Metastable high-entropy alloys (HEAs) offer a practical strategy for achieving a good balance between strength and ductility through both deformation-induced (martensitic) phase transformations and solid solution strengthening effects. However, HEAs often have a low yield strength (YS) and a tendency toward deformation-induced martensite coarsening, which impedes the formation of refined microstructures that would improve the mechanical properties. Here, we demonstrate that in a prototype metastable Fe _60 Mn _12 Cr _12 Ni _8 Si _8 HEA, a hierarchical γ / ϵ / γ -twin laminate structure can be achieved simply by cyclic tension–compression (CTC) processing. Compared to the as-received material, the engineered microstructure contains a higher density of coherent interfaces and exhibits more pronounced microstructural evolution during tensile deformation, resulting in a 130% increase in YS while maintaining comparable ductility. Atomic-scale characterization integrated with density functional theory calculations reveals that during successive CTC cycles, partial dislocations nucleate within the ϵ martensite and propagate along the {111} _γ /{0001} _ϵ planes, leading to retransformation back into γ or nano γ twins, thereby effectively reducing the interspacing. Crucially, in this metastable HEA, transformation-mediated twinning (TMT) exhibits a lower energy barrier than the classical layer-by-layer mechanism. Significant dislocation accumulation at the γ / ϵ interfaces generates intense local stresses, supplying the critical energy required to activate TMT. Our work offers a valuable insight into the twinning mechanism and highlights a practical new way of developing very fine hierarchical γ / ϵ / γ -twin laminate microstructures with improved strength.

Metastable beta-titanium alloys with low elastic modulus and high strength are promising candidates for orthopedic implant applications, and cold rolling deformation is an effective strategy to tailor such favorable mechanical properties. The present work systematically investigated the deformation mechanisms, texture evolution, and mechanical properties of two novel alloys (Ti-5Mo-20Nb-6Sn and Ti-5Mo-15Nb-9Sn) with different (3 stability controlled by adjusting the Nb/Sn ratio under different cold rolling conditions. The results indicated that the increase in Nb/Sn ratio enhanced the stability of the (3 phase, resulting in the 20Nb6Sn alloy undergoing a progressive transition from stress-induced {332}< 113 > twinning to kink deformation and finally to dislocation slip with increasing rolling reduction. In contrast, the less stable 15Nb9Sn alloy was dominated by stress-induced martensite (SIM) transformation throughout the process. In addition, compared with the dominant gamma texture in the 15Nb9Sn alloy, the extensive formation of kink bands (<110 >-type) promoted the development of low-modulus {001}< 110 > alpha texture, leading to the formation of alpha+ gamma composite texture in the 20Nb6Sn alloy. The favorable dual-texture, ductile (3-phase, and pre-existing kink bands resulted in the CR-75% 20Nb6Sn alloy having lower elastic modulus (42.3 GPa) and higher ductility (similar to 6.8%) while maintaining high strength (922 MPa), making it a promising candidate for high-performance implant materials. This study demonstrates that fine composition tuning, targeting a specific beta-phase stability, can activate desirable deformation mechanisms (e.g., kinking) during the cold rolling to simultaneously achieve low elastic modulus, high strength, and acceptable ductility, which provides valuable insights for the composition design and processing optimization of high-performance biomedical titanium alloys.

High-entropy alloys (HEAs) have attracted significant attention for their exceptional mechanical properties, yet the fundamental crystallographic constraints that dictate microcrack propagation remain a long-standing challenge. Here, we report an unconventional fracture behavior in an Al0.1CoCrFeNi HEA, characterized by intragranular zigzag crack propagation that exhibits a weak correlation with the initial crystallographic orientation of the matrix. Our multi-scale analysis reveals that this phenomenon stems from a dynamic lattice reorientation toward the (110) direction at tensile crack tips, accompanied by intragranular zigzag crack morphologies, and is associated with two synergistic energy-dissipation pathways: 1) rough {200} facets associated with local crystalto-amorphous transformations and nanoscale bridging, and 2) smooth {111} facets dominated by twin-mediated shear slip. These results demonstrate that the interplay between lattice reorientation and structural instability serves as robust mechanisms for damage tolerance. By uncovering crack-path decoupling from rigid crystallographic constraints, this work advances a microstructure-informed framework for designing fracture-resistant materials.

Boron is known as an effective strengthener in titanium alloys through TiB formation. However, the high melting-point of TiB drives its preferential heterogeneous formation along grain boundaries, severely compromising ductility. Here, we demonstrate that a fully homogeneous as-cast TiB dispersion, independent of grain boundaries, can be realized without any post-casting heat-treatment. Such uniformity originates from reduced B partitioning into the liquid during solidification and shortened diffusion free-paths under rapid cooling, which suppress solute accumulation at grain boundaries and shift TiB precipitation toward homogeneous nucleation. Consequently, the combination of strength and ductility is remarkably improved compared with those common non-uniform TiB-strengthened Ti alloys. These findings establish the feasibility of in-situ homogeneous TiB precipitation, providing guidance to enhancing mechanical performances in TiB-reinforced Ti alloys.

The β grain size in titanium alloys during industrial forging is critical for balancing toughness, cost-effectiveness, and processability. To address the industrial challenge of high cost and difficulty in refining β grains to the tens of micrometers scale, this study investigates the feasibility of achieving a superior strength-ductility balance in TC18 alloy with near-industrial coarse β grains (296~857 μm) under room temperature tension. A pronounced inverse correlation is observed between β grain size and both strength and ductility. The yield strength-grain size relationship follows the Hall-Petch effect, while the anomalous increase in ductility for fine-grained specimens is attributed to three factors. First, smaller grains provide a higher grain boundary density, promoting stress redistribution and mitigating stress concentrations. Second, more uniform stress distribution induces thinner, denser kink bands that enhance plasticity. Third, strain-induced martensite evolves from discrete nanoscale particles to discontinuous lines and ultimately coalesces into continuous planar bands along the (112)β and (110)β planes. This phase transformation, which initiates below a critical grain size of ~500 μm, further alleviates stress concentrations towards slip bands and contributes to dynamic work hardening. The findings demonstrate that coordinated deformation mechanisms enable excellent mechanical performance even in coarse-grained microstructures, providing a practical pathway for optimizing industrial-grade titanium alloys.

Metastable β titanium alloys with low elastic modulus and excellent plasticity represent highly attractive materials for biomedical stent application. Our work shows that Zr plays a crucial role in regulating β stability to significantly reduce the modulus and enhance plasticity. A series of Ti-25Nb-2Mo-xZr (x = 0, 3, 9, 12 wt%) alloys were designed based on the d-electron theory, and the influence of Zr content on the microstructure, mechanical properties, and deformation mechanism were systematically investigated. The results demonstrated that as the Zr content increases, the β phase stability was significantly enhanced. This leads to, first, the suppressed formation of the high modulus α″ phase and ω phase, which results in the decrease in apparent overall elastic modulus. Second, the dominant mode of deformation shifts from martensite dislocation slip (0Zr) to martensitic variant reorientation (3Zr), then to stress-induced martensite transform (SIMT, 9Zr), and finally to a combination of SIMT and deformation twinning (12Zr). Such shifting effectively increases the alloy's tensile plasticity. Among the series, the Ti-25Nb-2Mo-12Zr alloy exhibited the lowest elastic modulus of 56.3 GPa, together with the highest elongation to failure of 48.2%, demonstrating that the alloy possesses considerable potential for biomedical applications.

Boron has a low solubility in titanium alloys, making a thorough understanding on its alloying effects rather difficult. In this work, we demonstrate that the excessive alloying of boron (0.1 wt.%) in a low-density near-alpha titanium alloy can generate unexpected superb strengthening-toughening effects. The ultimate tensile strength increased from 1051 to 1199 MPa, which mainly originates from the refined dual-phase microstructure resulting from both the TiB stimulated spherical primary alpha formation, and the B, Si co-segregation retarded alpha p growth. Surprisingly, the elongation-to-failure even doubles, which is benefited by the co-segregation enhanced interface bonding, despite the fact that the TiB does facilitate crack nucleation.

A key challenge for spin-dominated functional materials is their suboptimal structural properties, a problem that restricts their widespread applications. Here, this limitation is addressed by introducing additional lattice degree of freedom. This is exemplified in a novel cobalt-based alloy, which is targeted to demonstrate both the spin-state transformation-induced zero thermal expansion (Invar effect, ensuring precision) and lattice transformation-induced plasticity (TRIP effect, enhancing safety), referred to as TRIP-Invar. An unusual martensitic transformation exhibiting three-phase coexistence has been observed under stressing at 77 K, which results in pronounced work hardening behavior and exceptional cryogenic toughness. Notably, reversible spin/lattice transformations enable intrinsic thermal repairability. This findings not only expand the categories within the Invar family, but also provide a reference for the discovery of other integrated structural and functional materials, enabling humanity's exploration of extreme environments like the poles and deep space.

Cubic perovskite-Ti3AlC carbides are essential strengthening particles in TiAl alloys, especially for application above 800 degrees C where coarsening is expected to occur. However, these carbides can decompose into small subparticles upon extended annealing, and the underlying atomic-scale mechanisms, especially structural and compositional changes, driving this unique splitting remain unclear. This study revisits this behavior in a Ti45Al-5Nb-0.75C alloy utilizing probe-corrected transmission electron microscopy, atom probe tomography and first-principle calculations. The results reveal that the elastic interactions significantly influence carbide evolution. While needle-like carbides transform to intact plates during aging, those in high-density regions tend to coalesce or align along elastically softest gamma-matrix directions, forming low-energy plate-like carbide conglomerates. With extended annealing, periodic chemical fluctuations driven by lattice misfit, especially along the needles induce splitting. Simultaneously, a gamma i-phase with a larger tetragonality and a 90 degrees-rotated c-axis relative to the gamma matrix emerges between the sub-particles, which exhibits near-zero lattice mismatch with carbides along [001], combined with mass-center shifts of carbides, further stabilizing the split configurations. This study provides atomic-scale insights into the evolution and stability of strengthening precipitates in systems with tetragonal misfit, and offers new strategies for improving creep properties of TiAl alloys by tailoring carbide configurations.

Alpha-titanium is renowned for its exceptional ductility but has been overlooked due to its limited strength. Alloying with other elements is a common strategy to enhance its strength. Nitrogen, the most potent hardening element in titanium, has been neglected because its hardening effect typically results in a significant sacrifice of ductility. In this study, we integrate alloy design with additive manufacturing processes to demonstrate the utilization of nitrogen for achieving outstanding tensile properties. We employed two scales of TiN powder as a nitrogen source during in-situ alloying via laser powder bed fusion and discovered that the addition of micron-sized TiN (15-53 mu m) resulted in leftover TiN particles in as-printed samples, which adversely affect ductility. Nonetheless, with the incorporation of nano-sized TiN powder (<100 nm), all nitrogen constituents manifest as interstitial nitrogen and distributed evenly. By incorporating compositional and process design, we achieved over a 60 % improvement in yield strength with almost no loss of elongation in the titanium-nitrogen alloy. A systematic exploration of deformation mechanisms suggests that the incorporation of nitrogen significantly refines grains, inhibits variant selection, and activates more dislocations, thereby synergistically strengthening the titanium-nitrogen alloys. These findings advance the development of solid solution-strengthened titanium alloys and provide novel insights for the exploration and creation of cost-effective, high-performance titanium alloys.

Critical engineering applications, such as landing gears and armor protection, require structural materials withstanding high strength and significant plastic deformation. Nanoprecipitate-strengthened high-entropy alloys (HEAs) are considered as promising candidates for structural applications due to their enhanced strength and exceptional work-hardening capability. Herein, we report a FeCoNiAlTi-type HEA that achieves ultrahigh gigapascal yield strength from quasi-static to dynamic loading conditions and superb resistance to adiabatic shear failure. This is accomplished by introducing high-density coherent L12 nanoprecipitates. Multiscale characterization and molecular dynamics simulation demonstrate that the L12 nanoprecipitates exhibit multiple functions during impact, not only as the dislocation barrier and the dislocation transmission medium, but also as energy-absorbing islands that disperse the stress spikes through order-to-disorder transition, which result in extraordinary impact resistance. These findings shed light on the development of novel impact-resistant metallic materials.

Precipitation strengthening is paramount in the development of high-performance medium/high entropy alloys (M/HEAs). In this work, we showcase a phase-selective precipitation design applied to a (Ni67.2V32.8)(90)Ti5Al5 MEA to enable enhanced strength-ductility synergy. Upon annealing at 950 degrees C, multiple precipitates form in this MEA, including L2(1), sigma and hexagonal close packed (HCP) phases. However, an increase of 50 degrees C in annealing temperature removes most of the aforementioned precipitates except for the L2(1) phase. Density functional theory calculations are conducted to elucidate the formation mechanisms of phase-selective precipitation. Such selective approach to precipitation induces a brittle to ductile transition, increasing tensile elongation from 4 % to 43 % in our MEAs. Remarkably, the ultimate tensile strength of 1000 degrees C annealing MEA is maintained at similar to 1.4 GPa, surpassing that of the precipitation-free Ni67.2V32.8 base alloy (similar to 1.1 GPa), but with a comparable tensile elongation. Analytical models suggest that the increase in strength is attributed to both precipitation strengthening and grain refinement strengthening due to the pinning effect of precipitates. In particular, we investigate the complex deformation response of the L2(1) phase, which includes the formation of slip steps and a phase transformation from body-centered cubic (BCC) to body-centered tetragonal (BCT) structures, with the underlying mechanisms revealed through experimental characterization and molecular dynamics simulations. This co-deformation of matrix and L2(1) precipitates alleviates stress concentration at phase boundaries during straining and further maintains the microband-induced plasticity in the matrix till later deformation stage. All these result in the excellent strain hardening and thus, markedly enhancing ductility. Our findings pave new ways to craft strong and ductile M/HEAs by selecting hard-yet-deformable intermetallic precipitates.

Using cross-confirmed characterization techniques, we unequivocally demonstrated the existence of V-centered CSRO in pure face-centered cubic CoNiVx alloys (x = 0.85-1.00), and correlated its average size with overall alloy strength. Notably, for x <= 0.95, CSRO is small (size <= 0.57 nm) and behaves like solid-solution atoms. This results in a strengthening trade-off between CSRO and solid-solution, providing only marginal strength increase with rising x. However, for x > 0.95, a sharp growth of CSRO to size over 0.72 nm enhances dislocation interaction, making CSRO alike shearable nanoprecipitates and causing a strength increment of over 50 MPa. [GRAPHICS] .

A combination of electro-probe microanalysis, transmission electron microscopy and atom probe tomography was employed to investigate the effects of high-temperature oxidation on the gradient of the microstructure and microchemistry of the oxygen-rich layer on a near-alpha Ti alloy, Ti6242s, with a bimodal microstructure. alpha(2) precipitation occurred within the oxygen-rich layer, more pronounced inside the primary alpha grains than within the secondary alpha laths. The degree of alpha(2) precipitation increases with increasing oxygen content, and the critical amount of oxygen triggering alpha(2) is similar to 3 at. % in the primary alpha grains, and even higher within the secondary alpha laths. These values are far greater than the reported value, similar to 0.6-0.75 at. %, for the bulk alloy. Heterogeneous Al segregation was observed within the secondary alpha laths while bcc-beta phase persisted even at the very surface where the oxygen content was highest. These findings indicate that oxygen ingress accelerates precipitation of alpha(2) at elevated temperature, and faster O diffusion along the dislocations and boundaries stimulates heterogeneous Al segregation. The lower degree of ordering within the secondary alpha laths was probably owing to the lower Si content and Al supersaturation.

Severe grain-boundary embrittlement at ambient temperatures poses one of the most critical challenges for wide applications of superlattice alloys as high-performance structural materials. Indispensable active constituents like Al are recognized as the major cause of such embrittlement by releasing atomic hydrogen from moisture, which violently weakens grain boundaries (GBs) and promotes stress localization. Challenging conventional wisdom, here we surprisingly discover an anomalous ductilization effect in the L1(2)-structured Co3Ti alloys, where Al alloying conversely suppresses the intergranular brittleness and meanwhile dramatically increases tensile ductility from similar to 4.1 % to 30 %. Further experiments and calculations revealed that the grain-boundary brittleness in bulk L1(2) Co3Ti alloys is directly related to the preservation of L1(2) chemical order up to the boundary plane, which fortunately, can be destroyed by inducing Co-atom segregation through the alloying of a L1(2) destabilizer Al, as well as Fe. Such chemical-partitioning-induced disordered intergranular buffer significantly reduces the resistance to dislocation slip across GBs, which retards the development of slip-induced stress concentrations at GBs and hence reduces the likelihood of intergranular fracture. Moreover, the Co-atom segregation-induced grain-boundary phase together with the secondary L2(1) Co2AlTi phase in the Al-alloyed alloy significantly improves thermal resistance to grain coarsening. The kinetic exponent and apparent activation energy for grain boundary migration in unalloyed Co3Ti increases dramatically from 3.2 to 263.7 kJ/mol to 5.2 and 641.0 kJ/mol, which surpass documented values of Ni- and Co- based superalloys, suggesting their promising potential as heat-resistant materials. These findings pave a new way for developing high-performance, heat-resistant superlattice alloys.

Anisotropy is one of the concerns of titanium matrix composites (TMCs) due to its impact on subsequent processing and safe serving. In this work, we demonstrate that simply by using cross-rolling (CR) rather than unidirectional rolling (UDR), significant plastic anisotropy can be removed and an excellent strength-ductility combination can be achieved in a new TiB-reinforced TMC (TiB-TMC). We attribute the occurrence of plastic anisotropy after UDR to be the strong rolling-induced orientation distribution of TiB whiskers parallel to the rolling direction (RD), while the elimination of anisotropy is therefore confirmed to be caused by the loss of such an orientation relationship. The underlying mechanism is revealed as the lower stress concentration along the lateral surface of the randomly distributed whiskers and the longer paths when cracks propagate in between each whisker, in the CR-processed TiB-TMC.

Excellent strength, ductility, and impact toughness at cryogenic temperatures are essential for ensuring the structural reliability of marine engineering titanium alloys. This study systematically investigates the mechanical properties and deformation mechanisms of a near-alpha Ti-6Al-3Nb-2Zr-1Mo alloy from 20 degrees C to -196 degrees C. The results demonstrate a synergistic enhancement of both strength and ductility with decreasing temperature, while the impact toughness exhibits severe deterioration. In-depth analysis revealed that during quasi-static tension, the low strain rate allows sufficient time for dislocation multiplication and mobility. Combined with the increased critical resolved shear stress (CRSS) for dislocation slip at low temperatures, the elevated flow stress promotes extensive {1012} twinning. The synergistic effect of these deformation mechanisms improves the homogeneous deformation capacity of the microstructure, promoting superior ductility at cryogenic temperatures. Under high-strain-rate impact loading at cryogenic temperatures, the markedly elevated CRSS for dislocation slip and limited deformation time strongly suppress both dislocation slip and twinning in the alpha phase. Although dislocation slip remains active in the softer beta phase, its confined morphology leads to dislocation pileups and stress concentration at beta/alpha interfaces. Meanwhile, the lack of effective deformation mechanisms in the alpha phase prevents the release of stress concentration at the crack tip, which results in rapid crack propagation along the beta/alpha interfaces, thus forming an extremely small plastic zone and sharply reducing impact toughness.

Coherent precipitation-hardened alloys often struggle to achieve both ultrahigh strength and exceptional ductility due to their limited resistance to dislocation motion and vulnerability to glide plane softening. Here, we tackle these challenges by introducing multicomponent precipitates with much increased antiphase boundary (APB) energy. In a model Ni3Al-type (L12) precipitation-hardened face-centered cubic (FCC) NiCo-based alloy, we incorporate multiple elements at the Al sublattice sites within the precipitates, reducing antisite defects and enhancing ordering degree. This process yields multicomponent precipitates with an ultrahigh APB energy (~308 ± 14 millijoules per square meter), which notably strengthens the alloy. Moreover, the exceptionally high APB energy transforms the deformation mechanism from dislocation shearing to stacking fault shearing, thereby avoiding glide plane softening. These result in a tensile yield strength of 1616 ± 9 megapascals, an ultimate tensile strength of 2155 ± 22 megapascals, and a uniform elongation of 10.1 ± 0.3% for the alloy.

Ti80 alloy with different microstructures, i.e., fully equiaxed alpha(p) (FE), equiaxed alpha(p) + colony-distributed thick lamellae alpha(l) (ECL), and equiaxed alpha(p) + disorder-distributed thin lamellae alpha(l) (EDL) were tailored to unravel the correlation between microstructure and impact toughness. In particular, the FE and ECL exhibited superior impact toughness (132.5 J/cm(2) and 110.0 J/cm(2) respectively), nearly twice that of EDL (65.0 J/cm(2)). By investigating the microstructure deformation mechanisms and crack deflection behaviors, we found that equiaxed alpha(p) and colony alpha(l) in FE or ECL possess superior abilities of plastic deformation and crack deflection, promoting severe deformation of them, tortuous crack paths as well as high energy dissipation. However, EDL exhibited a straight crack path caused by low resistance to crack propagation of disorder-distributed thin alpha(l). Furthermore, the activation of high-density {10 1(over bar) 2}<10 1(over bar)1> twins in FE and ECL, effectively released the local stress concentration, facilitated dislocation slip, and refined matrix grains, improving the deformation compatibility. Note that the interstitial beta-phase in the alpha(l) colony in ECL offered new alpha/beta interfaces and prevented dislocation mobility to a certain extent. This, on one hand, slightly lower the impact toughness as compared to FE, and on the other hand, greatly enhanced the overall strength level. Consequently, ECL demonstrated the best combination of strength and toughness.

In this work, by lowering the V amount, two thermodynamic processes, i.e., x-formation and gamma-recrystallization, are near-concurrently activated in a NiCoV0.9 medium entropy alloy (MEA) during 900 degrees C annealing. The NiCoV0.9 MEA with only 2 min annealing inherits the high strength from the cold-rolling structure while regains apparent work-hardening, endowing the alloy at this state with excellent strength-ductility synergy. By utilizing correlated observation methods, it is found that in the very beginning of annealing, gamma-recrystallization occurs closely prior to x transformation, which in turn enables elemental redistribution needed for x growth. Further insitu synchrotron high-energy X-ray diffraction reveals the synchronous onset of plastic deformation in both x and gamma, suggesting the good deformability of x regardless of its hard nature. With prolonged annealing at 900 degrees C, the yield strength drops sharply yet the ductility is not further enhanced. This is likely due to the fast increment in both size and volume fraction of the x phase that significantly raises the cracking sensitivity.