Evolution Of Precipitation Research Articles

Enhancing plasticity in BCC Mg-Li-Al alloys through controlled precipitation at grain boundaries

This study investigates the improvement of plasticity in body-centered cubic magnesium (Mg)-lithium (Li)-aluminum (Al) alloys, crucial for lightweight structural applications. The ternary Mg-Li-Al alloys exhibits high strength but low ductility. Precipitates at grain boundaries in these alloys, linked to reduced plasticity, are examined for their crystal structure and composition. Advanced microscopic techniques reveal the transformation of precipitates and the development of specific structures at grain boundaries. Thermodynamics of element diffusion at grain boundaries are explored through first-principles calculations, and a phase-field simulation models precipitate evolution. Molecular dynamics simulations elucidate nanoscale mechanisms governing the transition from brittle to ductile fracture modes during artificial aging. The D03−Mg3Al at grain boundaries is a brittle phase, and through a 170 °C aging treatment, it induces the precipitation of lamellar α-Mg phase with D03−Mg3Al as nucleation sites. The occupancy energy of Al atoms at Li sites in α-Mg is found to be lower than that in D03−Mg3Al, leading to the dissolution of D03−Mg3Al. The α-Mg, characterized by a stronger metallic nature, exhibits a better-matched modulus with the matrix and enhanced dislocation mobility. The precipitation of α-Mg plays a pivotal role in significantly improving the ductility of the alloy. This work contributes to the understanding of the complex interplay between alloy composition, grain boundary precipitates, and plasticity, as well as brings insights to guide interfacial control in the development of advanced Mg-Li-Al alloys for structural applications.

Microstructural stability and precipitate evolution of thermally treated 7075 aluminum alloy fabricated by cold spray

In this work, the effects of post-deposition heat treatment on microstructural stability of cold sprayed AA7075 aluminum coatings were thoroughly characterized. The as-atomized powder and annealed coatings were investigated using scanning electron microscopy, electron back-scattered diffraction, and microhardness measurements. Scanning transmission electron microscopy was further employed to evaluate grain/subgrain structure near the particle interface region. Precipitation in the coating was studied through differential scanning calorimetry and X-ray diffraction. The feedstock powder revealed dendritic/cellular-like structure accompanied by microsegregations of the main alloying elements at dendrite boundaries. The high-pressure Cold Spray process led to formation of lamellar subgrains and UFG grains via dynamic recovery/recrystallization mechanisms. GP zones present in the AA7075 powder continuously reprecipitated into more stable η´/η phases owing to propellant gas heating and extensive plastic strains induced during cold spraying. The applied annealing resulted in progressive softening of the AA7075 coatings and gradual transformation of LAGBs into HAGBs. The solute-rich grain boundary network observed in powder microstructure was fully retained after CS deposition but decomposed into coarse η and S precipitates upon high-temperature annealing. The CS AA7075 coating showed decent thermal stability up to 300 °C and rapid grain growth at 400 °C. The relationship between precipitate size and thermal stability was further discussed in terms of the Zener pinning theory.

Internally Driven Variability of the Angola Low is the Main Source of Uncertainty for the Future Changes in Southern African Precipitation

AbstractVariations in southern African precipitation have a major impact on local communities, increasing climate‐related risks and affecting water and food security, as well as natural ecosystems. However, future changes in southern African precipitation are uncertain, with climate models showing a wide range of responses from near‐term projections (2020–2040) to the end of the 21st century (2080–2100). Here, we assess the uncertainty in southern African precipitation change using five Ocean‐Atmosphere General Circulation single model initial‐condition large ensembles (30–50 ensemble members) and four emissions scenarios. We show that the main source of uncertainty in 21st Century projections of southern African precipitation is the internal climate variability. In addition, we find that differences between ensemble members in simulating future changes in the location of the Angola Low explain a large proportion (∼60%) of the uncertainty in precipitation change. Together, the internal variations in the large‐scale circulation over the Pacific Ocean and the Angola Low explain ∼64% of the uncertainty in southern African precipitation change. We suggest that a better understanding of the future evolutions of the southern African precipitation may be achieved by understanding better the model's ability to simulate the Angola Low and its effects on precipitation.

Establishing a limited‐area model based on a global model: A consistency study

AbstractA limited‐area model (LAM) is established based on a global model (Global–Regional Integrated Forecast System; GRIST). GRIST–LAM inherits all the technical features of its global counterpart, enabling independent regional weather and climate modeling. The key advancement involves extending the original dynamical core to integrate it under the lateral boundary conditions (LBCs). As an initial development and evaluation study, this paper focuses on the consistency issue between the LAM and the global model. Three perfect‐model tests, using global solutions as LBCs and background truths, were performed to evaluate the LAM behaviors. In the pure dynamical core test, the LBC errors do not compromise the solutions within the interior domain. However, certain configurations can lead to more discontinuous solutions at the domain boundary. The solution error for a specified region decreases as the domain size increases when all other factors are equal. A small error pulse is generated during the initial stage of integration due to the presence of artificial transient waves induced by the LBCs. The model generates fine‐scale details and smaller errors based on coarser‐resolution LBCs. The consistency between LAM and LBC also influences the errors. The climate simulations demonstrate that both hydrostatic and non‐hydrostatic LAMs can reach statistical equilibrium. Regional model climates in the interior domain have higher quality but are sensitive to domain size and LBC configuration. Using a variable LBC coefficient is helpful to alleviate the artificial precipitation at the boundary. In the kilometer‐scale test, the global variable‐resolution model and its LAM counterpart show comparable results. Their performance is competitive with that of a uniform‐resolution global storm‐resolving simulation. Global variable‐resolution and LAM generate higher magnitudes in the tail part of the kinetic energy spectra due to higher local resolution and produce a consistent time evolution of precipitation. The broad implication of this study is also discussed.

Computational Model for Predicting Precipitation Evolution in Two-Phase Steel: First Application to Grain-Oriented Electrical Steel

Computational Model for Predicting Precipitation Evolution in Two-Phase Steel: First Application to Grain-Oriented Electrical Steel

The Impact of Model Horizontal Resolution on Simulating Regional Climate Over East Asia Using Variable‐Resolution CESM2

AbstractIn this study, a variable‐resolution version of the Community Earth System Model (VR‐CESM) with mesh refinement (∼0.125°) over East Asia is used to simulate the regional climate in this region. For the evaluation of model performance and sensitivity to model resolution, the simulated near‐surface temperature and precipitation are compared with observations and simulation results from a globally quasi‐uniform (∼1°) CESM (UN‐CESM). Results show that VR‐CESM better simulates the spatial patterns and seasonal variations of mean temperature and precipitation than UN‐CESM over China. For extreme events, VR‐CESM improves the simulation of the occurrence frequency of wintertime daily minimum temperature and heavy precipitation. In regions with complex terrains, VR‐CESM better resolves the topographic forcing and captures the observed fine‐scale spatial patterns of temperature and precipitation, although precipitation is still overestimated. For East Asian summer monsoon precipitation, both UN‐CESM and VR‐CESM tend to overestimate (underestimate) the precipitation over northern (southern) China, which is associated with too strong meridional water vapor transport in the models and biases in the large‐scale circulation in the middle and upper troposphere. Different from previous studies with different physics parameterizations and refined domains, as the model resolution increases, simulated monsoon precipitation evolution is not obviously improved, and convective precipitation intensity decreases over eastern China. Despite this, our results indicate that VR‐CESM simulates regional climate, topographical forcing, and large‐scale circulations over East Asia reasonably well, and thus it can be applied for the future climate projection in the region.

Fracture behaviors and microstructure evolution of an Al–Mg–Mn-Sc-Zr alloy at elevated and cryogenic temperature

The mechanical properties and fracture behavior of Al-5.8Mg-0.4Mn-0.25Sc-0.1Zr alloy were investigated across cryogenic temperatures (−196.15 °C ∼ −56.15 °C) and elevated temperature (room temperature ∼ 250 °C), with results indicating sensitivity of the alloy's mechanical properties to temperature. Firstly, the tensile test at elevated temperatures shows a decrease in strength and strain hardening exponent (n) due to thermal softening effects, while elongation increases and then decreases, peaking at 100 °C. Within the temperature range of −196.15 °C ∼ −56.15 °C, the yield stress (YS), ultimate tensile strength (UTS), and ductility tend to increase with the decreasing temperature gradually, which can be attributed to the decrease in lattice thermal vibration energy at low temperatures, resulting in an elevated external force requirement for dislocation motion. Meanwhile, throughout the entire high-temperature range, the alloy exhibits ductile fracture, with the number of dimples peaking at 100 °C. Differently, when the alloy is deformed at low temperatures, dislocations tend to accumulate within the grains, and with the grain boundaries acting as weak bonding areas between grains and experiencing significant stress concentration, the fracture mechanism gradually transitions from transgranular to intergranular fracture. Microstructural analysis at low temperatures shows minimal texture content changes, while at elevated temperatures, regular changes in texture components occur due to grain orientation rearrangement. Furthermore, high-resolution transmission electron microscopy was employed to investigate the evolution of precipitates at various temperatures, and the results shows that uniform and fine Al3(Sc1−x, Zrx) precipitates are distributed within the crystal, acting as effective dislocation pinning sites and leading to a uniform intragranular dislocation arrangement after tensile test at cryogenic temperature. Notably, after tensile test at higher temperatures, a few precipitates lose coherency with the matrix and started growing, which diminishing grain boundary pinning effect and promoting recrystallization.

Understanding the differential precipitation behavior of friction stir welded Al-Zn-Mg-Fe alloy during long-term natural aging

Al-Zn-Mg-Fe (HE700) is a new generation cast alloy based on dilute Al-Fe hypoeutectic system. Being a new member, the precipitation behavior of the HE700 alloy is not fully understood unlike its conventional 7xxx series counterparts. Moreover, presence of Fe and friction stir welding (FSW) used to join such alloys add to the complexity of the precipitation phenomenon. The present study captured the microstructural features with atomic-scale resolution that provided new insights into the nature, distribution, and evolution of precipitates in this alloy. The stir zone (SZ) and heat-affected zone (HAZ) exhibited significantly different natural aging behavior. Finer precipitates identified as GPI and GPII (Guinier Preston zones) were found to coexist with very fine zinc-rich solute clusters in the SZ. The GP zones evolved gradually and transitioned into strengthening precipitates. The HAZ, on other hand, exhibited heterogeneous distribution of coarse pre-existed particles and fine MgZn2 precipitates that were heterogeneously nucleated by localized solute supersaturation and thermally induced dislocations. Hardness variations can be correlated to precipitates evolution thereby helping design a suitable post-weld heat treatment (PWHT) process.

First principles validation of energy barriers in Ni75Al25

Precipitates in nickel-based superalloys form during heat treatment on a time scale inaccessible to direct molecular dynamics simulation, but can be studied using kinetic Monte Carlo (KMC) modelling. This requires reliable values for the barrier energies separating distinct configurations over the trajectory of the system. In this study, we validate vacancy migration barriers found with the Activation-Relaxation Technique nouveau (ARTn) method in partially ordered Ni75Al25 with a monovacancy using published potentials for the atomic interactions against first-principles methods. In a first step, we confirm that the ARTn barrier energies agree with those determined with the nudged elastic band (NEB) method. As the number of atoms used in those calculations is too great for direct ab initio calculations, we cut the cell size to 255 atoms, thus controlling finite size effects. We then use the plane-wave density functional theory code CASTEP and its inbuilt NEB method in the smaller cells. This provides us with a continuous validation chain from first principles to KMC simulations with interatomic potentials (IPs). We evaluate the barrier energies of five further IPs with NEB, demonstrating that none yields values with sufficient reliability for KMC simulations, with some of them failing completely. This is a first step towards quantifying the errors incurred in KMC simulations of precipitate formation and evolution.

The historical to future linkage of Arctic amplification on extreme precipitation over the Northern Hemisphere using CMIP5 and CMIP6 models

Arctic warming played a dominant role in recent occurrences of extreme events over the Northern Hemisphere, but climate models cannot accurately simulate the relationship. Here a significant positive correlation (0.33–0.95) between extreme precipitation and Arctic amplification (AA) is found using observations and CMIP5/6 multi-model ensembles. However, CMIP6 models are superior to CMIP5 models in simulating the temporal evolution of extreme precipitation and AA. According to 14 optimal CMIP6 models, the maximum latitude of planetary waves and the strength of Northern Hemisphere annular mode (NAM) will increase with increasing AA, contributing to increased extreme precipitation over the Northern Hemisphere. Under the Shared Socioeconomic Pathway SSP5-8.5, AA is expected to increase by 0.85 °C per decade while the maximum latitude of planetary waves will increase by 2.82° per decade. Additionally, the amplitude of the NAM will increase by 0.21 hPa per decade, contributing to a rise in extreme precipitation of 1.17% per decade for R95pTOT and 0.86% per decade for R99pTOT by 2100.

Microstructural evolution and mechanical behavior of activated tungsten inert gas welded joint between P91 steel and Incoloy 800HT

This study examines the welded joint between P91 steel and Incoloy 800HT using the activated tungsten inert gas (A-TIG) welding process. The focus is on analyzing the microstructure and evaluating the mechanical properties of joints made with different compositions of activating flux. Owing to the reversal of the Marangoni effect in which the conventional direction of molten metal flow in the weld pool is reversed due to the application of oxide-based fluxes, a complete depth of penetration of 8 mm was successfully achieved. Conducting mechanical tests, such as microhardness, tensile, and Charpy impact toughness tests, elucidates the behavior of the welded specimens under different loading conditions. The findings highlight the effects of grain size, dislocations, and the evolution of fine-sized precipitates in the high-temperature matrix. This study highlights the importance of choosing suitable flux compositions to achieve consistent penetration and dilution in the base metals. Insights into different failure modes and the influence of temperature on the tensile strength were evaluated. Beneficial mechanical properties of the joints (meeting the criteria of ISO and ASTM standards) were found: ultimate tensile strength of 585 ± 5 MPa, elongation 38 ± 2%, impact toughness of 96 ± 5 J, and maximum microhardness of 345 ± 5 HV.

Aging hardening and precipitation evolution of Mg-3.0Sm-1.4Nd-0.4Zn-0.5Zr alloy

Precipitation-hardenable Mg-Sm-Nd-Zn-Zr alloy is a high-performance magnesium alloy with great potential for aviation applications. A more comprehensive understanding of the precipitation evolution will help fully exert its mechanical properties. The hardness initially rose and then fell with alloy aging to 100 h at 200 °C. A peak hardness of 84.1 HV was achieved at the aging time of 20 h, with a 39.7 % increase in hardness compared to the unaged alloy. The primary precipitates were the GP zones and β′ phase at the under-aged stage. As the aging time was extended to 20 h, a more abundant β′ phase precipitated in the matrix, and the alloy achieved the peak-aged stage. Eventually, the over-aging stage came with the aging process continuing, where the β′ phase coarsened severely and further transformed into the β1 phase. When the aging temperature was raised to 350 °C, even under a short aging time of 1 h, the coarse β1 phase formed rapidly, and the β phase could also nucleate and grow directly on the β1 phase. This work offers a guide for developing aging treatment processes for Mg-RE alloys.

Impact of Nb and Zr on the precipitation evolution of Laves phase and the properties of laser cladding coating of AlCoCrFeNi high entropy alloy

The impact of Nb, Zr, and their synergies on the phase composition, wear and high oxidation resistance of a high entropy laser cladding coating consisting of AlCoCrFeNi on Q235 steel was thoroughly investigated in this work. From our analysis, it was demonstrated that the addition of Nb and Zr promoted the formation of the Laves phase except the BCC phase, and a small amount of MC phase was formed in the coatings containing Zr. Although both of them can refine the grain to different degrees, the grain refinement degree was the highest when they were added together. The solid solution strengthening, fine crystal strengthening, and Laves phase precipitation strengthening induced by the addition of Nb and Zr can significantly improve the microhardness of the coating, which was 1.1–1.5 times that of S1-S3 coatings. The formation of ternary Laves phase, grain refinement, and increase of the microhardness enhanced the plastic deformation and micro-cutting resistance of S4 coating, and the wear resistance was 1.3–2.5 times that of S1-S3 coatings. The unstable oxide Nb2O5 produced by the addition of Nb led to a reduction in the stability of the oxide layer. However, when the two were added cooperatively, the formation of unstable oxide Nb2O5 was reduced by the presence of Zr. Moreover, grain refinement was induced by the collaboration of the two making the protective oxide layer form faster, and stronger bonding with the coating, the high temperature oxidation resistance was significantly improved, which was 1.3–4.3 times that of S1-S3 coatings.

A new salt-precipitation-based self-remediation model for CO2 leakage along fault during geological CO2 storage

Salt precipitation occurring in fault zone, due to CO2-brine co-leakage, would create an opportunity to prevent CO2 leakage along fault, i.e., salt-precipitation-based self-remediation model. To investigate the new model, the physical model on salt precipitation was proposed, considering co-leakage of CO2 and brine along fault. Theoretical model was given on salt precipitation, and the numerical model was established to validate the salt precipitation occurring in fault zone. The numerical results indicated that salt precipitation indeed occurred in fault zone, and CO2 leakage rate was obviously decreased after salt precipitation. Importantly, evolution of salt precipitation in fault was concluded, from viewpoint of co-leakage of CO2 and brine along fault, and degree of salt precipitation was characterized, using representative parameters such as the starting time, ending time, lasting time of salt precipitation, and solid saturation. Especially, the self-remediation model for CO2 leakage based on salt precipitation was confirmed feasibly. The self-remediation capacity was closely related to degree of salt precipitation (or lasting time of salt precipitation), and was directly evaluated by the decreasing in CO2 leakage rate before and after salt precipitation. Finally, the parametric analyses showed that: (1) the potential correlation was found among the lasting time of salt precipitation, solid saturation and self-remediation capacity; (2) the higher CO2 injection rate and fault permeability, the smaller fault width and permeability of lower saline aquifer were helpful for salt precipitation and self-remediation capacity; (3) no salt precipitation occurred for the smaller CO2 injection rate and fault permeability, the larger fault width and permeability of lower saline aquifer.

Effect of Pre-Deformation on Precipitation in Al–Zn–Mg–Cu Alloy

AbstractIn this work, strengthening effects and evolution of precipitates in a pre-deformed Al–Zn–Mg–Cu alloy during ageing were investigated using Vickers hardness measurements, tensile tests, and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). It was found that all cold rolled conditions had higher mechanical strength than the non-deformed condition for all ageing times and that this effect increases at higher deformation ratios. It was also found that the non-deformed condition has a higher age hardening response than that of the cold rolled conditions. A homogeneous precipitate distribution was observed in the non-deformed condition, while the cold rolled conditions contained non-uniformly distributed precipitates due to the introduced dislocations. This led to larger precipitate sizes and a reduction in the precipitate number densities in the pre-deformed conditions. HAADF-STEM analysis revealed differences in the fraction of different precipitate types between the non-deformed and the cold rolled conditions. η', η2, and disordered η phase were observed in the non-deformed condition, while η', η2 and the newly identified Y phase were observed in the cold rolled conditions. The disordered η phase contained structural units of the η1 phase and was associated with reducing the lattice misfit between this phase and the Al matrix. Formation of the Y phase was related to an accelerated nucleation rate in the regions of high dislocation density. Graphical abstract

Fractional precipitation of copiapite-halotrichite efflorescent salts on Au[sbnd]Cu mine tailings under semi-arid climates in northern Chile

The oxidation of pyrite involves a series of chemical reactions that, depending on climatic conditions, can give rise to different mineral phases and morphologies. When oxidation takes place in semi-arid climate, the development of efflorescent salts on the surface of mine tailings is characteristic. These salts are mainly composed of Fe, Al and Mg sulfates and may accumulate valuable metals liberated through the dissolution of tailing minerals.This research aims to describe the evolution of salt precipitation from the economic and environmental perspective. For this purpose, we sampled efflorescent salts formed during the summer season on the surface of a tailing impoundment located in the north of Chile. The materials underwent comprehensive characterization utilizing X-ray techniques and scanning electron microscopy.The findings reveal a fractional precipitation in the crystallized salts. In an advanced oxidation system, characterized by multiple seasons of crystallization, dissolution and oxidation, the dry season begins with the precipitation of sulfates from a highly acidic solution dominated by Fe3+. This solution results from the dissolution and oxidation of the previous season sulfates. This initial stage is characterized by the presence of jarosite and gypsum, which are subsequently replaced by ferricopiapite. Towards the progress of the dry season, copiapite becomes more magnesian and precipitates alongside coquimbite and alunogen. Finally, halotrichite and pickeringite begin to crystallize. Base metal cations such as Co, Cu, Mn, Ni and Zn are preferentially incorporated into halotrichite-pickeringite sulfates during the most advanced evaporation phase.

Multifrequency radar observations of marine clouds during the EPCAPE campaign

Abstract. The Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) was a year-round campaign conducted by the US Department of Energy at the Scripps Institution of Oceanography in La Jolla, CA, USA, with a focus on characterizing atmospheric processes at a coastal location. The ground-based prototype of a new Ka-, W-, and G-band (35.75, 94.88, and 238.8 GHz) profiling atmospheric radar, named CloudCube, which was developed at the Jet Propulsion Laboratory, took part in the experiment during 6 weeks in March and April 2023. This article describes the unique data sets that were obtained during the field campaign from a variety of marine clouds and light precipitation. These are, to the best of the authors' knowledge, the first observations of atmospheric clouds using simultaneous multifrequency measurements including 238.8 GHz. These data sets therefore provide an exceptional opportunity to study and analyze hydrometeors with diameters in the millimeter- and submillimeter size range that can be used to better understand cloud and precipitation structure, formation, and evolution. The data sets referenced in this article are intended to provide a complete, extensive, and high-quality collection of G-band data in the form of Doppler spectra and Doppler moments. In addition, Ka-band and W-band reflectivity and Ka-, W-, and G-band reflectivity ratio profiles are included for several cases of interest on 6 different days. The data sets can be found at https://doi.org/10.5281/zenodo.10076227 (Socuellamos et al., 2024).

Assessing the Link between Wildfires, Vulnerability, and Climate Change: Insights from the Regions of Greece

Forests provide a wide range of ecosystem services which are important for achieving sustainable development. Anthropogenic climate change has led to the increased frequency and severity of forest fires, which imply losses of valuable ecosystem services. This paper provides a methodological framework based on Multiple Criteria Decision Aid methods for determining relative regional vulnerabilities associated with forest fires. Different notions of ex-post vulnerability are defined based on the forest area burned and the frequency of forest fires, and their relation to the regions’ area and certain socioeconomic characteristics. The climatic drivers of forest fire occurrence are explored by linking forest fires with summer and spring temperatures and precipitation, using econometric count data analysis. The methodology is applied to Greece and its administrative regions for the period 2000–2022. Ex-post vulnerability of regions to forest fires based on physical and socioeconomic characteristics is calculated, and expected changes in the frequency of fires of specific size classes conditional on the evolution of mean seasonal regional temperature and precipitation according to IPCC scenarios are predicted. Relative vulnerability estimates and the impact of specific climatic drivers on forest fires will be useful in designing policies for preserving forests as natural capital and promoting sustainability.

Precipitation evolution and properties of Cu-15Ni-8Sn alloys via Al microalloying during ageing

Precipitation evolution and properties of Cu-15Ni-8Sn alloys via Al microalloying during ageing

Dislocation loop and irradiation-induced synergistic-competitive mechanism in Cu-rich precipitates: a phase-field study

Both irradiation and dislocations have been proposed as routes to rationally manipulate spatial distribution and micromorphology of precipitate. An interesting effect emerges in Fe–10at.%Cu–3at.%Mn–1.5at.%Ni–1.5at.%Al alloy due to the synergistic-competitive roles of dislocation loop and irradiation. Base on cascade mixing, vacancy-interstitial atoms and dislocation stress field model, we examine nucleation and growth dynamics of Cu-rich precipitates, where both dislocation loop and irradiation act in conjunction. Analytical treatments identify regimes, where the distribution of elements and point defects due to irradiation and dislocations are specific to the Cu-rich precipitates. Simulation results reveal that density, size and distribution of Cu-rich precipitates are a manifestation of the competing effects of the dislocation loop and the irradiation rate. More specifically, the dislocation loop preferentially assists the formation of precipitates and new dislocations at lower irradiation rates. Only the irradiation induces the formation of Cu-rich precipitates with the irradiation rate continues to increase. Equipped with molecular dynamics, where reproduces major interaction features of the solutes with point defects under displacement cascade, can verify multi-component morphologies of Cu-rich precipitates. This modeling framework provides an avenue to explore the role of dislocation loop and irradiation on the microstructural evolution of Cu-rich precipitates.