4.76 g/cm3, 99.36%, 15.38 GPa, 5.38 MPa m1/2, and 562.3 MPa. The friction coefficient and wear rate of the TiC matrix composites sintered at 1500 °C reached the values of 0.48 and 3.04 × 10-9 mm3N-1m-1 at room temperature, and 0.55 and 6.63 × 10-9 mm3N-1m-1 at 500 °C, respectively. The wear mechanism of the TiC matrix composites was mainly ascribed to adhesive wear both at room temperature and 500 °C. A Fe–Si-oxide-Ti 3 SiC 2 lubricating film was formed on the friction surface of the TiC matrix composites after a friction test at room temperature, while a Ti–Si–Fe-oxide lubricating film was formed after a friction test at 500 °C. [ABSTRACT FROM AUTHOR]

Significantly enhanced thermoelectric performance of Nb-doped TiO 2 ceramics has been achieved through in-situ formation of β-Sn grain boundary inclusions. The ceramics were prepared by mixed oxide route and sintered at 1473 K (lower than usual for TiO 2) and strongly reducing conditions. All sample microstructures contain a high density of β-Sn structured inclusions at grain boundaries which assist densification. A variety of crystalline defects occur inside the rutile grains; the β-Sn inclusions contain nano-regions with severe lattice distortion. Through the formation of a highly conductive β-Sn phase, the carrier concentration and electrical conductivity were significantly enhanced, resulting in a ∼27% increase in power factor and much-improved ZT values of 0.20 at 873 K. Our approach based on grain boundary engineering provides a simple and eco-friendly route to enhance the thermoelectric performance of low-cost, oxide-based ceramics. [ABSTRACT FROM AUTHOR]

In this work, an as-rolled AZ31 square bar with c-axis//ND (normal direction) texture was used. Side-rolling and reciprocating torsion were performed to treat the bar. Microstructure evolution and tensile-compressive properties were investigated in detail. Initial rolled AZ31 bar exhibits a large yield asymmetry along the rolling direction (RD). Reciprocating torsion can generate extension twins to introduce twin boundaries and twin-texture. The twin structure can reduce yield asymmetry. However, only limited regions in the rolled AZ31 bar can be twinned during torsion. Pre-side-rolling along the transverse direction (TD) can generate two texture components (c-axis//TD texture and c-axis//ND texture) by introducing profuse {10–12} twins. Such dual texture components help increase the regions which are favorable for twinning during torsion. Finally, combining side-rolling and reciprocating torsion generates hybrid {10–12} twins structure on the entire cross-section, resulting in a remarkably low yield asymmetry. The relevant mechanisms were discussed in detail. [ABSTRACT FROM AUTHOR]

A bulk nanocrystalline AZ31B Mg alloy with extraordinarily high strength was prepared via cryogenic rotary swaging in this study. The obtained alloy shows finer grains, higher strength, and a negligible tension-compression yield asymmetry, compared with that prepared via room-temperature rotary swaging. Transmission electron microscopy investigations showed that at the initial stage, multiple twins, mostly tension twins, were activated and intersected with each other, thereby refining the coarse grains into a fine lamellar structure. Then, two types of nanoscale subgrains were generated with increasing swaging strain. The first type of nanoscale subgrain contained twin boundaries and low-angle grain boundaries. This type of subgrain appeared at the twin-twin intersections and was mainly driven by high local stress. The second type of nanoscale subgrain was formed within the twin lamellae. The boundaries of this type of subgrain did not contain twin boundaries and were transformed from massive dislocation arrays. Finally, randomly oriented nanograins were obtained via dynamic recrystallization, under the combined function of deformation heat and increased stored energy. Compared with room-temperature rotary swaging, cryogenic rotary swaging exhibits a slower grain refinement process but a remarkably enhanced grain refinement effect after the same five-pass swaging. [ABSTRACT FROM AUTHOR]

We studied the microstructure evolution of Mg-4Y-3Nd-2Sm-0.5Zr alloy by quasi-in-situ electron backscatter diffraction (EBSD) along with several strains under compression tests, which provided direct evidence for the influence of different twin-twin geometric structure on the twinning behavior. The results showed that the mechanical properties of the alloy were higher than traditional magnesium alloys (the maximum compressive strength reaches 402.5 MPa) due to the strengthening effect of Sm and Nd elements addition on solution strengthening, precipitation strengthening, and grain refinement. Combined with the quasi-in-situ EBSD technique, two different twin-twin geometric structures, 'parallel structure' and 'cross structure', were observed directly in the alloy. In the later stage of deformation, for 'parallel structure', residual stress and a large number of dislocations mainly existed in the twin boundary and tip position. For the 'cross structure', there was a lot of dislocation density in the interior of twins after fusion. The twin growth rate of 'parallel structure' was much faster than that of 'cross structure' because the stress of twins was mainly concentrated on the tip of twin. When the movement for the tip of twin was blocked, the growth rate of twin would be obviously decreased. Moreover, the 'cross structure' was easy to produce closed space. Due to the constraints of surrounding twins, the confined space was easy to stress concentration, thus inhibiting the growth of twins. At the same time, the 'cross structure' of twins needed a more external force to continue to deform, which also served as a strengthening structure. [ABSTRACT FROM AUTHOR]

{ 10 1 ¯ 2 } twins were introduced into the magnesium (Mg) plate AZ31 via pre-rolling along its transverse direction. The plates, both with and without the pre-induced { 10 1 ¯ 2 } twins, were subjected to uniaxial tension along different directions. Using crystal plasticity modeling, we found that the strengthening effect of the pre-induced { 10 1 ¯ 2 } twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries, rather than the orientation hardening due to the twinning reorientation (although the latter did make its contribution in some specific loading directions). Besides, the pre-existing { 10 1 ¯ 2 } twins were found, by both experiments and simulation, to promote the activity of prismatic 〈a〉 and pyramidal in the parent matrix of the material. Further analysis showed that the enhanced non-basal slip activity is related to the { 10 1 ¯ 2 } twin boundaries' low micro Hall-Petch slope ratios of non-basal slips to basal slip. With the critical resolved shear stress (CRSS) obtained from crystal plasticity modeling and the orientation data from EBSD, a probability-based slip transfer model was proposed. The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at { 10 1 ¯ 2 } twin boundaries than that at grain boundaries, which agrees with the experimental observation that the strain localization was primarily associated with the latter. The present findings are helpful scientifically, in deepening our understanding of how the pre-induced { 10 1 ¯ 2 } twins affect the strength and slip activity of Mg alloys, and technologically, in guiding the design of the pre-strain protocol of Mg alloys. [ABSTRACT FROM AUTHOR]

The interactions between a plate-like precipitate and two twin boundaries (TBs) ({ 10 1 ¯ 2 } , { 11 2 ¯ 1 }) in magnesium alloys are studied using molecular dynamics (MD) simulations. The precipitate is not sheared by { 10 1 ¯ 2 } TB, but sheared by { 11 2 ¯ 1 } TB. Shearing on the (110) plane is the predominant deformation mode in the sheared precipitate. Then, the blocking effects of precipitates with different sizes are studied for { 11 2 ¯ 1 } twinning. All the precipitates show a blocking effect on { 11 2 ¯ 1 } twinning although they are sheared, while the blocking effects of precipitates with different sizes are different. The blocking effect increases significantly with the increasing precipitate length (in-plane size along TB) and thickness, whereas changes weakly as the precipitate width changes. Based on the revealed interaction mechanisms, a critical twin shear is calculated theoretically by the Eshelby solutions to determine which TB is able to shear the precipitate. In addition, an analytical hardening model of sheared precipitates is proposed by analyzing the force equilibrium during TB-precipitate interactions. This model indicates that the blocking effect depends solely on the area fraction of the precipitate cross-section, and shows good agreement with the current MD simulations. Finally, the blocking effects of plate-like precipitates on the { 10 1 ¯ 2 } twinning (non-sheared precipitate), { 11 2 ¯ 1 } twinning (sheared precipitate) and basal dislocations (non-sheared precipitate) are compared together. Results show that the blocking effect on { 11 2 ¯ 1 } twinning is stronger than that on { 10 1 ¯ 2 } twinning, while the effect on basal dislocations is weakest. The precipitate-TB interaction mechanisms and precipitation hardening models revealed in this work are of great significance for improving the mechanical property of magnesium alloys by designing microstructure. [ABSTRACT FROM AUTHOR]

In this study, the role of twin-twin interactions on the distributions of local defects (e.g., dislocations) and stress fields in a magnesium alloy is investigated. A co-zone (10 1 ¯ 2) - (1 ¯ 012) tensile twin junction in a deformed Mg-3wt.%Y alloy is analyzed using transmission electron microscopy (TEM). The results show that the morphology of the impinging (1 ¯ 012) twin is asymmetric, and the non-interacting boundary of the recipient (10 1 ¯ 2) twin is irregular. Detailed analysis of TEM images reveals that type-II pyramidal [ 1 ¯ 2 1 ¯ 3 ] (1 2 ¯ 12) dislocations concentrate in the vicinity of the twin-twin junction site. The same 〈c + a〉 dislocations are also observed inside the interacting twin domains along with a few 〈a〉 dislocations. The 〈c + a〉 dislocations emanating from the impinging (1 ¯ 012) twin boundary have edge character and are extended with faults parallel to the basal plane. In contrast, the 〈c + a〉 dislocations connected to the recipient (10 1 ¯ 2) twin are predominantly screw orientation and compact. Elasto-viscoplastic fast Fourier transform based crystal plasticity calculations are performed to rationalize the observed twin morphology and local dislocation distribution. The model calculations suggest that the local stress fields generated at the junction site where the two twins meet are responsible for the experimentally observed concentration of 〈c + a〉 dislocations. The calculated stress fields are asymmetric with respect to the junction site, explaining the observed asymmetric morphology of the impinging twin. Overall, these findings show strong effects of twin-twin interactions on the distribution of dislocations as well as the evolution of the twinned microstructure and as such, can help advance understanding of twinning in Mg alloys and their effect on mechanical behavior. [ABSTRACT FROM AUTHOR]

Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4% (±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at -2% strain gradually increased from 26.3% to 43.5%; the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number; and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of -component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy. [ABSTRACT FROM AUTHOR]

• CPFE simulations identify twin boundaries as key sites for fatigue crack initiation in IN718. • Δ ε eps (increment of equivalent plastic strain) is proposed as an effective parameter for predicting fatigue life. • A material-level CPFE model effectively predicts the fatigue life of notched IN718 specimens. The aim of this study was to establish a method for evaluating notch fatigue behavior through crystal plasticity finite element (CPFE) simulations based on the actual microstructure of the nickel-based alloy Inconel 718 (IN718). Initially, the equivalent plastic strain, ε eps , which reflects the comprehensive slip at the grain scale, was employed to analyze the fatigue crack initiation mechanism of IN718, revealing that twinning and triple junctions of grain boundaries were high-risk locations for fatigue crack initiation. Next, fatigue simulations were performed on notched specimens using the CPFE model, with a material-level CPFE model particularly employed at the notch root. The increment of ε eps , Δ ε eps , in a stable cycle was used as the fatigue damage control parameter and correlated with the fatigue life, N f , revealing that the Δ ε eps - N f relationship at material-level satisfied the form of the Mason-Coffin model. Finally, fatigue life prediction of IN718 notched specimens was carried out based on the Δ ε eps - N f relationship, with the predicted results falling within the 2-fold scatter band, demonstrating good prediction accuracy. [ABSTRACT FROM AUTHOR]

AZ31 magnesium alloy bar with radial gradient microstructure was prepared by three-roll skew rolling process (TRS), and achieving an excellent combination of ductility and strength. To elucidate the formation mechanism of this gradient microstructure, the deformation behavior during rolling was analyzed through experiments and simulations. The simulation results indicated that the metal flow of the bar in a spatial helical trajectory during rolling, with the trajectory inclination angle gradually decreasing from the center to the surface, promoting dynamic recrystallization in the surface and near-surface regions. The radial equivalent strain decreased from 1.5 at the surface to 0.01 at the center, and the shear strain decreased from 0.051 at the surface to 0.00012 at the center. Experimental results showed that the grain size of the bars decreased from 49.77 µm at the center to 19.72 µm at the surface, and the tensile twin volume fraction decreased from 34.1 % to 19.4 %. Dynamic recrystallization predominantly occurred in the outer ring region of the bars, while significant {10−12} tensile twin activation was observed in the central region, with twin-induced dynamic recrystallization observed at the twin boundaries. Mechanical property tests demonstrated that the gradient structure endowed the bars with a favorable combination of strength and elongation, with hardness significantly increasing from 50 HV at the center to 90 HV at the surface. This indicates that the three-roll skew rolling technology effectively promotes dynamic recrystallization at the surface, and the resulting gradient microstructure achieves an excellent combination of strength and plasticity in magnesium alloy bars. • A new method for preparing AZ31 magnesium alloy bars with radial gradient structure were provided. • Gradient structure formulation were revealed in terms of simulation, microstructure evolution and mechanical properties. • Microcosmic orientation changes during rolling were analyzed from the prospects of metal flow and stress-strain evolution. [ABSTRACT FROM AUTHOR]

The industrial application of high Mn twinning-induced plasticity (TWIP) steels is limited by their low yield strength (YS). In this work, a combination of grain refinement and partial recrystallization was applied to increase the YS of a high Mn TWIP steel to 1215 MPa, along with a total elongation (TE) of 16 %. The high YS of the partially recrystallized steel mainly originates from the combination effect of high dislocation density up to 8.3 × 1014 m−2, fine grain size of about 1 μm in recrystallized regions, and dense mechanical twins with a small spacing of about 20 nm in unrecrystallized regions. This work provides a potential way to improve the YS-ductility synergy and broaden the application of TWIP steels. • Combined grain refinement and partial recrystallization to increase yield strength. • Applied neutron diffraction to measure dislocation density of austenite. • Produced a TWIP steel with a high yield strength of 1215 MPa and an elongation of 16 %. • Grain and twin boundary contribute about 560 MPa to the yield strength. • Dislocation strengthening contributes about 450 MPa to the yield strength. [ABSTRACT FROM AUTHOR]

The development of high-entropy alloys (HEAs) has been historically constrained by trade-off between strength and ductility. In this study, the Al 0.25 FeCoNiV duplex HEA showed a yield strength of 625 ± 35.2 MPa and a fracture elongation of 48 ± 1.5 % after rolling and annealing. These values are 43 % and 60 % higher, respectively, than the as-cast specimens, demonstrating an excellent synergy between strength and ductility. Through in-situ electron backscatter diffraction (EBSD) tensile experiments and transmission electron microscopy characterization of the as-cast and annealed specimens, respectively, it is found that the superior mechanical properties of the annealed specimens are primarily attributable to the multilevel strengthening and strain-hardening coupling mechanism established by the synergistic action of phase boundaries (PBs), twin boundaries (TBs), and high-angle grain boundaries. This mechanism effectively suppresses strain localization and prevents premature fracture caused by local stress concentration at PBs. The strengthening mechanism of TBs on the mechanical properties of HEAs was investigated by examining the interaction mechanisms between annealed TBs and dislocations, as well as the coordinated plastic deformation mechanism of twins. This study provides novel insights into the development of innovative HEAs with enhanced properties and advances the understanding of the role of TBs in the strengthening mechanisms of materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The evolution of microstructure and texture during the thermomechanical processing of a Fe-Co-Ni-Cr-Al-Ti dual phase high entropy alloy consists of L1 2 (γ′) ordered precipitates in the disordered FCC (γ) matrix and its effect on the mechanical properties was investigated. The as-cast alloy was annealed at 1100 °C after 25 % and 50 % hot rolling reduction. The grain size becomes finer, and a considerable amount of annealing twin boundaries (Ʃ3 boundaries) developed in the hot rolling and annealed (HRA) samples. The α-fiber (ND||<110>) texture and twin-related texture components increase after HRA treatment. The mechanical response at room temperature is evaluated employing hardness and uniaxial tensile tests. A significant reduction in hardness, from 448 ± 6 HV to 381 ± 12 HV, is observed in the 50 % hot rolled annealed sample compared to the as-cast sample. Additionally, the yield strength reduced from 779 to 595 MPa with an increment in the ductility from 12.5 to 17.2 % in the as-cast and HR50A samples, respectively. Finally, it has been demonstrated that the increase in coherent twin boundaries and grain size excluding twin boundaries, led to the observed mechanical behavior. • A dual-phase Fe-Co-Ni-Cr-Al-Ti HEA was prepared using arc-melting techniques. • The hot rolled annealing (HRA) refines the grains to 86.7 ± 27 μm and 89.2 ± 28 μm for HR25A and HR50A, respectively. • HRA enables the annealing twins (Ʃ3 boundaries) formation with an increase in its fraction with rolling reduction. • After HRA treatment, randomization of crystallographic texture, with predominating alpha fiber texture, is observed. • An increase in uniform elongation and a significant reduction in hardness and yield strength are observed with HRA. [ABSTRACT FROM AUTHOR]

• Microstructure effects on nanoscratch behaviors of gold-platinum alloy are revealed. • Hardness and surface quality tend to improve in the [ 1 1 ¯ 0 ] (111) orientation. • Twinning boundary greatly strengthens the plasticity by promoting dislocation nucleation. • Grain boundary or twinning boundary migration contributes to the high removal rate. The microstructural effect on the mechanical behaviors of gold-platinum alloys during nanoscratch is revealed. By adjusting the microstructures (crystallographic orientation, interface type, grain size, twinning thickness), the hardness, plasticity, removal rate and surface roughness of the alloys are significantly improved. The nanoscratch is performed by molecular dynamics (MD). For the single-crystal (SC) alloys, the [ 1 1 ¯ 0 ] (111) -oriented SC alloy shows the high hardness, wear resistance and low roughness. The high dislocation density induces the strong work hardening while the horizontal twinning boundaries (HTBs) effectively improve the surface quality by hindering the elastic recovery. For the bi-crystal (BC) alloys, the BC alloy with TB exhibits the excellent plasticity and low roughness. TB can uniformly limit the dislocation slip and promote the dislocation nucleation to strengthen the plasticity and surface quality. For the polycrystal (PC) and nanotwinned-polycrystal (NTPC) alloys, the alloys with small grain size or small twinning thickness show the high removal rate and low roughness. The reduction in grain size or twinning thickness inhibits the dislocation motion and promotes the GB or TB migration to improve the surface quality and atomic removal. These results provide an important theoretical basis for the microstructural design and nanofabrication of gold-platinum alloys with smooth surface and remarkable mechanical property, expanding the application for the bimetallic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• The first-ever identification of twin structures within TiC in SiC f /Ti 2 AlNb composite interfaces. • The interfacial reaction products of the composites are TiC and α 2. • Interfacial elemental interdiffusion leading to the presence of Al atoms in the TiC layer. • Al atoms reduced the SFE of TiC, which is beneficial for the formation and stability of Σ3{1 1 1} twin boundaries. SiC f /Ti 2 AlNb composites were fabricated using the magnetron sputtering precursor wires method in conjunction with the hot isostatic pressing (HIP) technique. The morphology, elemental distribution, and structural characteristics of the interfacial reaction layer (RL) were examined through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and wavelength dispersive spectroscopy (WDS). The results showed that the interface between SiC fibers and Ti 2 AlNb reacted to form TiC and α 2. Due to the interdiffusion of elements at the interface, a small amount of Al atoms existed in the TiC layer. These Al atoms reduced the stacking fault energy (SFE) of TiC, which is beneficial for the formation and stability of Σ3{1 1 1} twin boundaries. [ABSTRACT FROM AUTHOR]

Recent studies have revealed unprecedented fracture toughness in synthesized nanotwinned diamond (nt-diamond) due to the obstruction of dislocations by twin boundary. However, the atomic-scale interactions between dislocations and twin boundary in diamond remain elusive and unclear. In this work, we take advantage of the recently published interatomic potential for diamond's dislocation activity to study the interactions between (001) dislocation and (111) twin boundary in molecular dynamics (MD) simulations. The twin boundaries show obvious hindrance for (001) dislocation. In the penetrations, the shuffle-set dislocation will climb to the upper gliding plane and leave a vacancy tube behind. With the gradual increase of applied shear stress, the vacancy left on the twin boundary could launch another shuffle-set dislocation in the opposite direction in matrix. The mechanism revealed in this work show obvious difference between the interaction between twinning and dislocation in metals. This study will provide a fundamental understanding of the dislocation behaviors and their strengthening and toughing mechanisms in nt-diamond materials and the related materials. Atomic configuration of nanotwinned diamond with edge dislocations on {001} plane was established in this work to explore the interaction mechanisms between dislocations and twin boundarys. All molecular dynamics simulations are driven under high hydrostatic pressure witch can effectively suppress microcrack propagation in diamond and activate dislocation slip. The contact of dislocation gliding on (001) plane with TB1 could be divided into two stages, distortion and contraction. In the followed penetration process, the emitted partial dislocation continues to glide in the twin region and eventually makes contact with the TB2, leaving a long stacking fault behind witch is transient and has interesting healing mechanisms. During the interaction, the edge dislocation will climb to the adjacent shuffle plane on (001) plane, leaving a vacancy behind witch can lead to the nucleation of additional dislocations. [Display omitted] • The novel interaction mechanisms between (001) dislocation and (111) twin boundary in diamond. • The climbing mechanism for (001) dislocation and related dislocation emissionfrom vacancies on twin boundary in diamond. • The novel strengthening mechanism of (111) coherent twin boundary in diamond. [ABSTRACT FROM AUTHOR]

Twin boundary (TB) migration, facilitated by the motion of disconnections, plays a pivotal role in the deformation of body-centered cubic (BCC) crystals. Comprehending the migration rules of twinning disconnections (TDs) under shear stress is significant in elucidating the role of twin migration in BCC plasticity. Nevertheless, our understanding of the atomic structure and migration mechanics of TDs remains incomplete. In this study, we employ the theory of interfacial defects and molecular dynamics (MD) simulations to thoroughly investigate potential { 112 } [ 111 ] TDs in BCC tantalum (Ta). These TDs are characterized by their Burgers vectors, which were predicted through related dichromatic pattern analysis. We reveal that single-layer and double-layer TDs represent the fundamental building blocks (units) of multi-layer TDs. Their migration directions are entirely opposite under the same shear loading, and they cannot annihilate each other when they migrate "face to face". Furthermore, these migration rules governing single-layer and double-layer TDs offer a comprehensive explanation for the complex composition and decomposition patterns observed among various multi-layer TDs. What's more, we demonstrated that TDs with zero Burgers vector can only be driven as a whole under coupled loading conditions. These findings significantly enhance our understanding of TB migrations in BCC metals. [Display omitted] [ABSTRACT FROM AUTHOR]

This study presents a detailed investigation into the deformation behaviour and the factors affecting the strength and ductility of laser powder bed fusion (LPBF) Ni-based superalloy 718 (Inconel 718) in both as-printed and heat-treated conditions using in-situ SEM + EBSD. The results show that following post-deposition high homogenization temperatures, the columnar grain structure of the as-printed Inconel 718 alloy successfully transformed to a nearly uniform grain size and the subsequent aging processes facilitated the precipitation of strengthening phases (γ′, γ''). The specimen subjected to heat treatment (HT1) exhibited higher strength but lower ductility, while the as-printed specimen shows higher tensile elongation due to high initial dislocation density. In contrast, the heat-treated (HT2) specimen presented a more optimal combination of strength and ductility. The underlying mechanism for the enhanced tensile properties in the HT2 specimen was nearly homogeneous deformation trend across the grains and ultrafine precipitation of hardening phases. In addition, the twin boundaries were stable in the early deformation stages and maintained their orientation. Multiple slip systems were activated at the high-deformation stage, resulting in a high proportion of geometric necessary dislocations. Further, the interaction of deformation-induced dislocation with twin boundaries transformed them into general boundaries such as high and low-angle grain boundaries, ultimately increasing ductility. On contrary, in the HT1 specimen, the deformation inhomogeneity in grains enabled the strain localization at grain boundaries, which ultimately caused the early formation of cracks. [ABSTRACT FROM AUTHOR]

We perform neutron diffraction on a bulk Ni 50.0 Mn 27.5 Ga 22.5 single crystal to investigate the evolution of its five-layered modulated (10M) martensite structure, from 300 K down to 10 K. Close to martensite transformation, the modulation is nearly commensurate, with q = 0.402 in a modulation vector (q, q , 0). Upon cooling, the shift in diffraction satellites indicates a transition to an incommensurate modulation with increasing q. However, the observed fifth-order diffraction satellites below 260 K and even more complex satellite landscape at 10 K cannot be explained by incommensurability alone. Our analysis reveals that the modulation function is highly anharmonic, encompassing Fourier components up to the eighth order. We have developed a single-parameter description of the evolution of modulation across the entire temperature interval of the 10M phase existence. Surprisingly, the structure evolution from commensurate to incommensurate modulation has no significant effect on twin boundary mobility. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of hydrogen on the creep rates of Zircaloy-4 claddings especially in the low hydrogen concentration remains largely unexplored while creep is considered a main mechanism for spent nuclear fuel failure along with hydride-induced mechanisms. Here, we study the influence of hydrogen on the creep behavior of low burnup Zircaloy-4 cladding from a microstructural perspective. The creep tests at 450 °C and 120 MPa reveal that specimens with hydrogen contents below the terminal solid solubility for dissolution (TSSD) at the test temperature exhibited decreased creep resistance as hydrogen concentration increased, while those with hydrogen contents above the TSSD demonstrated increased creep resistance with higher hydrogen concentration. The lowest creep resistance occurs at the hydrogen concentration corresponding to the TSSD. Additional microstructural analyses using electron backscattered diffraction (EBSD) show the increasing intra-granular/inter-granular hydride ratio in the post-crept specimens as the hydrogen concentration decreases, suggesting that hydrogen atoms in solid solution aid creep progression. Also, an increased amount of twin boundaries is observed in post-crept specimens with hydrogen concentration above TSSD. These results suggest that creep assessment in spent nuclear fuels may require caution especially in low-burnup regime. [ABSTRACT FROM AUTHOR]

The influence of graphene layers and crystal structure types on the nanoindentation reinforcement mechanism of Al 0.3 CoCrFeNi high-entropy alloy/graphene (HEA/Gp) composite materials was studied using molecular dynamics (MD) simulations. The results indicate that the influence of graphene layers on composite materials is related to the position of the indenter. Before the indenter contacts the graphene layer, some dislocations are absorbed by the graphene, unable to form dislocation cells and dislocation locks to hinder the deformation of the matrix, resulting in the hardness of the composite material being lower than that of the HEA matrix. After the indentation contacts the graphene layer, dislocations can penetrate the graphene to form a high-density dislocation cell. Due to graphene's excellent deformation resistance, the composite material's load-bearing capacity is much greater than that of the HEA matrix. In addition, stress propagates along the grain boundaries in polycrystalline and twinned polycrystalline structures. Grain boundaries decrease the material strength, while twinned boundaries can refine grain size and enhance grain stability. Additionally, composite materials' elastic recovery increases first and then decreases with the increase in graphene layers and twinning. The hardness of the material shows an anomalous phenomenon about grain size following a Hall-Petch relationship. When the angle between graphene layers is 0, the stress distribution inside the material is most uniform. • The change in hardness and mechanism of composite materials is studied before and after contact with the indenter and graphene. • Grain boundaries reduce the material strength, while twin boundaries can refine the grains and improve grain stability. • The influence of graphene layers, grain size, twin crystal number, and interlayer angles of graphene on composite materials is being studied. • After loading and unloading pressure, the change of the C-C bond was analyzed. [ABSTRACT FROM AUTHOR]

• Micro-diamond (MD) disrupts the symmetric equilibrium of the complete structure onion-like carbon (OLC). • MD has changed the initial path of the diffusionless phase transition from OLC to nano-polycrystalline diamond (nPCD). • MD and nPCD have formed interfaces of twin boundaries, cubic diamonds, stacking faults, and amorphous grain boundaries. The interfacial microstructure of micro-diamond and nano-polycrystalline diamond (nPCD), as well as their effect on the phase transition of complete structure onion-like carbon (OLC), were investigated using molecular dynamics simulations and experimental methods under high pressure and temperature (HPHT). Introducing micro-diamond disrupted the symmetric equilibrium structure of complete structure OLC, reduced the diamond nucleation process, and formed a coherent interface ((111) CD // (002) Gr), where cubic diamond (111) crystal plane was parallel to graphite (002) crystal plane. This transformed the initial diffusionless phase transition path of complete structure OLC into a low potential path for phase transition along the graphite crystal direction [002] by (111) CD // (002) Gr , thereby reducing the phase transition conditions. Additionally, due to different stacking orders or breakages in the graphite layers of the complete structure OLC, micro-diamond, and nPCD formed four interfacial microstructures containing twin boundaries (TB), cubic diamond, stacking fault (SF), and amorphous grain boundary (aB). Furthermore, under HPHT effects, numerous TBs and SFs were generated inside micro-diamonds as well as at their edges, resulting in a Vickers hardness of 167 GPa for polycrystalline diamond (PCD) composite. This simple yet effective method reduces synthesis conditions for OLC precursors while producing high-performance PCD composites with promising applications. [ABSTRACT FROM AUTHOR]

The work focuses on the numerical investigation of compressive mechanical behaviors and energy absorption properties of high entropy alloys (HEAs) with stochastic bicontinuous nanostructures (SBNs) and octet nanostructures (ONs). The study reveals a strong correlation between mechanical behaviors and the relative density of the nanostructures. The findings show that for both ONs and SBNs, the plateau stress increases with increasing the relative density, while an opposite trend is observed for densification strain. The maximum energy absorption capacity is achieved for ONs and SBNs at a relative density 0.6. Additionally, the energy absorption capacity of ONs is higher than that of SBNs across all relative densities, attributed to the higher plateau stress in ONs compared to SBNs. The distinction in mechanical characteristics is further explored by considering the dislocation evolution in ONs and SBNs. The study shows in SBNs that the dislocation increases rapidly, leading to a significant release of stored elastic energy and low plateau stress. Conversely, in ONs, the dislocation increases monotonically, allowing for a gradual release of stored elastic energy and maintenance of high plateau stress. Furthermore, the evolution of atomic configurations demonstrates that intrinsic and extrinsic stacking faults dominate planar defects in ONs, while several types of planar defects play a role in SBNs, including intrinsic stacking fault, extrinsic stacking fault, twin boundary, and hexagonal close-packed laths. The study also shows the effect of temperature on the energy absorption capacity. • Compressive mechanical behaviors of octet lattice and stochastic bicontinuous nanostructures are investigated. • Octet lattice nanostructures demonstrate higher plateau stresses compared to stochastic nanostructures. • The energy absorption capacity of octet nanostructures surpasses that of stochastic nanostructures across all relative densities. • Various planar defects during plastic deformation can be distinguished and quantitatively assessed. • Distinguishable characteristics of dislocation evolution and planar defect of octet nanostructures are clarified. [ABSTRACT FROM AUTHOR]

Preparation of pure titanium foil by cold rolling deformation often confronts the strength-ductility trade-off dilemma, how to obtain an excellent strength-ductility combination remains a great challenge. In the present work, we have prepared a pure titanium foil with a bimodal grain (BG) structure consisting of coarse grain (CG) and ultrafine grain (UFG), coupling with high-density deformation twins (DT) via a cryogenic-temperature rolling (CTR) and partial recrystallization annealing (PRA) process. Notably, a high strength-ductility synergy with YS of ∼483 MPa, UTS of ∼517 MPa and elongation of ∼21 % is achieved. The high strength is mainly caused by pronounced fine grain strengthening from the UFG region and twin boundary strengthening from strong interactions between DT and dislocations activated in the CG region. The GND caused by the hetero-deformation between CG and UFG, along with the activation of pyramidal dislocation via DT in the CG region endows the pure titanium foil with excellent ductility. [ABSTRACT FROM AUTHOR]

In this research work, a face centered cubic (FCC) structured single-phase Ni-rich (Ni 46 Al 12 Co 18 Cr 8 Fe 12 Mo 4 , at. %) high entropy alloy (HEA) was synthesized directly from blended elemental powder by spark plasma sintering, while varying the sintering parameters. The parameters were optimized with the objective to achieve a single-phase solid solution by dissolving the undesirable sigma (σ) and mu (μ) phases, and further to assist the precipitation of essential L1 2 phase in the FCC matrix. The HEA exhibits excellent strength-ductility trade-off, where the compressive yield strength and ultimate compressive strength reached up to 733 MPa and 1578 MPa, respectively, with an appreciable strain to failure of 36 %. The promising mechanical properties are mainly attributed to the formation of FCC single-phase solid solution that in turn provides the inherent solid solution strengthening along with thinner twin boundary and grain boundary effects, and precipitation strengthening from L1 2 phase. Fracture surface investigation revealed presence of highly concentrated dimples of different sizes, formation of multiple slip bands and lattice distortion predominately near the grain boundaries due to dislocation accumulation, all of which demonstrate the superior plasticity of the investigated HEA. The novel approach of synthesizing single-phase HEA with commendable strength-ductility synergy from blended elemental powder is anticipated to open a new paradigm for the development of high-performance HEAs and to expand their scope to engineering applications. • Bulk Ni-rich HEA was synthesized directly from blended elemental powders without mechanical alloying using SPS. • Microstructure consists of FCC structured single phase solid solution with scare dispersion of σ and μ phases. • The HEA sintered at 1200 °C exhibited excellent strength-ductility trade-off. • Formation of multiple slip bands within the grain upon deformation demonstrates superior plasticity. • Presence of annealing twins act as barrier for crack propagation and void nucleation. [ABSTRACT FROM AUTHOR]

Advancements in the manufacturing of aeroengine components with superior mechanical properties rely on the microstructure homogeneity of industrially forged Ni-based superalloys. Billets often contain microstructural heterogeneities that can persist throughout the process, potentially compromising the integrity of the final product. Rene 65 is a relatively new superalloy with high-temperature mechanical properties superior to those of Alloy 718. However, systematic studies on its microstructure-property relationships are scarce. Here, we correlate the microstructural evolution with the hardness of a Rene 65 billet subjected to industrial processing and standard heat treatments. Multiscale microstructural heterogeneities, including grain size, geometrically necessary dislocations, twin boundary density, and the multimodal distribution of γʹ precipitates, are characterised. Grain growth occurs near the billet centre. Precipitation varies with radial position, showing up to a two-fold change in primary and secondary γʹ fractions. Tertiary γʹ precipitates exhibit variations in morphology and chemical composition, with Cr and Co enrichment near the billet surface. These heterogeneities arise from varying strain distributions and cooling rates during radial forging. Sub-solvus annealing and ageing are shown to mitigate these heterogeneities by promoting recrystallisation, recovery, and homogeneous precipitation of tertiary γʹ. A strengthening model elucidates the active mechanisms in as-received and heat-tread conditions, predicting hardness with a deviation of <8 %. Analyses of grain boundaries and γ/γʹ interfaces reveal strong segregation of Mo, W, Nb, C and B before and after heat treatment, with Mo and B showing the highest interfacial excess values. Insights into the microstructural evolution and its impact on properties could guide the development of next-generation aerospace parts. [Display omitted] [ABSTRACT FROM AUTHOR]

Titanium alloys produced by additive manufacturing show excellent mechanical properties at room temperature. However, their deformation behavior at low temperature is still not fully understood. In this study, the microstructural evolution and tensile behavior of the near-α titanium alloy Ti-6.5Al-2Zr-Mo-V (TA15), fabricated via laser powder bed fusion (LPBF), were determined at both 25 °C and −196 °C. The LPBFed TA15 alloy shows the microstructure of α laths and acicular α′ martensite due to the rapid cooling rate during LPBF processing. Pyramidal slip and numerous twins, including nano-twins and triple twins, were activated at cryogenic temperature, leading to the high ultimate tensile strength (UTS) up to 1750±8 MPa and yield strength (YS) up to 1548±25 MPa, which is higher than the strength at room temperature (YS∼1103 MPa, UTS∼1281 MPa). The dominant deformation mechanism changes from dislocation slip to twinning with decreasing temperature, leading to uniform deformation with an elongation of 5.2±0.1 %. The results can guide the control of the microstructure of LPBFed near-α titanium alloys at cryogenic temperature. • The LPBFed TA15 showed excellent tensile strength (YS∼1548 MPa, UTS∼ 1750 MPa, elongation∼5.2±0.1 %) at −196 °C. • A large number of 10 1 ̅ 1 < 10 1 ̅ 2 > nano-twins, including the nanotwins and triple twins, were activated at cryogenic temperature. • The dominant strengthening mechanism varies from dislocation strengthening to twin boundary strengthening. [ABSTRACT FROM AUTHOR]