High entropy alloys (HEAs) offer the opportunity to achieve an unprecedented balance of properties by accessing novel multi-scale microstructural combinations. Despite the large range of combinations ...of strength and ductility reported in HEAs, the complex interplay between multiple strengthening mechanisms has not been addressed. The single-phase fcc solid solution state of the Al0.3CoCrFeNi alloy exhibits a strong Hall-Petch hardening effect with reducing grain size. While the same alloy can be strengthened by a composite-reinforcement effect of hard intermetallic B2 and sigma precipitates, within a fine-grained fcc matrix. Such precipitation leads to solute depletion within the parent fcc matrix, resulting in a substantially reduced Hall-Petch hardening effect. Additional formation of nano-clusters within the fcc matrix can strengthen the same alloy to 1.85 GPa at room temperature, via an Orowan strengthening mechanism. This paper presents the complex interplay between strengthening mechanisms operative at different length scales.
Magnesium–lithium (Mg–Li) alloy, as the lightest metal structure material, has unparalleled market prospects in aerospace, weapons and equipment, electronic technology, transportation, and many other ...fields. However, it is hard to balance the superlight and high strength of Mg–Li alloy, and the inferior high-temperature strength and poor high-temperature stability limit the wide application of Mg–Li alloy. At present, the main methods to improve the mechanical properties of Mg–Li alloy are alloying, grain refinement, and compound strengthening. The domestic and overseas research progress in the strengthening and toughening methods and mechanisms of Mg–Li alloy are reviewed, and the future development of the high strength and high toughness Mg–Li alloy is prospected.
The precipitates play a significant role in not only enhancing the strength, but also maintaining the high toughness in alloys. However, the interactions of the nanoscale precipitates with ...dislocations in the high entropy alloys (HEAs) are difficult to observe directly by in-situ TEM experiments due to the limits of the resolution and time. Here, using atomic simulations we report the synergistic strengthening of the coherent precipitate and atomic-scale lattice distortion in the HEAs at cryogenic/elevated temperatures. The effects of temperature, chemical disorder, precipitate spacing, precipitate size, elemental segregation, and dislocation-cutting number on the critical stress for the dislocation to overcome a row of precipitates are studied. A random stacking fault energy landscape along the slip plane, the lattice distortion at different temperatures, and the interface/surface energy at various crystallographic orientations are obtained. Compared with the traditional metals and alloys, HEAs have the severe atomic-scale lattice distortions to generate the local high tensile/compressive stress fields. This complex stress causes the dislocation line to bend, and thus improves the dislocation slip resistance, resulting in the strong solid-solution strengthening. The stacking fault strengthening induced by the obvious difference of the stacking fault energies between the HEA matrix and precipitate (within the inner of the HEA matrix), and the formation of the antiphase domain boundary contribute to the high strength. The precipitate embedded by the solute atoms produces the strong lattice distortion to enhance the dislocation slip resistance at high temperatures. Hence, the current results provide the mechanistic insight into the phenomenon that the coherent precipitate combined with the severe atomic-scale lattice distortion can enhance the strength at cryogenic/elevated temperatures to further broaden the scope of applications of advanced HEAs.
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•Interaction between dislocation and precipitate in HEAs is studied using atomic simulations.•Stacking fault energy landscape is obtained along the dislocation-slip plane.•Stacking fault strengthening is found owing to the chemical disorder.•Theoretical model provides insight into precipitate-strengthened HEAs.
3D printing of high‐strength and antiswelling hydrogel‐based load‐bearing soft tissue scaffolds with similar geometric shape to natural tissues remains a great challenge owing to insurmountable ...trade‐off between strength and printability. Herein, capitalizing on the concentration‐dependent H‐bonding‐strengthened mechanism of supramolecular poly(N‐acryloyl glycinamide) (PNAGA) hydrogel, a self‐thickening and self‐strengthening strategy, that is, loading the concentrated NAGA monomer into the thermoreversible low‐strength PNAGA hydrogel is proposed to directly 3D printing latently H‐bonding‐reinforced hydrogels. The low‐strength PNAGA serves to thicken the concentrated NAGA monomer, affording an appropriate viscosity for thermal‐assisted extrusion 3D printing of soft PNAGA hydrogels bearing NAGA monomer and initiator, which are further polymerized to eventually generate high‐strength and antiswelling hydrogels, due to the reconstruction of strong H‐bonding interactions from postcompensatory PNAGA. Diverse polymer hydrogels can be printed with self‐thickened corresponding monomer inks. Further, the self‐thickened high‐strength PNAGA hydrogel is printed into a meniscus, which is implanted in rabbit's knee as a substitute with in vivo outcome showing an appealing ability to efficiently alleviate the cartilage surface wear. The self‐thickening strategy is applicable to directly printing a variety of polymer‐hydrogel‐based tissue engineering scaffolds without sacrificing mechanical strength, thus circumventing problems of printing high‐strength hydrogels and facilitating their application scope.
A self‐thickening and self‐strengthening strategy is developed to directly 3D print supramolecular poly(N‐acryloyl glycinamide) (PNAGA) hydrogels, and extended to printing a wide variety of polymer hydrogels with an ability to maintain robust mechanical strengths. The high‐strength and antiswelling PNAGA hydrogel is printed into a meniscus scaffold that is implanted into the knees of rabbits, eventually efficiently protecting cartilage.
In this paper, two high Fe containing Al–Mg–Si–Mn–Fe alloys with Mg, Si and Mn modified were prepared, and their microstructures and mechanical properties were comparatively studied with a common ...applied alloy. Furthermore, the effects of alloying elements on their microstructures and the corresponding strengthening mechanisms were analyzed. It was found that the two Al–Mg–Si–Mn–Fe alloys exhibited good combination of strength and elongation in spite of their high Fe content. When compared with the common applied alloy, the yield strength of the two alloys was increased by 28 MPa and 50 MPa respectively, whereas the elongation was only slightly decreased. The higher strength of the two Al–Mg–Si–Mn–Fe alloys was mainly attributed to precipitation and solid solution strengthening which were substantially caused by the appropriated proportion of Mg and Si. Owing to the appropriate addition of Mn, no β–AlFeSi phases were found in the alloys, and the detriments of Fe were fully eliminated. The submicron scaled α–Al(FeMn)Si phases slightly improved the yield strength because of their contribution to grain refinement and dispersion strengthening. The results of this paper provide a valuable insight into the strengthening and industrial manufacturing of Al–Mg–Si alloys.
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