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In concentration gradient (CG) nano-polycrystalline Ni-Co alloy, the deformation mechanism of each region is different with the increase of Co content. It is found that in the Co-free region, grain boundary diffusion and dislocation slip mechanisms are dominant, while in other regions, there is a synergistic effect of solid solution strengthening. Moreover, the formation of new small grains by the migration of GB atoms will assist in the deformation of large grains, and the alloy exhibits gentle and stable stress–strain curve pattern. Meantime, although the dislocation density of each region is different, the dislocation density still changes stably before and after shearing. Compared with the uniform structure, the flow stress fluctuation is small when the CG structure is plastically deformed, which proves that this kind of structure is more stable. Moreover, it is found that at different temperatures, the CG alloy also shows stable dislocation density and coordination of various mechanisms, which ensures the strength stability. It is revealed that the CG structure has important properties that make the material strength more stable. This work demonstrates the excellent properties of CG alloy and has positive guiding significance for the development of low-cost, high-performance materials in terms of theoretical and practical applications. [ABSTRACT FROM AUTHOR]

The influence of microstructures (bimodal and basketweave) on the tensile properties and deformation mechanism of Ti-5Al-1V-1Sn-1Zr-0.8Mo alloy was investigated via an in situ tensile test monitored by electron backscatter diffraction (EBSD)-assisted slip trace analysis. The bimodal structure exhibited good plasticity, but its tensile strength was lower than that of the basketweave structure. These variations could be attributed to the larger α colony structure in the basketweave structure. In situ tensile testing showed that the α colony in the basketweave structure can promote the formation of shear bands, leading to decreased plasticity. The activation of numerous slip systems in αp of the bimodal structure ensured good plasticity. Meanwhile, deformation twins were occasionally observed in the bimodal structure. However, dislocation slip and deformation twins were observed inside the large-sized grain boundary α (αGB) phase in the basketweave structure. The results of this study can extend the potential application of Ti alloys. [ABSTRACT FROM AUTHOR]

Grain boundary engineering is an effective and feasible metal strengthening strategy to enhance the properties of nanopolycrystalline alloys by changing the number, configuration, and connectivity of different types of grain boundaries, especially for the twin boundaries. In the present contribution, the effect of twin spacing and loading mode on the deformation behavior and mechanism of NiCoAl columnar polycrystalline alloy is investigated. The results show that the nanotwins can not only increase the bearing capacity of dislocations but also emit many dislocations, resulting in the coupling effect of dislocation strengthening and twin strengthening. When the twin spacing is large, intrinsic stacking faults occur and gradually transform into deformation twins. In this stage, Shockley partial dislocation controls plastic deformation. When the twin spacing is small, the high‐density twin layers and stacking faults are more likely to interweave, showing a combination action of Shockley partial dislocation and stair‐rod dislocation. With the loading changing to Z axis, the yield strength decreases due to reduced resistance to the dislocation and a weakened number of Shockley partial dislocations of the emission, leading to less strengthening of the twins. The insights provide a solid theoretical foundation for the further application of NiCoAl in industrial production. [ABSTRACT FROM AUTHOR]

The addition of oxygen atoms in solid solution to α‐Ti alloy can increase not only its hardness but also its brittleness. Herein, the edge dislocation mobility of Ti–O single crystals at oxygen concentrations of 0–2 at% and temperatures of 100–900 K is investigated by molecular dynamics simulations. The results show that the interstitial oxygen atoms have a strong hindering effect on the a/3 [112¯0] edge dislocations on the {1¯100} prismatic planes, which is attributed to the pinning effect of the vacancy clusters on the dislocation movement due to the interstitial oxygen atoms, thus leading to pronounced dislocation strengthening and hardening. The critical resolved shear stress (CRSS) for dislocation movement increases with increasing oxygen content and decreases with increasing temperature. Moreover, the effect of oxygen concentration on dislocation mobility also diminishes with increasing temperature. [ABSTRACT FROM AUTHOR]

Herein, the effects of different Co content and temperature factors on the shear mechanical properties of nano‐polycrystalline nickel–cobalt alloy are analyzed by molecular dynamics (MD) simulations. It is found in the work that the highest shear modulus of 63.03 GPa is obtained when the Co content is 10%, attributed to the lattice distortion caused by the difference in the lattice parameters between two elements. During the shearing process, the multilevel twins are present with intensification of the deformation process, resulting in excellent dynamic shear performance. Shockley dislocations will drive the stacking faults and other partial dislocations to constitute a tetrahedral edge, and finally forms a tetrahedral structure. In addition, as the temperature of the shear environment increases, the highest strain and stress decrease. The grain boundary atoms increase significantly, and the atoms inside the grains decrease accordingly. As the degree of atomic disorder increases, the grain boundaries will melt gradually. The decrease of partial dislocation density can weaken the entanglement effect caused by dislocations. The previous conclusions promote the product development and application of nano‐polycrystalline alloys in the future, and provide important guidance significant for the engineering application of nickel–cobalt alloys. [ABSTRACT FROM AUTHOR]

The ω-phase in metastable β-titanium (Ti) alloys attracts great research interests owing to the metastability and the involved microstructural complexity upon straining, while the fundamental understanding on its formation mechanism is still insufficient. In this study, deformation-induced ω-plates have been systematically investigated using Ti-10 wt% Cr metastable β-Ti alloy containing athermal ω-precipitates. It is found that single-variant ω-plates form either along {332}β twin interfaces or in the twin interiors, which closely depends on twin morphologies. For the acicular β-twin, the ω-plate appears in the twin interiors accompanied by high density of parallel straight dislocations, while for the lenticular twin, the ω-plate attaches to the twin interface without the surrounding dense parallel straight dislocations. These unique formation characteristics result from local stress field induced by the twinning itself and the passive transformation of athermal ω-precipitates. It is further revealed that the passive transformation of athermal ω-precipitates dominates the formation of ω-plates inside the acicular twins, while it is the locally preferential twin thickening that promotes the ω-plates to form along the lenticular twin interfaces. These findings provide new insight into deformation-induced ω-phase transformation and the intricate deformation microstructures in metastable β-Ti alloys. [ABSTRACT FROM AUTHOR]

The Charpy impact toughness of Ti–2.5Al–2Zr–1Fe alloy plate with a bimodal and normal grain size distribution was comparatively studied. The sample with the bimodal grain size structure exhibits the larger impact absorbed energy and lower anisotropy than that with the normal grain size structure, which is mainly attributed to the coordination of prismatic slips in the fine α grains and { 10 1 ‾ 2 } 10 1 ‾ 1 deformation twins in the coarse α grains. The current work provides a promising approach for improving impact toughness and reducing anisotropy through microstructure optimization in near-alpha Ti alloys. • An improved impact absorbed energy and decreased anisotropy were obtained in Ti–2.5Al–2Zr–1Fe alloy with bimodal grain size. • The improved impact absorbed energy was attributed to the prismatic slip associated with the twining inducing plasticity. • Microstructural optimization can improve the impact toughness and reduce anisotropy of near-alpha titanium alloys. [ABSTRACT FROM AUTHOR]

The fatigue crack growth (FCG) behaviors of a twin inducing plasticity (TWIP) Ti-5Al-1 V-Sn-1Zr-0.8Mo (Ti5111) alloy with three typical microstructures were investigated. Compared with the equiaxed and bimodal structures, the lamellar structure exhibited a higher resistance to the FCG rate, but it displayed a lower strength and elongation to failure. Many 10 1 ¯ 2 10 1 ¯ 1 deformation twins (DTs) spanning multiple α/β layers were observed in the lamellar structure near the FCG path. The same type of DT was also observed in the equiaxed structure, although its density was significantly lower than that of the lamellar structure, and no DTs were found in the bimodal structure. The higher resistance to FCG of the lamellar structure results from its large effective microstructural unit size (α colony), which is most favorable to deflecting cracks and increasing crack path tortuosity, and is associated with the blocking effect of deformation twin boundaries on crack propagation. • Compared with equiaxed and bimodal structure, the lamellar structure exhibits the highest resistance to FCG rate. • The high resistance to FCG of lamellar structure is due to the coupling effect of crack deflection and twin boundary barrier. • Deformation twins spanning multiple α/β layers were observed in lamellar structure near the fatigue crack propagation path. [ABSTRACT FROM AUTHOR]

Precipitated phases are generally considered to be beneficial to mechanical strengthening, while harmful to corrosion resistance. However, this study found that the Ti-induced precipitated Laves phase in FeCrVTi x medium-entropy alloys (MEAs) improves both corrosion resistance and mechanical properties than FeCrV MEA. Results reveal that the selective dissolution of precipitated phase enhances the corrosion resistance by the segregation of TiO 2 and increased V oxide content in the passive film. Only appropriate distribution, size, and content of the precipitated phase induced by specific Ti addition can achieve synergy between corrosion resistance and mechanical properties, suggesting potential reliable materials for nuclear systems. [Display omitted] • The precipitated phase make the synergy of corrosion resistance and mechanical properties in BCC+Laves structure MEAs. • The selective dissolution of the precipitated phase makes TiO 2 segregated at the surface of passive film. • The Ti addition increase the content of V oxides in the passive film to improve the corrosion resistance. • The Ti addition mainly induces precipitation strengthening, grain refinement strengthening to improve mechanical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] The effect of alloying element segregation on the interface properties of the fcc-Fe/Ni 3 Al was investigated using the first-principles approach based on density functional theory, revealing the element segregation mechanisms from the perspectives of atoms and electrons. The results show that the alloying elements tend to replace position 1 on the interface of fcc-Fe phase side, and the order of stability after replacement is Ti, Nb, Mo, Cr and Mn. The state density diagrams show that the 4d orbital electrons of Mo and Nb contribute to increase the peak of Al atom 2p orbital at −5 eV, while the 3d orbital electrons of Cr and Ti tend to weaken the peak of Fe atom 3d orbital at 1 eV. The degrees of electron cloud enrichment and consumption increase between interface atoms of the difference charge diagrams indicate that the bonding strength increases and the interface stability is improved. The result of bond population is consistent with the differential charge density diagram. The study has a certain guiding significance for interfacial segregation behavior of alloying elements in heat-resistant steels. [ABSTRACT FROM AUTHOR]

The thermodynamic stability and mechanical strength of grain boundaries (GBs) govern many key properties of nanocrystalline or polycrystalline metals. In order to design novel Cu-based alloys with extraordinary properties and broaden the application scopes of Cu alloys, it is essential to clarify the effects of GB structure and composition on the stability and cohesion of Cu GBs. Firstly, the GB energies and works of separation of 12 Cu symmetrical tilt GBs with various GB orientations were figured out by using first-principles calculations, to link the GB properties with structures. Our results shown that the GB energies and works of separation of 12 Cu GBs are notably anisotropic. The GB energies for these GBs have an inverted and linear relationship with their works of separation. As to GB composition, the segregation tendencies of 8 alloying elements (Mg, Ca, Cr, Ni, Zn, Zr, Ag and Sn) in the Cu Σ5 [001](210) symmetrical tilt GB and their cohesive and embrittling effects on the GB were studied. It was found that all considered solutes excluding the element Ni can segregate to the Cu GB and thus play stabilizing roles into the Cu GB. Among 8 solutes, only the Zr and Cr segregations can improve the thermodynamic stability and fracture strength of Cu GB simultaneously. The GB strengthening effects of Zr and Cr segregations was attributed to their significant chemical contributions to the embrittling potencies, i.e., the presence of covalent-like bonding features in newly-formed Cu–Zr/Cr bonds. The reduction/increase of anti-bonding/bonding states below the Fermi level in Cu–Zr/Cr atomic pairs should be responsible for the GB stabilizing effects of Zr and Cr segregations. [Display omitted] • Zr and Cr segregation can strengthen Cu Σ5 [001](210) symmetrical tilt grain boundary. • Zr and Cr segregation can stabilize Cu Σ5 [001](210) symmetrical tilt grain boundary. • Grain boundary energy present inverted linear relationship with work of separation. [ABSTRACT FROM AUTHOR]