Assessing the predictive capabilities of precipitation strengthening models for deformation twinning in Mg alloys using phase-field simulations

Precipitation strengthening is a key strategy for improving the overall mechanical properties of Mg alloys. In Mg-Al alloys, basal precipitates are known to strengthen against twinning, resulting in an increase in the critical resolved shear stress(CRSS) necessary for continued deformation. Although several models have been proposed to quantify the influence of precipitate shape, size, and distribution on the CRSS, the accuracy, scope, and applicability of these models has not been fully assessed. Accordingly, the objectives of this study are:(i)to analyze the accuracy of analytical models proposed in the literature for precipitation strengthening against twin thickening and propagation(in Mg-Al alloys) using phase-field(PF) simulations,(ii) to propose modifications to these model forms to better capture the observed trends in the PF data, and(iii) to subsequently test the predictiveness of the extended models in extrapolating to experimental strengthening data.First, using an atomistically-informed phase-field method, the interactions between migrating twin boundaries(during the propagation and thickening stages) and basal plates are simulated for different precipitate sizes and arrangements. In general, comparison of the increase in CRSS determined from the PF simulations and the predictions from four precipitation strengthening models reveals that modifications are necessary to the model forms to extend their applicability to precipitation strengthening against both twin thickening and propagation. A subsequent comparison between predictions from the extended models and experimental strengthening data for peak age-hardened samples reveals that the(extended) single dislocation and dislocation wall models provide reasonably accurate values of the increase in CRSS.Ultimately, the results presented here help elucidate the fidelity and applicability of the various hardening models in predicting precipitation strenghtening effects in technologically important alloys.

Collision Energy Dependence of Defect Formation in Graphene

Molecular dynamics simulations are performed using an empirical potential to simulate the collision process of an energetic carbon atom hitting a graphene sheet.According to the different impact locations within the graphene sheet,the incident threshold energies of different defects caused by the collision are determined to be 22eV for a single vacancy,36eV for a divacancy,60eV for a Stone-Wales defect,and 65eV for a hexavacancy.Study of the evolution and stability of the defects formed by thee collisions suggests that the single vacancy reconstructs into a pentagon pair and the divacancy transforms into a pentagon-octagon-pentagon configuration.The displacement threshold energy in graphene is investigated by using the dyuanical method,and a reasonable value 22.42eV is clarified by eliminating the heating effect induced by the collision.

Petrography and geochemistry of exported Colombian coals:Implications from correlation and regression analyses

The petrology of coal,as determined by the microscopic analysis of organic and inorganic elemental constituents of coal,provides information on its nature and characteristics.Coal is used worldwide in the production of thermal energy and coke.In the case of high-quality Colombian coals,only limited studies have been carried out.The present study presents the geochemical,mineralogical,and petrological characteristics of coal samples collected from Puerto Drummond in Cienaga,Colombia,to predict their potential uses.Therefore,the ultimate,proximate,petrographic,gross calorific value(GCV),ash fusion temperature,Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray fluorescence(XRF),and Thermogravimetric(TG)analyses were employed in this study.The petrological analysis reveals that Colombian coals are naturally more abundant in vitrinite(72%)than inertinite(14e23%)macerals.Silicates and aluminosilicate are the main minerals present as fine particles mixed with macerals.The XRD and FTIR analyses show that the most common and dominant minerals are quartz,while gypsum,hematite,calcite and mica occur in lesser amounts.The oxide composition of the coal ashes consists of 51e58%SiO2 and 18e25%Al2O3 as determined by XRF analysis.In correlation and regression analysis,the moisture content shows a reverse correlation with GCV(Regression value of R2¼0.68).This study helps researchers to comprehend the importance of Colombian coals and presents various techniques for characterisation of coals.

Molecular Scaffold Growth of Two-Dimensional, Strong Interlayer-Bonding-Layered Materials

Currently,most two-dimensional(2D)materials that are of interest to emergent applications have focused on van der Waals–layered materials(VLMs)because of the ease with which the layers can be separated(e.g.,graphene).Strong interlayer-bonding-layered materials(SLMs)in general have not been thoroughly explored,and one of the most critical present issues is the huge challenge of their preparation,although their physicochemical proper-ty transformation should be richer than VLMs and deserves greater attention.MAX phases are a classi-cal kind of SLM.

Uncovering electron scattering mechanisms in NiFeCoCrMn derived concentrated solid solution and high entropy alloys

Whilst it has long been known that disorder profoundly affects transport properties,recent measurements on a series of solid solution 3d-transition metal alloys reveal two orders of magnitude variations in the residual resistivity.Using ab initio methods,we demonstrate that,while the carrier density of all alloys is as high as in normal metals,the electron mean-free-path can vary from~10Å(strong scattering limit)to~103Å(weak scattering limit).Here,we delineate the underlying electron scattering mechanisms responsible for this disparate behavior.While site-diagonal,spin dependent,potential scattering is always dominant,for alloys containing only Fe,Co,and Ni the majority-spin channel experiences negligible disorder scattering,thereby providing a short circuit,while for Cr/Mn containing alloys both spin channels experience strong disorder scattering due to an electron filling effect.Somewhat surprisingly,other scattering mechanisms-including displacement,or size effect,scattering which has been shown to strongly correlate with such diverse properties as yield strength—are found to be relatively weak in most cases.

Structural damage response of lanthanum and yttrium aluminate crystals to nuclear collisions and electronic excitation:Threshold assessment of irradiation damage

A comparative analysis is performed on the structural damage response and associated mechanisms in lanthanum aluminate and yttrium aluminate crystals under various irradiation conditions by a combination of experimental and theoretical approaches.Under low-energy Au~+irradiation,the damage accumulation curve shows a higher damage rate for LaAlO_(3)crystals than YAlO_(3)crystals.The relatively low irradiation tolerance of LaAlO_(3)to the action of nuclear collisions is ascribed to the large amorphization cross-section and effective cross-section for defect-stimulated amorphization.Under swift Ar^(12+),Ni^(19+)and Kr^(17+)irradiation with different ion energies and velocities,the formed highly-disordered/amorphous latent tracks with different morphologies in pristine and predamaged crystals are discussed,and the corresponding electronic energy loss and lattice temperature thresholds are quantitatively determined.Compared to YAlO_(3),LaAlO_(3)exhibits lower sensitivity and higher damage tolerance to the electronic energy loss process,attributing to its relatively high recrystallization efficiency during the rapid quenching process.Furthermore,the introduction of lattice defects into LaAlO_(3)and YAlO_(3)crystals considerably enhances the sensitivity and intensity of thermal spike response to the electronic energy loss,and the induced effective modification of track morphologies demonstrates the synergistic effect between the electronic energy loss and pre-existing defects created by nuclear collisions.In this case,even under the action of electronic energy loss below the threshold,the lattice temperature in the nuclear-collision damaged crystalline system could still meet the criterion for track production.The irradiation energy deposited to atoms and induced lattice temperature evolution discussed in this work provide a deeper insight into the complex processes involved in irradiation-induced latent track behaviors.

Electronic energy loss and ion velocity correlation effects in track production in swift-ion-irradiated LiNbO_(3):A quantitative assessment between structural damage morphology and energy deposition

The primary motivation for studying how irradiation modifies the structures and properties of solid materials involves the understanding of undesirable phenomena,including irradiation-induced degradation of components in nuclear reactors and space exploration,and beneficial applications,including material performance tailoring through ion beam modification and defect engineering.In this work,the formation mechanism of latent tracks with different damage morphologies in LiNbO_(3)crystals under 0.09-6.17 Me V/u ion irradiation with an electronic energy loss from 2.6-13.2 ke V/nm is analyzed by experimental characterizations and numerical calculations.Irradiation-induced damage is preliminarily evaluated via the prism coupling technique to analyze the correlation between the dark-mode spectra and energy loss profiles of irradiated regions.Under the irradiation conditions of different ion velocities and electronic energy losses,different damage morphologies,from individual spherical defects to discontinuous and continuous tracks,are experimentally characterized.During ion penetration process,the ion velocity determines the spatiotemporal distribution of deposited irradiation energy induced by electronic energy loss,meaning that the two essential factors including electronic energy loss and ion velocity coaffect the track damage.The inelastic thermal spike model is used to numerically calculate the spatiotemporal evolutions of energy deposition and the corresponding atomic temperature under different irradiation conditions,and a quantitative relationship is proposed by comparison with corresponding experimentally observed track damage morphologies.The obtained quantitative relationship between irradiation conditions and track damage provides deep insight and guidance for understanding the damage behavior of crystal materials in extreme radiation environments and selecting irradiation parameters,including ion species and energies,for ion beam technique application in atomic-level defect manipulation,material modification,and micro/nanofabrication.