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Body-centred cubic refractory multi-principal element alloys (MPEAs), with several refractory metal elements as constituents and featuring a yield strength greater than one gigapascal, are promising materials to meet the demands of aggressive structural applications 1-6 . Their low-to-no tensile ductility at room temperature, however, limits their processability and scaled-up application 7-10 . Here we present a HfNbTiVAl 10 alloy that shows remarkable tensile ductility (roughly 20%) and ultrahigh yield strength (roughly 1,390 megapascals). Notably, these are among the best synergies compared with other related alloys. Such superb synergies derive from the addition of aluminium to the HfNbTiV alloy, resulting in a negative mixing enthalpy solid solution, which promotes strength and favours the formation of hierarchical chemical fluctuations (HCFs). The HCFs span many length scales, ranging from submicrometre to atomic scale, and create a high density of diffusive boundaries that act as effective barriers for dislocation motion. Consequently, versatile dislocation configurations are sequentially stimulated, enabling the alloy to accommodate plastic deformation while fostering substantial interactions that give rise to two unusual strain-hardening rate upturns. Thus, plastic instability is significantly delayed, which expands the plastic regime as ultralarge tensile ductility. This study provides valuable insights into achieving a synergistic combination of ultrahigh strength and large tensile ductility in MPEAs., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Two-phase titanium-based alloys are widely used in aerospace and biomedical applications, and they are obtained through phase transformations between a low-temperature hexagonal closed-packed α-phase and a high-temperature body-centred cubic β-phase. Understanding how a new phase evolves from its parent phase is critical to controlling the transforming microstructures and thus material properties. Here, we report time-resolved experimental evidence, at sub-ångström resolution, of a non-classically nucleated metastable phase that bridges the α-phase and the β-phase, in a technologically important titanium-molybdenum alloy. We observed a nanosized and chemically ordered superstructure in the α-phase matrix; its composition, chemical order and crystal structure are all found to be different from both the parent and the product phases, but instigating a vanishingly low energy barrier for the transformation into the β-phase. This latter phase transition can proceed instantly via vibrational switching when the molybdenum concentration in the superstructure exceeds a critical value. We expect that such a non-classical phase evolution mechanism is much more common than previously believed for solid-state transformations., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

In this study, we aimed to investigate changes to the fabric of Talent stent-grafts following implantation of aortic endografts and to determine the possible causes of fatigue and/or failure of the grafts. Six devices were explanted at reoperation (N=5) and autopsy (N=1). Selected segments were assessed nondestructively by gross observation and destructively by analyzing textile characteristics and chemical properties. All of the devices showed a 4/4 twill woven fabric of monofilament polyester. These devices, explanted at reoperation and autopsy, presented different levels of fatigue and/or failure. Numerous holes were found in the fabric of two devices. The minor damage caused by the passage of the sutures through the weave to fasten the Nitinol wires did not progress significantly over time. The sutures remained relatively intact, except for some distortions. The main failure mode was the abrasion of the yarns at the apices of adjacent Nitinol stents. In two devices, this abrasion resulted in fraying of the yarns and holes in the fabric tubes. This short series of explanted devices provides evidence of damage to polyester fabric used in aortic endografts and raises questions regarding their resistance to abrasion and the risk of endoleak associated with monofilament fabric yarn.

The biodurability of the Nitinol wires used in stent-grafts retrieved from reoperations and autopsy was analyzed to assess the possible causes of fracture and/or corrosion of the stents. The Nitinol wires of six explanted devices presented a corrosion-free surface after in vivo service. The drawing lines in the control wires were still present, but neither burrs nor flakes were observed. Pits and crevices were rare, but some shallow ones were present. Some abrasions of the surfaces of the Nitinol wires were also observed. The chemical composition of the explanted devices showed the presence of organic contamination that covered the thick layer of titanium oxide before reaching the Nitinol itself. The durability of the Nitinol employed in the manufacture of the Talent stent-grafts was confirmed; the results of this study show the Nitinol to be resistant to corrosion. We have also concluded that the fractures of the Nitinol wires in two devices were unique adverse incidents caused by compression and bending related to the sharp angle of the Nitinol wires.

Purpose: To validate the deployment, in vivo performance, biostability, and healing capacity of the Anaconda self-expanding endoprosthesis in a canine aortic aneurysm model., Methods: Aneurysms were surgically created in 12 dogs by sewing a woven polyester patch onto the anterior side of the thoracic or abdominal aorta. Anaconda prostheses were implanted transfemorally for prescheduled periods (1 or 3 months). Aneurysm exclusion and stent-graft patency were monitored angiographically. Healing was assessed with histological analysis and scanning electron microscopy (SEM). Textile analysis determined the physical and chemical stability of the woven polyester material, while the biostability of the nitinol wires was evaluated with SEM and spectroscopy., Results: All prostheses were intact at explantation. After 1 month, endothelial-like cells were migrating in a discontinuous manner both proximally and distally over the internal collagenous pannus at the device-host boundary. After 3 months, endothelialization had reached the midsections of the devices, with a thicker collagenous internal capsule. Patches of endothelial-like cells were sharing the luminal surface with thrombotic deposits. However, the wall of the device at the level of the aneurysm was generally poorly healed, with multiple thrombi scattered irregularly over the luminal surface. The polyester fabric was intact except for some filaments that were ruptured adjacent to the sutures and some abrasion caused by the nitinol wires. No evidence of corrosion was found on the nitinol stents., Conclusions: This Anaconda stent-graft has demonstrated its ability to exclude arterial aneurysms. The device used in this study was an experimental prototype, and the manufacturer has incorporated new immobilization features into the model for clinical use. The constituent materials appear to be suitable in terms of biocompatibility, biofunctionality, and short-term durability.

Crack initiation plays a major role in very high cycle fatigue (VHCF) life, and the initiation of cracks is related to slip behavior. There is a need for improvement in the understanding of the influence of Ti-6Al-4V microstructures on VHCF performance and crack initiation modes. In this study, through an investigation of Ti-6Al-4V VHCF in equiaxed and bimodal microstructures, two different crack initiation modes were identified. The change in crack initiation mode is related to the variation in microtexture, for which a corresponding model is proposed. The VHCF performance of the bimodal microstructure is significantly improved compared to that of the equiaxed microstructure. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) of high-temperature alloys involves intricate interdependencies among key process parameters, such as laser power and scanning speed, affecting properties such as density and tensile strength. However, relying solely on experiential knowledge for process parameter design often hampers the precise attainment of target requirements. To address this challenge, we propose an innovative approach that integrates the analytic hierarchy process (AHP) and weighted particle swarm optimization (WPSO) to recommend SLM process parameters for high-temperature alloy fabrication. Our proposed AHP–WPSO model consists of three main steps. First, a comprehensive historical database is established, capturing the process parameters and performance metrics of high-temperature alloy SLM parts. Utilizing an AHP framework, we compute the performance similarity between target and historical cases, applying rational thresholds to identify analogous cases. When suitable analogs are elusive, the model seamlessly transitions to the second step. Here, the WPSO model optimizes and recommends process parameters according to target specifications. Lastly, our experimental validation of the GH4169 high-temperature alloy through SLM experiments corroborates the effectiveness of our AHP–WPSO model in making process parameter recommendations. The outcomes underscore the model's high accuracy, attaining a recommendation precision of 99.81% and 96.32% when historical analogs are present and absent, respectively. This innovative approach offers a robust and reliable solution to the challenges posed in SLM process parameter optimization for high-temperature alloy applications. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) are designed based on a blend of polymer donor and small molecular acceptor whereby the thermodynamic relaxation of the morphology raises the concerns related to operational stability. Herein, it is demonstrated that the classical Y6‐based binary device can be stabilized by using its derivative of ZCCF3 as the third component, which is designed with the replacing of the thiadiazole group on Y6 with the trifluoromethyl substituted diazepine unit. ZCCF3 delivers not only higher glass transition temperature (Tg) than Y6 but also have hyper‐miscibility with Y6, contributing to a favorable diffusion‐limited Y6:ZCCF3 alloy when blended with polymer donor. Consequently, a champion power conversion efficiency of 18.54% is achieved in the optimal PM6: Y6: ZCCF3 devices, which can retain their 80% initial efficiency of up to 360 h. This study highlights the importance of high Tg of the third component and its derived hyper‐miscible accepter alloys in achieving highly efficient and stable OSCs. [ABSTRACT FROM AUTHOR]

Oxidation behaviors of three Ni-based model alloys and pure Ni in the temperature range of 700–1200 °C are investigated to reveal effects of Cr, Al, and Si on the oxidation resistance of Ni-based superalloys. The formation and integrity of consecutive chromia or alumina layers are important for excellent oxidation resistance. The addition of 20 at.% Cr can effectively improve the oxidation resistance of Ni-based alloys by forming a thin chromia film below 1000 °C, while adding 15 at.% Al has a beneficial effect on the oxidation resistance of Ni-based alloys at temperatures above 900 °C. The addition of 2 at.% Si to Ni-Al alloy is insufficient to form a protective SiO2 layer but can accelerate the formation of alumina, which enables Ni-Al alloy to form a consecutive inner alumina layer at a relatively low temperature of 800 °C and further improve the oxidation resistance above 800 °C. [ABSTRACT FROM AUTHOR]

Strategies involving metastable phases have been the basis of the design of numerous alloys, yet research on metastable high-entropy alloys is still in its infancy. In dual-phase high-entropy alloys, the combination of local chemical environments and loading-induced crystal structure changes suggests a relationship between deformation mechanisms and chemical atomic distribution, which we examine in here in a Cantor-like Cr20Mn6Fe34Co34Ni6 alloy, comprising both face-centered cubic (fcc) and hexagonal closed packed (hcp) phases. We observe that partial dislocation activities result in stable three-dimensional stacking-fault networks. Additionally, the fraction of the stronger hcp phase progressively increases during plastic deformation by forming at the stacking-fault network boundaries in the fcc phase, serving as the major source of strain hardening. In this context, variations in local chemical composition promote a high density of Lomer-Cottrell locks, which facilitate the construction of the stacking-fault networks to provide nucleation sites for the hcp phase transformation. In dual-phase Cantor-like high entropy alloys, how local chemistry affects enhanced deformation mechanisms remains unclear. Here, the authors image 3D stacking fault networks formation and show they both impede dislocations and facilitate phase transformations via local chemical composition variations. [ABSTRACT FROM AUTHOR]

Deformation twinning is an important plastic carrier competing with the ordinary dislocation slip in a broad class of crystalline solids, which critically controls the mechanical properties, plasticity, and fracture of crystalline materials across different length scales. Compared with the well-established twinning theories in their close-packed metallic counterparts, a comprehensive understanding of twinning dynamics and twinning mechanisms in body-centered cubic (BCC) metals and alloys remains largely elusive, though some important progresses have been made in past few decades. In this review, we systematically summarize recent advances of deformation twinning in BCC metals and alloys in past few decades, by focusing on the various aspects of the most common {1 1 2}〈11 1 ¯ 〉 twins, including the atomic structures of twin boundaries, twin nucleation and growth mechanisms, asymmetry of twinning and anti-twinning, factors influencing the deformation twins, twin-induced fractures and some other unique properties. {3 3 2}〈11 3 ¯ 〉 and other types of high-index deformation twins that have been extensively observed in BCC alloys are also summarized and discussed. The comprehensive understanding of deformation twinning in BCC metals and alloys not only advances our knowledge of twinning in metallic materials, but also has broad implications for the design of high-performance BCC metals and alloys by regulating deformation twins. [ABSTRACT FROM AUTHOR]

• The biosafety ZWEM2100 alloy with low rare earth element content were developed. • The ZWEM2100 alloy presented outstanding corrosion resistance and mechanical properties in vitro. • In vivo experiments demonstrated that ZWEM2100 alloy has an excellent ability to promote osteogenesis. The purpose of this work was to validate the osteogenic characteristics and biosafety of Mg-Zn-Y-Gd-Mn alloys with low rare earth content for orthopedic applications. The as-extruded Mg-1.96Zn-0.97Y-0.47Gd-0.38Mn alloy exhibited excellent corrosion resistance and mechanical properties. The tissue surrounding the SD rats femoral implants was studied using micro-CT and H&E staining techniques. Around the Mg-1.96Zn-0.97Y-0.47Gd-0.38Mn alloy implants, there was evidently significant bone development with increased thickness and quantity of trabeculae. In addition, no partial or systemic adverse effects were observed after surgery. [ABSTRACT FROM AUTHOR]

A comprehensive and integrated review of the hypergravity field applied to solidifying alloys is provided. The hypergravity field refers to an environment in which the acceleration of gravity is more significant than the gravitational acceleration through rotation, resulting in significant changes in the solidification behavior of the alloy. The convection mode of the melt is closely related to the level and direction of hypergravity. Obvious floatation or sedimentation of solutes and crystals of different densities is induced. Columnar-to-equiaxed transition, grain refinement, and gradients in composition and microstructure are readily available under hypergravity. Furthermore, the nucleation and growth of crystals and their migration under enhanced convection are gradually revealed through simulations and in-situ observations. This review aims to summarize the universal law of the effect of the hypergravity field on the composition distribution and microstructure evolution of alloys during solidification. Based on the development of hypergravity equipment and characterization methods, it is expected to broaden the theoretical framework of hypergravity solidification. To provide a theoretical reference for developing new solidification processes and high-performance materials. [Display omitted] • A comprehensive review on the principles and development of hypergravity technology is presented. • Microstructure evolution, segregation, and mechanisms are provided during alloy solidification under hypergravity. • Point out the unsettled issues and desirable future work in hypergravity solidification. [ABSTRACT FROM AUTHOR]

The alloying effects on the microstructure, especially precipitation of harmful phases and solvus temperature of L1 2 -structured γʹ phase, etc., are essential for alloy design and development of precipitation strengthened Co-based superalloys. Based on the newly reported Co30Ni9Al5Mo10Cr2Ta0.03B alloy, alloying elements Mo, Cr, Al, Ta and Ni are systematically changed and alloys are fabricated to investigate their microstructures in two heat treatment statuses, namely homogenization and aging, respectively. Results show that Mo and Cr are γ forming elements and have limited effect on γʹ solvus temperature, but high concentration of Mo and Cr facilitates the formation of harmful μ phase. Al, Ta, and Ni are all γʹ stabilizers and can effectively increase γʹ solvus temperature, but roles of Al, Ta and Ni are different. Increasing Al and Ta would result in other harmful phases, such as the μ phase in the 6Ta and 4Ta alloys, and μ + B2 phases in the 13Al and 11.5Al alloys. However, Ni addition significantly increases solvus temperature and area fraction of γʹ phase without occurrence of harmful phases. The current findings might provide guidelines for design and development of precipitation strengthened Co-based alloys. [Display omitted] • The alloying effects of Mo, Cr, Ta, Al & Ni are systematically investigated. • Mo & Cr are γ formers, which facilitate the formation of μ phase. • Ta is a strong γˊ former, but excessive Ta facilitates the formation of TCP phase. • Al is necessary for γˊ phase, but excessive Al results in B2 & TCP phases. • Ni stabilizes γˊ phase without forming the harmful phases in Co-based alloys. [ABSTRACT FROM AUTHOR]

The article discussed the effects of hypergravity fields on the dendrite structure, macrosegregation, and mechanical properties of Al7050 alloy. Compared to normal gravity, the average size of α-Al grains at the bottom of the sample was significantly reduced under hypergravity. The melt superheating temperature influenced atomic clusters, which, along with dendrite fragmentation, facilitated heterogeneous nucleation. Subsequently, the "crystal rain" mechanism led to the migration and accumulation of primary crystals. The emergence of coarse columnar dendrites under hypergravity may result from high-speed forced convection transferring solutes at the dendrite tips, thereby promoting dendrite growth through increased concentration gradients. Under hypergravity, Zn, Mg, and Cu elements were enriched at the bottom of the sample, possibly due to solutes expelled during α-Al dendrite growth entering the liquid phase. The denser solute-rich liquid settled at the bottom under hypergravity, precipitating numerous secondary phases. The compressive strength and strain of the hypergravity specimen increased due to its special density-dependent layered structure. • The microstructure evolution, mechanical properties, and mechanisms of Al7050 alloy under hypergravity were studied. • The heterogeneous nucleation and "crystal rain" mechanisms jointly led to grain refinement under hypergravity. • Hypergravity altered solute distribution in alloy melt, causing macrosegregation and equiaxed-to-columnar grain transition. • At 3000 g , compressive strength and strain of solidified Al7050 alloys rose by 24.3% and 47.4%, respectively, versus 1 g. [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]

A Co 30 Cr 20 Fe 18 Mn 18 Ni 11 Si 3 high-entropy alloy (HEA) with low stacking fault energy and high strengthen was designed based on the principle of heterostructure strengthening. The alloy was processed into a multiscale heterogeneous microstructure containing hierarchical twins. The alloy achieved an ultrahigh yield strength of 1500 MPa, ultimate tensile strength of 1750 MPa and a large ductility of 20 % at 77 K. These mechanical properties were superior to those of most FCC HEAs reported in the literature, breaking the strength-ductility trade-off of conventional metal alloys. Such extraordinary mechanical properties were attributed to a suitable strain hardening capability, stemming from the synergistic effect of hetero-deformation-induced hardening, twinning-induced plasticity, and deformation-induced phase transformation during tensile deformation. [Display omitted] [ABSTRACT FROM AUTHOR]

The cyclic oxidation behavior of fourth-generation nickel-based single crystal superalloys with 2–4 wt% Mo content were studied at 900 ℃ and 1100 ℃. At 900 ℃, with the increase of Mo content, the oxide layer accumulates more growth stress, resulting in the interface between the outer oxide layer and the inner oxide layer more prone to crack initiation. At 1100 ℃, the oxidation layer accumulates more growth stress and thermal stress, so the oxidation layer occurs large scale spalling, which is more severe in 4Mo alloy. The results show that the increase of Mo content of alloy promotes the oxidation of containing W-Re alloy, which promotes the volatilization of oxides and the spalling of oxide, decreases the protection of oxide layer, and deteriorates the oxidation resistance of the alloy. • The increase of Mo content of alloy promotes the oxidation of containing W-Re alloy. • With the increase of Mo content, the volatilization of oxides and the spalling of oxide of alloy was promoted. • Mo has more severe harm to the oxidation resistance of the alloy at higher temperature. • The alloy with 2 wt% Mo addition has the highest oxidation resistance. [ABSTRACT FROM AUTHOR]

Technologically important mechanical properties of engineering materials often degrade at low temperatures. One class of materials that defy this trend are CrCoNi-based medium- and high-entropy alloys, as they display enhanced strength, ductility, and toughness with decreasing temperature. Here we show, using in situ straining in the transmission electron microscope at 93 K (−180 °C) that their exceptional damage tolerance involves a synergy of deformation mechanisms, including twinning, glide of partials and full dislocations, extensive cross-slip, and multiple slip activated by dislocation and grain-boundary interactions. In particular, massive cross-slip occurs at the early stages of plastic deformation, thereby promoting multiple slip and dislocation interactions. These results indicate that the reduced intensity of thermal activation of defects at low temperatures and the required increase of applied stress for continued plastic flow, together with high lattice resistance, play a pivotal role in promoting the concurrent operation of multiple deformation mechanisms, which collectively enable the outstanding mechanical properties of these alloys. [ABSTRACT FROM AUTHOR]

Eutectic high-entropy alloys (EHEAs) are gaining interest due to their excellent mechanical properties, superior liquidity and castability, and reduced compositional segregation. Here, we developed and successfully prepared Al 19 Co 23 Fe 21 Ni 37 EHEA using vacuum arc melting. By adjusting the Co content and introducing V, we also obtained near-eutectic high entropy alloys (Al 18 Co 27 Fe 20 Ni 35 and Al 18 Co 22 Fe 20 Ni 35 V 5). The Al 19 Co 23 Fe 21 Ni 37 and Al 18 Co 27 Fe 20 Ni 35 alloys consist of alternating face-centered cubic (FCC) and ordered body-centered cubic (B2) phases, whereas the Al 18 Co 22 Fe 20 Ni 35 V 5 alloy consists of FCC, ordered face-centered cubic (L1 2) and B2 phases. The heterostructure not only restricts dislocation motion but also induces significant hetero-deformation-induced hardening, resulting in a high-strain hardening effect. Furthermore, the high volume fraction of the hard B2 phase contributes to the increased strength of the alloy due to its high-stress partition relative to the other phases. As such, Al 18 Co 22 Fe 20 Ni 35 V 5 alloy exhibits an excellent tensile ductility of 16.1%, yield strength of 571 MPa, and ultimate tensile strength of 1157 MPa. • A series of eutectic and near-eutectic high entropy alloys were successfully designed and prepared by arc melting. • The heterostructure not only restricts dislocation motion but also induces significant hetero-deformation induced (HDI) hardening, resulting in a high-strain hardening effect. • The hypereutectic Al 18 Co 22 Fe 20 Ni 35 V 5 alloy exhibits the best strength-ductility synergy. [ABSTRACT FROM AUTHOR]

As the blade material of engine, nickel-base single crystal superalloy has been subjected to complex service environment such as high temperature and alternating load for a long time. In this work, the mechanism of fatigue microcrack initiation and propagation in a nickel-based single crystal at 950 °C and 1050 °C was studied by using the in-situ scanning electron microscope high temperature fatigue test system. At 950 °C, the alloy deformation was controlled by slip and the crack shear γ/γ' phase cracking, showing Stage I mode. At 1050 °C, the alloy crack tearing occurred at the γ phase parallel to the loading direction and γ/γ' interface perpendicular to the loading direction and presents a Stage II mode perpendicular to the loading axis, then changes into Stage I in the accelerating stage. The deformation mechanism of fatigue cracking at two temperatures was compared. Besides, the influence of the microstructure defects on the fatigue crack behavior was discussed. The results show that the propagation of the microcrack below 100 μm shows evident fluctuations, which is closely related to the microstructure and the development stage of the fatigue crack. • The fatigue crack behavior of a nickel-base single crystal superalloy was investigated by in-situ SEM at 950 °C and 1050 °C. • The microscopic deformation mechanism of fatigue cracking at 950 °C and 1050 °C was revealed. • The effect of microstructure defects on the initiation and propagation behavior of fatigue cracks was discussed. [ABSTRACT FROM AUTHOR]

To determine the influence of Re and Ru on the phase morphologies and microstructure in Ni-based superalloys, a series of model alloys derived from the 4th generation TMS-138 superalloy have been investigated with systemically changing Re and Ru additions. All alloys are subjected to solid solution and aging treatments to achieve the typical γ/γ′ two phases microstructure. Phase transition temperatures are measured by using differential scanning calorimetry. The Re is found to increase the γ′-solvus temperature with a slope of roughly 5.4 ℃ per wt% Re in Ru-free alloys and 2.3 ℃ per wt% Re in 2Ru alloys, while the Ru exhibits much weaker effect. Microstructure and composition of the two phases are examined to understand the Re and Ru effects on γ′ size, shape, volume fraction, the elemental partition behavior, and the γ/γ′ lattice misfit. The results show that the addition of Re affects size and shape of γ′ precipitates, and also reduces γ/γ′ lattice misfit significantly. Meanwhile, Re increases partition coefficients of Cr and Ru. In comparison, the addition of Ru seems to have little effect on morphology of γ′ precipitates and the γ/γ′ lattice misfit, but Ru appears to alter partitioning behaviors of other elements. Because Re and Ru are two key elements for high generation Ni-based single crystal (SX) superalloys, this work might provide guidelines for designing next generation of SX superalloys. [Display omitted] • Re effectively increases the γ′ solvus temperature of superalloys, while Ru has slight effect on the γ′ solvus temperature. • Re addition decreases the size of γ′ phase and γ/γ′ lattice misfit, facilitating cubic precipitation of γ′ phase. • Ru addition only has little effect on the γ′ morphology and γ/γ′ lattice misfit of superalloys. • Partitioning behaviors of other alloying elements depend on the Re and Ru additions, especially Ru. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co alleviates large-scale heterogeneity of multiple microstructures of the alloys. • Co significantly reduces the partitioning coefficient of γ forming elements, which alleviates small-scale heterogeneity. • Co additions suppress TCP precipitation and increase microstructure stability. The effects of Co on multi-scale elemental distributions were studied in an advanced Ru-containing Ni-based single crystal superalloys. Two types scales of microstructural heterogeneities, the large-scale dendritic segregations and small-scale elemental partitions between γ/γ' phase were compared in as-cast, heat-treated and thermal-exposed alloys. The elemental homogeneities on both large and small scale were shown to be enhanced with Co additions, giving rise to the restricted precipitation of TCP phase. It is thus expected the potential role of Co to replace part of Ru in advanced superalloys. [ABSTRACT FROM AUTHOR]

The deformation behavior in polycrystalline Laser melting deposited (LMD) TA15 alloy was investigated at a temperature of 500°C using advanced in-situ Secondary electron microscopy (SEM) tensile setup coupled with Electron backscatter diffraction (EBSD). The grains morphology, crystal orientation, preferred pole texture, activated slip traces, grain boundaries evolution, and strain-induced misorientation were systematically analyzed during tensile straining. It was determined that the diverse α-grains (crystal orientation and morphology) revealed inhomogeneous deformation under tensile loading. The overall strain was allocated by grain rotation and substructure formation. The preferred oriented (0001) pole texture maximum was increased during initial strain level. In contrast, at higher strain, the texture intensity was decreased due to the formation and relocation of the newly formed substructures. The fraction of low angle grain boundaries (LAGBs 2–10°) was increased continually with increasing strain. Strain-induced dislocations within larger grains formed new LAGBs, and the increasing fraction of LAGBs was validated by Kernel average misorientation (KAM) map. The prismatic slip mode was identified as the primary active slip system at the initial deformation stage. The fraction of basal and pyramidal slips increased as the strain increased, describing the opposite trend to prismatic slip. The grains rotation and strain accumulation at the grain boundaries accommodated the plastic deformation, ultimately causing boundary sliding. • In-situ EBSD reveals real time microstructure evolution during tensile deformation. • Laser deposited TA15 demonstrate inhomogeneous deformation under tensile stress. • Basal slip system activates at higher SF values throughout the deformation process. • Large size grains endure subdivision under stress to accumulate the tensile strain. [ABSTRACT FROM AUTHOR]

Titanium alloy was extensively used in aerospace industrial field. It has a great significance to directly reveal the deformation process as a function of application conditions. This work investigates the real-time deformation behavior of laser direct metal deposited (LDMD) Ti–6Al–4V alloy at 200 °C, using self-developed high temperature in-situ scanning electron microscope (SEM) tensile stage with a controlled heating system. The results showed that the microstructure of the sample comprised of columnar β grains with zigzag grain boundaries decorated by tilted α plates along the building direction. During uniaxial tensile, slip bands develop along the grain boundaries between α plates with increasing stress. Grain boundary sliding contributes to the high tensile elongation. Compared the mechanical properties along transvers tensile with those at room temperature, the tensile stress decreased and displacement increased at 200 °C. Therefore, higher elongation and reduction in cross-sectional area were identified at 200 °C than those at room temperature. The fracture of specimen at 200 °C shows obvious necking character and deep dimples with thin rims. Coalescence of slip bands at α/α interface creates voids and the coupling of voids nucleates micro-crack. α/α grain boundary interface constitutes path to the crack propagation. The high misorientation angle at columnar β grain boundary hinders the cracks propagation. Finally, the cracks accumulate along the columnar β grain boundary leading to fracture. • The microstructure deformation of LDMD Ti–6Al–4V alloy is studied by high temperature in-situ SEM tensile stage at 200 °C. • Slip bands development, cracks propagation, and columnar β GB hindering at 200 °C are investigated. • Temperature effect on the deformation mode and corresponding mechanical properties have been revealed. [ABSTRACT FROM AUTHOR]

Abstract This study investigated a novel hypothesis on the influences of residual or pre-dislocation structures on creep life of Ni-based single crystal superalloys. Different types of anisotropic dislocation structures were created by pre-straining the samples at a relatively low temperature under different constant bias load conditions. After such pre-straining treatment, the samples were subjected to creep testing at higher temperatures under uniaxial tension. It was found that the pre-straining treatment was effective in creating different anisotropic dislocation structures without affecting the γ′ phase cuboid morphology and that the samples containing different anisotropic dislocation structures have all significantly reduced creep lives. The difference in the anisotropy of the dislocation structures has little influence on the reduction of the creep life or the rafting morphology of the γ′ phase cuboids. By using a Re-free alloy, the influence of the TCP phase precipitation on creep life is also clarified. These observations suggest that interruption to high temperature straining is the main contributor to the reduced creep lives. This finding raises a serious concern on the validity, or reliability, of creep life assessment based on continuous laboratory creep tests for real life applications, where the services are almost always interrupted into intermittent sessions. Graphical abstract Unlabelled Image Highlights • Different anisotropic dislocation network structures were created by pre-straining at an elevated temperature. • The pre-existing anisotropic dislocation structures have no influence on the rafting behavior of the γ′ phase cuboids. • The pre-existing dislocations promote the formation of TCP phases during creep testing. • All pre-strained samples showed significantly reduced creep life. [ABSTRACT FROM AUTHOR]