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Fretting wear has an adverse impact on the fatigue life of turbine blade roots. The current work is to comparatively investigate the fretting wear behaviour of the nickel-based superalloy surfaces produced by polishing and creep-feed profile grinding, respectively, in terms of surface/subsurface fretting damage, the friction coefficient, wear volume and wear rate. Experimental results show that the granulated tribolayer aggravates the workpiece wear, while the flat compacted tribolayer enhances the wear resistance ability of workpiece, irrespective of whether the workpiece is processed by polishing or grinding. However, the wear behaviors of tribolayers are different. For the polished surface, when the normal load exceeds 100 N, the main defects are crack, rupture, delamination and peeling of workpiece materials; the wear mechanism changes from severe oxidative wear to fatigue wear and abrasive wear when the loads increase from 50 to 180 N. As for the ground surface, the main wear mechanism is abrasive wear. Particularly, the ground surface possesses better wear-resistant ability than the polished surface because the former has the lower values in coefficient friction (0.23), wear volume (0.06×106 μm3) and wear rate (0.25×10-16 Pa-1). Finally, an illustration is given to characterize the evolution of wear debris on such nickel-based superalloy on the ground surface.

The ω-phase precipitates in β-Ti alloys increase the strength but significantly degrade the ductility of the alloys. In the present work, the mechanism of ω-strengthening and embrittlement is investigated by using a first principles method based on density functional theory. The generalized stacking fault energies of various slip systems in both the β and ω phases are calculated. The strengthening and embrittlement effects of the ω phase are discussed by comparing the slip energy barriers of slip systems in the β and ω phases with different orientation relationships. It is found that the slip energy barriers of slip systems in the ω phase, except for $$(\bar 2020){[0001]_\omega },$$ are much higher than those of slip systems in the β phase, which explains the ω-strengthening and embrittlement effects. The slip energy barrier of the most active slip system in the phase, $$(\bar 2020){[0001]_\omega },$$ increases with the depletion of Mo and increasing extent of structure collapse, suggesting that aging treatment enhances the -strengthening and embrittlement effects.

Compared to conventional grinding, ultrasonic face grinding of SiC ceramic with vibration amplitude more than 3 μm has been proved to improve the machining efficiency but usually face the problem of reducing the workpiece surface quality. The material removal mechanism and ground surface quality by ultrasonic face grinding using minor vibration amplitude (less than 1 μm) still remains uncertain and needs to be further investigated. In the present work, experiments of ultrasonic face grinding of SiC ceramic are carried out to study the influence of processing parameters (e.g. depth of cut, wheel speed and ultrasonic vibration amplitude) on the surface finish. The results show that both the grinding forces and ground surface roughness increase significantly with the increase of depth of cut and the decrease of wheel speed. However, with the increase of ultrasonic vibration amplitude, the grinding forces decrease rapidly first and then keep steady, and the ground surface roughness shows three variation stages: dropping, climbing and stabilizing, which achieves the smallest value of 0.04 μm at the amplitude of 0.216 μm. From the analysis of acquired workpiece surface morphology and image processing result, the proportion of chunks and pits on the workpiece surface is reduced due to ductile removal in case of ultrasonic vibration amplitude less than 0.2 μm, but increases when the amplitude is more than 0.2 μm because the material is removed in brittle domain. Finally, a sample machined at relatively high wheel speed and minor vibration amplitude is provided to support the findings. The proposed investigation provides a new approach to achieve mirror surface of SiC ceramic using ultrasonic face grinding.

The B6Ca2 and B8Ca2 clusters adopt interesting inverse sandwich architectures, featuring a prolate B6 (or perfect B8) ring jammed with two capping Ca atoms. Both clusters show the high thermodynamic stability due to the double (σ and π) electronic delocalization. In present paper, we computationally studied the hydrogen storage of them. The results suggest that each Ca site in B6Ca2 and B8Ca2 clusters could store up six H2, yielding a gravimetric density of 14.2 wt% for B6Ca2 and 12.6 wt% for B8Ca2. The average adsorption energy for H2-adsorbed B6Ca2 and B8Ca2 complexes is within the scope of 0.12–0.15 eV per H2 at wB97XD level, hinting that two clusters could reversibly store and release hydrogen, which is positively confirmed by the Born-Oppenheimer molecular dynamics simulations. Both B6Ca2 and B8Ca2 nanoclusters are feasible hydrogen storage media under the ambient condition.

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure, microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to 25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

Pickering emulsions have attracted extensive attention due to their good properties including easy to manufacture, high stability, and superparamagnetic response. To improve the emulsifying transportation of crude oil, a Pickering emulsion of crude oil and water stabilized by Fe3O4 nanoparticles was prepared and its rheological properties were tested in this research. It was found that the particle size of dispersion droplet polymerization group in stable crude oil Pickering emulsion is negatively correlated with solid content and water content, and the equilibrium apparent viscosity {\mu }_{\text{ap}} of emulsion follows the power law fluid equation. Besides, this kind of Pickering emulsion has higher elasticity of interface membrane, which means by adding functional particles, it obtains good dynamic stability, and thus, has a great application property in crude oil industry.

The substitutional solute atom induced local lattice distortion (LLD) in dilute metal solid solution was believed to be uniform that may even be modeled by using soap bubble raft. Contrary to this conventional picture, we report in this manuscript that the Mo induced LLD in dilute Ti-Mo solid solution is highly non-uniform as evidenced by our first principles calculations. The non-uniform LLD is ascribed to the Jahn-Teller splitting of the degenerated d states of Mo atom. We propose that the substitutional solid solutions with non-uniform LLD should satisfy two conditions. With which, the solid-solutions suffering from non-uniform LLD are predicted. The non-uniform LLD is expected to result in non-spherical stress field around the solute atom, and, therefore, challenges the application of classical solid solution hardening model to this kind of solid solutions., Comment: 8 pages and 4 figures

In this paper, we report a transient absorption microscopy study of photocarrier dynamics in CuS crystals at room temperature. The photocarriers are injected into the sample by interband absorption...

In this study, the machined surface quality of powder metallurgy nickel-based superalloy FGH96 (similar to Rene88DT) and the grinding characteristics of brown alumina (BA) and microcrystalline alumina (MA) abrasive wheels were comparatively analyzed during creep feed grinding. The influences of the grinding parameters (abrasive wheel speed, workpiece infeed speed, and depth of cut) on the grinding force, grinding temperature, surface roughness, surface morphology, tool wear, and grinding ratio were analyzed comprehensively. The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels. This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material. Moreover, both the BA and MA abrasive wheels exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion. Finally, an analytical model for prediction of the grinding ratio was established by combining the tool wear volume, grinding force, and grinding length. The acceptable errors between the predicted and experimental grinding ratios (ranging from 0.6 to 1.8) were 7.56% and 6.31% for the BA and MA abrasive wheels, respectively. This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel, and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.

The B6Be2 and B8Be2 clusters, adopting fascinating inverse sandwich-like geometries, were recently predicted with quantum chemical calculations. Both systems exhibit the high stability and double aromaticity with 4σ/6π or 6σ/6π delocalized electrons. The hydrogen storage of two systems is studied in the present paper. Our calculations show that B6Be2 and B8Be2 clusters have the ultra-high capacity hydrogen storage, each Be site can bound up with seven H2 molecules, corresponding to a gravimetric density of 25.3 wt percentage (wt%) for B6Be2 and 21.1 wt% for B8Be2, respectively, which far exceeds the target (5.5 wt%) proposed by the US department of energy (DOE) in 2017. The average absorption energies of 0.10–0.45 eV/H2 for B6Be2 and 0.11–0.50 eV/H2 for B8Be2 at the wB97XD level suggest that both systems are ideal for reversible hydrogen storage and release. The reversibility of H2 molecules on B6Be2 and B8Be2 complexes are faithfully demonstrated with the Born-Oppenheimer molecular dynamics (BOMD) simulations. The Be-doped boron nanostructure is a promising candidate for ultra-high hydrogen storage materials.

Comparative study was conducted on the grindability of wrought GH4169, equiaxial cast K403, directionally solidified cast DZ408 and single crystal DD6 superalloys by using the brown alumina wheels during the creep feed grinding process with regard to the grinding force, grinding ratio, wheel wear and surface integrity. The grinding forces were found to increase in the following order: DD6, GH4169, K403 and DZ408; and DD6 alloy had the largest grinding ratio, followed by GH4169, K403 and DZ408. In addition, the workpiece material adhesion and grain wear flats were found to be the main pattern of wheel wear in the grinding of DZ408, K403 and GH4169 alloys, while it was the wheel clogging for DD6 alloy. Irrespective of the workpiece material, the microhardness alternation of subsurface induced by thermal effect dominated over the mechanical effect with the increasing material removal rate (up to 6 mm3/(mm s)) and the softened level was 10–16.5 % to a depth of around 40 μm in this study. The surface defects, the highly deformed subsurface and the generation of micro cracks within the workpiece were found to be the main types of damage induced by the grinding operation. These results can provide insights into the effect of workpiece material on the grindability of different nickel-based superalloys in the investigation.

Computational evidence is reported on a boron-based ternary Rb6Be2B6 cluster as the “Big Mac” sandwich on a subnanoscale with thickness of 0.58 nm. The core hexagonal B6 ring, occurring in the naked form due to double 6π/6σ aromaticity, is capped by two tetrahedral BeRb3 ligands. Such a B6 motif is scarce in boron clusters. The sandwich cluster has four-fold 2σ/6π/6σ/2σ aromaticity and its tetrahedral BeRb3 ligand is the simplest case of three-dimensional aromaticity (or spherical aromaticity). The sandwich can be formulated as a charge-transfer complex, [Rb3Be]3+[B6]6−[BeRb3]3+, whose components are held together by robust electrostatics, facilitating dual-mode dynamic fluxionality.

The typical electron-deficiency of the boron element renders fascinating architectures and chemical bonding to boron-based nanoclusters. We theoretically predict two di-Ca-doped boron clusters, B6Ca2 (D2h, 1Ag) and B8Ca2 (D8h, 1A1g), and both adopt interesting inverse sandwich geometries, showing an elongated D2h B6 or perfectly planar D8h B8 ring being sandwiched by two Ca atoms only, respectively. Natural atomic charge analyses indicate that the Ca atoms donate nearly all the 4s electrons to the B6 (or B8) ring, forming [Ca]2+[B6]4−[Ca]2+ and [Ca]2+[B8]4−[Ca]2+ charge transfer complexes. The interaction between the two Ca atoms and the boron rings is governed by robust electrostatics albeit by weaker B–Ca covalent interaction. Chemical bonding analyses show that B6Ca2 has 4σ and 6π delocalized electrons on the elongated B6 ring, leading to a conflicting aromatic system. B8Ca2, possessing 6σ and 6π delocalized electrons on the B8 ring, is doubly aromatic. Additionally, the B6Ca2 and B8Ca2 clusters show noticeable structural and electronic transmutation relative to their equivalent electronic B6Be2 and B8Mg2 clusters, respectively. The intrinsic reasons behind the transmutations are elucidated via in-depth bonding analyses.

Precipitates, including silicides and Ti3Al (α2) phase, and alloying elements distribution in a near α titanium alloy Ti65 (Ti-5.8Al-4.0Sn-3.5Zr-0.5Mo-0.3Nb- 1.0Ta-0.4Si-0.8W-0.05C) after solution treatment and aging process were characterized by using transmission electron microscopy (TEM) and atom probe tomography (APT). Quantitative composition analysis and TEM observation indicate that the silicides fit to (Ti, Zr)6(Si, Sn)3. Zr exhibits a β-stabilizing effect in near α titanium alloys but is weaker than other β stabilizing elements. The enriching tendency of the alloying elements in the retained β phase is in the order of Zr

We fabricated a van der Waals heterostructure of WS2–ReSe2 and studied its charge-transfer properties. Monolayers of WS2 and ReSe2 were obtained by mechanical exfoliation and chemical vapor deposition, respectively. The heterostructure sample was fabricated by transferring the WS2 monolayer on top of ReSe2 by a dry transfer process. Photoluminescence quenching was observed in the heterostructure, indicating efficient interlayer charge transfer. Transient absorption measurements show that holes can efficiently transfer from WS2 to ReSe2 on an ultrafast timescale. Meanwhile, electron transfer from ReSe2 to WS2 was also observed. The charge-transfer properties show that monolayers of ReSe2 and WS2 form a type-II band alignment, instead of type-I as predicted by theory. The type-II alignment is further confirmed by the observation of extended photocarrier lifetimes in the heterostructure. These results provide useful information for developing van der Waals heterostructure involving ReSe2 for novel electronic and optoelectronic applications and introduce ReSe2 to the family of two-dimensional materials to construct van der Waals heterostructures.

CdSiP2 (CSP) with outstanding mid-infrared nonlinear optical properties in the 3–5 μm and 8–12 μm windows has always been expected for application requirement, whereas the inadequate of absorption losses cannot be ignored as practical usage. The defect formation energies, electronic structure characteristics, structure distortion and related optical properties of CSP with some traditional and basic dopants M= (Mg, Al, Cu, Fe, and Mn) substituting Cd or Si sites are investigated by employing density functional theory (DFT). The calculations show that the energetically and thermally stable states in CSP crystals are Mg0, Al1+, Cu4+, Fe4+, Mn4+ at Cd sites and FeSi1+ at SiP2 reference states. Fe and Mn dopants at Cd sites bring abundant valences, including 0, +1, +2 and +4 charged states, and result in a mean absorption spectrum increase. New peaks appear in the density of states as the CuCd4+, FeCd4+, and MnCd4+ take shape, and thus affect the absorption spectrum. According to the calculation results, highly localized d orbitals of dopants should be mainly responsible for the absorption aberrance, because they not only lead to a mean absorption spectrum increase, but also bring new absorption peaks affecting the conversion efficiency along X/Y or Z directions.

Self-propulsion of droplets is of great significance in many fields. The spontaneous horizontal motion and self-jumping of droplets have been well realized in various ways. However, there is still a lack of an effective method to enable a droplet to rotate spontaneously and steadily. In this paper, by employing an acid droplet and a liquid metal, the spontaneous and steady rotation of droplets is achieved. For an acid droplet, it may spontaneously move when it is deposited on the surface of the liquid metal. By adjusting experimental parameters to the proper range, the self-rotation of droplet happens. This phenomenon originates from the fluctuation of the droplet boundary and the collective movement of bubbles that are generated by the chemical reactions between the acid droplet and liquid metal. This rotation has a simpler implementation method and more steady rotation state. Its angular velocity is much higher than that driven by other mechanisms. Moreover, the movements of acid droplets on the liquid metal are classified according to experimental conditions. The internal flow fields, the movements and distribution of bubbles, and the fluctuation of the droplet boundary are also explored and discussed. The theoretical model describing the rotational droplet is given. Our work may deepen the understanding of the physical system transition affected by chemical reactions and provide a new way for the design of potential applications, e.g., micro- and nanodevices.

Atomic-scale simulations are performed to investigate the interaction between prismatic interstitial loops and moving dislocations in nickel. Depending on their relative position, a loop either drags a dislocation elastically or decorates a dislocation with jogs, resulting in a systematic change of the critical stress for subsequent dislocation glide. Loop-decoration significantly reduces the mobility of a dislocation, and the critical shear stress can increase up to ten times larger than the conventional Peierls stress. This work presents the atomic-scale details of loop-dislocation interaction, thus providing reliable information for parameterizing debris-dislocation interaction in meso- or macro-scale simulations.

Microalloying is an effective approach to improve the mechanical properties of γ-TiAl intermetallic compound. Knowledge about the site occupancy of the ternary alloying element in the crystal lattice of γ-TiAl is highly demanded in order to understand the physics underlying the alloying effect. Previous first-principle methods-based thermodynamic models for the determination of the site occupancy were based on the point defect gas approximation with the interaction between the point defects neglected. In the present work, we include the point defect interaction energy in the thermodynamic model, which allows us to predict the site occupancy of the ternary alloying element in γ-TiAl beyond the point defect gas approximation. The model is applied to the γ-TiAl–Nb alloy. We show that, at low temperature, the site occupancy of Nb atoms depends on the composition of the alloy: Nb atoms occupy the Al sublattice for the Ti-rich alloy but occupy Ti sublattice for the Al-rich alloy. The fraction of Nb atoms occupying Al sublattice in the Ti-rich alloy decreases drastically, whereas the fraction of Nb atoms on the Ti sublattice in the Al-rich alloy decreases slightly with increasing temperature. At high temperature, Nb atoms occupy dominantly the Ti sublattice for both the Ti-rich and Al-rich alloys. The interaction between the point defects makes the Ti sublattice more favorable for the Nb atoms to occupy.

The volume modeling of the sigma phase is an indispensable complement to the integrated computational material design of technologically important materials, such as high-alloy steels and Ni-based superalloys. The molar volume of the sigma phase is influenced by both the atomic mixing (the volume variation affected by this factor is caused by composition alteration rather than site occupation change) and atomic order (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal). In the present work, we developed a new integrated thermodynamic and molar volume model to consider physically both mixing and order factors. The integrated model was built within the compound energy formalism (CEF), enabling the thermodynamic calculations to determine equilibrium site occupancies for the subsequent volume calculations. The model parameters of the CEF were assigned by using the first-principles calculated energies and molar volumes of the complete sets of ordered configurations of the sigma phase, as well as the extrapolated molar volumes of the pure elements in the hypothetic sigma phase structure. Such extrapolation for pure elements is based on the experimental data from the literature and the first-principles calculations. We applied the integrated model to study the binary compounds, e.g. Cr-Co, Cr-Fe, Cr-Mn, Mo-Fe, Mo-Mn, Mo-Re, Re-Cr, Re-Fe, Re-Mn, Nb-Al, Ta-Al, V-Fe, V-Ni, and ternary compounds Cr-Fe-X (X = Co and Ni). The integrated thermodynamic and molar volume databases can predict successfully the molar volume of the binary and ternary sigma compounds. As most experimental volume data were measured at room temperature and atmospheric pressure, and the first-principles calculations were performed at 0 K, the present model parameters are valid at about room temperature and atmospheric pressure.

Employing atomic-scale simulations, the response of a high-angle grain boundary (GB), the soft/hard GB, against external loading was systematically investigated. Under tensile loading close to the hard orientation, strain-induced dynamic recrystallization was observed to initiate through direct soft-to-hard grain reorientation, which was triggered by stress mismatch, inhibited by surface tension from the soft-hard GB, and proceeded by interface ledges. Such grain reorientation corresponds with expansion and contraction of the hard grain along and perpendicular to the loading direction, respectively, accompanied by local atomic shuffling, providing relatively large normal strain of 8.3% with activation energy of 0.04 eV per atom. Tensile strain and residual dislocations on the hard/soft GB facilitate the initiation of dynamic recrystallization by lowering the energy barrier and the critical stress for grain reorientation, respectively.

The ductile-to-brittle transition is commonly observed in metastable β-titanium (Ti) alloys containing ω-precipitates, while the fundamental understanding on ω-embrittlement hitherto remains elusive. In this work, the prototypical Ti-20 wt% Mo metastable β-Ti alloy has been systematically investigated by coupling experiments and first-principles calculation to eliminate this puzzle. It is shown that the structural evolution of ω-phase controls the deformation mechanism transition of twinning-to-slip in Ti Mo alloy, being the origin of ductile-to-brittle transition of this alloy. The initial trigonal ω-structure continuously collapses to hexagonal ω-structure (structural collapse) whilst Mo-atoms are rejected out concurrently (stoichiometric varieties), both leading to hardening of ω-precipitates. This self-hardening of ω-precipitates was further rationalized in terms of the enhanced propensity for a covalent character of the atomic bond demonstrated by the electronic density of states (DOS) from first-principles calculation. Specifically, the self-hardening behavior of ω-precipitates promotes dislocation slip on isolated planes in lieu of correlative slip on successive planes inside ω1-variant, while dislocations are completely blocked ahead ω2/ω3/ω4-variants. This in turn renders the transition from deformation twinning that contributes to great macro-plasticity to ordinary dislocation slip that contributes to localized deformation bands in the present Ti Mo alloy.

This study investigates the comparative wear behavior of brown alumina (BA) and microcrystalline alumina (MA) alumina abrasive wheels and its effect on the creep feed ground surface of different nickel-based superalloys, such as wrought alloy GH4169, directional solidified alloy DZ408 and single crystal solidified alloy DD6. The abrasive wheel wear topography was characterized and an analytical model was developed to evaluate the abrasive wheel wear comprehensively. Finally, the effects of tool wear on the grinding performance and ground surface were discussed. Results obtained indicate that, compared with BA abrasive wheel, the MA wheel performed better in terms of the grinding ratio and tool wear behavior. Strong adhesion wear and attritious wear of the abrasive wheels were generated during grinding of GH4169 and DZ408 alloys, while great wheel clogging occurred during grinding of DD6 alloy. Moreover, DZ408 alloy produced the most severe tool wear and largest grinding forces, followed by GH4169 and DD6 alloys. The defects pattern of ground surface with BA wheel was unparallel to the grinding direction due to the grain dislodging and fracture; however, when grinding with MA wheel, groove defects were created along the grinding direction due to high ductility and hardness of grains.

ω phase precipitating in a β -Ti alloy is generally detrimental to the ductility and plasticity of the alloy.To understand the influence of ω phase on the mechanical properties of β -Ti alloys, the property of the β/ω interface is demanded.In this regard, we calculate the interface energies ( γ int ), cleavage energies ( γ cl ), and generalized stacking fault energies ( γ ) of the β/ω interfaces with different orientations using a first-principles method.Our calculations predict interface energies of 0.32 J m−2 and 0.03 J m−2 for the ( 1 1 1 ¯ ) β / ( 0 0 0 1 ) ω and ( 1 1 2 ) β / ( 1 0 1 ¯ 0 ) ω interfaces, respectively.The strong anisotropy of the interface energy contributes to the ellipsoid-like morphology of ω phase with its major axis parallel to the 〈 1 1 1 〉 β direction.The influence of the interface on the ductility of the alloy is discussed with the calculated cleavage energies and the unstable stacking fault energies ( γ us ) extracted from the generalized stacking fault energy (GSFE). The γ cl / γ us ratio of the ( 1 1 2 ) β / ( 1 0 1 ¯ 0 ) ω interface is lower than those of the main slip planes of the bulk phases, indicating that this interface is prone to crack initiation and propagation as compared to the bulk and contributes to theω-embrittlement of β -Ti alloys.

Variant selection during solid–solid phase transformation in titanium alloys affects greatly the microstructure and mechanical properties of the alloys. Theoretical investigations of the variant selection were generally performed by using phase field simulation that considers solely the elastic coherency strain energy. In the present work, we develop a model to determine the variant selection directly from first-principles calculations. The source of the variant selection is considered to be the varying free energy gains (including both bulk and interface contributions) induced by the transformation from the parent phase to different variants of the product phase. This model is applied to investigate the effects of shear stress and alloy composition on ω variant selection during athermal β → ω transformation in binary Ti-xMo ( x ≤ 25 at.%) alloys. The random distribution of the atoms in the alloy is described by using virtual crystal approximation (VCA). We show that the tendency of variant selection becomes stronger with increasing shear stress. With increasing Mo concentration, the favorable ω variant transfers from one to another, except for the ω phase with very small particle size (e.g., radius R ≤ 1 nm) where one variant is always selected. The critical Mo concentration for the transfer of the favorable ω variant approaches to 5 at.% with increasing size of the ω phase particles and remains almost unchanged against the shear stress. At the critical Mo concentration, the considered variants have equal free energy gains and there is no variant selection. This finding opens the possibility of controlling the variant selection and the associated microstructure by changing the composition of the alloys.

Dissolutive wetting, i.e. droplet wets and simultaneously dissolves its solid substrates, is of great significance in both academic research and practical applications. The diffusion interface at the moving contact line is one of the answers to the Huh-Scriven paradox. Besides, dissolutive wetting is the bottleneck problem in many practical fields, such as metal alloy processes, shale gas exploitation, drug release, etc. Furthermore, dissolutive wetting involves complex physical processes, i.e. wetting, diffusion and convection. The coupling transport of mass and momentum as well as the internal convection in the droplet increases the difficulty in studying dissolutive wetting. Even though previous works have been done on metal/metal, metal/ceramic systems, there has been no experimental observation on the flow details in droplets and changes of the solid-liquid interface due to the opacity of the materials in dissolutive wetting. Thus, the physical mechanism of dissolutive wetting is still far from being well understood. Based on the problems mentioned above, in this paper, dynamics of dissolutive wetting of droplets on solid surfaces is investigated by physical mechanics. From a new perspective, we carry out the molecular dynamic simulations of glucose and water dissolution pairs. we match the parameters that dominate the dissolutive wetting in our simulations with real experimental parameters. By this method, the simulation systems are simplified and the glucose molecules can be regarded as Lennard Jones particles. Experiments are also designed to show the in situ real time measurement of the dissolutive wetting. In order to obtain the flow details in the droplet, we select three pairs of high transparent materials. Beyond that, we built a dimensionless number space that divides the dissolutive wetting into two types. For small Pelect number, the convection effect is ignored. But when Pelect number is greater than one, the convection effect that leads to the uniform of the solute distribution must be considered. Morever, we obtain that the droplet follows different scaling laws in different dissolutive wetting stages. In the early stage, the surface tension dominates and the scaling law satisfies the Tanner law. Whereas scaling law in dissolutive wetting changes while diffusion and convection effect are more obvious with the dissolution of solutes. Compared with the non-convective process, the internal convection increases the energy dissipation within the dissolution pairs in our experiments and inhibits the spreading of the droplets to a certain extent. We also find that the coupling effect of dissolution and wetting process will have important influences on the molecular structure of the droplet. Overall, we establish multiscale dissolutive wetting model and reveal the scaling laws of droplet spreading in dissolutive wetting by physical mechanics. Our findings may help to further understand the mechanisms of dissolutive wetting and provide theoretical guidance of practical applications that involve dissolutive wetting.

The development of synthetic methods to obtain high value-added mesoporous Al-MCM-41 from a low-cost silicon-aluminum source with low toxicity is an active research topic in solid waste resource utilization. In particular, the controlled synthesis of MCM-41 with a two-level pore distribution is a challenging task. In this work, the synthesis of unimodal and bimodal mesoporous Al-MCM-41s was achieved using acids with different degrees of ionization from coal gasification fine residue (CGFR) as bulk solid waste generated by the coal gasification process. We determined that the degree of acid ionization affected the self-assembly of inorganic/organic species as well as condensation processes, resulting in some changes of the hexagonal mesoscopic structure. The unimodal mesoporous Al-MCM-41 with acetic acid HAc and bimodal mesoporous Al-MCM-41s with an inorganic acid environment (HCl, HNO3 or H2SO4) could be effectively prepared in a controllable manner by the silicon and aluminum source obtained at alkali dissolution time 6 h and crystallization conditions at pH 10.5 and 383 K in 72 h. Moreover, the synthesis of Al-MCM-41-HAc with different SiO2/Al2O3 molar ratios (18–89) could also be realized by different alkali dissolution times. And alkali dissolution time (2–24 h) and the crystallization conditions (pH 4.5–11.5, temperatures 373–393 K, and time 48–96 h) also affected the formation of unimodal and bimodal mesoporous Al-MCM-41-HAc. In addition, the maximum adsorption amount onto bimodal mesoporous Al-MCM-41-H2SO4 (476.19 mg g−1 at 308 K) was larger than that onto unimodal mesoporous Al-MCM-41-HAc (243.90 mg g−1 at 303 K). The mesoporous Al-MCM-41s showed good stability.

Phase decomposition influences significantly the mechanical properties of high entropy alloys (HEAs). Prediction of the phase decomposition of HEA is greatly hindered by the hyper-dimensional composition space of the alloys. In the present work, we propose to represent the HEAs as various pseudo-binary alloys of which the temperature dependent free energies as functions of compositions may be readily calculated by using first-principles methods in combination with thermodynamic models. With the calculated free energies, the phase diagrams of the pseudo-binary alloys may be constructed and the phase decomposition can be predicted. This procedure is applied to Hf-Nb-Ta-Ti-Zr alloy with body-centered cubic (BCC) structure. We predict that the equiatomic HfNbTaTiZr HEA suffers from phase decomposition below critical temperature of 1298 K. The HEA decomposes most favorably to BCC NbTa-rich and HfZr-rich phases. The BCC HfZr-rich phase transfers to a hexagonal close-packed structure (HCP) phase at low temperature. The predicted compositions of the decomposed phases are in good agreement with experiment and Thermal-Calc modeling. Furthermore, the effect of the phase decomposition on the strength of the HEA is evaluated by considering the solid-solution and precipitation strengthening mechanisms. The precipitation strengthening effect is stronger than the solid-solution strengthening at the low annealing temperature but becomes weaker at high annealing temperature.

In this contribution, novel bio-derived rosin acid ester compounds have been developed and used as internal electron donors to prepare MgCl2 supported titanium catalysts for propylene polymerization. The results of the polymerization showed that tri-n-amyl maleate, triiso-amyl maleate and tri-n-heptyl maleate as internal electron donors in Ziegler-Natta catalysts all have high polymerization activity and stereoregularity. In particular, the Ziegler-Natta catalyst with tri-n-amyl maleate as the internal electron donor has the highest activity (up to 33.4 kgPP·gCat−1·h−1) for propylene polymerization and the isotacticity of polypropylene is as high as 96.8% determined by 13C NMR. Simultaneously, the obtained polypropylene with a relatively broad molecular weight distribution of 9.0 and melt flow rate of 160.3 g/10 min, which is beneficial to processing and has practical industrial application value when used as the basic material of melt blown cloth for medical mask.

The gradient microstructures of surface layer in single crystal nickel-based superalloy were produced by creep-feed grinding. The mechanical properties (i.e., hardness, elastic modulus) and room-temperature (RT) creep behavior of such structures were evaluated using a nano-indentation technique. Results show that the gradient structures along depth from ground surface consisted of nanograins, submicron grains and lamellar-shape structures, and dislocation structures. Furthermore, it was found that the hardness and elastic modulus of gradient structures were higher by 8–10% than that of bulk material on average. However, the regions containing nanograins showed a remarkable increase in creep depth compared to bulk material, implying that the creep behavior of ground layer was changed unfavorably. The obtained stress exponents of gradient structures suggested that dislocation activities were the main mechanism for indentation creep deformation.

Atomically thin bismuth oxyselenide (Bi2 O2 Se) exhibits attractive properties for electronic and optoelectronic applications, such as high charge-carrier mobility and good air stability. Recently, the development of Bi2 O2 Se-based heterostructures have attracted enormous interests with promising prospects for diverse device applications. Although the electrical properties of Bi2 O2 Se-based heterostructures have been widely studied, the interlayer charge transfer in these heterostructures remains elusive, despite its importance in harnessing their emergent functionalities. Here, a comprehensive experimental investigation on the interlayer charge transfer properties of two heterostructures formed by Bi2 O2 Se and representative transition metal dichalcogenides (namely, WS2 /Bi2 O2 Se and MoS2 /Bi2 O2 Se) is reported. Kelvin probe force microscopy is used to measure the work functions of the samples, which are further employed to establish type-II band alignment of both heterostructures. Photoluminescence quenching is observed in each heterostructure, suggesting high charge transfer efficiency. Time-resolved and layer-selective pump-probe measurements further prove the ultrafast interlayer charge transfer processes and formation of long-lived interlayer excitons. These results establish the feasibility of integrating 2D Bi2 O2 Se with other 2D semiconductors to fabricate heterostructures with novel charge transfer properties and provide insight for understanding the performance of optoelectronic devices based on such 2D heterostructures.

Local chemical ordering influences significantly the mechanical properties of refractory high entropy alloys. In this work, the effects of local chemical ordering on the structural stability and mechanical properties of AlNbVTiZr are investigated by using first-principles simulations. It is shown that the Al Zr bond dominates the chemical ordering for ordered configurations. The local ordering enhances the structural stability, elastic property and ideal strength. By taking into account the effects of temperature and pressure, we found that chemical ordering mediates the thermodynamic properties of the AlNbVTiZr alloy, but it has little effect at high pressure.

International audience; We report a comprehensive study on the structure and elastic constants of epitaxial cubic δ-TaxN (x ≈ 1) layers deposited by reactive magnetron sputtering at 570 °C on MgO(001), MgO(110) and MgO(111) substrates. X-ray diffraction shows that all layers are single-phase and have a single-crystal rocksalt-structure, growing with an epitaxial cube-on-cube relationship with respect to their MgO substrates. For (001)-orientation, Brillouin light scattering provides the measurement of c44 (137 ± 3 GPa) and c12 (130 ± 5 GPa) single-crystal elastic constants, while picosecond laser ultrasonics (PLU) provides the third independent one, c11 (530 ± 10 GPa). For (110)- and (111)-orientations, PLU provides selectively the following combinations, (c11+c12+2c44)/2 and (c11+2c12+4c44)/3, respectively. Electrical resistivity measurements show evidence of point defects in the films despite a composition close to 1:1 stoichiometry. Point defects (metal and nitrogen vacancies) are considered in our first-principles calculations to find closer agreement between experimental and theoretical lattice parameter, mass density, sound velocities and elastic constants. Sound velocities and elastic constants are found to be particularly sensitive to the presence of vacancies, resulting into a more compliant and less anisotropic material. While only ∼ − 1% mismatch is found between predicted defect-free and experimental lattice parameters, huge differences of −27% and +180% are observed for c11 and c44, respectively. These discrepancies can be rationalized by considering the presence of point defects (metal vacancy and/or Schottky defect) in concentration ∼11% in the as-deposited TaN films, a compositional value that corresponds to the lowest formation energy of δ-TaNx structure.

We investigated surface properties of metals by performing first-principles calculations. A systematic database was established for the surface relaxation, surface energy (γ), and surface stress (τ) for metallic elements in the periodic table. The surfaces were modeled by multi-layered slab structures along the direction of low-index surfaces. The surface energy γ of simple metals decreases as the atomic number increases in a given group, while the surface stress τ has its minimum in the middle. The transition metal series show parabolic trends for both γ and τ with a dip in the middle. The dip occurs at half-band filling due to a long-range Friedel oscillation of the surface charge density, which induces a strong stability to the Peierls-like transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for γ and τ, respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative τ for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing γ trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.

These data are supplied for supporting their interpretations and discussions provided in the research article “Large influence of vacancies on the elastic constants of cubic epitaxial tantalum nitride layers grown by reactive magnetron sputtering” by Abadias et al. (2020) [doi: 10.1016/j.actamat.2019.11.041 ]. The datasheet describes the experimental methods used to measure the longitudinal (VL) and transverse (VT) sound velocities of cubic epitaxial TaN/MgO thin films, and their related cubic elastic constants (c11, c12 and c44), by the picosecond laser ultrasonic (PLU) and the Brillouin light scattering (BLS) techniques, respectively. First-principles numerical simulations provide additional data using specifically designed supercells of TaN structures, generated either by hand or using the alloy theoretical automated toolkit (ATAT) method [A. Zunger et al. (1990)], with different configurations (random, cluster and ordered) of defects (Ta and N vacancies). Phonons calculations support discussion of dynamical mechanical stability of defected TaN cubic structures. The data illustrate the huge role of vacancies in elastic properties and phase stability of TaN films.

International audience; The formation of the sigma phase in technologically important materials influences greatly their mechanical properties. Fundamental knowledge on the sigma phase is demanded to understand the phase stability and reasonably control its precipitation. The present work clarifies the atomic bonding characteristics of the binary sigma phase including A-Al (A = Nb, Ta) and transition metal systems (TM-TM) based on the electronic density of states (DOS) and electron localization function (ELF) calculated by using first-principles methods. We show that the atomic bonds of the binary sigma phase exhibit both metallic and covalent characters. The completely ordered A66.7Al33.3 (A = Nb, Ta) sigma compounds bear higher stability than their counterparts with atomic disordering. Besides, for a TM-TM sigma compound, the constituent atom with more electron shells or less valence electrons presents stronger electronic stability. When increasing its atomic occupancy on a specific site, the atomic bonding on the site becomes stronger.

International audience; The present work systematically clarifies the influence of the atomic mixing and the atomic order (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal) on the molar volume of the binary sigma phase. We calculated the molar volumes of 21 binary sigma compounds with different atomic order by using EMTO-CPA (Exact Muffin-Tin Orbitals - Coherent Potential Approximation) method. The calculation results follow a similar trend as the experimental data. Moreover, the calculated molar volumes with respect to the composition of the sigma phase in disordered states show that the sigma compounds do not comply with the linear volume-composition relationship. This is due to the influence of the atomic mixing and the deviation can be either negative or positive depending on the tendency of electron loss or gain of the two constituent elements. Additionally, we compared the molar volume difference (ΔVm = Vdisorder-Vorder) between the hypothetically disordered and ordered states of the binary sigma compounds. The results indicate that the effect of the atomic order on the molar volume of the sigma phase depends on the size difference and the electron configurations of the two constituent elements

An intricate understanding of the fundamental β→α phase transformation upon the presence of metastable ω phase is vital for tailoring the multiphase microstructures of titanium and titanium alloys for various specific applications. To approach this, the structures and energetics of heterophase interfaces among α, β, and ω in titanium were thoroughly investigated, using the combination of high-resolution transmission electron microscopy and first-principles density functional theory calculations. The results strongly suggest that metastable ω does not necessarily act as the precursor of α but can reduce the energy barrier for α nucleation in β. The ω/β interfaces acts as favorable nucleation sites for α which, once forms, tends to grow favorably into the β matrix. These findings validate the ω-assisted α nucleation mechanism, and adequately rationalize many TEM observations on titanium alloys.

Four silver(I) coordination polymers (CPs), namely {Ag3(cpyz)(btc)}n (1), {Ag2(cpyz)(pta)}n (2), {Ag3(mpyz)2(btc)·2(H2O)}n (3), {Ag2(mpyz)(pta)·2(H2O)}n (4), [cpyz = 2-chloropyrazine, H3btc = 1,3,5-benzene tricarboxylic, mpyz = 2,6-dimethylpyrazine, H2pta = phthalic acid] have been synthesized and characterized. X-ray diffraction indicates that, 1 shows a 3D supramolecular structure with a 1D silver chain containing an infinite Ag3 units; 2 features a 3D supramolecular framework with Ag-O and Ag-Ag interaction and cpyz ligand adopts monodentate mode making no contribution to the dimensionality; in 3, the silver atom links mpyz ligand and btc anion into a 2D layer connected by Ag-Ag interaction between neighboring layers into the 3D network, with Zigzag Ag4 units; in 4, Ag(I) coordinates pta benzene dicarboxylates to generate a one-dimensional infinite chain, connecting by nitrogen ligand to exhibit a 2D 44-sql network. The results suggest that benzene dicarboxylates and the kinds of pyrazine derivatives play significant roles in the formation of such coordination architectures. The photoluminescence and thermogravimetric analysis (TGA) of the complexes were measured.

Solute atoms such as Fe, Co, and Ni diffuse abnormally fast in α-Ti, which influences significantly the mechanical properties of the titanium alloys. Various mechanisms (e.g., the interstitial diffusion mechanism and solute-vacancy complex mechanism) have been proposed to account for the fast diffusion of these solutes in α-Ti. To elucidate such diffusion mechanism, a first-principles method is employed to calculate the formation energies, migration energy barriers, and solute-vacancy binding energies of the substitutional and interstitial solute atoms including Al, Si, Sn, V, Mn, Fe, Co, Ni, and Cu in α-Ti. Based on the calculated parameters, the diffusion mechanisms are discussed. Comparing the formation energies of the substitutional and interstitial solutes, we find that all the solute atoms prefer the substitutional configuration to the interstitial one. The interstitial migration energy barriers are quite low for all the solutes. Al and Sn diffuse mainly through normal vacancy mediated mechanism due to the high substitutional to interstitial preferential energy that leads to very low fraction of interstitial solutes (about 10 − 15 ∼ 10 − 16 at 1000 K) at thermal equilibrium state and high interstitial diffusion activation energy. The 3d metal solute atoms, especially Mn, Fe, and Co, are fast diffusers and the diffusion coefficients are dominated by the interstitial mechanism because of their sizable thermal equilibrium interstitial fractions (several percent at 1000 K). The solute-vacancy complex mechanism is not likely to account for the fast diffusions in α-Ti. We show that the direct chemical interaction between the solute and matrix atoms determines the site-occupancy of the solute atoms in α-Ti besides the atomic size effect that was commonly believed to be responsible for the fast diffusions.

Breakdown of Schmid's law is a long-standing problem for exploring the orientation-dependent deformation mechanism in intermetallics. The lack of atomic-level understanding of the selection rules f ...

Brittle ω-precipitates in bcc β-Ti alloys are well known to dramatically degrade material plasticity and even trigger macroscopic premature fracture, posing an obstacle for structural applications. The embrittlement mechanism is intimately related to dislocation pile-up at the ω/β interface that leads to stress concentration and undesirable failure. The underlying physics of improving ductility remains to be further uncovered. Here we report a new finding in β-Ti alloy single crystal micropillar compression that the plasticity can be substantially improved by means of increasing strain rate, while mechanical strength simultaneously exhibits striking “faster is stronger” fashion. The results reveal that the improvement of micropillar plasticity upon higher loading rate can be ascribed to the wider deformation band, in contrast to equivalents under quasi-static mode. The microscopic examination shows that cross slip induced by screw dislocations governs the plasticity improvement, which is further validated by crystallographic analysis and first principle energy landscape calculations. This “dynamic self-toughening” behavior advances our fundamental understanding to the plastic deformation mechanism of ω-precipitate contained bcc β-Ti alloys. Keywords: Ti alloy micropillars, Omega-precipitates, Strain rate, Plasticity, Deformation band, Dislocations

Three-dimensional hierarchical metal oxide core/shell nanowire arrays (HMONAs) have become promising pseudocapacitive materials due to their integrated smart architectures. However, these core/shell nanostructures have unsatisfactory structural stability and frequently suffer destruction during their fabrication process and their charge–discharge cycles, thus limiting their application lifespan. Herein, a general strategy based on the minimization of the lattice mismatch between the shell and the backbone at the nanoscale interface has been proposed to improve the cycling stability of the HMONAs. This strategy is achieved by a facile hydrothermal pretreatment under mild acidic condition, where a selective dissolution process occurs for interface optimization. To prove the concept, three typical HMONAs, α-MnO2 nanotube@δ-MnO2 nanosheet core/shell arrays, α-MnO2 nanotube@NiO nanosheet core/shell arrays and Co3O4@MnO2 core/shell nanoarrays, were synthesized for interface optimization. It was found that these thermodynamically unstable nanostructures in the shells of HMONAs can be selectively dissolved under a hydrothermal process, leading to enhanced stability of HMONAs. The comparison study indicates that all treated HMONAs exhibit excellent capacitance retention of 93.2% (MnO2@MnO2), 94.3% (MnO2@NiO) and 95.3% (Co3O4@MnO2) after 5000 cycles, which are 22.9%, 9.3% and 20.1% higher, respectively, than those of the untreated HMONAs. Furthermore, the symmetrical supercapacitors based on treated MnO2@MnO2 nanoarrays electrodes also demonstrate 92% capacitance retention after 5000 cycles, showing better comprehensive performance than their untreated counterpart (78% capacitance retention). The general strategy of nanoscale interface optimization provides new opportunities in pushing the cycling stability limit of HMONAs.

Increasing the solubility of Al and inhibiting the growth of Ti3Al precipitates in high temperature titanium alloy improve both the thermal strength and thermal stability of the alloy. In principle, this may be achieved by adding some other alloying atoms which attract Al so as to serve as traps for Al in the alloy. In the present work, the interaction energies between Al and alloying atoms X with X covering all the transition metal (TM) and noble metal (NM) elements in the Chemical Elemental Period Table (CEPT) are calculated by using a first principles method in order to screen the traps for Al. The effects of temperature (taking Mo-Al interaction as an example) as well as the newly found off-center site-occupation of alloying atoms (Acta Mater. 197, 2020, 91) on the interaction energies are considered. We show that the interactions between Al and the TM alloying atoms early in the CEPT are weak. The middle TM alloying atoms attract but the late TM and NM ones repel Al. At finite temperature, the lattice vibration enhances whereas the configurational entropy weakens the Mo-Al attraction. Both effects become stronger with increasing temperature. The physical origins underlying the X-Al interactions are revealed by analyzing the electronic density of states and bonding charge density. Alloying atoms such as Mo, Tc, Ru, W, Re, and Os are identified to benefit the strength and thermal stability of high temperature titanium alloys. This work is helpful to the rational design of high temperature titanium alloys.

The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer. This work investigated the surface deformation structures of turbine blade root of single crystal nickel-based superalloy produced under different creep feed grinding conditions. Gradient microstructures in the superficial layer were clarified and composed of a severely deformed layer (DFL) with nano-sized grains (48–67 nm) at the topmost surface, a DFL with submicron-sized grains (66–158 nm) and micron-sized laminated structures at the subsurface, and a dislocation accumulated layer extending to the bulk material. The formation of such gradient microstructures was found to be related to the graded variations in the plastic strain and strain rate induced in the creep feed grinding process, which were as high as 6.67 and 8.17 × 107 s−1, respectively. In the current study, the evolution of surface gradient microstructures was essentially a transition process from a coarse single crystal to nano-sized grains and, simultaneously, from one orientation of a single crystal to random orientations of polycrystals, during which the dislocation slips dominated the creep feed grinding induced microstructure deformation of single crystal nickel-based superalloy.

Using density-functional theory, we determine the generalized stacking fault energy (GSFE) for the { 1 1 ¯ 2 } 〈 1 ¯ 11 〉 twinning system in ferromagnetic (FM) body-centered cubic Fe and Fe-Cr alloys with molar fraction of Cr ≤ 0.5 . We adopt both reflection and isosceles twinning pathways and reveal the magnetic ordering effects on the GSFE by contrasting the FM results to those obtained for the magnetically disordered paramagnetic (PM) state. The results show that the isosceles twin boundary configuration is energetically preferred in this binary. The loss of long-range magnetic order lowers the GSFE amplitude but increases the twin boundary migration (TBM) energy regardless of the Cr content. The twin boundary formation (TBF) energy and the TBM energy show non-linear dependences on Cr content in the FM and PM states, and the effect of Cr on these properties critically depends on the magnetic state. We discuss our results in regard to the stable twin boundary structure and deformation twinning experimentally observed in homogeneous Fe-50 wt.% Cr alloy up to temperatures slightly above the magnetic ordering temperature.

ω-embrittlement is ubiquitous in metastable β-titanium (Ti) alloys, while the fundamental understanding on the damage-fracture mechanism hitherto remains elusive. In this study, we systematically investigate ω-embrittlement of high misfit Ti-10Cr (wt.%) alloys by coupling experiments and first-principles calculation. It is found that brittle cleavage-like fracture prevails in tensile samples, irrespective of the quenching or subsequent aging states. Microscopically, cracks nucleation and propagation proceed along slip bands, inside which ω-lattices are first disordered and then the localized (β + ω)-amorphous-like structures are developed in the shape of white patches. The underlying mechanism of mechanically-driven localized amorphization is that due to the remarkable covalent character of atomic bonding of ω-precipitates caused by composition partitioning of the Cr element, ω-precipitates impart extremely high energy barrier opposed to dislocation gliding and render dislocations pile-up ahead of ω-precipitates, thus leading to their lattice disordering. It is unveiled that the hydrostatic pressure, serving as the driving force for dislocations pile-up, plays a critical role in this unusual cleavage-like fracture of Ti-10Cr alloys caused by mechanically-driven ω-mediated localized amorphization. Accompanied by the transition from the co-operation of deformation twining and ordinary dislocation slip in the quenched Ti-10Cr alloys to the exclusive ordinary dislocation slip in the long-time aged Ti-10Cr samples, it is unexpected that the resulting tensile fracture strength monotonically decreases to a stress level of ~ 100 MPa. These findings provide new insights into the damage and fracture behavior of high misfit β-titanium alloys, such as Ti-Cr alloys.

The incorporation of fluorine into polyolefin can dramatically improve its own mechanical properties and compatibility with other polymers, which has revolutionized the development of polyolefin industry. However, there were no fluorinated isotactic polypropylene (iPP) on the market which remains a formidable challenge. Here, a novel approach is presented that fluorinated iPP was prepared by free radical reaction using N-fluorobenzenesulfonimide (NFSI) as fluorine transfer reagent and benzoyl peroxide (BPO) as initiator in solution reaction. By conducting the tests of water contact angle (CA), DSC and TGA, the results indicated that the surface property and the thermal stability of fluorinated iPP (F-iPP) were greatly improved. In this contribution, a direct and economical route to fluorinate polyolefin was provided.

In order to improve the performance of metal-bonded grinding wheels, the graphite particles with several different contents (i.e., 5, 10, 15, and 20 wt%) were added to Cu-Sn-Ti alloy powders as the bonding materials. The influence of graphite addition on bonding properties of the abrasive layer was investigated. Firstly, microstructural examination results show that the joining between graphite and Cu-Sn-Ti alloy was achieved and provided a weak bonding strength compared to the pure Cu-Sn-Ti matrix. Secondly, the transgranular fracture and intergranular fracture were determined as the main fracture patterns of abrasive layer in the current investigation. Then, an optimized graphite content of 10 wt% was decided, at which the porosity of abrasive layer can reach 25% as well as the bending strength reached 125 MPa and was favorable to meet the high-speed grinding requirements. Finally, the finite element simulation results suggested that the graphite addition had little effect on the residual thermal stresses of abrasive layer.

Individual solute interstitial atoms in Mg alloys were directly observed through aberration-corrected Z-contrast imaging. The atomic species and local positions of solute interstitials were further determined in combination of density functional theory calculations based on their formation energy. Individual octahedral and tetrahedral interstitials in hexagonal-close-packed Mg are Zn and Y, respectively. Interestingly, there are six positions around the center of each octahedral interstice, which can also accommodate a Zn interstitial, besides the ideal octahedral interstice. Y tetrahedral interstitials evolve to [0001] Y-Mg dumbbells. Moreover, an Y atom can form a crowdion between two neighboring Mg atoms along the 20 2 − 3 > direction. In particular, small clusters consisting of various point defects were observed, providing direct evidence for enthalpy-driven clustering of point defects, which may have implications for atomic-scale understanding of nucleation mechanisms of strengthening precipitates.