Continuous Precipitation Research Articles

Characterization of Solid-Solution and Aging Process in Mg-5 wt.%Sn Alloy

Firstly, the properties and the microstructure evolution of the solid-solution process of Mg-5 wt.%Sn were studied. From the motion analysis of resistivity and microhardness during solution treatment, the reasonable solution technology of Mg-5 wt.%Sn should be 12–16 h at 480 °C. After solution treatment at 480 °C for 16 h, the precipitating behavior in supersaturated solid solution. Mg-5 wt.%Sn alloy was investigated. In the aging process, it was observed that there were precipitated phases in the both grain and grain boundaries, and continuous inhomogeneous precipitation occurred along the grain boundaries, and continuous homogeneous precipitation happened in the grain. Transmission Electron Microscope (TEM) analysis indicated the plate- and lath-shaped precipitates within the grains and only the plate-shaped precipitates along the grain boundary. High-Resolution Electron Microscopy (HRTEM) studies have shown that metastable precipitates may occur during aging, coherently or semi-coherent with the matrix. Energy Dispersive Analysis by X-ray (EDAX) analysis showed that the Mg/Sn ratio was not actually constant, and the Sn content of the metastable phase was lower than that of the Mg2Sn equilibrium phase. X-ray diffraction (XRD) studies confirm the existence of this metastable phase, which is supposed to be GP zone and metastable Mg3Sn phase.

Unusual recent prolonged low flow in the Moqu River, northeastern Tibetan Plateau, inferred from tree-ring width variations

The runoff of Moqu river in Zoige, one of most important water conservation ecological function areas in the upper reaches of the Yellow River, located in the north-east of the Tibetan Plateau, is highly sensitive to climate change. However, the current understanding of the long-term changes in the hydrology of this rives is still fragmentary. In this study, we created a regional tree-ring width chronology from two sample sites in Moqu River Basin and analysed the relationships between tree-ring width, climate, and runoff. We found significant positive correlations between tree-ring width and runoff in multiple months, the highest correlation coefficient occurred with annual runoff from previous July to current June (r = 0.617, 1981–2013). Based on this highly significant (p < 0.01) relationship, we reconstructed runoff variations of Moqu River for the period 1672 to 2019. The reconstructed runoff showed unusual prolonged and frequent low flow periods in recent decades. We found that the continuous low precipitation and the high temperature in the context of global warming are the main reasons for the abnormal runoff in recent decades. We assume that a weakening of the Indian summer monsoon (ISM) circulation system may be the key large-scale factor that caused the unusually prolonged low flow. With global warming, the weakening of ISM intensity leads to reduced water vapor transport from the tropical Indian Ocean to High Asia, resulting in less precipitation and low runoff events in Zoige. Our reconstruction improves the understanding of regional runoff variability over multiple timescales, and also provides a scientific basis for the protection, development, and utilization of water resources related to ongoing global warming.

Electrochemical behavior of steel bars in magnesium phosphate cement

The electrochemical characteristics of steel bars in magnesium phosphate cement (MPC) are crucial when applying MPC to reinforced concrete. In this study, the electrochemical behaviors of steel bars in MPC were investigated via electrochemical tests combined with surface analyses. The results indicated that the steel bars in the simulated MPC pore solution could effectively passivate, forming films that mainly consisted of FePO4. In the MPC matrices, the continuous precipitation of phosphates led to the accumulation of passive films, which were responsible for the superior corrosion protection of MPC compared to traditional cement materials. MPC exhibited a self-healing corrosion feature after the depassivation of steel bars, which could be characterized by the dramatic recovery of passive film resistance and charge transfer resistance. Furthermore, the corroded steel bars in MPC with a low magnesia-to-phosphate ratio could re-passivate and stabilize for long periods of time.

A comparative analysis of merging strategies for satellite precipitation estimates and ground observations over Chinese mainland

Satellite precipitation estimates are attractive for providing spatially continuous precipitation measurement on the global scale, but improvements in accuracy are still needed relative to the point-scale gauge observations. In this study, two integration frameworks named Geographical Differential Analysis (GDA) and Geographical Ratio Analysis (GRA) combined with two interpolation techniques named Ordinary Kriging (OK) and Inverse Distance Weighting (IDW) were adopted to merge the satellite precipitation with ground-based observations. The Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) research product was merged with the ground rain gauges derived from CGDPA (China Gauge-based Daily Precipitation Analysis) at a monthly scale over the Chinese mainland from 2011 to 2015, and the merged precipitation products were evaluated by 10-fold cross-validation. Results showed that the merged precipitation products based on the GDA integration framework had significant improvements relative to the original TMPA. Moreover, the method based on GDA combined with Ordinary Kriging (GDA-OK) delivered better performances compared to the GDA-IDW (method based on GDA combined with Inverse Distance Weighting) since the OK considers the global spatial correlation. However, the GRA-based merged precipitation products had systematic underestimations over Chinese mainland during all seasons and were not recommended for satellite-gauge precipitation merging over the large spatial scale of Chinese mainland. In addition, we found that the OK is quite sensitive to the density gauge network, the shrinkage of the number of rain gauges may result in great uncertainties and errors in the OK interpolation technique.

Continuous single-stage elemental sulfur reduction and copper sulfide precipitation under thermoacidophilic conditions

Metal sulfide precipitation is a viable technology for high-yield metal recovery from hydrometallurgical streams, with the potential to streamline the process design. A single-stage elemental sulfur (S0)-reducing and metal sulfide precipitating process can optimize the operational and capital costs associated with this technology, boosting the competitiveness of this technology for wider industrial application. However, limited research is available on biological sulfur reduction at high temperature and low pH, frequent conditions of hydrometallurgical process waters. Here we assessed the sulfidogenic activity of an industrial granular sludge previously shown to reduce S0 under hot (60–80 °C) and acidic conditions (pH 3.6). A 4 L gas-lift reactor was operated for 206 days and fed continuously with culture medium and copper. During the reactor operation, we explored the effect of the hydraulic retention time, copper loading rates, temperature, and H2 and CO2 flow rates on the volumetric sulfide production rates (VSPR). A maximum VSPR of 274 ± 6 mg·L−1·d−1 was reached, a 3.9-fold increase of the VSPR previously reported with this inoculum in batch operation. Interestingly, the maximum VSPR was achieved at the highest copper loading rates. At the maximum copper loading rate (509 mg·L−1·d−1), a 99.96% copper removal efficiency was observed. 16 s rRNA gene amplicon sequencing revealed an increased abundance of reads assigned to Desulfurella and Thermoanaerobacterium in periods of higher sulfidogenic activity.

Dynamic comparative analysis of different types of precipitation caused by landfalling strong typhoons over South China

Based on multiple datasets, a comparative analysis has investigated the different rainfall distributions and the factors related to strong (weak) rainfall induced by landfalling strong typhoons moving northwest (SR-NWLFSTYs, WR-NWLFSTYs) which are defined from the tracks, the locations, and intensities of the rainfall center of LFSTYs based on a dynamic composite analysis method.The obviously stronger rainfall induced by SR-NWLFSTYs, with the intensive rainfall center presenting a cyclonic rotation in the lifecycle of typhoons, tends to be accompanied by the pronouncedly enhanced low-level jet and a warmer SST before and during landfall. Owing to the enhanced low-level jet, moisture convergence experiences an intensification, resulting in a warmer and more humid circulation. Sufficient water vapor and latent heat is favorable for the enhancement of the mid-troposphere warm core structure with longer maintenance which can prolong the impact period of typhoons, leading to continuous precipitation. Simultaneously, the coupling of low-level convergence and upper-level divergence provides favorable dynamic conditions, thus further promoting the upward transportation of moisture through Ekman pumping, which tends to increase the mid-troposphere moisture through moisture advection. The changes in the mid-troposphere moisture coincide well with the evolution of rainfall over the same region during the lifecycle of typhoons.Comparatively, the asymmetric rainfall features of WR-NWLFSTYs with intense rainfall center mainly placed in the northeast quarter of the TC center during the lifecycle of TCs is likely related to the relatively weaker low-level jet which remains almost constant during and after landfall. The weaker low-level flow transports less moisture into the cyclone, and prohibits the weakening of vertical wind shear after landfall, leading to reduced precipitation with an obvious asymmetric distribution. Concurrently, the configuration of the weakening upper-level divergence and low-level convergence after landfall has been unable to maintain the upward motion for precipitation, resulting in relatively weaker rainfall for WR-NWLFSTYs.

Evaluation on static mechanical stability of wrought Inconel 718 superalloy; effect of grain configuration and δ precipitation

Wrought nickel alloys are widely applied in hot static components for aero-engines, acquisition for the underlying mechanism of microstructural evolutions controlling mechanical degradation during elevated-temperature exposure is fundamentally vital to processing optimization as well as serving life prediction. In present work, the differential hot tensile characteristics during 500–2000 h exposure at 650 °C of wrought Inconel 718 alloy having specific microstructures designed via different processing routes were comparatively evaluated. The experimental results showed the static mechanical stability of Inconel 718 alloy was predominantly tailored by the complicated interaction of γ-matrix grain configuration and δ precipitation on grain boundaries (GBs). It mainly involved continuous GB-δ precipitation during the 500–2000 h exposure at 650 °C, which played opposite roles in homogeneous or heterogeneous grain configurations. GB-δ precipitation can improve hot ductility but deteriorate strength for homogeneous grain configuration, adequate GB-δ particles can improve the deformation compatibility between GBs and γ-matrix to achieve good balance between the strength and ductility as well as smaller mechanical fluctuations. The heterogeneous duplexing grain configuration exhibited enhanced mechanical sensitivity to sluggish GB-δ precipitation since the hot ductility was rapidly reduced by tiny δ particles with fracture mode transition. In comparison, appropriate sub-solvus solution prior to aging cycles can introduce GB-δ particles pre-existed in homogeneous grain configuration to benefit in superior long-term static mechanical stability for Inconel 718 alloy.

Variations of extreme precipitation events with sub-daily data: a case study in the Ganjiang River basin

Abstract. Climate warming increases the intensity of extreme precipitation. Studying extreme precipitation patterns and changes is vital to reducing risk. This paper investigates thresholds, changes and timescales for extreme precipitation using sub-daily records from meteorological stations in the Ganjiang River basin. We use the gamma distribution and select the L-moment method to estimate the parameters α and β. Results show that (1) continuous precipitation events of 36 h contributed the most precipitation to the total but with lower frequency, which would be key events for flood monitoring; (2) the intensity and the occasional probability of extreme precipitation will increase in spring in the future in stations like Yifeng, Zhangshu and Ningdu, which will in turn increase the risk of storm floods; and (3) spatial distribution of extreme precipitation risk shows that the risk increases as elevation increases in the northern lowland and the Jitai Basin in the midstream region, while the risk in the southern mountainous region decreases as elevation increases. These findings will facilitate emergency preparedness, including risk management and disaster assistance, in the study areas.

Remote Sensing Monitoring and Analysis of Jinwuco Lateral Moraine Landslide-Glacial Lake Outburst in Southeast Tibet

On 25 June 2020, a glacial lake outburst flood (GLOF) occurred in Jinwuco, Nidou Zangbo, and southeast Tibet, causing catastrophic damage to multiple infrastructures such as roads, bridges, and farmlands in the surrounding and downstream areas. Due to the lack of long-term monitoring of glacial lake and glacier changes in the region and the surrounding surface, the spatial and temporal evolutionary characteristics and triggering factors of the disaster still need to be determined. Here, we combine multi-temporal optical remote sensing image interpretation, surface deformation monitoring with synthetic aperture radar (SAR)/InSAR, meteorological observation data, and corresponding soil moisture change information to systematically analyze the spatial and temporal evolution characteristics and triggering factors of this GLOF disaster. Optical images taken between 1987 and 2020 indicate that the glacial lake’s initial area of 0.39 km2 quickly grew to 0.56 km2, then plummeted to 0.26 km2 after the catastrophe. Meanwhile, we found obvious signs of slippage beside the lateral moraine at the junction of the glacier’s terminus and the glacial lake. The pixel offset tracking (POT) results based on SAR images acquired before and after the disaster reveal that the western lateral moraine underwent a 40 m line of sight (LOS) deformation. The small baseline subset InSAR (SBAS-InSAR) results from 2017 to 2021 show that the cumulative deformation of the slope around the lateral moraine increased in the rainy season before the disaster, with a maximum cumulative deformation of −52 mm in 120 days and gradually stabilized after the disaster. However, there are three long-term deformation areas on the slope above it, showing an increasing trend after the disaster, with cumulative deformation exceeding −30 mm during the monitoring period. The lateral moraine collapse occurred in a warm climate with continuous and intense precipitation, and the low backscatter intensity prior to the slide suggests that the soil was very moist. Intense rainfall is thought to be the catalyst for lateral moraine collapse, whereas the lateral moraine falling into the glacier lake is the direct cause of the GLOF. This study shows that the joint active–passive remote sensing technique can accurately obtain the spatial and temporal evolution characteristics and triggering factors of GLOF. It is helpful to understand the GLOF event caused by the slide of lateral moraine more comprehensively, which is essential for further work related to glacial lake hazard assessment.

Effect of Isothermal Treatment on Microstructure and Performance of Micro/Nanostructure 2205 Duplex Stainless Steel Prepared by Aluminothermic Reaction

Using an appropriate heat treatment process to control the precipitation of the σ phase, while regulating the alloy structure and grain size, is one of the effective ways to obtain good comprehensive properties of duplex stainless steel (DSS). Herein, the feasibility and preparation parameters of micro/nanostructure 2205 DSS prepared by the aluminothermic reaction are explored. The microstructure and properties are further controlled by isothermal treatment at 1000 °C for a different time. The results show that the volume percentages of α and γ phases in the 1.0 h isothermal treated steel obtain a maximum value and a minimum value, corresponding to 60% and 36%, respectively. The evolution of microstructure with isothermal treatment also affects the content and morphology of the precipitated σ phase, which changes from continuous precipitation to granular precipitation at the α/γ phase boundaries, and its volume percentage obtains a minimum value when the isothermal treatment is performed for 1.0 h. With the increase of heat treatment time, the average grain size and volume fraction of nanocrystals increase gradually. Corresponding to the changes in microstructure and grain size, the maximum values of Vickers hardness and tensile properties of the alloy are obtained after 1.0 h isothermal treatment.

Variations of stable isotope in Typhoon Lupit (2021) rainfall and its response to upstream convective processes

AbstractTyphoons produce a large amount of rainfall with a highly depleted isotopic composition. However, the mechanisms of isotope fractionation during typhoons remain poorly understood. Here, we present the hourly resolution isotope composition of rainfall during Typhoon Lupit (2021) in Fuzhou, on the southeast coast of China, to better understand these processes. Our results showed that the rainfall of Typhoon Lupit had significant fluctuations in δ18O values, ranging from −20.1‰ to −6.3‰, and exhibited a three‐stage variation with distinctly negative δ18O values in the second stage. In the first stage of Lupit, water vapour originated primarily from the nearby sea area, which did not undergo sustained convective activity, resulting in relatively enriched δ18O values. In the second stage, the δ18O values were extremely negative mainly because of the accumulated convective activity and continuous precipitation as they travelled towards the centre of the typhoon. In the third stage, the mixing of more localized and nearby sea water vapour caused an increase in the δ18O values. In summary, the three‐stage characteristics of Typhoon Lupit were largely caused by the integration of accumulated convective activity and moisture sources. Our findings reveal how upstream rainout affects the isotopic behaviour of rainfall and may have implications for understanding the dynamics of typhoon rainfall isotopes.

Study on microstructure and properties of Mg-Al-Si-Ca alloy by heat treatment

The effect of heat treatment on the microstructure and properties of Mg-4Al-0.25Si-0.3Ca alloy was systematically studied. The results showed that after solution treatment at 420 ℃ for 10 h and 500 ℃ for 3 h, then aging at 220 ℃ for 7.5 h, the shape of Mg2Si and CaMgSi phases changed from continuous to discontinuous, while the Mg17Al12 phased precipitated in the way of continuous precipitation in grains and discontinuous precipitation at grain boundaries during aging. The UTS of the alloy increased from 174.3 ± 4.0 MPa to 194.0 ± 5.0 MPa, and the corrosion current density decreased by 54%, The corrosion resistance was also improved, but the elongation decreased from 10.38 ± 0.37% to 9.1 ± 0.46%.

Continuous precipitation loss induced more pronounced compositional and diversity changes in the lotic phytobenthos than one-off drought events

Changing precipitation dynamics is one of the most important mechanisms that, by affecting the water regime, modifies the physical and chemical environment of aquatic assemblages. Thus, hydrological extremes can be considered as key drivers that shape algal assemblages and lead to diversity changes even in large rivers. Here, we investigated the long-term changes in the benthic diatom composition of the Rába River (River Raab), the watershed of which experienced continuous loss of precipitation in the last five years. We aim to answer the main question: Do one-off drought events and trend-like (continuous) precipitation decrease result in similar changes within diatom assemblages of this perennial river? Because, it has been already demonstrated that resilience and resistance of assemblages may vary depending on whether the drought occurs regularly or only occasionally. Our results demonstrated that one-off dry events hardly affected either assemblages’ composition or biodiversity. In contrast, continuously decreasing precipitation (drying period) had a pronounced effect on taxa and trait distribution and resulted in a significant decrease in taxonomic diversity and in functional richness. It is important to stress that the observed deteriorating diversity anticipates that a lasting drought period is likely to upset the ecological balance of the ecosystem and lead to remarkable natural damage. Since the climate scenarios project extremes in water regime in the near future, including longer periods of low precipitation, any knowledge that predicts changes in microflora can help to develop action plans by authorities to save lotic ecosystems.

Pred-SF: A Precipitation Prediction Model Based on Deep Neural Networks.

How to predict precipitation accurately and efficiently is the key and difficult problem in the field of weather forecasting. At present, we can obtain accurate meteorological data through many high-precision weather sensors and use them to forecast precipitation. However, the common numerical weather forecasting methods and radar echo extrapolation methods have insurmountable defects. Based on some common characteristics of meteorological data, this paper proposes a Pred-SF model for precipitation prediction in target areas. The model focuses on the combination of multiple meteorological modal data to carry out self-cyclic prediction and a step-by-step prediction structure. The model divides the precipitation prediction into two steps. In the first step, the spatial encoding structure and PredRNN-V2 network are used to construct the autoregressive spatio-temporal prediction network for the multi-modal data, and the preliminary predicted value of the multi-modal data is generated frame by frame. In the second step, the spatial information fusion network is used to further extract and fuse the spatial characteristics of the preliminary predicted value and, finally, output the predicted precipitation value of the target region. In this paper, ERA5 multi-meteorological mode data and GPM precipitation measurement data are used for testing to predict the continuous precipitation of a specific area for 4 h. The experimental results show that Pred-SF has strong precipitation prediction ability. Some comparative experiments were also set up for comparison to demonstrate the advantages of the combined prediction method of multi-modal data and the stepwise prediction method of Pred-SF.

Cu(II)-Metallized Three-Layered Cu–8HQ Complex with Hierarchical Crystallite Morphologies Synthesized via Reaction–Diffusion

Self-organization of regular band patterns of the precipitate via a reaction-diffusion (RD) framework is called Liesegang phenomenon. This non-equilibrium system is emerging as an efficient method for synthesizing materials with unique morphologies that may have desired properties. The formation of continuous precipitation inside a band with poor control over the shape and size of sparingly soluble salts has been well documented. However, only a few reports on forming organic-inorganic bonds are available. In the present work, we demonstrate the formation of 2D frameworks of bis-(8-hydroxyquinoline) copper(II) in the agar gel via RD. The macroscopic particles were dumbbell-shaped, with aspect ratios ranging from 2.7 (inner bands) to 0.7 (outer bands). The particles were composed of ribbon-shaped crystallites at the microscopic level, each with three layers of parallelogram prismatic monoclinic sheets stacked over one another, which could easily be exfoliated. The powder X-ray diffraction patterns at low angles and the surface areas of the crystallites indicated the formation of metal-organic frameworks. It was observed that the sizes of the particles could be tuned by controlling the extent of diffusion using reactant concentrations. Since such heterostructures have energy storage capacity, the cyclic voltammograms of the unexfoliated and exfoliated materials showed that they fall in the pseudocapacitor category with potential application as the electrode material. The frameworks were further characterized by techniques such as optical and electron microscopy, X-ray diffraction, IR spectroscopy, and UV-visible spectrophotometry.

Study on the Impact of Future Climate Change on Extreme Meteorological and Hydrological Elements in the Upper Reaches of the Minjiang River

Global warming increases global average precipitation and evaporation, causing extreme climate and hydrological events to occur frequently. Future changes in temperature, precipitation, and runoff from 2021 to 2050 in the upper reaches of the Minjiang River were analyzed using a distributed hydrological model, the SWAT (Soil and Water Assessment Tool), under a future climate scenario. Simultaneously, future variation characteristics of extreme climate hydrological elements in the upper reaches of the Minjiang River were analyzed using extreme climate and runoff indicators. The research shows that the frequency and intensity of the extreme temperature warming index will increase, while those of the extreme temperature cooling index will increase and then weaken in the upper reaches of the Minjiang River under a future climate scenario. The duration of precipitation, the intensity of continuous heavy precipitation, and the frequency of heavy precipitation will increase, whereas the intensity of short-term heavy precipitation and the frequency of heavy precipitation will decrease. However, spatial distribution of flood in the upper reaches is different, and thus flood risk in the upstream source area will still tend to increase. Particular attention should be given to the increase in autumn flood risk in the upper reaches of the Minjiang River.

Influence of Mg Content on the Corrosion Behavior and Precipitation of Aged Al-Cu-Li-xMg Alloys

Aluminum (Al)–copper (Cu)–lithium (Li) alloys are susceptible to environmental degradation, which limits the in-service lifetime of the components. Because of their complex composition, there are seldom studies focusing on corrosion behavior influenced by one single element, which is essential to clarify the corrosion mechanism. Herein, the sole influence of Mg on the corrosion behavior of Al–Cu–Li–xMg alloys was analyzed. Results revealed that the addition of Mg can affect the nucleation and precipitation process of the T1 precipitate, resulting in a difference of potential between grain interior and grain boundary. The precipitation of the T1 precipitate was promoted in a 0.7Mg alloy while impeded in a 1.1Mg alloy, due to the competition of Cu atoms and nucleation sites between T1 and S′. Two types of corrosion behavior of Al–Cu–Li–xMg alloys appeared due to the potential difference and continuity of grain boundaries. Continuous precipitates in grain boundaries and less precipitates within the grain are likely to cause intergranular corrosion (IGC), while more precipitates within the grain will result in pitting.

Acceleration of aging behavior and improvement of mechanical properties of extruded AZ80 alloy through (10–12) twinning

The effects of pre-existing {10–12} extension twins on the precipitation behavior of an extruded AZ80 material during aging and on its mechanical properties after peak aging are investigated. The material containing {10–12} twins—which are formed by compression before aging (twinned material)—has a finer grain size and higher dislocation density than the extruded material. Although the peak hardnesses of the twinned and extruded materials are almost the same, the time to reach the peak hardness is considerably shorter in the former material than in the latter (4 h and 24 h, respectively). In the twinned material, the high dislocation density of the {10–12} twins promotes continuous precipitation, which results in the formation of numerous fine Mg17Al12 precipitates within the twins in the early stage of aging. The formation of these continuous precipitates reduces the driving force for discontinuous precipitation, which consequently suppresses the formation and growth of coarse Mg17Al12 precipitates at the grain boundaries. Despite its shorter peak-aging time, the 4 h-peak-aged twinned material shows higher tensile strength and elongation than the 24 h-peak-aged extruded material. These higher mechanical properties of the former material are attributed primarily to the presence of more abundant fine continuous precipitates, which are effective in strengthening the material, and less abundant coarse discontinuous precipitates, which can act as crack initiation sites. These results demonstrate that the introduction of {10–12} twins into wrought Mg–Al-based alloys can accelerate the Mg17Al12 precipitation kinetics considerably and improve the strength and ductility of the peak-aged alloys simultaneously.

Suppression of discontinuous precipitation and strength improvement by Sc doping in Cu-6 wt%Ag alloys

• Sc doping significantly suppressed discontinuous Ag precipitates in Cu-Ag alloys. • Sc-doping led to a 55 MPa increase in strength, with only a slight decrease in conductivity. • Sc segregation at grain boundaries inhibited the nucleation of discontinuous precipitates • The UTS of Sc-doped samples was 1080 MPa, 205 MPa higher than that of non-doped samples. In low-Ag Cu matrix alloys, the presence of coarse discontinuous precipitates may limit strength. We demonstrated that discontinuous precipitation was suppressed, and continuous precipitation was enhanced by the doping of Cu-6 wt%Ag with Sc. A high-volume fraction of continuous precipitates, which nucleated on {111} planes, led to a 55 MPa increase in strength, with only a slight decrease in electrical conductivity. The addition of Sc inhibited the nucleation of discontinuous precipitates by causing the Sc and the Ag to co-segregate onto grain boundaries, thus forming a thin intermetallic compound layer between grains. After deformation, both discontinuous and continuous precipitates were drawn into Ag fibers. The combination of deformation strain and doping caused an increase in density and a decrease in the diameter of Ag fibers, resulting in about 205 MPa increase in doped samples when the deformation strain reached 4.9. The thinner, denser Ag fibers in the doped samples also caused higher electron scattering at interfaces, leading to electrical conductivity that was 11% IACS lower than in non-doped samples. For reference, 100% IACS (International Annealed Copper Standard) is equivalent to 1.7241 μΩ cm.

A CALPHAD-MD coupled method to reveal the strengthening mechanism in precipitation-strengthening Cu-Ni-Al alloy with evolving microstructures

With the aging temperature decreasing from 973 K to 773 K for the Cu-14.7Ni-3.1Al (wt.%) alloys, a simultaneous increase of the tensile strength (from 563 MPa to 729 MPa) and the ductility (from 5.4% to 13.5%) is observed due to the decreasing size of the (Ni, Cu)3Al precipitates (L12) dispersed in the Cu-rich solid solution (FCC). Calculation of phase diagram (CALPHAD) is employed to calculate the composition and fraction of the phases at the best aging temperature 773 K. Molecular dynamics (MD) models of the Cu-14.7Ni-3.1Al alloys with L12 phases in a size of 3 nm to 12 nm are established to investigate the function mechanism of the precipitates. The composition and fraction of the FCC and L12 phases in the MD models are precisely established based on the above CALPHAD results. A simultaneous increase of tensile strength and ductility is also observed during the MD tensile tests with the decreasing size of precipitates, indicating that L12 phases with the size of 3 nm efficiently interrupt the expanding path of cracks and contribute to the homogeneous distribution of dislocations during deformation. It is also proven by MD that cracks firstly form and expand in the discontinuous precipitation (DP) region in which precipitates have the larger size than that in a continuous precipitation (CP) region. In this work, a CALPHAD-MD coupled method is proposed to quantitatively reveal the relationship between microstructures and mechanical properties of the precipitation-strengthening Cu-Ni-Al alloy with the specific composition and microstructure, which can be effectively extended to the design of novel precipitation-strengthening alloys.