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Existing additively manufactured aluminum alloys exhibit unfavorable tensile strength above 200 °C due to the strengthening phase coarsening, microstructure instability and cracking. This paper designed a novel Al-5Fe-1Mg-0.6Sc-0.3Zr alloy for powder bed fusion using laser beam (PBF-LB) with tensile strength of 189 MPa at 400 °C, which is the highest value reported. The main strengthening phases of the alloy were Al 6 Fe particle and nano-scaled L1 2 -Al 3 (Sc, Zr) precipitates. The exceptional high-temperature performance is attributed to high volume fraction (∼35%) of nanoprecipitates Al 6 Fe modified by Sc and Zr elements, showing enhanced thermal stability and refined particle dimension. The addition of Sc and Zr elements also significantly retards the phase transformation from Al 6 Fe to θ-Al 13 Fe 4 and inhibits brittle θ phase growth during thermal exposure. IMPACT STATEMENT: The paper designed a heat-resistant Al-Fe-Mg-Sc-Zr alloy with exceptional high-temperature performance (UST of 189 MPa at 400 °C) for PBF-LB. Adding Sc/Zr element can effectively enhance the thermal stability of Al 6 Fe and delays its transition to Al 13 Fe 4 phase. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper describes insights from an experimental investigation into tailoring microstructure of an Al–Y eutectic alloy to improve its trade-off between strength and electrical conductivity via casting, cold rolling, and annealing. Mechanical testing, ex-situ microscopy, and in-situ synchrotron X-ray diffraction were employed to characterize microstructural evolution as well as strengthening and conduction mechanisms. The as-rolled alloy exhibited substantially improved strength and electrical conductivity compared to the as-cast alloy. The rolling deformation induced a lamellar structure in the alloy consisting of coarse primary α-Al grains organized into fibers floating within ultrafine eutectic matrix of α-Al grains and β-Al 3 Y particles. Subsequent annealing at 280 °C for 1-h caused partial recrystallization of the primary α-Al phase, while annealing at 400 °C for 1 h cause both α-Al and β-Al 3 Y phases to undergo recrystallization with coarsening of α-Al but reduction in size of β-Al 3 Y. Interestingly, stacking faults were observed to be thermally stable during the annealing processing contributing to the heat resistance of the alloy. Relative to the cold-rolled state, the alloy after annealing at 280 °C for 1 h retained a tensile strength of 90 % with improved ductility and electrical conductivity. Furthermore, the alloy after annealing at 400 °C for 1 h lost some strength but electrical conductivity further increased. The effects of cold rolling on the lamellar-structure creation and subsequent annealing on the microstructural changes and resulting strength and electrical conductivity of the alloy are discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper investigated the microstructure and mechanical properties of AISI 430 ferritic stainless steel (FSS) after annealing in either the single-phase or two-phase region, followed by different cooling manners: water cooling, air cooling and furnace cooling. After annealing at 840 °C in the single-phase region, the sample consisted primarily of ferrite, with M 23 C 6 and M 2 (C, N) precipitates aligned mainly along the rolling direction (RD). For the water-cooled and air-cooled samples annealed at 950 °C in the double-phase region, they formed a dual-phase structure comprising ferrite and martensite, with precipitations primarily located within the martensite lath. Conversely, the sample subjected to annealing at 950 °C followed by furnace cooling displayed a single ferrite structure, owing to the decomposition of austenite. In this case, the precipitations were mainly found along the grain boundaries, with some also forming within the ferrite grain. The paper delved into the analysis of mechanical properties and strengthening mechanism through tensile experiments and fracture morphology examination. The influence of heating range and cooling manner on the yield characteristics of FSS was discussed. The results indicated that the air-cooled and furnace-cooled samples annealed at 840 °C displayed a clear yield platform in their tensile curves. Conversely, the samples treated with other heat treatments exhibited continuous yielding or no obvious yield platform. This difference may be attributed to the influence of heating temperature range and cooling manner on the distribution of dislocations and interstitial atoms within the ferrite grains. [ABSTRACT FROM AUTHOR]

A significant challenge in improving metal-based wire-arc directed energy deposition (WDED) for additive manufacturing is the lack of knowledge about microstructure evolution and its correlation with layer-wise plastic response and bulk tensile behavior. For the first time, this paper establishes the role of crystalline orientation, dislocation densities, and layer-by-layer strength on the anisotropy of bulk uniaxial tensile deformation in commercially pure titanium (cp-Ti) processed by WDED. An integrated approach that combines microscopy, spectroscopy, millimeter-scale indentation and centimeter-scale uniaxial tensile techniques is adopted. The variation in thermal cycles during WDED results in a higher grain orientation spread greater than 5° in the longitudinal direction (LD) parallel to arc motion compared to about 4° along the normal direction (ND) of additive buildup. Similarly, the statistically stored dislocation density in LD, 1.8 x 1016 m−2, is double that in ND, 0.9 x 1016 m−2. These factors result in a greater strain localization in the LD than in ND. The higher strain localization results in plastic anisotropy manifested as material buildup and ductility, which are 40 μm and 33 % higher in ND than in LD. On the other hand, the monolithic macrostructure and absence of weak points at layer interfaces of the cp-Ti component led to comparable yield and ultimate tensile strengths across the individual layers and the bulk component at 311–328 MPa and 369–385 MPa, respectively. These properties are about 90 % of those in conventionally cast commercially cast titanium. Thus, the comprehensive understanding of titanium's nuanced isotropic strength and anisotropic ductility constitutes a major step in advancing WDED as a large-scale additive manufacturing technology and establishing a standardized database of mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, Ti–43Al–6Nb–1Mo–1Cr, Ti–43Al–6Nb–1Mo–1Cr-0.5C and Ti–43Al–6Nb–1Mo–1Cr-0.5C-0.05Y 2 O 3 alloys were prepared by induction skull melting under argon atmosphere. Creep tests were carried out on three alloys to reveal the effects of C and Y 2 O 3 on the creep properties of alloys and to clarify the precipitation behavior of Ti 2 AlC and B2 phases. The results show that adding C and Y 2 O 3 can significantly reduce the steady-state creep rate and improve the creep properties of the alloy. After adding C and Y 2 O 3 , the parallel decomposition of α 2 lamellae occurs, and the fine γ lamellae precipitates from coarse α 2 lamellae. The lamellar degradation occurs obviously during creep, and the reaction is α 2 →γ+B2. The B2 phase preferentially grows into α 2 lamellae after nucleation at the lamellar interface. Furthermore, the precipitated B2 phase can induce the formation of stacking faults in α 2 lamellae. The strengthening mechanism of C is mainly solid solution strengthening and the precipitation hardening. The dynamically precipitated Ti 2 AlC during creep can hinder the movement of dislocations and improve the bonding strength of the lamellar interface. Y 2 O 3 mainly plays a role of second phase strengthening, which can share the stress of the matrix and prevent the crack propagation. Finally, the voids nucleation and crack propagation process of the alloy are analyzed and summarized. • The creep properties of the alloy are significantly improved after adding C and Y 2 O 3. • The degradation reaction and the parallel decomposition of α 2 lamellae were elaborated. • The effect of Ti 2 AlC on the creep behavior of the alloy was analyzed. • The nucleation and growth process of B2 phase were summarized. [ABSTRACT FROM AUTHOR]

In this paper, a comparative investigation was conducted on the tensile properties, microstructure evolution, and work hardening behavior of Fe18Mn0.6C and Fe18Mn1.0C TWIP steels at 298 K and 223 K by tensile tests and multi-scale microscopic characterization. With decreasing deformation temperature, two steels exhibit increased yield strength and ultimate tensile strength. However, the total elongation decreases for both, with Fe18Mn0.6C steel showing a more pronounced decrease. The work hardening behavior of two steels at 298 K and 223 K was analyzed. It is observed that the work hardening rate of both steels is higher at 223 K compared to 298 K, attributed to enhanced dislocation accumulation and the formation of deformation twins or martensite at lower temperatures. Particularly, Fe18Mn1.0C steel exhibits a continuous upward stage in work hardening at any temperature, driven by its higher dislocation density. On the other hand, Fe18Mn0.6C steel at 233 K shows a relatively stable trend in work hardening rate, attributed to the presence of martensite generated during deformation, which enhances its work hardening ability. Furthermore, the contribution of different strengthening mechanisms to the total flow stress was evaluated. The calculation results highlight dislocation strengthening as the primary source of flow stress in two steels at different temperatures. These findings provide theoretical support for understanding the mechanical properties of Fe–Mn–C TWIP steel at low temperature and optimizing the material design. [ABSTRACT FROM AUTHOR]

In the present paper, the effects of macrostructure and microstructure on fatigue crack growth (FCG) behavior of wire and arc additive manufacturing (WAAM) and hybrid additive manufacturing with in-situ rolling (HAMR) were investigated in three sampling directions for Ti6Al4V ELI. The results demonstrate that WAAMed samples exhibit coarse columnar grains with zigzag boundaries, interlayer heat affected band (HAB), and basketweave microstructures. The fatigue crack growth rate (FCGR) is lowest in the Y-X direction while being similar between the X–Y and X-Z directions, indicating significant anisotropy. This difference can be attributed to changes in plastic region size and internal slip characteristics near the crack tip caused by variations in macrostructure and microstructure. After applying HAMR with quasi-β heat treatment, interlayer HABs are eliminated, resulting in uniform equiaxed grains and colony microstructures. The FCGR curves in three directions significantly overlap without any observed anisotropy, which are lower than those obtained for traditionally forged materials. Therefore, the isotropic FCGR of plastic materials can be reduced by achieving a nearly flawless metallurgical quality and ensuring uniform equiaxed grain matching with the corresponding critical colony size and fine thickness lamellae. The findings suggest that the application of quasi-β heat treatment in conjunction with HAMR offers a promising high-efficiency manufacturing technique for producing isotropic titanium alloy forgings characterized by exceptional damage tolerance. [ABSTRACT FROM AUTHOR]

The aging Al–Zn–Mg–Cu alloy exhibits a significant decrease in performance after undergoing thermal shock. In order to improve the resistance of this type of alloy to thermal shocks, the influence of deep cryogenic treatment (DCT) on the high temperature mechanical properties and microstructure of thermal shocked Al–Zn–Mg–Cu alloy is investigated in this paper. It was found that the mechanical properties of Al–Zn–Mg–Cu alloys decrease significantly with the increase of electric heating temperature. The deep cryogenic treatment reduced the grain size of Al–Zn–Mg–Cu alloy, increased the density of the precipitates, and also inhibited the coarsening of the precipitates. Therefore, the deep cryogenic treatment can slow down the weakening effect of Al–Zn–Mg–Cu alloy at high temperatures. [ABSTRACT FROM AUTHOR]

In this paper, the effects of cyclic deep cryogenic treatment (CDCT) on the mechanical properties and the precipitated phases evolution of 7B55 aluminum alloy produced by wire arc directed energy deposition (WA-DED) were systematically investigated. The findings revealed that, under both T6 and CDCT conditions, the microstructure of the 7B55 aluminum alloy exhibited fine-equiaxed grains. Under the T6 condition, the precipitated phases within the grains were primarily composed of clustered GP zones and η ′ phases. Meanwhile, the η phases were continuously distributed along the grain boundaries. Upon subjecting the material to three cycles of CDCT, a noticeable reduction in the number of GP zones within the grains was observed. Simultaneously, there was a substantial increase in the number of η ′ phases, accompanied by the occurrence of dislocation lines. The distribution of η phases along the grain boundary transitioned to an interrupted pattern. Under the CDCT-Cycle 3 (CDCT-C3) condition, the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) achieved 658.6 ± 4.5 MPa, 624.2 ± 5.2 MPa, and 8.42 ± 0.18 %, respectively. However, with the progression to four cycles of CDCT, the GP zones within the grains disappeared and the number of η ′ phases started to decrease with the formation of a large number of η phases. The η phase along the grain boundary continuously grew by merging and absorbing solute atoms from the Al matrix near the grain boundaries. This led to the formation of coarsen and interrupted η phases and the Precipitate-Free Zone (PFZ) along the grain boundaries. Subsequently, the mechanical properties experienced a substantial decrease after the CDCT-Cycle 4 (CDCT-C4). • The effect of CDCT on the evolution of precipitated phases WA-DED Al–Zn–Mg–Cu alloy was investigated. • The number of η ′ phase and the dislocation density within grains were increased after CDCT-C3. • The η phases along grain boundaries were changed to interrupted distribution and PFZs were formed after CDCT-C4. • The UTS reached 658 MPa and a breakthrough was achieved among WA-DED aluminum alloys. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) is a transformative technology that facilitates the production of intricate geometries with high precision, customization, and speed. While conventional AM processes for metallic components have traditionally involved single materials, there is a growing demand for hybrid components made from two or more metals. This paper comprehensively reviews the state-of-the-art in multi-material AM for metallic parts using Laser Powder Bed Fusion (LPBF). It delves into an in-depth analysis of the interface characteristics and properties of bimetallic LPBF parts, offering valuable insights into the complex process-structure-property relations involved in joining similar and dissimilar metals. Research on similar hybrid metals has emphasized the significant potential of this method for efficiently producing robust joints across various classes of ferrous and non-ferrous metals. Moreover, the article addresses the inherent challenges in hybrid 3D printing of dissimilar metals, including substantial differences in physical and chemical properties, the formation of detrimental intermetallic compounds, and element segregation. In response to these obstacles, the study thoroughly explores various strategies proposed in the literature, such as adjusting process parameters, integrating an interlayer of a third material, and utilizing machine learning algorithms. Additionally, it outlines the applications and future directions in AM of hybrid LPBF structures, providing a complete roadmap for potential research in this rapidly evolving field. [Display omitted] • The existing literature on multi-material and hybrid metal AM via LPBF is critically reviewed. • The contrasting complexities in hybrid AM of similar and dissimilar metals are highlighted. • Microstructural, electrochemical, and mechanical attributes of hybrid AM parts are discussed. • Applications, limitations and future directions of hybrid metal AM are explored. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the second-stage rolling deformation of Cu–Ni–Si alloy on its stress relaxation resistance was studied, and the mechanism of the change in microstructure and properties before and after stress relaxation was explored. The results show that the tensile strength and yield strength of Two-stage rolling peak aging (TRPA) 43.7 %, TRPA68.8 %, TRPA80.3 % and TRPA96.1 % alloys at 150 °C are close. After stress relaxation, the stress relaxation rates of these alloys are 7.7 %, 11.24 %, 14.69 % and 19.4 %, respectively. It is found that the smaller the second-stage rolling deformation, the better the stress relaxation resistance of the alloy, especially the stress relaxation resistance of the TRPA43.7 % alloy, which is 60.31 % higher than that of the TRPA96.1 % alloy. According to EBSD analysis, it was found that the increase in the number of twins can improve the stress relaxation resistance of the alloy. However, the occurrence of recrystallization reduces the stress relaxation resistance. Additionally, it was determined that the precipitated phase is the δ-Ni 2 Si phase with an orthogonal structure. Before stress relaxation, the size of the precipitated phase of the alloy with TRPA96.1 % is larger than that of the alloy with TRPA43.7 %, and after stress relaxation, the precipitated phase further grows. The influence of the interface relationship between δ-Ni 2 Si phase and Cu matrix on the stress relaxation properties of TRPA43.7 % and TRPA96.1 % alloys before and after stress relaxation was investigated using the mismatch theory. In summary, this study reveals that the size of δ-Ni 2 Si phase, dislocation density and recrystallization are the key factors affecting the stress relaxation resistance of Cu–Ni–Si alloy. • In the two-stage rolling aging process, by applying a smaller deformation in the second-stage rolling and then undergoing a second-stage peak aging, the stress relaxation resistance of the alloy is improved by 60.31 % while ensuring that the hardness, strength, and electrical conductivity of the alloy undergo minimal changes. • The influence of the second-stage rolling deformation on the stress relaxation resistance of Cu–Ni–Si alloy was analyzed. Through the two-stage rolling aging process, δ-Ni 2 Si phases with sizes in the range of 5–10 nm and an orthogonal structure were obtained. Additionally, the formation of twinning effectively pinned mobile dislocations, thereby enhancing the stress relaxation resistance of the alloy. • The mechanism for enhancing stress relaxation resistance was elucidated through analysis of the morphology, size, phase interface relationships, dislocation density, twinning, recrystallization, and other factors of the second phase. • A stress relaxation dynamic regression equation was established. This equation not only predicts the residual stress and stress relaxation rate within a specific time frame but also provides a rough assessment of the alloy's stress relaxation resistance. [ABSTRACT FROM AUTHOR]

Although FeCoNiAlTaB alloys with better properties and formability can be prepared by LPBF, higher strength is still necessary through post-treatment to expand applications. This paper examines post-printing aging to enhance their strength, showing that aging increases the yield strength from 704 to 1025 MPa due to precipitation strengthening. [ABSTRACT FROM AUTHOR]

As the core component of proton exchange membrane fuel cell (PEMFC), pure titanium bipolar plate has been faced with cracking and thinning problems in the forming process. It is considered that the stamping and tensile deformation of the bipolar plate have similar stress states. In this paper, the plastic deformation mechanism of TA1 pure titanium plate is analyzed from the aspects of twin, texture evolution and dislocation slip by in-situ tensile combined with SEM/EBSD. During tensile deformation, a large number of dislocation slips occur inside α grain, and obvious slip traces are produced on the surface of the sample. Within grains with different crystallographic orientations, the degree and direction of the trace are different, which leads to the increased disharmony between grains. Especially in the triple junction of grain boundary, soft/hard orientation grain junction and other deformation disharmony locations are easy to crack. The tensile deformation causes obvious changes in the texture, and the initial strong bimodal texture becomes weak bimodal texture. This phenomenon is explained by intragranular misorientation, crystal rotation and twins. The main mechanism of tensile deformation of titanium plate is slip and twinning. A large number of {11–22}<11-2-3> compression twins are formed due to most c-axis bearing compressive stress. The types of initiating slip systems are different in different stages. The cylindrical slip system is preferentially activated and occupies a dominant position before yielding, which is conducive to the plastic forming of the plate. After yielding, the start-up ratio of the pyramidal slip system is increased due to the deflection of the observed surface of sample during tensile process, which improves the deformation resistance of the thin plate. [ABSTRACT FROM AUTHOR]

Modelling the microstructural evolutions and mechanical properties during the tempering of Dual Phase steels is a key objective for industrials as this phenomenon has a strong impact on the final properties. After having determined the tempering kinetics of fully martensitic steels between 100 °C and 550 °C using thermoelectric Power and hardness measurements, time–temperature equivalences were applied to determine the activation energies of the mechanisms controlling martensite tempering. Two tempering stages were clearly identified and thanks to the use of TEM, SEM and tomography techniques, they could be attributed to cementite precipitation, its spheroidization and recovery phenomena. The second stage was found to be retarded with increasing the manganese content of the steel contrary to the first stage. From these studies, a JMAK model was developed to predict the microstructurals evolutions during tempering. Then, an extension of the Hybrid-mean Field Composite model developed in a previous paper to predict the tensile curves of fresh martensite was proposed to take into account the microstructural evolutions of martensite during tempering. The model was tested for a wide range of physical parameters of the microstructure (phase fraction and chemical composition) and for different tempering heat treatments and gave good agreement with experimental tensile curves. • Modelling of the tensile properties of tempered Dual Phase steels was investigated. • Carbon departure from solid solution during tempering was implemented in the model • The influence of the Mn content on tempering was taken into account • The effect of the tempering parameters was well reproduced by the model. [ABSTRACT FROM AUTHOR]

Industrial design and new product development benefit from the adaptable processing approach offered by laser direct energy deposition (LDED). In this paper, a novel Ti65 alloy was successfully prepared by LDED and subjected to thermal exposure at 650 °C and 750 °C, respectively. The results showed that the as-deposited microstructure varies in different regions due to the cooling rate. Silicide precipitation was observed at the α/β interface, and a coherent α 2 phase was generated in the matrix after thermal exposure at 650 °C. Two-scale silicides were observed at the α/β interface and inside the α laths after thermal exposure at 750 °C. The as-deposited ultimate tensile strength (UTS) was 1058 MPa and 690 MPa at room temperature and 650 °C, respectively. After thermal exposure at 650 °C, the room temperature UTS was 1135 MPa, and the elongation (EL) at 650 °C was 27.5 %. After thermal exposure at 750 °C, the room temperature EL was 11.05 %, and both UTS and EL at 650 °C showed a decrease. The quantitative analysis showed that silicide precipitation was primarily responsible for the strengthening mechanism of the specimens thermally exposed at 650 °C at room temperature. The results provide scientific data for the manufacture of Ti65 alloy with excellent mechanical properties, laying the foundation for its application in aerospace. • LDED successfully fabricated a novel near-α Ti65 titanium alloy. • Thermal exposure at 750 °C eliminates the α 2 phase coherent with the matrix. • Thermal exposure temperature has a significant effect on the size and morphology of the precipitates. • The influence of microstructure and silicides on the tensile properties was discussed. • As-deposited exhibits an optimal combination of mechanical properties at RT and 650 °C. [ABSTRACT FROM AUTHOR]

A model developed previously to treat steady state isotropic superplastic deformation turned out to be of generic value and relevant to many classes of materials from metallic materials, ceramics, intermetallic compounds, composites, bulk metallic glasses, and geological materials. The present paper demonstrates the applicability of the concept of "oblate spheroidal ensembles of atoms containing quantified excess free volume present in a general grain boundary" to predict quantitatively the response of general, high-angle grain boundaries when subjected to external stimuli, e.g., an external stress, irrespective of the nature of the atomic bonds (metallic, ionic, or covalent) in preference to purely geometric descriptions of the grain boundary. The emergence of "oblate spheroids" as a response to an external stimulus is regarded in this analysis as self-organizing and a basic phenomenon that cuts across material classes and the nature of the chemical bonds. [ABSTRACT FROM AUTHOR]

The microstructure evolution of ferritic stainless steels during hot deformation is complex and needs to be finely described. Quantifying the evolution of the misorientation of low-angle boundaries depending on the thermomechanical path is a key point in controlling the recrystallization of such steels. This paper proposes an experimental methodology based on large-scale electron back-scattered diffraction (EBSD) mapping characterization using a Symmetry 2 camera to track the low-angle boundary evolution. Different thermomechanical paths, from 900 to 1100 °C with strain from 0.3 to 0.9, were studied using uniaxial compression tests. Flow stress follows a usual hardening stage, followed by a slight softening regime, mostly attributed to continuous dynamic recrystallization. Distributions of low-angle boundary populations (density vs sub-grain size) are quantified by two populations either near grain boundaries or inside grain bulk; the proportion of sub-grains at grain boundaries increases with strain. This bimodal distribution is made with a probabilistic Gaussian mixture model. These results are discussed using a modified mean-field model of Gourdet-Montheillet. This model is insufficient to capture the transient stage of continuous dynamic recrystallization unless its set of parameters is adjusted to accommodate the saturation of the density of low-angle boundaries near grain boundaries. This saturation is a result of the low-angle boundary density gradients in the grains. [ABSTRACT FROM AUTHOR]

In this paper, the strength-ductility tradeoff was overcome in a designed Al-4.9Mg-1.6Li-0.4Cu-0.3Zr-0.2Sc (wt.%) alloy via tailoring the intragranular and intergranular precipitates. After ageing for 8–32 h at 165 °C, the fine Al 3 Li and Al 3 (Sc, Zr, Li) phases were formed intragranularly, which increased both the yield strength and strain hardening rate. Meanwhile, the banded distributed fine intergranular phases of Al 2 MgLi were formed, which reinforced grain boundaries by suppressing crack propagation, thus improving ductility of alloy. Based on these, the optimal comprehensive tensile properties of this alloy were obtained (Ultimate tensile strength = 538–577 MPa, Elongation = 14.0–18.9 %), which are the highest values among the reported cast Al–Li alloy families at present. [ABSTRACT FROM AUTHOR]

In this paper, the strength-ductility tradeoff was overcome in a designed Al-4.9Mg-1.6Li-0.4Cu-0.3Zr-0.2Sc (wt.%) alloy via tailoring the intragranular and intergranular precipitates. After ageing for 8–32 h at 165 °C, the fine Al 3 Li and Al 3 (Sc, Zr, Li) phases were formed intragranularly, which increased both the yield strength and strain hardening rate. Meanwhile, the banded distributed fine intergranular phases of Al 2 MgLi were formed, which reinforced grain boundaries by suppressing crack propagation, thus improving ductility of alloy. Based on these, the optimal comprehensive tensile properties of this alloy were obtained (Ultimate tensile strength = 538–577 MPa, Elongation = 14.0–18.9 %), which are the highest values among the reported cast Al–Li alloy families at present. [ABSTRACT FROM AUTHOR]

The design and development of heat treatment regimes adapted to the laser powder bed fusion technology for specific service conditions have become a hot topic of research in the field of additive manufacturing. This paper systematically studies the microstructure changes of the L-PBFed IN738LC alloy, solution heat treated at 1250 °C for various durations (1 h, 3 h, 5 h) and then aged at 850 °C for 24 h. The delayed recrystallization behavior was revealed, and the selective precipitation pattern of the M 23 C 6 carbide on different types of grain boundaries was discussed. Additionally, the tensile deformation mechanism of the alloy before and after heat treatment is clarified. The results indicate that grain boundary migration and transformation are impeded under 1250 °C/1 h conditions due to carbide particle pinning and solute atom segregation during the initial stage of solution treatment, which accounts for the delayed recrystallization behavior, and the microstructure is mainly undergoing recovery. At 1250 °C/5 h, M 23 C 6 carbides selectively precipitate at twin boundaries, accompanied by recrystallization. The samples treated at 1250 °C/1 h exhibit the highest mechanical property (σ YS = 1305 ± 21 MPa, σ UTS = 1462 ± 11 MPa, ε EL = 5.4 ± 0.7 %) owing to the precipitation of γ′ phase and the presence of sub-grain boundaries. The deformation mechanism shows that the as-built samples mainly experience planar dislocations slipping, while the heat-treated samples undergo stacking faults shearing and anti-phase boundary shearing. The dominant mechanism among these is anti-phase boundary shearing. [ABSTRACT FROM AUTHOR]

Under harsh service conditions, it is very difficult to achieve multi-scale diversified synergy of the heterogeneous brazed joint. The ideal brazed joint should build a "morphology-structure-stress" synergy mode to achieve high-quality and high-reliability brazing. In this paper, the graphene nickel-based foam self-reinforcement was realized by upgrading the in-situ compression, to construct the foam-filler integrated interlayer, and then realize the filler re-optimization. The multi-interface fusion of graphene non-metallic properties and nickel-based skeleton metallic properties effectively inhibited intermetallic compounds. Micro-scale SEM and nano-scale TEM were used to jointly characterize the microstructure, and the 3D structure was thinning layer by layer in the joint fracture, which fully verified the high stability of high-density foam. The room temperature shear strength was as high as 434 MPa, and the properties were almost without damage after 200 cycles of high-low temperature life. This research could provide technical support for the microstructure-property regulation of next-generation aero engines. [ABSTRACT FROM AUTHOR]

The inhomogeneous tempered sorbite/bainite (TS/B) with various morphologies and orientations play a significant role in deformation coordination and damage evolution. In this paper, the influence of distinct morphologies and orientations of the mixed-grain structure with TS/B on the deformation heterogeneity were extensively investigated by in-situ tensile testing. Furthermore, a multi-scale model of dislocation density-based crystal plasticity (CP) coupled with the phase field method (PFM) was developed to illustrate the damage nucleation and its evolution via the representative volume element (RVE) modelling. The results shows that mixed-grain structure with TS/B exhibits non-homogeneous deformation during the tensile process, and the coarse grains bear the main plastic deformation, resulting in cross-slip traces and the wrinkling phenomenon at the grain boundary and the interior of coarse grains. Furthermore, the activation of slip systems was determined through slip trace analysis, and the slip transfer behavior between adjacent microstructure was analyzed. According to the critical resolved shear stress (CRSS), the {123}<111> slip system was determined to be the most activated slip system during the in-situ deformation. Hard-orientated lath-shaped B (M1) is more prone to accumulate low angle grain boundaries (LAGBs) than hard-orientated TS (M2) and soft-orientated granular B (M3), resulting in higher orientation rotation degree and geometrically necessary dislocations (GNDs) density of M1 than M2 and M3. The M1 exhibits the nucleation of damage during the initial deformation stage. In addition, compared with the M2 and M3, the Schmid factor (SF) of M1 dominates the transformation from hard orientation to soft orientation and the higher value of damage factor (φ) of M1 results in the more activated slip systems and local damage at high strain levels. This study provides new insights into elucidate the effects of TS/B morphologies and orientations on deformation heterogeneity and damage evolution in large-scale forged spindles for offshore wind power. • A new multi-scale model to describe the deformation heterogeneity and damage was established. • Hard-orientated lath-shaped bainite was prone to induce non-uniform deformation and a pronounced work hardening effect. • The damage heterogeneity can be attributed to the hard-oriented lath-shaped bainite. • To eliminate hard-orientated bainite and obtain uniform TS is beneficial to improve deformation uniformity and avoid local damage. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) is a process to significantly improve the mechanical properties of materials by grain refinement. For forming at room temperature (RT), higher strengths can thus be achieved; for increased temperatures (HT), greater elongations can be achieved. This great potential has been chiefly applied only on laboratory scale due to a lack of industrial process design. Equal-channel angular pressing (ECAP) offers the possibility to integrate these advantages in industrial processes. This paper investigates a modified ECAP process for aluminum AA5083 sheet metal. Two passes of ECAP for sheet metal and an additional heat treatment were used. To study the material deformation on a micro-scale, in-situ synchrotron measurements at DESY (Hamburg) were performed to analyze the evolution of lattice strains and dislocation densities during tensile testing. The mechanical properties of the ECAP-processed sheet material reveal an increase in yield strength and a decrease in elongation at RT. Higher strains can be measured for the processed material at elevated test temperatures. In-situ diffraction results show a changed behavior of the ECAP sheet material compared to the reference material for both temperature regimes. These changes are based on the increased defect density in the material, which leads to increased strength at RT. At HT, dynamic recrystallization occurs during tensile testing, and the prevailing deformation mechanisms reconfigure. Electron backscatter diffraction (EBSD) and micrographs are used to interpret and supplement the observations. The findings provide the basis for the in-depth understanding of the deformation behavior of the material and help to apply the ECAP process on an industrial scale. [ABSTRACT FROM AUTHOR]

In this paper, in-situ Al 3 Ti-reinforced Al–Cu alloys were fabricated by Ti alloying and exhibit outstanding high-temperature properties. The results show that when the volume fraction of Al 3 Ti is 7.8 %, the ultimate strengths of the alloy can reach 203.9 MPa and 144.1 MPa at 300 °C and 350 °C, which are 31.0 % and 51.4 % higher than the base alloy, respectively. The analysis indicates that in addition to precipitation strengthening, dislocation strengthening, and load-transfer strengthening, low-angle grain boundaries also play an important role in improving the high-temperature properties of the alloy. When the Ti concentration in the alloy melt is high, Al 3 Ti grows into the two-dimensional lamellar dendrite with a complex structure and serves as the heterogeneous nucleation site of multiple α-Al cores, which results in the abnormal grain growth behavior and increase of low-angle grain boundaries. Moreover, fracture mechanism analysis suggests that the existence of Al 3 Ti increases the number of initial cracks, which increases the risk of splitting the matrix. The deformation behavior of Al 3 Ti is mainly controlled by twins, stacking faults, and dislocations. Under tensile stress, cracks first form in Al 3 Ti and then evolve into non-equiaxed voids in the matrix, which eventually connect and lead to the fracture of the alloy. [ABSTRACT FROM AUTHOR]

Ti/Al laminated composites have high strength and excellent corrosion resistance, while the relatively low interface bonding strength has still restricted its wide usage. This paper proposes a new method to improve the interface bonding strength of Ti/Al laminated composites through surface nano-crystallization pretreatment using ultrasonic rolling technique. The mechanical property, interface characteristics and interface bonding mechanism are thoroughly studied. The results show that ultrasonic rolling surface pretreatment enables the strong interface bonding of Ti/Al laminated composites and greatly reduces the rolling reduction threshold. It is revealed that ultrasonic rolling surface pretreatment can generate periodic grooves and nanocrystalline layer with low ductility on the Ti surface, which can effectively promote cracking of the Ti hardening layer and increase the contact area of virginal Ti and Al metals during rolling process. Besides, ultrasonic rolling forms nanocrystals and high-density defects on the top surface of the titanium layer, which promote the migration, exchange and rearrangement of atoms under severe plastic deformation and eventually lead to the formation of amorphous structures in the transition layer of the Ti/Al interface. Therefore, the Ti/Al laminated composites pretreated using ultrasonic rolling technique exhibit outstanding interface bonding strength, especially at relatively low rolling reduction conditions. [ABSTRACT FROM AUTHOR]

The evolution and formation mechanism of microstructures in a high-entropy CoNiCr-based superalloy induced by cold-drawing deformation at cryogenic temperature were investigated. The improvement of strength while maintaining the ductility during cryogenic-drawing deformation in the CoNiCr-based high-entropy superalloy originated from the activation of multiple deformation mechanisms including deformation twins, dislocations, 9R phase and hexagonal close-packed (HCP) phase transformation. Two dominant contributions have been suggested for the increase in strength, namely, nanotwins strengthening and the existence of 9R and HCP phase. In this paper, cryogenic-deformation-induced phase transformation from face-centered cubic (FCC) to HCP in the CoNiCr-based high-entropy superalloy was found, and the atomic-scale mechanism of FCC-9R-Twin/HCP transformation was revealed. A new crystallographic model was established to explain the FCC→9R→Twin/HCP transformation. The phase transformation is significant for the comprehensive understanding of the deformation behavior of this CoNiCr-based high-entropy superalloy at cryogenic temperature, and for guiding the design of high-entropy superalloy with advanced mechanical properties. • The cryogenic-drawn samples of CoNiCr-based high-entropy superalloy exhibit superior strength while maintaining the ductility. • The strength increment originates from multiple deformation mechanisms, including deformation twins, 9R and HCP phase. • The atomic-scale mechanism of the FCC-9R-Twin/HCP transformation was revealed. • A new crystallographic model is established to explain the FCC.→9R→Twin/HCP transformation processes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel idea of controlling microstructure and mechanical properties based on the non-equilibrium microstructure of nickel-based superalloy fabricated by laser powder bed fusion (LPBF). The network microstructures were firstly built in LPBF nickel-based superalloys by direct aging (DA) heat treatment. Thermodynamic calculations were conducted to design the DA and homogenizing + DA (HDA) heat treatments for elucidating the control mechanism. The results showed that the non-equilibrium microstructures in as-built nickel-based superalloy contributed to the network microstructure formation and recrystallization during DA heat treatment. The grains were refined and the <001> texture was eliminated after DA heat treatment. The non-equilibrium microstructures were removed and the recrystallized grains tended to coarsen after HDA heat treatment due to high temperature homogenizing treatment. The in-situ nano γ′ phase uniformly distributed in the grains of HAD-treated microstructures, which was also found inside network microstructures of DA-treated microstructures. Due to the additional strengthening effect of refined grains and network microstructures, the strength of DA-treated sample was higher than those of as-built and HAD-treated samples, while the ductility was lower than that of as-built sample, and but was close to that of HAD-treated sample. This study will provide guidance for developing a suitable heat treatment process of LPBF nickel-based superalloys. [ABSTRACT FROM AUTHOR]

Nickel-based GH3536 alloy exhibits high strength but low ductility when produced by selective laser melting (SLM), which hinders its widespread application in aerospace. This paper employed a 'two-step' method of heat treatment to optimize the microstructure of the SLM GH3536 alloy and investigated the mechanical properties. Tensile tests were conducted on SLM GH3536 alloy before and after heat treatment at 750 °C, using an in-situ high-temperature tensile stage. The relationship between the microstructural evolution and deformation behavior of the alloys was investigated by combining the in-situ tensile experiments and crystal plasticity finite element method (CPFEM). The results suggested that the elongation can be increased by 80% without a significant reduction in tensile strength. The improved elongation is attributed to the complete recrystallization, formation of annealed twins and serrated grain boundaries after heat treatment. The study also investigated the deformation behavior and fracture mode of the alloy before and after heat treatment. Discussion was done on the influence of the microstructure, particularly the twin and serrated grain boundaries on the alloy's plastic deformation. This study enhanced the understanding of plastic deformation of SLM GH3536 alloy and provided a valuable reference for the design and post-treatment of superalloy. • A two-step heat treatment method is proposed to prepare GH3536 alloy with high ductility and acceptable strength. • High-temperature microplastic deformation and damage of GH3536 alloy were observed in-situ SEM technique and its influencing factors were analyzed. • The effects of twins and serrated grain boundaries on the properties were simulated using the CPFEM model. [ABSTRACT FROM AUTHOR]

In industrial production, highly alloyed tool steels (HATSs) are usually fabricated by powder consolidation using hot isostatic pressing (HIP) technology; HIP's primary disadvantage is very high production cost. However, a well-developed cost-effective powder consolidation technology, termed as vacuum hot-pressing (VHP) that is also able to produce HATSs in an industrial scale, has heretofore attracted few attentions, primarily attributable to nonuniform density distribution in VHP consolidated HATSs. In this paper, an innovative VHP processing approach was designed as follows, aiming not only to overcome the aforementioned VHP's disadvantage but also to enhance mechanical properties relative to those of its counterpart produced by HIP approach: first, inert gas-atomized prealloyed powders are consolidated via VHP purposely at a temperature lower than those used during HIP, in order to retain very fine carbides, but which likely yields partial densification with non-uniform density distribution and incomplete metallurgical bond between powders; then, identical full densification and complete metallurgical bond are achieved throughout the consolidated HATS by using hot-working at a temperature no higher than the VHP temperature, minimizing carbide growth. A HATS, T15 steel with nominal composition of Fe-1.5C–12W–4Cr–5V–5Co (wt%) as model material, was produced to assess and validate the designed VIP processing approach. The experimental results reveal submicrometric average carbide size in the as-VHP T15 steel smaller than that in its as-HIP counterpart, together with essentially unchanged carbides relative to those in the as-VHP T15 steel, identical full densification and complete metallurgical bond in the entire VHP plus hot-rolled (HR) T15 steel. After quenching and tempering (QT), the VHP + HR + QT T15 steel still retains submicrometric average remaining carbide size and displays refined average prior austenite grain size, with both smaller than, and exhibits bend fracture strength higher than, accompanied by hardness similar to, those in its counterpart produced by HIP approach. The mechanisms underlying microstructural evolutions associated with carbides, densification and metallurgical bond in the designed VHP processing approach were discussed. The aforementioned mechanical property characteristics were rationalized. VHP plus subsequent hot-working at lower temperatures provides a cost-effective commercialized avenue to manufacture HATSs with enhanced mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, 2A12-T3 aluminum alloy is first solution-treated and then experienced an artificial aging for different time to induce different S phase characteristics. By using this method, the texture formation behavior solely contributed from S phase characteristic could be determined during hot rolling. It is found that the increase of S phase in size and density has a positive effect on Brass texture formation, which is attributive to the increased Dislocation Shear Slipping (DSS) near S /Al interface. The relative slip tendency factor (M s x ) is proposed to quantitatively evaluate the impact of S phase characteristic on Brass formation. It is revealed that Brass volume fraction (V Brass) has a better positively linear relationship with M s x than texture intensity. Then, the effect of Brass texture on tensile property is analyzed in details. Crystal plasticity simulation shows that Brass texture can improve the yield stress and tensile strength and simultaneously keep the elongation. Comparatively, the rolling sheet aged for 3 h obtains an excellent combination of strength and ductility. [ABSTRACT FROM AUTHOR]

In this paper, the effect of grain sizes on mechanical properties and microstructure evolution of pure Al sheet at cryogenic temperatures were studied by uniaxial tensile tests and microstructure observations. The results show a great exciting strain hardening ability for the sheet with ultra-fine grain (UFG) at cryogenic temperature, and the cooperative increasing in strength and ductility of pure Al at cryogenic temperatures become more and more prominent with the decrease of grain size. With the decrease of grain size, the increase of yield strength by decreasing temperature becomes more dramatic. The mechanism of increase in yield strength at cryogenic temperatures is attributed to the contribution of three temperature-dependent factors: grain boundary strengthening, lattice friction resistance and dislocation strengthening, in which grain boundary strengthening plays a dominant role. The grain size dependence of the strain hardening ability increased with decreasing temperature is mainly related to the inhibition of cross-slip in the grain interiors and the dislocation annihilation at grain boundaries, so that dislocation can effectively multiply and accumulate, which is totally different from the strain softening and poor plasticity of UFG pure Al at room temperature (RT) caused by the enhanced dislocation annihilation. As a result, the trade-off relationship between the strength and plasticity caused by different grain sizes is significantly weakened at cryogenic temperatures, which provides a very potential method for the complex parts forming of UFG sheets and mechanical properties improvement. • The increase of yield strength with decreasing temperature is more significant with decreasing grain size. • The increase of yield strength at cryogenic temperatures is mainly attributed to grain boundary strengthening. • The enhancements in uniform elongation at cryogenic temperatures become more prominent with the decrease of grain size. • With the decrease of temperature, the UFG pure Al gradually transitions from strain softening to strain hardening. • The trade-off relationship between the strength and plasticity is significantly weakened at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

In this paper, a novel Cu-0.60Cr-0.20Nb-0.05Si-0.02Ca-0.02Ce (CCNSCC, wt.%) alloy is designed. By comparing the differences in the properties and microstructure with the Cu-0.60Cr-0.20Nb (CCN, wt.%) alloy under the same process, the effects of trace Si, Ca, and Ce elements on the CCNSCC alloy are disclosed. After undergoing cold rolling by 80% and aging at 450 °C for 60 min, the CCNSCC alloy exhibits a tensile strength of 524 MPa and a softening temperature of 600 °C. These values represent an increase of 104 MPa and 90 °C respectively compared with the CCN alloy. After a multi-stage combined thermo-mechanical treatment including preaging at 400 °C for 30 min, the tensile strength and electrical conductivity of the CCNSCC alloy reach 618 MPa and 75.2%IACS respectively. Microstructure analysis shows the existence of rod-like and polygonal Cr 8 Nb 3 Si particles, as well as globular, ellipsoidal, and crescent-shaped (Ca,Ce)Cu 5 particles. During the process of aging, the precipitation of the Cr phase occurs at the phase boundaries of Cr 8 Nb 3 Si particles. Additionally, significant quantities of fine Cr particles at the nanoscale surround the Cr 8 Nb 3 Si particles, exerting a beneficial influence on the strength and electrical conductivity of the CCNSCC alloy. Besides, the CCNSCC alloy has finer Cr particle size and lower volume fraction of recrystallized grains after aging in comparison to the CCN alloy. This indicates that the addition of trace Si, Ca, and Ce elements significantly inhibits the growth of Cr particles and occurrence of recrystallization. Plenty of dislocations are observed in different states of the CCNSCC alloy, and their interaction with the Cr precipitates is the primary factor contributing to the excellent mechanical properties of the CCNSCC alloy. The findings of this study provide valuable insights for improving the properties and microstructure of Cu–Cr–Nb alloys. • A novel Cu-0.60Cr-0.20Nb-0.05Si-0.02Ca-0.02Ce (wt.%) with excellent comprehensive properties is designed. • Cr particles and (Ca,Ce)Cu 5 particles precipitate at the boundaries of nanoscale Cr 8 Nb 3 Si particles during aging. • The addition of trace Si, Ca, and Ce significantly inhibits the growth of Cr particles and occurrence of recrystallization. [ABSTRACT FROM AUTHOR]

The uncontrollable directional grain growth and non-equilibrium microstructure of Inconel 718 will form during laser direct energy deposition (LDED), which seriously limits the promotion and application, so it is necessary to consider the heat treatment to improve the microstructure and mechanical properties. In this paper, the effects adopting different heat treatments on the phase composition, precipitation behavior, grain structure, tensile and tribological properties of LDED Inconel 718 have been systematically investigated, with as-deposited samples compared. The results show that the number and size of γ″ phases can be significantly changed under different aging and solution conditions, and the strength and wear resistance increase while elongation decreases since the fine grain and precipitation strengthening occurring during heat treatment. By comparing the different samples, the SA1100A exhibits the highest yield and tensile strength, with 140.6% of yield strength and 83.9% of ultimate tensile strength increasing compared to as-deposited samples, also showing the narrowest wear mark width and the lowest average mass loss. [ABSTRACT FROM AUTHOR]

Directed Energy Deposition-Arc (DED-Arc) was utilized to fabricate Inconel-copper bimetallic structures, with the aim of improving manufacturing modes and reducing costs for rocket engine thrust chambers. In this paper, bimetallic Inconel superalloy (GH4169) and copper alloy (C18150) structures were deposited using different deposition strategies. The formation mechanisms of grain-size gradients and heterogeneous interfacial microstructural evolution were comprehensive investigated and further discussed. Both strategies produced high-quality bimetallic samples with tensile strength exceeding 260.2 MPa. Fractures occurred within the C18150 metal rather than at the interface, indicating successful interface strengthening of the bimetallic samples. Gradual gradients in grain size distribution and nano-hardness were observed across the interface. The crystal structures of C18150 were unaffected by GH4169, and no new phases were generated in the interfacial region. The crystallographic orientation relationship between Ni and Cu was determined to be [011] Cu //[011] Ni and (111) Cu //(111) Ni , and interfaces were strengthened by grain boundary and dislocation strengthening through. This work demonstrates an approach for fabricating large, high-performance bimetallic structures with tailored grain-size gradients and heterogeneous microstructures, suitable for rocket engine thrust chamber applications. • Novel Inconel-copper functional bimetallic were developed by DED-Arc. • Evolution of grain size and interfacial characteristic were exhibited in detail. • Copper-on-Inconel(C/G) sample provides superior mechanical properties. [ABSTRACT FROM AUTHOR]

Nickel matrix composites reinforced by ceramic particles typically exhibit elevated strength but diminished toughness. In this paper, a novel in-situ micron-size TiC and nano-size γ′ phases reinforced Ni–Fe–Cr matrix composite was successfully prepared using the electron beam freeform fabrication (EBF3). Subsequently, the as-built composite was subjected to solution heat treatment at different temperatures. At a solution temperature of 1150 °C, the composite demonstrates superior strength-toughness synergy (ultimate tensile strength = 1109.4 ± 25.4 MPa, elongation = 12.08 ± 0.62%), exhibiting an increase of 17.1% and 104.4%, respectively, compared to the as-built composite. A systematic analysis of the strengthening and toughening mechanisms revealed that the γ′ phase played a predominant role in enhancing strength, while the size, morphology, and content of TiC phase significantly influence fracture toughness. After being solution heat treated at 1150 °C for 2 h, the γ′ phase precipitated uniformly with its size coarsening to 93.85 nm, demonstrating an optimal strengthening effect by shearing mechanism. Meanwhile, the TiC phase partially dissolved into the matrix and transformed from a long-strip shape to a more stable spherical shape. This transformation significantly reduced the formation of microvoids along the TiC/matrix interface during tensile loading, enhancing the fracture toughness. The γ′ and TiC phases were regulated by solution heat treatment to reach a balance of optimising properties, achieving synergistic enhancements in strength and toughness. • A novel in-situ TiC-γ'/Ni–Fe–Cr composite was designed and fabricated by EBF3. • The composite was subjected to solution heat treatment to regulate precipitates. • The roles of TiC and γ′ phases in affecting mechanical properties were clarified. • Superior strength-toughness synergy was achieved by regulating the γ′ and TiC phases. [ABSTRACT FROM AUTHOR]

The influence of annealing temperature (450 °C ∼ 800 °C) on the microstructure and mechanical properties of the novel α + β titanium alloy Ti-6Al-4V-2Mo-2Fe (Ti6422) designed by the authors was investigated systematically in this paper, and the strength-plasticity enhancement mechanism was addressed comprehensively. The results showed that the microstructure of the samples annealed at 450 °C ∼ 700 °C was composed of primary α p phase and β trans structure. And as the annealing temperature increased, the size of α p and α s phase, as well as, the content of β phase gradually increased. When annealed at 750 °C and 800 °C, the microstructure consisted of equiaxed α p phase and irregular β phase without α s precipitates. As the annealing temperature increased from 450 °C to 800 °C, the yield strength of the samples climbed and subsequently declined, while the elongation after fracture kept rising. Ultrahigh strength (σ y ≥ 1340 MPa, σ b ≥ 1390 MPa) and considerable plasticity (δ ≥ 11.8%) were obtained under the annealing temperature of 500 °C and 550 °C. During deformation, annealed samples with higher content and slighter size of nanoscale α s and microscale α p phase accumulated an abundance of dislocation at the α p / β and α s / β interfaces. This resulted in notable interface strengthening and improved the strength. Moreover, the considerable plasticity was attributed to the superior coordinated deformation ability of the α p phase and certain coarse α s phase, which was conducive to delaying the reduction of the work-hardening rate and thus postponing the occurrence of necking. The microscale α p phase could withstand most of the plastic deformation. While high-density dislocation entanglement and local kink occurred in certain coarse α s phase, which alleviated the strain incompatibility in the hard β trans structure. • Ti6422 alloy exhibits an improved strength-plasticity combination through simple annealing. • Ultrahigh strength of ∼1340 MPa together with considerable plasticity of ∼12% is achieved. • Notable interface strengthening is the primary source of the ultrahigh strength. • The considerable plasticity is attributed to the superior deformation ability of the α p and coarse α s phase. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is getting significant attention in realizing customizable nitinol (NiTi) devices for biomedical applications. However, due to the change in composition and constituent phases occurring during printing and the microstructural inhomogeneity in the printed parts, obtaining a desired set of phase transformation behaviors and superelastic properties is a major challenge. In this work, laser powder bed fusion (LPBF) was used to fabricate NiTi at a very low laser energy density (35 J/mm3) on a titanium base plate while keeping these behaviors and properties within desirable ranges without any structural defects such as crack and delamination. Our measurements showed that the as-printed NiTi exhibited distinct one-step phase transformation with the austenite finish (A f) temperature of 2.1 °C. To increase the A f temperature to 30.2 °C (within the recommended range of A f temperature for biomedical applications), a heat treatment protocol was developed, which includes a solution cycle (at 900 °C for 1 h) followed by an aging cycle (at 450 °C for 30 min). The heat treatment protocol enabled us to attain the homogenized microstructure while creating ultrafine metastable Ni-rich precipitate, Ni 4 Ti 3 , which facilitated the desirable phase transformation behavior with the increased A f temperature. The heat-treated sample showed narrower and sharper two-step martensitic phase transformation with the formation of intermediate R-phase. The presence of both Ni 4 Ti 3 and the R-phase was confirmed by the transmission electron microscopic (TEM) analysis. In the superelasticity test at the body temperature, these samples, starting from the 2nd cycle, demonstrated a recovery ratio of more than 90% and a recoverable strain of more than 6.5%. After 10th cycles, the stable recoverable strain was 6.52% with a recovery ratio of 96%, which is the highest superelasticity reported for the LPBF processed NiTi to the best of our knowledge. After the initial deformation process, we expect these NiTi samples to attain near full superelasticity during service. The micro-hardness study also showed that the hardness of the heat-treated samples is less affected by the cyclic loading. Therefore, this paper presents a viable heat treatment protocol, which provides an important processing roadmap in making NiTi implants by AM while maintaining excellent functional properties of NiTi for biomedical applications. [ABSTRACT FROM AUTHOR]

Predicting mechanical behavior and microstructure evolution via numerical simulation is an effective way to improve the quality of superplastic-formed products for nickel-based superalloys. Analysis of mechanical and microstructures during the stable superplastic deformation of Inconel 718 indicates that dislocation propagation and grain growth lead to stress increase, while recovery and dynamic recrystallization are responsible for flow softening. Moreover, the δ phase has an indirect effect on the flow stress by fixing grain boundaries and dislocations. The variation of δ phase content during superplasticity is attributed to the precipitate coarsening caused by thermal diffusion and the particle density decrease due to grain boundary movement. This paper proposes a viscoplastic constitutive model that accounts for the impact of internal state variables on the superplastic flow, such as dislocation density, recrystallization, grain size, and δ phase evolution. By describing changes in the average radius and volume fraction of particles, the model reflects the contribution of precipitate as a pinning point to promote dislocation proliferation and restrict grain boundary slip and grain growth. Moreover, the true strain rate varying with time step was introduced into the parameter optimization involving genetic algorithm to realize the adaptability of the model to large deformation. After encoding the material subroutine UMAT, the constructed model effectually forecasted the change in flow stress and internal variables during superplastic stretching under random conditions. Finally, the simulation and experiment of the bipolar plate forming verified the practicability of the model in predicting the thickness distribution and microstructure evolution for superplastic parts. • The internal state variables such as dislocation density, recrystallization, grain size, and δ phase evolution are coupled with the superplastic flow. • The impeding effects of precipitate on the movement of dislocations and grain boundaries are incorporated into the model. • During parameter optimization using a genetic algorithm, the true strain rate is introduced to make the model adapt to large deformation. • The internal structure and thickness distribution of bipolar plates after superplastic forming were used to verify the accuracy of the model prediction. [ABSTRACT FROM AUTHOR]

High strength low alloy (HSLA) steels are important metallic materials especially in the defense and military sectors due to their superior mechanical properties and cost-effectiveness compared to superalloys. This study investigates monotonic tension/compression strength and fatigue strength, including both the low cyclic fatigue (LCF) and high cyclic fatigue (HCF), of a HSLA steel produced using laser powder bed fusion (LPBF) additive manufacturing (AM). The LCF tests were strain-controlled (from 0.45% to 1.2% strain amplitudes) achieving a constant strain rate of 0.0005/s, while the HCF tests were stress-controlled (from 467 MPa to 1007 MPa stress range), all carried out at room temperature. Specimens of the alloy were manufactured in two build orientations to evaluate anisotropy. Moreover, a set of rolled plate and as-cast specimens were tested to facilitate comparisons. The alloy exhibited excellent performance confirming the potential of LPBF AM to manufacture HSLA steels with significant performance gains over as-cast counterparts. Nevertheless, the rolled material exhibited the highest performances. Details pertaining to the processing along with the testing results and characterization of microstructural origins of the high strength are presented and discussed in this paper. [ABSTRACT FROM AUTHOR]

In this paper, laser aided additive manufacturing (LAAM) of stainless steel 316L (SS 316L) in a controlled argon environment was investigated. The controlled argon environment can significantly reduce the oxidation and fundamentally change the process conditions. It was found that after inhibiting oxidation, the surface of the deposited SS 316L showed remarkably high reflectance (71%) to laser radiation, which minimised heat accumulation. Subsequently, stable melt pool temperature and high cooling rate (4.1 × 104 K/s) were also observed. Furthermore, nano-sized oxides were found to be nucleated owing to excessively low internal oxygen content (220 ppm). The unique process condition resulted in enhanced strengthening effect due to cellular structure refinement and dispersed nano-sized oxides. Consequently, a desirable balance of high strength and ductility was achieved for the as-deposited materials under both quasi-static tension (strain rate 10−3 s−1, yield stress 560.0 MPa, ultimate tensile strength 717.2 MPa, and elongation 64.0%) and dynamic tension (strain rate 3150 s−1, maximum flow stress 1241 MPa, and elongation 37.5%). • Laser aided additive manufacturing SS 316L in controlled Ar chamber was studied. • A significant change of laser-material interaction was observed. • It resulted in a remarkable oxidation reduction and high cooling rate. • A superior combination of tensile strength and elongation was achieved. [ABSTRACT FROM AUTHOR]

This paper focused on the correlation between the (002) texture, columnar grain size and mechanical properties of Ti films prepared by magnetron sputtering. The (002) texture and columnar grain evolution were controlled under a combination of substrate bias voltage and argon flow rate. It was found that the substrate bias voltage was the key factor to dominate the (002) texture and columnar grain size. At constant substrate bias voltage of −100 V, all of Ti films showed a strong (002) texture. The micropillar compression test indicated that the Ti film with a strong (002) texture and nanocolumnar grain obtained an ultra-strength of 3838.2 MPa and an ultra-high work hardening exponent of 0.64 at substrate bias voltage of −100 V and argon flow rate of 20 sccm. The ultra-strength of Ti film stemmed from the fact that the nano-sized grain inhibited the generation of deformation twin and the (002) texture inhibited the activation of slips, and finally the slips with high Peierls-Nabarro stress were forced to be activated. Moreover, based on the TEM observation, the source of the ultra-strength of Ti film was explained by the proposed strength formula. Texture optimization and nanocolumnar strengthening are effective methods to improving the strength of pure Ti films. These results provided a new perspective of designing ultra-strength of Ti film materials. [ABSTRACT FROM AUTHOR]

In the paper, in terms of the new developed additively manufactured Ti-6.9Al-6.8Zr-2.3Mo-2.2V alloy, different microstructural design strategies were proposed to tune the morphology and content of α phase to optimize the mechanical properties of the alloy and the corresponding deformation mechanism of the alloy were characterized and analyzed. The results show that after cyclic heat treatment and solution-aging, the best comprehensive mechanical properties (yield strength ∼ l009 MPa, and elongation ∼12%) are obtained. The better comprehensive tensile properties are attributable to the microstructure consisting 16% equiaxed α p and β t structure. The cycle heat treatment can effectively decrease the length-width ratio of lamellar α phase and improve spheroidization of primary α phase. The equiaxed primary α phase has higher ability to coordinate local plastic strain, leading to the activation of extensive prismatic slip and improving the ductility of the alloy. After aging-solution, large amount of fine α s precipitate from β phase. The high hetero-deformation induced stress at α s /β interfaces in β t structure promotes the activation of the pyramidal slip systems, thereby increasing the yield strength. The present findings provide significant guidance for additive manufactured titanium alloy having good combination of tensile ductility and strength. • In terms of the new developed additively manufactured Ti-6.9Al-6.8Zr-2.3Mo-2.2V alloy, different heat treatments were proposed to improve the mechanical properties. The best matching of strength and ductility (yield strength ∼ l015 MPa, and elongation ∼10.5%) was obtained after cyclic heat treatment and solution-aging. • Owing to the high hetero-deformation induced stress at αs/β interfaces, the pyramidal and slip systems were operated, resulting in an increase of yield strength. • The prismatic slip plays a dominant role in accommodating the external strain and promoting deformation. [ABSTRACT FROM AUTHOR]

This paper presents an in-situ observation, using neutron imaging, of delayed crack propagation in a high-strength martensitic steel specimen. Delayed cracking is believed to be caused by hydrogen embrittlement occurring due to the slow diffusion and accumulation of hydrogen ahead of a crack front, causing decreased ductility and eventual cracking under constant load. The experiment involved mechanical loading of a single-edge-notch bend specimen while submerged in an electrolyte solution (H 2 O + 3.5% NaCl) under cathodic polarization to facilitate hydrogen ingress. Intermittent crack propagation was observed for 12 h after the environment had been removed. The stress state at each crack configuration was extracted from a three-dimensional elastic–plastic finite element simulation, which was tailored to match the quantitative information acquired from the neutron radiographs of the fracture process. To gain insight into the evolution of hydrogen concentration with crack propagation, a modeling scheme for stress-assisted hydrogen diffusion was also employed. [ABSTRACT FROM AUTHOR]

The CoCrFeMnNi high entropy alloy (HEA) is the most studied HEA because of its excellent combination of strength and ductility. However, despite the advantage of CoCrFeMnNi HEA, its application is limited owing to its low yield strength. In this study, an emerging cold spray additive manufacturing technique was applied to fabricate a bulk CrCoFeMnNi high entropy alloy to improve the yield strength of CrCoFeMnNi. The paper presented an experimental investigation of the microstructure and mechanical properties of the as-sprayed and heat-treated CrCoFeMnNi high entropy alloy samples under compressive loading conditions at different strain rates. The microstructural analysis of the as-sprayed samples exhibited undeformed particles, numerous refined grains, and an interparticle incomplete interface. Post-heat treatment was applied to tune inter-particle bonding and ductility. Quasi-static compression tests (at 0.001 s − 1 ) and dynamic impact tests (up to 3900 s − 1 ) were carried out on the as-sprayed and heat-treated samples along the printing direction (vertical samples) and perpendicular to the printing direction (horizontal samples). The extraordinary mechanical properties of the as-sprayed vertical samples reached a yield strength of ∼ 1036.6 MPa and an ultimate compressive strength of ∼ 1117.8 MPa at a strain deformation of 10.1%. The as-sprayed horizontal samples had a yield strength of ∼ 1033.1 MPa and an ultimate compressive strength of ∼ 1102 MPa at a strain of 5.6%. Thus, the as-sprayed (vertical and horizontal) samples showed mechanical anisotropic properties. Further, the as-sprayed samples showed brittle behavior. However, as-sprayed samples exhibit high ductility, up to 70%, and high plastic deformation after heat treatment. The deformation mechanism of as-sprayed and heat-treated samples is dominated by deformation twinning. This work showed excellent yield and ultimate compressive strength compared to other CrCoFeMnNi high entropy alloy manufacturing methods. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis of microstructural and high-temperature mechanical properties of Inconel 625 (IN 625) cast Ni-based superalloy welded using two different processes, i.e. gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW). For GTAW and SMAW processes, ERNiCrMo-3 and ENiCrMo-3 filler metals were employed, respectively. The base metal exhibited a γ-matrix with a sparse distribution of the Laves phase, which was attributed to the microsegregation of Nb at the interdendritic region. After GTAW and SMAW, the fusion zone exhibited fine columnar grains resulting from rapid solidification. GTAWed and SMAWed IN 625 (G625 and S625, respectively) displayed the overmatched microhardness traverse. S625 exhibited slightly higher yield and tensile strengths than G625 at temperatures of 25, 650, 700, and 750 °C. Tensile fracture occurred at the Laves phase in the base metal, showing similar features in the two welds. However, the creep lives of G625 (8915–17044 h) were significantly longer than those of S625 (894–3125 h) at 700–750 °C, exhibiting different rupture behavior. After creep deformation, fracture occurred at the fusion line in G625, whereas in S625, the weld metal was fractured. In the crept weld metal of G625, although the Laves phase was slightly grown at the interdendritic regions, it rarely influenced creep rupture. Meanwhile, in the weld metal of S625, the Laves phase was noticeably grown despite the shorter creep time compared to that of G625. Higher contents of Fe and Si in the weld metal of S625 was responsible for the acceleration of the coarsening rate of the Laves phase, causing the short creep lives of S625 by acting as a crack initiation site. Accelerated cracking in the Laves phase can be evidenced by the low density of dislocations resulting from brittle fracture with minimal plastic deformation in the weld metal. • As-SMAWed weld metal exhibited more promoted Laves phase than of as-GTAWed weld metal. • SMAWed weld metal was vulnerable to creep compared to GTAWed weld metal at 700–750 °C. • Laves phase was promoted in the SMAWed weld metal due to its high content of Fe and Si. • Laves phase was much less developed in the GTAWed weld metal even after longer creep lives. [ABSTRACT FROM AUTHOR]

Iron contamination is a major concern in aluminum alloys recycling. It is considered the main deleterious contamination due to its low solubility in the aluminum matrix leading to the formation of Fe-rich intermetallic phases with platelet-like morphology, which act as stress risers deteriorating the mechanical properties. This paper investigates the effect of Fe contamination in the microstructure and mechanical properties of Al–7Si-0.7Mg-2.8Fe alloy processed by Laser Powder Bed Fusion (LPBF). Microstructure characterization was carried out by Optical Microscopy (OM), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscope (TEM). The mechanical characterization was performed by Vickers microhardness and tensile tests. The LPBF sample was analyzed in two directions, vertical and horizontal. The results show that the LPBF process provided a microstructural refinement and reduction of the aspect ratio of α-AlFeSi phase and silicon particles, leading to a strong improvement in mechanical properties when compared to the Fe-contaminated as-cast Al–7Si-0.7Mg-2.8Fe alloy. [ABSTRACT FROM AUTHOR]

The strength-ductility trade-off of Ni3Al alloy is a significant factor that impacts its potential applications. This paper explores the application of a static magnetic field to enhance the microstructure and mechanical properties of Al-rich β (NiAl)/γ' (Ni3Al) two-phase Ni3Al alloy during directional solidification. The results revealed that the implementation of a 0.5 T magnetic field led to the formation of oriented NiAl particles with a single crystal Ni3Al composite structure. This novel composite structure exhibited higher yield strength (307.5 MPa), ultimate strength (525.6 MPa), and good ductility (8.2 %), surpassing the sample without a magnetic field by 13.7 %, 16.6 %, and 49 % respectively. These results indicate an excellent combination of strength and ductility. The synergetic improvement of strength and ductility can be primarily attributed to the particulate reinforcement effect and the maintenance of the so-called K–S orientation relationship, which enables dislocation transfer between the plastic γʹ-Ni3Al phase and the brittle β-NiAl phase. This study provides a promising strategy for obtaining desirable microstructures and properties by utilizing a magnetic field to form a composite structure. • Composite structure with oriented NiAl particles and Ni 3 Al matrix is obtained. • Both strength and ductility are enhanced for this novel composite structure. • The formation mechanism of this novel composite structures is presented. • The maintained K–S orientation relation enables dislocation transfer from β to γʹ. [ABSTRACT FROM AUTHOR]

To improve the mechanical properties of the pre-deformed SUS 304 ultra-thin strip by regulating its microstructure, the paper uses high energy pulsed current to treat the pre-deformed SUS 304 ultra-thin strip. Uniaxial tensile samples with different pre-deformation (10%, 30%, 50%) are prepared by tensile testing machine and used to study the changes in microstructure and mechanical properties of the pre-deformed samples before and after the electric pulse treatment. The results show that the electric pulse treatment results in a complete recovery of plasticity and a 10% increase in elongation at break for the 10% pre-deformed sample, and leads to a 6.8% decrease in yield strength, a 13.2% increase in tensile strength and a 34.4% increase in elongation at break for the 50% pre-deformed sample. The electric pulse treatment causes recovery and static recrystallization of pre-deformed samples at lower temperatures, and some annealing twins are formed within the recrystallized grains. The electric pulse treatment reduces the dislocation density, refines the deformed grains, alleviates the {111} silk texture generated during pre-tensile deformation, and improves the anisotropy. It can be seen that the electric pulse treatment can significantly improve the mechanical properties of pre-deformed samples and promote the plastic deformation capacity of the SUS 304 ultra-thin strip. [ABSTRACT FROM AUTHOR]

This paper designed a novel (CoFeNi) 82 Ti 5 Al 5 V 8 medium entropy alloy (MEA) with "fcc + L1 2 " typical structure using JMatPro. The microstructure of the alloy, like recrystallization/non-recrystallization and L1 2 nanoparticle size, can be well controlled by thermal-mechanical processing. The result shows that the (CoFeNi) 82 Ti 5 Al 5 V 8 MEA exhibits a good combination of ultra high yield strength of ∼1500 MPa and ultimate tensile strength of ∼1747 MPa with total ductility of ∼10.8 % when the volume fraction of non-recrystallized region with high-density L1 2 nanoparticles (∼46 nm) is up to ∼91 %. Here, the high volume fraction non-recrystallization region is along with the high-density dislocations (∼6.29 × 1014 m−2). Thus, the high strength of present MEA is mainly attributed to L1 2 nanoparticle precipitation strengthening and dislocation strengthening, which contributes ∼686 MPa and ∼305 MPa to the total yield strength (accounting for ∼66 %), respectively. Therefore, the idea of combining precipitation strengthening with dislocation strengthening offers a paradigm to develop advanced structural materials for modern industrial applications. • A new L1 2 nanoparticles-strengthened (CoFeNi) 82 Ti 5 Al 5 V 8 MEA is successfully designed. • The L1 2 nanoparticle is identified as the novel (Ni,Co,Fe) 3 (Ti,Al,V) phase. • CRCA (CoFeNi) 82 Ti 5 Al 5 V 8 has an excellent property (σ s ∼1500 MPa, σ b ∼1747 MPa, δ∼10.8 %). • CRCA (CoFeNi) 82 Ti 5 Al 5 V 8 consists of N nad NR (high-density dislocations) regions. • High strength is mainly due to precipitation strengthening and dislocation strengthening. [ABSTRACT FROM AUTHOR]

The effects of Mn content on the Sn distributions, grain sizes, second phases, and mechanical properties of Cu–9Ni–6Sn- X Mn alloys (wt.%, X = 0, 0.1, 0.5, and 1.0) were studied in this paper. The mechanisms of acting and strengthening through which Mn could promote grain refinement in the alloy were discussed. The results showed that the addition of Mn transforms the as-cast microstructure of the alloy into equiaxed grains, and the grains are obviously refined. When the amount of Mn is approximately 0.1 wt%, the average grain size of this alloy is 91.75 μm, and the grain refinement effect is greatest in the experimental range. In addition, Mn increases the uniformity of the distribution of Sn in the as-cast microstructure. Differential scanning calorimetry (DSC) analysis revealed that the addition of Mn increases the undercooling of the as-cast Cu–9Ni–6Sn alloy and decreases in the critical nucleation radii of the grains. Further microstructure observation showed that Mn is dissolved mainly in the γ-(Cu,Ni) 3 Sn phase. Consequently, the interfacial relationship between the γ-(Cu,Ni) 3 Sn phase and the matrix transforms from incoherent to semicoherent. Compared with those of the Cu–9Ni–6Sn alloy, the strength and elongation of the alloy with added Mn are relatively great. When the content of Mn is 0.1 wt%, the strength of the alloy increases from 359.75 MPa to 423.54 MPa, while the elongation remains at 19.14 %. The synergistic effect of solution strengthening and fine grain strengthening of Mn is the main reason for the great improvement in the mechanical properties of the alloy. [ABSTRACT FROM AUTHOR]