Increasing the yield strength of metallic materials is observed to almost always substantially reduce their tensile ductility. Here we unravel the origin of this perplexing “strength-ductility trade-off”, and conclude that this dilemma does not necessarily preclude concurrent high strength and high ductility. We discuss several strengthening and work hardening mechanisms that regulate dislocation behavior, including traditional ones that have been pushed to their extreme in recent years, as well as new ones that take advantage of the heightened structural and chemical heterogeneities; all these mechanisms are rendered more powerful by emerging complex concentrated alloys that bring in multiple principal elements. These mechanisms, while offering elevated strength, contribute to sustainable strain hardening under high flow stresses, delaying strain localization to allow prolonged uniform elongation. The current status in the pursuit for concurrent high strength and high ductility is reviewed. The goal we set for high yield strength ~2 GPa (rivaling super steels) together with large uniform elongation ~30% (much like un-strengthened elemental metals) is projected to be soon within reach. These take-home messages shed light on some existing puzzles regarding the strength-ductility synergy, and offer new insight into the innovative design of alloys.

Complex phase (CP) steels are widely used in automotive components such as frame rails, rocker panels, and tunnel stiffeners owing to their high strength and good local formability. The subtle hardness difference between microstructures allows CP steels to exhibit excellent hole expansion performance, with the high-hardness martensite-austenite (MA) constituents being the critical structure. The distribution of MA constituents is crucial to the mechanical properties of the product. This study aims to improve the hole expansion property by constructing a continuous distribution of MA constituents along the rolling direction at the thickness center. Microstructures and hole expansion behavior were investigated using CLSM, SEM, EBSD, and hole expansion tests. Results indicate that after thermodynamic treatment, the MA constituents were aggregated at the thickness center in a continuous distribution along the rolling direction with a long axis of approximately 1.25 μm, and an average distance of less than 1.0 μm. Microhardness quantification of the plastic damage on the punching edge suggests that the advanced steel exhibits the highest hardening at the thickness center with a 41% hardness increase after punching, which is higher than the 31% hardening in the maximum hardening burr zone of the base steel. The advanced steel, despite suffering severe punching damage, exhibited a hole expansion ratio of approximately 43%, higher than the 34% of the base steel. Quasi in situ interrupted hole expansion tests indicate that at the thickness center of the advanced steel, the circumferential cracks formed through a multiple void interaction mechanism which promotes the stress release. In the matrix, pit-like damage is caused by a void coalescence mechanism. Both mechanisms lead to the mechanical instability and eventual failure of the steel. The damaging position of the hole edge had a decisive impact on the fracture mode.

The reversed austenite obtained through a tempering process can effectively improve the toughness and ductility of super martensitic stainless steel (SMSS). Overcoming the trade-off between thermal stability and quantity of the reversed austenite is the key to improving the cryogenic impact toughness of SMSS. In this study, the mechanical properties at room temperature and cryogenic impact toughness at -196 ^oC of 0Cr16Ni5Mo1 SMSS after quenching and tempering (QT) were investigated, along with quenching, intercritical annealing, and tempering (QIT) processes. Reverse transformation behavior during the heat treatment was studied using a thermal dilatometer, and the microstructure evolution was characterized by XRD, EBSD, and TEM. Additionally, the effect of reversed austenite on cryogenic impact toughness was extensively analyzed. The results showed that full martensite was obtained in 0Cr16Ni5Mo1 SMSS after quenching at 1100 ^oC. The volume fraction of reversed austenite in the QT samples tempered at 620 ^oC was found to be 16.4%, which decreased to 5.0% after cryogenic treatment with liquid nitrogen, and the cryogenic impact toughness of the QT samples was obtained to be only 36.4 J/cm². The microstructure of samples after intercritical annealing at 680 ^oC mainly consisted of Ni-poor tempered martensite and Ni-rich fresh martensite. Furthermore, the volume fraction of reversed austenite in the QIT samples increased to 23.8% during the subsequent tempering process at 620 ^oC while the plasticity increased by 6% and the strength decreased by 7% at room temperature. The average Ni content of reversed austenite in the QIT samples reached 13% (mass fraction), which considerably improved the thermal stability of reversed austenite. Moreover, ~18.3% (volume fraction) reversed austenite remained stable in QIT samples at -196 ^oC, thereby substantially improving the cryogenic impact toughness to 115.4 J/cm² by absorbing the impact energy through transformation into martensite. The impact fracture of the QIT samples was dominated by dimples, but there remained a little quasicleavage morphology indicating a mixed fracture mode.

The Fe-Cr-B-C alloy is a new wear-resistant boron cast iron alloy developed from high-chromium cast iron. This alloy is inexpensive, easy to process, and exhibits excellent wear resistance and good formability, making it suitable for the manufacturing of wear-resistant parts with high dimensional accuracy. The Fe-Cr-B-C alloy has great potential for application and is gradually replacing chromium wear-resistant alloys. In recent years, studies have shown that after composition optimization, the Fe-Cr-B-C alloy can be directly used in the as-cast state without subsequent heat treatment, resulting in a significant decrease in cost. Thus, optimization of the composition of the Fe-Cr-B-C alloy is of great significance for the development of wear-resistant materials. The strength-toughness and wear resistance of the boron cast iron mainly depend on the characteristics of the B-rich precipitates. Reasonable control of the B addition can optimize the characteristic of the B-rich precipitates, thereby improving the service properties of the as-cast Fe-Cr-B-C alloy. However, the role of B in the Fe-Cr-B-C alloy has been scarcely investigated. Therefore, the effects of B content on the solidification behavior, as-cast microstructure, hardness, impact toughness, and wear resistance of the Fe-Cr-B-C alloy were examined in this study. The results show that with increasing B content, the liquidus temperature and formation temperature of precipitates significantly decrease, the formation range of precipitates expands, and the solidification temperature range first increases and then decreases. At a B content of 0.0006% (mass fraction), the solidification of the Fe-Cr-B-C alloy proceeds as follows: L→δ→γ dendrite→primary Nb(C, B)→eutectic [γ + Cr₇C₃]. After solidification, the dendrite arm comprised of martensite, and the interdendritic region was composed of residual γ and trace amounts of Nb(C, B), [γ + Cr₇C₃]. With the increase in the B content to 0.51%, the growth of γ dendrites was significantly hindered, resulting in the refinement of the dendritic structure. The solidification process changed to L→γ dendrite→primary (Fe, Cr)₂(B, C)→primary Nb(C, B)→eutectic [γ + (Fe, Cr)₂(B, C)]. After solidification, martensitic transformation occurred in both the interdendritic region and dendrite arms, and a continuous boron-carbide network was formed along the interdendritic region. With the further increase in B content to 2.89%, a large amount of boron-carbide was formed at the initial stage of solidification, which not only caused the disappearance of the dendritic structure but also consumed most of the B atoms, seriously reducing the hardenability of γ matrix and inhibiting its martensite transformation. The solidification process changed to L→primary γ→primary (Fe, Cr)₂(B, C)→eutectic [γ + (Fe, Cr)₂(B, C)]→peritectic [γ + (Fe, Cr)₂(B, C) + (Fe, Cr)₃(C, B)]. The alloy with a B content of 0.0006% possesses the highest impact toughness, and moderate Rockwell hardness and wear resistance. The alloy with a B content of 0.51% possesses the highest Rockwell hardness, optimal wear resistance, and moderate impact toughness. The alloy with a B content of 2.89% possesses the lowest Rockwell hardness and impact toughness, and the poorest wear resistance. The change in boron-carbide characteristic and the martensitic transformation of matrix are the main reasons for the significant differences in strength-toughness and wear resistance among these alloys. The obtained results provide a theoretical basis for optimizing the composition and improving the wear resistance of the as-cast Fe-Cr-B-C alloy.

Titanium alloy has emerged as the preferred structural material in the aerospace and marine industries because of its exceptional strength-to-weight ratio, corrosion resistance, and fatigue resistance. The primary application of titanium alloy in aerospace is evident in aeroengines, emphasizing the importance of developing lightweight, high-performance components to enhance engine reliability. Despite these advantages, challenges arise during hot processing because the alloy forms a strong texture, resulting in anisotropic mechanical properties. In addition, the formation of “macrozones”, areas with similar grain orientations during hot processing, further complicates matters by facilitating stress concentration during hot deformation, thereby increasing the likelihood of crack nucleation. Rapid crack propagation within “macrozones” reduces the service life of titanium alloy components, necessitating a thorough investigation of the formation mechanism and control methods for “macrozones”. This study delves into the microstructure evolution and texture formation of TC4 titanium alloy under various hot compression conditions, aiming to elucidate the role of weakening texture and “macrozone”. The microstructure and texture evolution of the α phase after α + β phase field, β phase field, and continuous through-transus thermal compression were examined in TC4 alloy through thermal compression tests, optical microscopy, electron backscatter diffraction, and reconstruction of the high-temperature β phase. The results indicate that specimens primarily comprised equiaxed α phase after compression in the α + β phase field. The activation of {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}<\mathrm{11}\overline{\mathrm{2}}\mathrm{0}> prismatic slip systems caused α phase rotation toward {\mathrm{11}\overline{\mathrm{2}}\mathrm{0}}//forging direction (FD) orientation during deformation. With increased deformation and strain rate, α grains gradually rotated to {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD orientation. Cooling after holding or compression in the β phase field resulted in the development of lamellar α phase with a {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture. In the β phase field, 30% compression induced β grain rotation to \left\{\mathrm{001}\right\}//FD orientation, enhancing β phase\left\{\mathrm{001}\right\}//FD texture and promoting the formation of α phase{\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD transformation texture during cooling. Increased deformation and strain rate facilitated dynamic recrystallization of the β phase, reducing β grain size, weakening α phase {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture, and refining α grain size. After continuous through-transus thermal compression, the dominant {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture formation occurred because of prismatic slip system activation. Under specific conditions, such as 30% compression in the β phase field and 30% compression in the α + β phase field at 0.01 s^-1, inhibition of {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture formation was observed as α grains rotated to {\mathrm{11}\overline{\mathrm{2}}\mathrm{0}}//FD orientation during dynamic precipitation. Increased deformation in the α + β phase field led to further rotation of α grains to {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD orientation, intensifying {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture. Conversely, holding in the β phase field (undeformed), then cooled to the α + β phase field and compressed at 0.01^-1 to a 60% reduction resulted in weak variant selection during dynamic precipitation of α phase, with large deformation promoting dynamic recrystallization of α phase and yielding the weakest α phase {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture. And at a strain rate of 0.05 s^-1, extensive deformation promoting dynamic recrystallization of α phase, and weakening {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture. Continuous through-transus thermal compression was identified as a method for obtaining lamellar-structured titanium alloys with weak texture. Subsequent mechanical property testing at room temperature (around 20 ^oC) revealed that the through-transus thermal compressed specimen at 1020 ^oC, 5 min (undeformed) + 920 ^oC, 60%, and 0.01 s^-1 exhibited the weakest {\mathrm{10}\overline{\mathrm{1}}\mathrm{0}}//FD texture intensity and the smallest grain size of α phase. This specimen demonstrated strong crack initiation and propagation resistance, resulting in the highest elongation.

Boiler steel is prone to thermal corrosion and abrasion in high-temperature environments, making thermal spray protective coatings a vital solution for enhancing the corrosion and abrasion resistance of boilers. This study focuses on the development of a novel AlCrCu_0.5Mo_0.5Ni high-entropy alloy powder synthesized through mechanical alloying (MA) using monolithic metal powders as starting materials. The effects of milling time on the phase structure, grain size, and microstructure evolution of the MA powder were investigated. Phase characterization was performed using XRD; grain size, lattice strain, and lattice constant were measured; morphological and microstructural analyses were performed using SEM and TEM. Phase regulation through vacuum isothermal annealing techniques was also explored. The findings indicated the formation of two bcc (bcc1, bcc2) and one fcc solid solution phases within the high-entropy alloy powder. With increased milling time, the MA powder experienced plastic deformation, which led to a reduction in grain size and an augmentation of lattice strain. Powder particle fragmentation and refinement of the element-enriched zones facilitated enhanced diffusion and alloying of the elements. At 40 h of milling, the powder particles exhibited a more homogeneous elemental distribution, with phase contents of 41% bcc1, 37% bcc2, and 22% fcc, and an average particle size of 24 μm, making them suitable for thermal spray applications. Annealing at 800 ^oC led to the decomposition of the bcc2 solid solution structure after 40 h of ball milling. Upon increasing the annealing temperature to 1000 ^oC, complete decomposition of the bcc2 solid solution was observed, resulting in 68% bcc1 and 21% fcc phases, with the emergence of 11% CrMo phase. As the annealing temperature was increased, the MA powder released significant strain energy, increasing grain size and a reduction in lattice strain. The maximum hardness and elasticity modulus were achieved after annealing at 800 ^oC, recorded at (6.54 ± 0.58) and (65.62 ± 3.07) GPa, respectively.

In recent years, advanced ultra-supercritical (A-USC) power plants have developed rapidly to increase the thermal efficiency and decrease CO₂ emission. Inconel 740H (IN 740H) is one of the Ni-based superalloys with the highest creep strength and good corrosion resistance at elevated temperatures. Owing to its excellent comprehensive properties, IN 740H is considered one of the best candidate materials for superheater and reheater in A-USC power plants. Further improving the mechanical properties of IN 740H welded joint enhances the safety and economic viability of the power plants. In this study, IN 740H tubes were welded by multipass tungsten inert gas hot-wire welding followed by a post weld heat treatment (PWHT) at 800 ^oC for 5 h. The formation mechanism of the γ′-denuded zone in the IN 740H welded joint after creep at different temperatures was systematically investigated using OM, SEM, and TEM, and its effect on the mechanical properties was analyzed.Results show that the small rod-like γ′ phase only discontinuously precipitates at grain boundaries in the weld metal during PWHT. After creep at different temperatures, an earlier formation of a coarse rod-like γ′ phase and γ′-denuded zone is observed at grain boundaries in the weld metal than in the base metal. The formation of the coarse rod-like γ′ phase at grain boundaries in the base metal results from the discontinuous coarsening of the spherical γ′ phase near grain boundaries, whereas that in the weld metal results from the discontinuous coarsening of the discontinuously precipitated rod-like γ′ phase at the grain boundaries and spherical γ′ phase near the grain boundaries. The discontinuous coarsening of the rod-like γ′ phase and precipitation of M₂₃C₆ carbides at grain boundaries lead to the formation of the γ′-denuded zone. Increasing the creep temperature and creep time when the temperature is in the range of 700-800 ^oC increases the size of the rod-like γ′ phase and width of the γ′-denuded zone at grain boundaries, whereas the number of rod-like γ′ phase initially decreases and then increases with the increase of creep temperature. The spherical γ′ phase in the grain interiors plays a vital role in changing the hardness of the IN 740H welded joint. The discontinuous coarsening of the γ′ phase and the formation of the γ′-denuded zone at the grain boundaries not only decrease the hardness, but also deteriorate the creep rupture strength of the IN 740H welded joint. Controlling the discontinuous coarsening of the rod-like γ′ phase at grain boundaries, suppressing the formation of the γ′-denuded zone, and controlling the growth of the spherical γ′ phase in the grain interiors are necessary to improve the mechanical properties of the IN 740H welded joint.

Turbine discs, manufactured using powder metallurgy nickel-based superalloys, serve as critical hot-end components in aviation engines. Considering that the disc rim and hub has to function under different temperatures and stresses, their dual microstructure had been paid close attention. In this study, the coarse- and fine-grained microstructures were obtained by controlling the solution treatment temperature, and the creep behavior of the superalloy at 700 ^oC and under various stresses was investigated. The effect of stress on the creep deformation mechanism and fracture behavior of the alloy was investigated via SEM and TEM. In the coarse-grained microstructure, the creep deformation mechanism at 780 MPa was primarily isolated by stacking faults and microtwin shearing, while the stress increased to 900 MPa, the extended stacking fault shearing and microtwinning jointly dominated creep deformation. Nevertheless, within the stress range of 780-900 MPa, the creep deformation mechanism remained consistent in the fine-grained structure, which was characterized by the coexistence of extended stacking fault shearing and microtwinning. In addition, this study indicated that the grain boundaries exhibited a diminishing promotion effect on the minimum creep rate as the applied stress increased for both grain microstructures. The high stress sensitivity of the experimental alloy resulted in the occurrence of twinning with elevated stress levels. This phenomenon accelerated plastic deformation, resulting in an increased creep rate. Moreover, the creep fracture source zone was predominantly an intergranular fracture, whereas the propagation region was predominantly a transgranular fracture in both grain microstructures. The tendency for intergranular fracture in coarse-grained microstructures decreased with the increase in the creep stress level, vice versa was observed in fine-grained microstructures.

Superalloys are widely used in aviation, aerospace, energy, transportation, and petrochemical industries due to their excellent properties, such as high-temperature strength, plasticity, fracture toughness, oxidation resistance, and hot corrosion resistance. They are primarily employed in aircraft engines and gas turbines within aviation, marine, and power generation sectors. Furthermore, due to the unique properties of superalloys and continuous advancements of superalloy technology, their applications are expanding into increasingly extreme service environments. In order to simulate the harsh working conditions of materials under high temperature and high concentration HCl environment, the hot corrosion behavior of a nickel-based superalloy was investigated at 960 ^oC in a mixed atmosphere of 5%HCl + 0.5%O₂ + Ar (volume fraction) using XRD, SEM, EDS, and EPMA techniques. Hot corrosion tests were conducted for 200 h. Analysis of corrosion kinetics, types and distribution of corrosion products, and cross-sectional elemental mapping revealed two distinct stages (0-75 h and 75-200 h), both showing an initial increase followed by a decrease in corrosion rate. Volatile chlorides containing Mo, Ti, and Cr formed extensively. The corrosion layer exhibited a poorly protective (Cr, Ti)-rich oxide layer, while no continuous Al₂O₃ layer was observed. The Ta-rich spinel layer inhibited outward diffusion of metal ions. The corrosion layer of the experimental alloy did not exhibit any significant chloride concentration on its cross-section. In addition to HCl and O₂ in the atmosphere, Cl₂ generated through chlorination and oxidation processes reacted with the alloy and played an important role in accelerating oxidation at 960 ^oC, without evidence of intermediate-temperature activated oxidation.

Superhydrophobic surfaces are promising anti-icing solutions for industrial applications such as spacecraft wings and wind turbine fans. However, the complexity of traditional processes, poor durability, and low interfacial adhesion between the substrate and fluorocarbon polymer films restrict their widespread use. This study validates a one-step electroplating method for Ni_0.12Co_{0.88 - x} Zn_x (x = 0-0.36, %, mass fraction) coatings on honeycomb porous Ti surfaces, achieving super hydrophobicity without secondary modifications. SEM, XRD, and wettability tests are employed to characterize the surface features and hydrophobic properties. Optimized conditions (50 g/L Zn²⁺ (x = 0.24) and 5 g/L Na₃Cit concentration) resulted in a compact microstructural texture and refined crystal size (300 nm), enhancing the interfacial bonding strength. The as-deposited coating exhibited hydrophobic features, with a maximum water contact angle (WCA) of 126.3° and a sliding angle (SA) of 17.5° after 14 d of natural aging. The textural evolution from Zn nanocrystals to ZnO dendrites with a multi-antenna structure was attributed to this phenomenon. Artificial aging at 100, 200, and 300 ^oC achieved a superhydrophobic surface in less than 7 d. The sample aged at 200 ^oC displayed a WCA exceeding 153.2° and an SA below 7.8° due to out-migration of the active ZnO phase and self-assembly evolution, forming xanthium-like spherical structures with nanocrystalline Ni or Co shells and multi-tentacle ZnO dendrites. Comparatively, anti-icing performances were assessed at -10 ^oC, showing a peach blossom ice shape on all coating samples. The sample aged at 200 ^oC exhibited an ice-resistant time of over 1418 s, 20 times longer than that of the porous Ti substrate, indicating excellent anti-icing performances. In summary, electroplating Ni-Co-Zn coatings onto porous Ti is a practical solution that meets the evolving requirements for superhydrophobic films in spacecraft shells for anti-icing and warship surfaces for anti-salt spray corrosion.

Tantalum and its alloys have high melting points and good wear resistance, which are primarily used in fields such as the aerospace and nuclear energy industry. Surface modification techniques such as carburization can be used to obtain a modified layer containing tantalum carbide on the surface of tantalum and its alloys, thereby significantly improving their surface properties. However, the structure and properties of tantalum carbide precipitated on the surface of different tantalum alloys remain unclear. This study focuses on Ta-Mo and Ta-W alloys, and constructs fcc and hcp complex tantalum carbide (Ta, M)C (M = Mo, W) models with different alloying elements and their contents. The energy and mechanical properties of different complex tantalum carbide structures were calculated using the first principles method based on the density functional theory to explore the strengthening and toughening mechanisms of complex tantalum carbides. Calculation results indicate that when the content of Mo and W is less than 50%, fcc structured complex tantalum carbide can be easily formed, and the higher the concentration of Mo and W atoms, the lower the modulus and hardness of the complex tantalum carbide with an fcc structure, and the better the toughness. When the content of Mo and W exceeds 50%, tantalum carbides with an hcp structure are easy to form. As the concentration of Mo and W atoms increases, the modulus and hardness of complex tantalum carbides with an hcp structure increase, whereas the toughness decreases.