Dominant Mechanism Research Articles

High-performance resistive random access memory using two-dimensional electron gas electrode and its switching mechanism analysis

In this study, a two-dimensional electron gas (2DEG), which is a conductive layer formed at the interface of Al2O3 and TiO2, was used as an electrode for resistive random access memory (RRAM) and implemented in a cell size down to 30 nm. For an RRAM device comprising W/2DEG/TiO2/W, we confirmed that the dominant switching mechanism changed from interfacial to filamentary as the cell size decreased from 500 nm to 30 nm. Through analyses of changes in forming characteristics and conduction mechanisms in the low resistive state depending on the cell size, it was identified that the 2DEG acted as an oxygen-scavenging layer of TiO2 during the resistive switching process. By comparing the switching characteristics of RRAM devices with and without 2DEG for a 30 nm cell size, we confirmed that a high-performance 2DEG RRAM was realized, with highly uniform current–voltage characteristics, a low operating voltage (∼1 V), and a high on/off ratio (>102). Finally, the applicability of the proposed device to a crossbar array was validated by evaluating 1S1R operation with an NbO2-based selector. Considering the improved switching uniformity, the 2DEG RRAM shows promise for high-density memory applications.

Enhanced strength-ductility synergy of magnesium alloy fabricated by ultrasound assisted directed energy deposition

Investigations on the fabrication of large-size lightweight Mg alloy components by wire-arc directed energy deposition (DED) are steadily flourishing. Nevertheless, most of these components still suffer from inferior performance due to internal defects and inherent columnar grains. Herein, external ultrasound fields with different powers were successfully introduced into the wire-arc DED of AZ31 Mg alloy. The microstructure, defects, and mechanical properties of the fabricated components were carefully characterized and compared. The results show that the external ultrasound fields lead to decreased porosity, complete columnar to equiaxed transition (CET), and enhanced performance. Consequently, the UA90 samples exhibited a remarkable increase of ∼30%, ∼45%, and ∼189% in yield strength, ultimate tensile strength, and elongation, respectively. The dominant mechanisms of enhanced strength-ductility synergy were analyzed in detail. This study thus sheds new light on wire-arc DED of Mg alloy components with excellent performance via external ultrasound fields.

Polyester conversion by homogeneous catalysis for separating and recycling ammonia from biogas

Biogas is being promoted as a renewable and clean energy source. However, NH3 is a precursor of NOx and PM2.5 within the biogas, threatening ecological and human health. Therein, recycling waste NH3 from the biogas as a raw material of nitrogen fertilizer was tested by optimizing polyester as a sorbent material. After homogeneous catalysis, the converted polyester significantly increased the NH3 adsorption sites within polyester nanopores; correspondingly, the NH3 adsorption capacity increased from 0.56 mg·g−1 to 84.07 mg·g−1. Based on the structural characterization of polyesters, functional groups analysis before and after adsorption, and kinetic analysis during adsorption, chemical adsorption was identified as the dominant mechanism for NH3 adsorption. Moreover, selective adsorption and the regeneration experiments to optimize polyester indicated that NH3 could be efficiently separated from biogas with good regeneration performance. The results demonstrate the efficacy of recycling waste polyester and NH3 from the biogas.

Investigation on the Cracking Mechanism of Melt Growth Alumina/Aluminum Titanate Ceramics Prepared by Laser Directed Energy Deposition

Oxide melt growth ceramics (OMGCs) exhibit excellent performance and microstructure stability near their melting point and are expected to become a new structural material for long-term stable service in extremely high-temperature water-oxygen environments. Owing to its unique advantages of high efficiency, flexible manufacturing, and near-net shaping, laser directed energy deposition (LDED) has become a promising technology for the rapid preparation of high-performance OMGCs. However, owing to the limited understanding of the cracking mechanism, the severe cracking problem that hinders OMGCs-LDED towards engineering applications has not been resolved. Alumina/aluminum titanate (Al2O3/AlxTiyOz, A/AT) ceramics are prepared using an LDED system and their cracking characteristics are investigated. Subsequently, numerical simulations are conducted to reveal the dominant factors and influencing mechanisms of the cracking behavior. The results demonstrate that the cracking nucleation process is mainly controlled by solidification defects, whereas the cracking propagation process is determined primarily by both the microstructure and stress level. This study provides a theoretical basis for the development of appropriate cracking suppression methods for OMGCs-LDED.

Development of interactive friction model for machining considering the instantaneous interfacial characteristics

In this article, the transient and complex tribological characteristics of machining interfaces have been considered for developing a friction model. The interfacial characteristics – a condition where process parameters are in fluctuation rather than being constant – are identified. In an investigation of coated carbide tool wear in machining AISI H13 steel, the dominant wear mechanisms were identified as the abrasion, adhesion, and asperity deformation. Considering the complex loading, transient tribological behaviours, and observed wear mechanisms in machining, an interactive friction model is developed based on the mutually interactive nature of wear-and-friction. The evolution of the coefficient of friction with machining time is considered with different stages of tool wear. The adjusting capability of the developed model with respect to the complex loading is explored. The value of this research is to discover a unique behaviour at interfaces, additionally to identify the transient tribological conditions including wear mechanisms, and for the first time, to develop the interactive friction model for machining that adds scientific contribution to the domain of machining tribology.

Consolidation and wear resistance of Fe based bulk metallic glass composites by spark plasma sintering

High densification and wear resistance are essential for the application of Fe-based bulk metallic glass composites. In this work, Fe-based composites were fabricated by spark plasma sintering. Firstly, under the pressure of 150 MPa, all samples achieved high densification, the microcontact pressure between powder particles decreased with increasing density. Then, as the sintering temperature was increased from 350 °C to 450 °C, the crystalline phases were identified as Fe3Si and Fe2B. The hard borides improved the hardness and wear resistance of composites. Finally, at sintering temperature of 400 °C, the sample exhibited the highest micro-Vickers hardness of 1168.8 Hv and the lowest friction coefficient of 0.59, the coefficient of friction was lower than that of bearing steel. FeSiB BMG composites showed dominant abrasive and oxidative wear mechanisms. FeSiB composites showed excellent hardness and wear resistance, which extends the potential application of bulk metallic glass in the field of engineering structural materials.

Hierarchical Conical Metasurfaces as Ultra‐Broadband Perfect Absorbers from Visible to Far‐Infrared Regime

AbstractWideband perfect absorbers are widely demanded for various applications, including efficient photodetection, radiation cooling. However, achieving perfect absorption across an extensive range of wavelengths on engraved structured substrate remains a challenge due to the complex light responses. It presents a hierarchical conical metasurface that demonstrates distinct perfect absorption from visible to far‐infrared range (0.4–16 µm), which is composed of surface‐engraved high aspect ratio nanogratings on microcones. The perfect absorption in the typical reststrahlen band of 4H‐SiC primarily relies on a light‐trapping‐enhanced surface phonon polaritons (SPhPs) mechanism, where the microcones effectively confine and enhance the SPhPs excited by the nanogratings through light trapping. Outside the reststrahlen band, the dominant mechanism for light antireflection is the light trapping of microcones assisted by nanogratings, which act as an equivalent antireflection layer. The hierarchical cones exhibit exceptional broadband performance, achieving an average absorptance of 98% over the spectrum of 0.4–16 µm with wide‐angle feasibility, and are fabricated using one‐step ultrafast‐laser ablation with ring‐shaped vector beams. Notably, the hierarchical cones can be applied to various materials, showing significant potential for use in photodetectors.

In situ characterization of thermomechanically loaded solution strengthened, nanocrystalline nickel alloys

Nanocrystalline (NC) Ni-40Cu and Ni-40Cu-0.6P (at.%) alloys were mechanically loaded in tension at ambient (23 °C) and elevated (150 °C) temperatures with the deformed nanostructure captured by in situ transmission electron microscopy coupled with digital image correlation for data mining high strain regions prior to catastrophic failure. The addition of the P provided grain boundary partitioning that stabilized the NC structure under both loading cases, which was not found to be the case for the binary alloy. While mechanical strength softening was observed in each of the alloys upon thermomechanical loading, the retention of strength was substantially higher in the ternary alloy than its binary counterpart. Digital image correlation was found to be a useful means for image mining to identify different regions where failure mechanisms were initiated. Intergranular failure was observed as the dominant failure mechanism in all specimens with the binary alloy revealing a coarser fracture profile as compared to a finer fracture profile in the ternary alloy. Atomistic simulations are used to understand P solute strengthening of the grain boundaries against this fracture failure mode.

Enhanced synergistic removal of Cu(II) and Cr(VI) with multifunctional biomass hydrogel from strong-acid media

Simultaneous recovery of heavy metal ions (HMIs) such as Cu(II) and Cr(VI) from strong-acid media was a great challenge due to the inhibition of protons. Herein, a novel biomass hydrogel (CMC/PEI-PD) containing various groups (bis-picolylamine, amino, and hydroxyl groups) was newly prepared by a facile two-step process. The static experiments relating pH, kinetics and isothermal co-adsorption confirmed the synergistic effect towards Cu(II) and Cr(VI) consistently. Specifically, the adsorption capacities of Cu(II) and Cr(VI) at pH 2.0 increased by 23.73% and 40.18% in comparison with the single systems. Moreover, coexistence of inorganic anions and cations could further increase the adsorption of Cu(II) and Cr(VI) by 59.90% and 43.39%, respectively. At the same time, the adsorption and desorption ratios for both HMIs remained stable. The superior performance came from the two dominant mechanisms of co-removal. On the one hand, Cu(II) chelated by bis-picolylamine group attracted Cr(VI) in the form of cation bridge, thus promoting Cr(VI) adsorption. On the other hand, the protonated amine group attracted Cr(VI) by electrostatic interaction and weakened the inter-cationic repulsion by electrostatic shielding, thus promoting Cu(II) adsorption. In addition, the dynamic column experiment towards simulated acidic electroplating wastewater involving Cu(II)–Cr(VI)–Ni(II) certified the high efficiency and feasibility of the co-removal. Therefore, CMC/PEI-PD owned great potential in the separation of typical HMIs even directly from strong-acid media.

Thermo-hydrodynamical optimization of direct absorption solar collector from Stokes to low Reynolds numbers regimes of nanofluid flow

It has been proven that optical properties of base working fluids are significantly enhanced, where very small amount of nanoparticles are exploited. In the current study, numerical investigation of microchannel-based direct absorption flat solar collector (DAFSC) filled with graphite water based nanofluids at various volume fractions in an independent-scattering regime map of nanofluids were taken into account to evaluate thermo-hydrodynamical performance of DAFSC. Furthermore, multi-response optimization of DAFSC including thermodynamics second law efficiency (ηII), thermal efficiency (η(th)), heat loss rate (Q̇(out)), dimensionless temperature difference (θ), pressure drop (Δp), and also cost function (Cost) was carried out by response surface methodology. Fifty four numerical designs proposed by face-centred central composite designs (FCCD) have been used to provide sufficient data to obtain mathematical regression models of response functions in which the significant model's terms were evaluated by analysis of variance. Furthermore, composite desirability function approach was taken into account for multi-response optimization of direct absorption solar collector to maximize ηII, η(th), θ, and to minimize Q̇(out),Δp and Cost functions. Strikingly, the CFD results unveiled that maximum thermal efficiency of DAFSC with black back absorber surface, which was enhanced up to 18% compare to base case, is mainly shape-dependent rather than to that of nanoparticles volume fractions, which can be justified by presence of different dominant heat absorption mechanisms transforming from volumetric absorption for nanofluids to surface one for pure water.

Rolling and Sliding Modes of Nanodroplet Spreading: Molecular Simulations and a Continuum Approach.

Molecular simulations discover a new mode of dynamic wetting that manifests itself in the very earliest stages of spreading, after a droplet contacts a solid. The observed mode is a "rolling" type of motion, characterized by a contact angle lower than the classically assumed value of 180°, and precedes the conventional "sliding" mode of spreading. This motivates the development of a novel continuum framework that captures all modes of motion, allows the dominant physical mechanisms to be understood, and permits the study of larger droplets.

Microstructure and wear resistance of in-situ TiC reinforced Stellite 6 coating using PTA cladding

To enhance the durability of copper tuyeres in blast furnaces, it is necessary to apply coatings on their surfaces to protect against wear caused by high-temperature coke. In this study, a series of in-situ synthetic TiC-reinforced Stellite 6 alloy coatings containing a Ni60A interlayer were successfully produced on copper substrates using 5–45 wt% TiFe/Cr3C2 precursor powders. The coatings exhibited excellent metallurgical bonding with the Ni60A interlayer, and an elemental transition zone was formed at the interface between the coating and the interlayer. XRD Rietveld refinement analysis revealed that the T45 coating with 45 wt% of precursor powder showed the highest TiC phase content of 12.27 %, with an average hardness of 658.15 HV0.2, which was 31.2 % higher than that of the Stellite 6 alloy. The wear mechanism of the Stellite 6 coating was plastic delamination at 25 °C, and oxidative wear at 500 °C. As the TiC particle content in the coating increased, the dominant wear mechanism tended to shift towards abrasive wear. The specific wear mechanism of the coating was influenced by the content of coating phases and the operating temperature. The best wear resistance was achieved by the T45 coating, which showed an abrasive wear mechanism at both 25 °C and 500 °C, with a wear resistance of 4.47 and 5.94 times higher than that of the Stellite 6 alloy respectively.

Remarkable cryogenic properties by deformation twinning in a coherent precipitation-containing high entropy alloy

Developing structural alloys for critical cryogenic applications is a challenging yet essential task, primarily due to the ductile-brittle transition phenomenon. To address this issue, we developed a twinning-aided coherent precipitation-containing Co45Cr15Ni30Al5Ti5 high entropy alloy (HEA) with remarkable cryogenic properties. The activation threshold for twinning was successfully reduced via the disordering behavior of the L12 phase. In the present work, distinct temperature-dependent deformation behavior was observed. The dominant room-temperature strain accommodation mechanism was found to be the dislocation slip coupled with architectured stacking faults (SFs) and immobile Lomer-Cottrell (L-C) locks. Whereas, deformation twins were readily formed under cryogenic tensile loading, leading to significantly increased yield strength and ultimate tensile strength, approaching 1.5 GPa and 1.9 GPa, respectively. The remarkable cryogenic work hardening behavior contributes to persistent elongation of up to 31 % and the super-high ultimate tensile strength. The presence of SFs, deformation twins, and their interactions provide significant strain-hardening capability.

Towards strength-ductility synergy in a weak-textured Mg–3Y extruded sheet via pre-twinning and annealing

Mg-RE (magnesium-rare earth) binary alloys, such as Mg–Y alloys, usually exhibit weakened texture and excellent plasticity compared with traditional RE-free Mg alloys. However, the weakened texture could lead to a significant decrease in the strength of Mg-RE binary alloys. In this work, the weak-textured Mg–3Y (wt. %) extruded sheet displayed good strength-ductility synergy with a 41% increase in the yield strength and a good ductility similar to the initial sheet via simple pre-twinning and annealing treatment (PT). After PT, the average grain size of the sheet decreased from 11.2 μm to 6.0 μm and 34.2% initial soft texture component (<11–21> //normal direction (ND)) was transformed into the hard texture component (<0001> //transverse direction (TD)). The effect of pre-twinning on deformation mechanisms was systematically investigated by slip trace analysis and activation stress (τ) analysis. Basal slip was the dominant deformation mechanism during the tension of the as-extruded (AE) specimen while pre-twinning promoted the activation of non-basal slip, especially prismatic slip in the PT specimen. The texture transformation and reduced critical resolved shear stress (CRSS) ratio between non-basal slip and basal slip induced by pre-twinning were primarily responsible for the high activity of non-basal slip. The underlying strengthening mechanism and the reason for good ductility were also rationally discussed. The strengthening effect of single grain refinement was relatively lower in the weak-textured Mg–3Y alloy. Texture hardening could effectively improve the effect of fine-grain strengthening. The excellent deformation compatibility between basal slip of parent grains and prismatic slip of twins as well as relatively higher activity of the second-order pyramidal slip was the origin of the good ductility of the PT specimen.

Contrasting controls on convection at latitude zones near and away from the equator for the Indian summer monsoon

Understanding controls on convection on various timescales is crucial for improved monsoon rainfall forecasting. Although the literature points to vertically homogeneous vorticity signatures preceding rainfall during the Indian summer monsoon, we show using reanalysis data that, for rainfall associated with northward propagating intraseasonal oscillations (ISOs), different controls are present at different latitude zones. For the latitude zone close to the equator (5∘N–14∘N) and including the southern Indian region, a conventional dynamical control on rainfall exists with barotropic vorticity leading ISO rainfall by about five days. In contrast, for the latitude zone away from the equator (15∘N–24∘N; covering the central Indian region), thermodynamic fields control ISO rainfall, with barotropic vorticity following rainfall by two days on average. Over central India, the pre-moistening of the boundary layer (BL) yields maximum moist static energy (MSE) about four days prior to ISO rainfall. Analyzing the statistics of individual events verifies these observations. Similar thermodynamic control is also present for the large-scale extreme rainfall events (LEREs) occurring over central India. These high rainfall events are preceded by positive MSE anomalies arising from the moisture preconditioning of the BL. The resulting convection then leads to a maximum in barotropic vorticity 12 h after the rainfall maximum. Characterizing these influences on convection occurring over various timescales can help identify the dominant mechanisms that govern monsoon convection. This can help reduce climate model biases in simulating Indian monsoon rainfall.

Tensile deformation behavior of high-strength TA18 titanium alloy tube under warm forming conditions and constitutive model based on dislocation density

Understanding the deformation behavior of high-strength TA18 titanium alloy tube (HS-TA18 tube) under warm forming conditions and the accurate description of flow stress is the basis of tube bending forming research. To this end, in this study, the HS-TA18 tube of 18 mm × 1.5 mm (out diameter × wall thickness) as the objective, uniaxial tensile tests were conducted under a wide temperature range (25 ℃−500 ℃). Then the macroscopic mechanical behavior and microstructure evolution were analyzed. The results show that the flow stress decreases with the increase of temperature. In the temperature range of 200–450 ℃, the degree of decline slows down. Moreover, the effect of strain rate on flow stress is not obvious, which indicates that dynamic strain aging (DSA) occurs in this region. Dislocation slip is the dominant mechanism of plastic deformation in the studied temperature range. Although dynamic recrystallization at 500 ℃ leads to softening trend of flow stress, dynamic recovery (DRV) is still the main softening mechanism during deformation. Then, a constitutive model based on dislocation density is established, which includes common thermal and athermal stresses. In addition, back stresses associated with geometrically necessary dislocations (GNDs) and additional stress caused by DSA are also taken into account. The model is used to predict the flow stress of the HS-TA18 tube under warm forming conditions. The prediction results are in good agreement with the experimental results, indicating that the established model has excellent prediction ability.

Tribological and corrosion behaviour of medical grade 316LVM steel by low temperature hybrid gaseous nitriding and carburizing

This study approached a low temperature hybrid gaseous nitriding and carburizing at varying temperature and gas composition to develop S-phase layer on 316LVM steel. The hybrid gaseous treatment at 475 °C and 10 % CH4 developed a distinct S-phase layer that is harder (1444 ± 32 HV0.025) than untreated surface. The S-phase layers are effective in reducing specific wear rates by 67 % to 1.19 ± 0.05 × 10−3 mm3/Nm, coefficients of friction by 26 % to 0.49 ± 0.02, and corrosion rate by 23 % to 6.02 ± 0.32 µm/y. Both untreated and treated surfaces had dominant abrasive wear mechanisms but on treated surface spalling holes were observed. This research highlights low-temperature hybrid gaseous nitriding and carburizing is promising for improving 316 LVM steel surface for orthopedic.

Systematic investigation of the microstructure evolution and dynamic recrystallization mechanisms of as-cast Fe–TiB2 composites under different hot deformation parameters

Fe–TiB2 composite shows great potential in lightweight materials for automotive parts due to its lightweight, high strength and high specific modulus etc. However, challenges remain with regard to establishing a fine hot working process of Fe–TiB2 composites. Here, a series of isothermal hot compression tests was conducted to systematically investigate the microstructure evolution and the dynamic recrystallization (DRX) mechanisms of as-cast Fe–TiB2 composites at different sets of hot deformation parameters. The results indicate the true stress drops more significantly after reaching its peak at low temperatures compared to high temperatures, since low temperatures favors the DRX through particle stimulated nucleation (PSN) in Fe–TiB2 composites, as featured by layers of DRXed grains surrounding TiB2 particles. Continuous dynamic recrystallization (CDRX) process gradually dominates as strain rate increase from 0.01 s−1 to 1 s−1 in Fe–TiB2 composites hot compressed to the true strain of 0.69 at 900 °C, as evidenced by the presence of DRXed grains with larger size and uniform distribution in matrix. DRX through PSN is the primary DRX mechanism at low temperature and low strain rate, while CDRX dominates the DRX mechanism at high temperature and high strain rate. Both DRX behaviors deepen with the increase of the strain. Different hot deformation parameters favor different DRX mechanisms. The increase in temperature and strain rate leads to a transition of the dominant recrystallization mechanism from the DRX through PSN to CDRX which is attributed to the competition for stored energy between the DRX through PSN and CDRX process.

Modification of osimertinib to discover new potent EGFRC797S-TK inhibitors

The EGFRC797S mutation is a dominant mechanism of acquired resistance after the treatment of non-small cell lung cancer (NSCLC) with osimertinib in clinic. To date, there is no inhibitor approved to overcome the resistance caused by osimertinib. In this study, a series of compounds with phenylamino-pyrimidine scaffold deriving from osimertinib were designed, synthesized and evaluated as fourth-generation EGFRC797S-TK inhibitors. Consequently, compound Os30 exhibited potent inhibitory activities against both EGFRDel19/T790M/C797S TK and EGFRL858R/T790M/C797S TK with IC50 values of 18 nM and 113 nM, respectively. Moreover, Os30 can powerfully inhibit the proliferation of KC-0116 (BaF3-EGFRDel19/T790M/C797S) and KC-0122 (BaF3-EGFRL858R/T790M/C797S) cells. In addition, Os30 can suppress EGFR phosphorylation in a concentration-dependent manner in KC-0116 cells, arrest KC-0116 cells at G1 phase and induce the apoptosis of KC-0116 cells. More importantly, Os30 showed potent antitumor efficacy in the KC-0116 cells xenograft nude mice tumor model with the tumor growth inhibitory rate of 77.6% at a dosage of 40 mg/kg. These findings demonstrate that modification of osimertinib can discover new potent EGFRC797S-TK inhibitors, and compound Os30 is a potent fourth-generation EGFR inhibitor to treat NSCLC with EGFmRC797S mutation.

Coumarin N-Acylhydrazone Derivatives: Green Synthesis and Antioxidant Potential-Experimental and Theoretical Study.

Coumarin N-acylhydrazone derivatives were synthesized in the reaction of 3-acetylcoumarin and different benzohydrazides in the presence of molecular iodine as catalyst and at room temperature. All reactions were rapidly completed, and products were obtained in good to excellent yields. It is important to emphasize that four products were reported for the first time in this study. The obtained compounds were subjected to evaluation of their in vitro antioxidative activity using DPPH, ABTS, and FRAP methods. It was shown that products with a catechol moiety in their structure are the most potent antioxidant agents. The thermodynamic parameters and Gibbs free energies of reactions were used to determine the most probable mechanism of action. The results of in silico examination emphasize the need to take solvent polarity and free radical species into account when examining antiradical action. It was discovered by using computational approaches that HAT and SPLET are competitive molecular pathways for the radical scavenging activity of all compounds in polar mediums, while the HAT is the dominant mechanism in non-polar environments.