The formation of ultra-fine α precipitates in β-titanium alloys can significantly improve strength but may lead to rupture and low ductility. Here, we propose a simple two-step aging heat treatment ...to design a bimodal microstructure with distinctively different populations of fine-scale and coarse α precipitates in Ti-5Al-5Mo-5V-3Cr-1Zr (Ti-55531, wt. %) by involving two transformation mechanisms, i.e., classical nucleation and growth, and pseudo-spinodal decomposition. Such a multi-scale α microstructure exhibits a synergistic combination of yield strength (∼1.1 GPa) and ductility (∼19.5% elongation). TEM characterization shows that the appearance of deformation twins in coarse α precipitates contribute to increased ductility, and the higher strength may be attributed to dislocation tangles in fine-scale α precipitates. Our work provides a new strategy to overcome the strength-ductility trade-off by designing a heterogeneous microstructure.
•Bimodal lamellar α precipitate microstructures in Ti-alloys are designed via two-step aging.•Such a heterogeneous microstructure exhibits a superior combination of strength and ductility.•The good combination can be attributed to the deformation twins in coarse α precipitates and the dislocation tangles in fine α precipitates.
Refractory high-entropy alloys (RHEAs) have attracted considerable interest due to their elevated melting points and remarkable softening resistance. Nevertheless, the ambient-temperature brittleness ...and inadequate high-temperature oxidation resistance commonly limit the application of the body-centered-cubic (BCC) RHEAs. In this study, we achieved a Ti41V27Hf11.5Nb11.5Cr3Al6 RHEA with a desirable yield strength of ∼1178 MPa and tensile ductility of ∼19.5 %. Exploring the underlying mechanisms, we demonstrated that Cr and Al alloying induced a nanoscale spinodal structure and generated a significant lattice misfit, resulting in a notable strengthening effect and pinning behavior. Meanwhile, dislocation configurations involving loops and cross slips were stimulated by pinning, serving a reliable strain-hardening capability to large strains. Significantly, Cr and Al alloying improved oxidation resistance and prevented severe spallation at high temperatures by forming protective oxide layers. These results provide opportunities to design novel RHEAs.
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As an important precipitate in Zr-alloy, detailed study on the oxidation behavior of Zr(Fe,Nb)2 in atomic scale will help to develop safer materials for reactors. In this study, Zr(Fe,Nb)2 ...intermetallic was fabricated and exposed to subcritical water (320 °C, 15.5 MPa). On oxidation frontier, the interplay between element diffusion and structure evolution was analyzed. The oxidation process started with the incorporation of oxygen in local strips, which was perpendicular to the direction of oxygen diffusion. Fe was segregated from the oxygen-rich strips via an uphill diffusion process along {001} lattice plane. The “spinodal decomposition”-like phenomenon was observed and discussed.
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•High-density coherent nanoparticles are formed in a 3D-printed&aged Cu-based CCA.•The high density is due to the supersaturation state by rapid cooling of 3D printing.•The nanoparticles are formed ...by spinodal decomposition and thus coherent with matrix.•The CCA is notably strengthened by the nanoparticles without ductility loss.
Metallic 3D printing enables fast fabrication of net-shaped components for broad engineering applications, yet it restrains the use of most mechanical processing methods for strengthening alloys, e.g. forging, rolling, etc. Here, we proposed a new strategy for enhancing the strength of 3D printed complex concentrated alloys without losing ductility. This strategy relies on the rapid cooling of 3D printing to achieve a supersaturation state that is beyond conventional casting. Then, spinodal decomposition via aging is exploited to introduce high-density coherent nanoparticles for strengthening. The proposed strategy is demonstrated in a 3D printed Cu-based complex concentrated alloy. The rapid solidification during printing strongly inhibits elemental diffusion, leading to a high supersaturation state. High-density nanoparticles with coherent interface and size of ∼7 nm are introduced into the 3D printed samples through spinodal decomposition via simple aging treatment. The strength of the 3D printed alloy is increased by 30 % after aging with no ductility loss, leading to a strength-ductility combination superior to other Cu alloys. This strategy is readily applicable to other spinodal alloys fabricated by 3D printing for circumventing the strength-ductility trade-off dilemma.
For the crystallization of an API in supercritical CO2, a two – step nucleation mechanism involves the apparition of metastable liquid droplets in the vapour phase composed of the API dissolved in ...the CO2, before crystallization. To find out the pressure and temperature conditions such a two – step mechanism could be observed, we studied the stability / metastability / instability for {(S)-Naproxen + CO2} and {(RS)-Ibuprofen + CO2} vapour binary mixtures. Thermodynamic computations proposed in the paper, have shown that a mixture of API and CO2 at elevated pressures can be unstable and/or metastable with respect to a liquid-vapour equilibrium and at the same time with respect to a solid-vapour equilibrium. Depending on the degree of supersaturation, such a mixture can potentially first decompose via spinodal decomposition into coexisting liquid and vapour phases, which turn due to nucleation and growth theory to a solid-fluid equilibrium.
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•Thermodynamical evaluation of the two-step nucleation with PREOS.•Liquid droplets can precipitate at low supersaturation instead of solid particles.•The spinodal limits lie at higher supersaturation.•The metastable liquid phase composition depends slightly on the pressure.
Liquid-liquid phase separation plays a key role in the assembly of diverse intracellular structures. However, the biophysical principles by which phase separation can be precisely localized within ...subregions of the cell are still largely unclear, particularly for low-abundance proteins. Here, we introduce an oligomerizing biomimetic system, “Corelets,” and utilize its rapid and quantitative light-controlled tunability to map full intracellular phase diagrams, which dictate the concentrations at which phase separation occurs and the transition mechanism, in a protein sequence dependent manner. Surprisingly, both experiments and simulations show that while intracellular concentrations may be insufficient for global phase separation, sequestering protein ligands to slowly diffusing nucleation centers can move the cell into a different region of the phase diagram, resulting in localized phase separation. This diffusive capture mechanism liberates the cell from the constraints of global protein abundance and is likely exploited to pattern condensates associated with diverse biological processes.
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•Corelets are phase-separating photoinduced oligomers of self-interacting proteins•FUSN Corelets phase diagram with binodal and spinodal regimes mapped in live cells•Mutations reshape phase diagrams allowing quantitative sequence space interrogation•Localized oligomerization drives condensation even at undersaturated concentrations
Probing cellular phase separation with a biomimetic system suggests a mechanism for condensate formation with low abundance molecules.
A new set of AlFeCoNiCx (x = 0, 0.02, 0.04, 0.08, 0.17) high-entropy alloys (HEAs) were designed and fabricated. The microstructure, phase evolution and mechanical behaviors of the alloys were ...systematically investigated. Results show that the matrix alloy exhibits coarse columnar structure, while the C-doped alloys exhibit typical dendrite microstructure. The dendritic region (DR) is composed of single B2 phase, while the interdendritic region (ID) consists of FCC and E21 phases and presents an ultrafine cellar structure caused by the coexisting of ordering and spinodal decomposition. Interestingly, both the strength and compressive strain greatly increased with the increase of carbon content. Particularly, the AlFeCoNiC0.08 HEA possessed the most excellent mechanical properties, superior to many other HEAs with the yield strength, fracture strength, and fracture strain as high as 1115 MPa, 2517 MPa and 48.8%, respectively. The mechanical properties of the AlFeCoNiC0.17 alloy were weakened by the presence of graphite. Further, it is found that there is close relationship between the fracture morphology and alloy properties. Overall, in this study the improved microstructure and mechanical properties of the AlFeCoNi HEA have been accomplished by carbon doping, and our findings could shed light on a new alloy-design route to achieve bulk ultrafine structure materials with desired properties via the direct solidification.
Elemental segregation to grain boundaries (GBs) can induce structural and chemical transitions at GBs along with significant changes in material properties. The presence of multiple principal ...elements interacting in high-entropy alloys (HEAs) makes the GB segregation and interfacial phase transformation a rather challenging subject to investigate. Here, we explored the temporal evolution of the chemistry for general high-angle GBs in a typical equiatomic FeMnNiCoCr HEA during aging heat treatment through detailed atom probe tomography (APT) analysis. We found that the five principal elements segregate heterogeneously at the GBs. More specifically, Ni and Mn co-segregate to some regions of the GBs along with the depletion of Fe, Co and Cr, while Cr is enriched in other regions of the GBs where Ni and Mn are depleted. The redistribution of these elements on the GBs follow a periodic characteristic, spinodal-like compositional modulation. The accumulation of elements at the GBs can create local compositions by shifting their state from a solid solution (like in the adjacent bulk region) into a spinodal regime to promote interfacial phase-like transitions as segregation proceeds. These results not only shed light on phase precursor states and the associated nucleation mechanism at GBs in alloy systems with multiple principal elements but also help to guide the microstructure design of advanced HEAs in which formation of embrittling phases at interfaces must be avoided.
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Manganese based layered oxides have received increasing attention as cathode materials for sodium ion batteries due to their high theoretical capacities and good sodium ion conductivities. However, ...the Jahn-Teller distortion arising from the manganese (III) centers destabilizes the host structure and deteriorates the cycling life. Herein, we report that zinc-doped Na
Li
Mn
O
can not only suppress the Jahn-Teller effect but also reduce the inherent phase separations. The reduction of manganese (III) amount in the zinc-doped sample, as predicted by first-principles calculations, has been confirmed by its high binding energies and the reduced octahedral structural variations. In the viewpoint of thermodynamics, the zinc-doped sample has lower formation energy, more stable ground states, and fewer spinodal decomposition regions than those of the undoped sample, all of which make it charge or discharge without any phase transition. Hence, the zinc-doped sample shows superior cycling performance, demonstrating that zinc doping is an effective strategy for developing high-performance layered cathode materials.
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