Changes In Temperature Gradient Research Articles

Thermal Field Simulation and Optimization of PbF2 Single Crystal Growth by the Bridgman Method

PbF2 single crystals are usually grown in the temperature gradient region by the Bridgman–Stockbarger method. Temperature distribution during the growth process is particularly important for the preparation of high-quality crystals. In this study, the temperature field during the growth of the PbF2 single crystals was simulated based on the finite element method. The temperature distribution and temperature gradient changes in the crucible were investigated at different growth stages, including the seeding, shouldering, and iso-diameters stages. The calculated results show that as the crucible position continues downward during the growth process, the axial temperature gradient increases and then decreases from the bottom to the top of the crucible, with almost flat isotherms near the solid–liquid interface where the axial temperature gradient is larger. At the shoulder below the crucible, the solid–liquid interface was improved by adjusting the tilt angle. Furthermore, based on a novel design of the heat-insulating baffle, the concave solid–liquid interface in the iso-diameter stage can be effectively adjusted to realize a lower radial temperature gradient. This study provides theoretical guidance for the optimization of the growth of high-quality PbF2 crystals by the Bridgman method.

High-temperature transient-induced thermomechanical damage of fiber-reinforced ceramic-matrix composites in supersonic wind tunnel

This article is based on the supersonic directly connected wind tunnel. Through a specially designed experimental chamber, combined with infrared temperature measurement, high-speed camera, etc., in-situ monitoring of composite materials under airflow at Ma 3.0 with a total temperature of 950 ∼ 1473K was carried out. The dimensional analysis method was used to propose dimensionless parameters to characterize the thermal coupling caused by high-speed airflow thermal shock. Research has shown that the thermal coupling effect of supersonic airflow causes uneven temperature inside the material, and the thermal stress caused by temperature gradient changes (including increasing and decreasing processes) is the main reason for material damage. The damage of ceramic matrix composites under thermal shock mainly manifests as a decrease in surface roughness, surface fiber fracture and a decrease in elastic modulus. In addition, the study also found that there are damage thresholds for the thermal shock effect of airflow at different total temperatures, which helps to further understand the thermomechanical damage mechanism and degradation law of composite structure under high-temperature transient conditions.

Influence of Prandtl number on the chaos transition for pure natural and Rayleigh–Bénard convections inside a rectangular cavity

A peculiar flow instability known as multiple chaos transitions was recently reported for the free convection in an enclosure where the direction of the temperature gradient changes continuously; it has been explained to be attributed to the competition for dominance between pure natural and Rayleigh–Bérnard convections. In this study, the chaos transition of free convection is investigated when a horizontal or vertical temperature gradient forms in a rectangular cavity. Analyses are conducted under a laminar flow regime, with Prandtl numbers ranging from 0.01 to 50 and Rayleigh numbers up to 109. In the horizontal temperature gradient, the chaos-transition Rayleigh number increases monotonically with the Prandtl number. However, under vertical temperature gradient conditions, it reaches the maximum value at approximately Pr = 0.5. Contrary to the general knowledge that higher-Prandtl number fluids effectively stabilize natural convection, a free convection in a vertical temperature gradient initiates a new flow instability when the Prandtl number is over 1.0, where momentum and thermal diffusions balance each other. The oscillation pattern, 2D phase trajectory, power spectral density, and Poincaré point of equivalent thermal conductivity are used to assess the free-convection flow instability.

Nitrate denitrification rate response to temperature gradient change during river bank infiltration.

Nitrate attenuation during river bank infiltration is the key process for reducing nitrogen pollution. Temperature is considered to be an important factor affecting nitrate attenuation. However, the magnitude and mechanism of its impact have not been clear for a long time. In this study, the effects of temperature and temperature gradient on the nitrate denitrification rate were investigated via static batch and dynamic soil column simulation experiments. The results showed that temperature had a significant effect on the denitrification rate. Temperature effects were first observed in denitrifying bacteria. At low temperatures, the microorganism diversity was low, resulting in a lower denitrification rate constant. The static experimental results showed that the denitrification rate at 19°C was approximately 2.4 times that at 10°C. The dynamic soil column experiment established an exponential positive correlation between the nitrate denitrification decay kinetic constant and temperature. The affinity of denitrifying enzymes for nitrate in the reaction substrate was ordered as follows: decreasing temperature gradient (30°C → 10°C) > zero temperature gradient (10°C) > increasing temperature gradient condition (0°C → 10°C). This study provides a theoretical basis for the biogeochemical processes underlying river bank infiltration, which will help aid in the development and utilization of groundwater resources.

Температурные изменения в мясных изделиях при жарке в пароконвекционных печах

Combination steam ovens, or combi steamers, have entered all spheres of food production, including the meat industry. Their rational use requires a scientific and practical foundation. This research featured the changes in mean volume temperature and temperature gradient that occur in meat products (one-dimensional bodies with different nutrient compositions) during heat treatment in dry air and a steam-air mix.
 The research involved two samples of meat products with different moisture and fat contents. The chicken fillet sample had a moisture content of 74.5% and a fat content of 1.9% while the pork shoulder sample had a moisture content of 55.1% and a fat content of 29.4%. Shaped as a one-dimensional cylinder and a plate, the samples were subjected to heating at the temperature range of 160–240°C in a Unox-203G steam-convection oven (Italy). Dry air and a steam-air mix with a humidity of 80–85% served as a heating medium. The temperature was measured using thermocouples attached to a Sosna-004 meter.
 The research revealed some patterns in the mean volume temperature and temperature gradient. The temperature gradient involved three stages during processing in a steam-air mix and four stages when treated with dry air. The change in the mean volume temperature for the steam-air mix could be described by a power law equation; the dry air treatment was described using a linear equation. When heated in dry air, the rate of change in the temperature gradient was constant at first but started to decrease at a certain stage. The change rate in the mean volume temperature remained low for 5 min and started to increase onwards, maintaining its value until the end of the process. When heated in a steam-air mix, the change rate in the temperature gradient dropped to its minimum in 4–5 min and started to grow. The mean volume temperature demonstrated a high change rate during the first 5 min and went down. The chicken fillet with its low fat content warmed up faster by 13–26% when processed in a steam-air mix and by 9–23% when treated in dry air. The plate-shaped products needed longer heat treatment. The composition and form had no significant effect on the nature of the change in the temperature gradient and mean volume temperature.
 The obtained dependencies made it possible to select the optimal temperature and humidity conditions for convective frying of meat products.

Study on three-dimensional model of ventilation drying and heat and mass transfer of bulk grain pile based on discrete-continuous media

Abstract In order to ensure the safety of grain storage and explore the mechanisms of water and heat transfer during the drying process of grain piles, this paper takes wheat as the research object, uses a thermal conductivity analyzer to measure the thermal conductivity and specific heat capacity of wheat, and obtains a linear relationship between the heat constant and water content of wheat. COMSOL software was used to establish a three-dimensional model of ventilation drying and heat and mass transfer of bulk grain piles based on discrete continuum media, which simulated the temperature and humidity changes during the drying process of the grain pile. The model was verified by a thin layer drying experiment. The results show that the simulated values of temperature and water content obtained by the wet heat transfer model are in good agreement with the experimental values, and the maximum errors are 2.14 % and 5.68 % respectively. During the drying process, the grain temperature of wheat at the bottom of the grain pile increased rapidly, compared with that at the top of the grain pile, and the temperature of the wheat at the center was higher than that at the edge. At the end of drying, the moisture content from highest to lowest was top edge > top center > bottom edge > bottom center. Therefore, the model can be used to further study the changes of grain pile temperature gradient and water gradient.

Research on Classification Algorithm of Silicon Single-Crystal Growth Temperature Gradient Trend Based on Multi-Level Feature Fusion.

In the process of silicon single-crystal preparation, the timely identification and adjustment of abnormal conditions are crucial. Failure to promptly detect and resolve issues may result in a substandard silicon crystal product quality or even crystal pulling failure. Therefore, the early identification of abnormal furnace conditions is essential for ensuring the preparation of perfect silicon single crystals. Additionally, since the thermal field is the fundamental driving force for stable crystal growth and the primary assurance of crystal quality, this paper proposes a silicon single-crystal growth temperature gradient trend classification algorithm based on multi-level feature fusion. The aim is to accurately identify temperature gradient changes during silicon crystal growth, in order to promptly react to early growth failures and ensure the stable growth of high-quality silicon single crystals to meet industrial production requirements. The algorithm first divides the temperature gradient trend into reasonable categories based on expert knowledge and qualitative analysis methods. Then, it fuses the original features of actual production data, shallow features extracted based on statistical information, and deep features extracted through deep learning. During the fusion process, the algorithm considers the impact of different features on the target variable and calculates mutual information based on the difference between information entropy and conditional entropy, ultimately using mutual information for feature weighting. Subsequently, the fused multi-level feature vectors and their corresponding trend labels are input into a Deep Belief Network (DBN) model to capture process dynamics and classify trend changes. Finally, the experimental results demonstrate that the proposed algorithm can effectively predict the changing trend of thermal field temperature gradients. The introduction of this algorithm will help improve the accuracy of fault trend prediction in silicon single-crystal preparation, thereby minimizing product quality issues and production interruptions caused by abnormal conditions.

Orbital Controls on North Pacific Dust Flux During the Late Quaternary

AbstractAirborne mineral dust is sensitive to climatic changes, but its response to orbital forcing is still not fully understood. Here, we present a reconstruction of dust input to the Subarctic Pacific Ocean covering the past 190 kyr. The dust composition record is indicative of source moisture conditions, which were dominated by precessional variations. In contrast, the dust flux record is dominated by obliquity variations and displays an out‐of‐phase relationship with a dust record from the mid‐latitude North Pacific Ocean. Climate model simulations suggest precession likely drove changes in the aridity and extent of dust source regions. Additionally, the obliquity variations in dust flux can be explained by meridional shifts in the North Pacific westerly jet, driven by changes in the meridional atmospheric temperature gradient. Overall, our findings suggest that North Pacific dust input was primarily modulated by orbital‐controlled source aridity and the strength and position of the westerly winds.

Computational Fluid Dynamics Modeling and Analysis of Axial and Radial Temperature of Wellbore during Injection and Production Process

Summary To solve problems such as additional tubing/casing load, casing deformation, and packer failure caused by changes in annular temperature during oil and gas reservoir fracturing and production, based on the well structure of oil and gas reservoirs and transition transient heat transfer mechanism, a four-field coupling simulation model of the temperature field in the main fluid domain of the tubing, the temperature field in the solid domain of the tubing, the temperature field in the annular fluid domain, and the temperature field in the solid domain of the casing is proposed. Considering the coupling of fluid temperature, pressure, and physical parameters, boundary conditions are established based on reservoir characteristics, wellbore heat transfer characteristics, and fracturing and production conditions, and are compiled into Fluent software for simulation through the user-defined function (UDF) method. The effects of the temperature and flow rate of injected fracturing fluid and produced oil and gas on the distribution of the wellbore temperature field and temperature gradient are studied. The research results show that by applying D14-1 and D5-5 gas wells to the model, the simulated temperature is in good agreement with the measured wellbore temperature, and the maximum errors of the simulated values of the two different wells are 6.4% and 4.3%, respectively. As the injection and production operation time increase, the heat transfer between the wellbore and the formation gradually stabilizes. At this time, the injection and production flow rate have little impact on the wellbore temperature field, while the injection and production temperature have a greater impact on the wellbore temperature field. The injection and production temperature will cause changes in annular temperature and temperature gradient, leading to an increase or decrease in pressure within a limited annular volume, resulting in local stress on the tubing and casing. The research results can provide a theoretical basis for the analysis of the temperature field and pressure field of the wellbore during fracturing and oil and gas production, ensuring the safety and stability of fracturing and production.

Interhemispheric Temperature Gradient and Equatorial Pacific SSTs Drive Sahel Monsoon Uncertainties under Global Warming

Abstract The Sahel is one of the most vulnerable regions to climate change. Robust estimation of future changes in the Sahel monsoon is therefore essential for effective climate change adaptation. Unfortunately, state-of-the-art climate models show large uncertainties in their projections of Sahel rainfall. In this study, we use 32 models from CMIP6 to identify the sources of this large intermodel spread of Sahel rainfall. By using maximum covariance analysis, we first highlight two new key drivers of this spread during boreal summer: the interhemispheric temperature gradient and equatorial Pacific sea surface temperature (SST) changes. This contrasts with previous studies, which have focused mainly on the Northern Hemisphere rather than the global scale, and in which the Pacific Ocean has been neglected in favor of the Atlantic. Next, we unravel the physical mechanisms behind these statistical relationships. First, the modulation of the interhemispheric temperature gradient across the models leads to varying latitudinal positions of the intertropical convergence zone and, consequently, varying Sahel rainfall intensity. Second, models that exhibit less warming than the multimodel mean in the equatorial Pacific, thereby projecting a less “El Niño–like” mean state, simulate enhanced precipitation over the central Sahel in the future through modulations of the Walker circulation, the tropical easterly jet, the meridional tropospheric temperature gradient, and hence regional zonal wind shear. Finally, we show that these two indices collectively explain 62% of Sahel rainfall change uncertainty: 40% due to the interhemispheric temperature gradient and 22% through equatorial Pacific SST.

Revealing the influence of aerosol particle state on the high-quality α-Ga2O3 single crystal thin film growth by Mist CVD epitaxy

There is little research on α-Ga2O3 single crystal film because it is a metastable phase of Ga2O3 crystal and difficult for controllable fabrication. In this paper, highly crystallized Ga2O3 thin films of poly-crystalline, α-Ga2O3 and β-Ga2O3 were prepared by modulating the growth temperature from 400 °C to 700 °C by mist-assisted CVD (Mist CVD) method. The results show that films grown at 525 °C owes the best crystalline quality of α-Ga2O3 film. To further improve the crystallinity of α-Ga2O3 thin film, a systematic simulation revealing the distribution changes of aerosol particle size, flow field, and temperature gradient in the reaction chamber were explored. The optimal growth region C with uniform particle size, well-distribute temperature gradient and stable flow field is determined. Meanwhile, the experimental results of α-Ga2O3 thin films grown at different positions in the reaction chamber was proved to consistent with the simulation results. Furthermore, the optimal single crystallized α-Ga2O3 thin films with smooth surface morphology and optical property were obtained. The PL spectrum operated at room temperature show the α-Ga2O3 film with low defect density and high crystalline quality. It shows that the single crystallized α-Ga2O3 is orientated grown on sapphire substrate with epitaxial relationship of α-Ga2O3 (0006)//c-Al2O3 (0006). Although, slight lattice mismatch is observed on the selected area electron diffraction pattern of the interface between sapphire and α-Ga2O3 film, it is ideal for further application in devices. This work reveals the key point for α-Ga2O3 single crystal film growth by mist CVD is to construct a steady and orderly environment through controlling aerosol particle state.

MODELING OF THREE-LAYER FLOWS WITH NON-UNIFORM EVAPORATION BASED ON THE EXACT SOLUTION OF CONVECTION EQUATIONS

Mathematical modeling of three-layer convective flows of two liquids and a gas-vapor mixture in a horizontal channel is based on the exact solution of the Navier-Stokes equations in the Boussinesq approximation. Thermocapillary interfaces are assumed to be non-deformable. The inhomogeneous mass transfer of the light liquid to the upper layer is considered. The Soret and Dufour effects are taken into account in the upper layer, and the gas flow rate is given. The influence of thermal load and flow geometry on the main characteristics of the flow was studied using the example of the water–benzine–air system. It is shown that the Soret effect has an impact on the nature of the flow. The influence of the effect of thermodiffusion, changes in the longitudinal temperature gradients, and thicknesses of the layers of the system on the dew point is revealed.

MODELING OF TEMPERATURE GRADIENTS DURING THE INTERACTION OF LASER RADIATION WITH BIOLOGICAL TISSUE

Modeling thermal gradients in biological tissues, when interacting with laser radiation, helps to understand how heat flows are distributed in the body and reflect heating zones. The main aspects of the simulation include the parameters of the laser source, such as the wavelength and power, the initial temperature conditions of the tissues, as well as the use of special numerical methods that help to optimally solve the heat conduction equations and visualize the obtained results. Temperature distribution in tissues plays an important role in determining the effectiveness and safety of laser treatment. This allows you to choose effective parameters of laser radiation and irradiation modes to achieve the desired result without negative consequences for the patient. However, it is important to consider that the actual behavior of tissues in response to laser radiation may be more complex due to the physiological characteristics of each person.Therefore, all models and calculations must take into account this feature and diversity and take into account safety regulations. Laser treatment should be carried out under the supervision of qualified specialists, in particular doctors who have relevant knowledge and experience in the field of medicine. This approach helps ensure the safety and effectiveness of laser procedures for patients. Modeling the distribution of tissue thermal gradients when interacting with laser radiation plays an important role in the development of modern medicine and scientific research and provides efficiency compared to the obtained experimental data. It helps to improve the understanding of thermal processes in biological tissues and to ensure the safety of patients receiving laser treatment. In this work, experiments were conducted on the effect of laser irradiation on biological tissue, as well as modeling of changes in temperature gradients during the effect of laser irradiation on biological tissue, using various models of heat and mass transfer, using the Matlab software environment. As a result of the modeling in this work, the patterns of changes in temperature gradients were obtained, which were compared with the experimentally obtained data, the errors of Pennes models and finite element methods, finite differences were analyzed, and conclusions were drawn.

Data-driven model based adaptive feedback-feed forward control schemes for open cycle - OTEC process

Open Cycle - Ocean Thermal Energy Conversion (OC-OTEC) is one of the most important renewable energy sources that generate electricity and fresh water from seawater utilizing the temperature gradient between the warm surface seawater and the cold deep seawater. This paper aims to develop non-linear data-driven model-based adaptive Feedback Control (FBC) schemes for the OC-OTEC process to track the output power and a dynamic Feed-Forward Control (FFC) scheme to reject the effects of temperature disturbance on power caused by climate variations in OC-OTEC. The experiments are conducted on a laboratory-scale OC-OTEC experimental setup at the National Institute of Ocean Technology, Chennai. Firstly, linear data-driven models are developed using system identification techniques. Based on the developed models, gain scheduling-based adaptive control schemes are developed: Proportional Integral (PI) control and Model Predictive Control (MPC). Secondly, the closed-loop performances of the developed FBC schemes are analysed under servo and regulatory operations. Furthermore, it is observed from the sensitivity analysis results that the temperature disturbance highly influences output over the manipulated variable. Hence, a dynamic FFC scheme is implemented to reject known disturbance of 1 °C variation in temperature gradient from 18 °C to 19 °C due to Sea Surface Temperature (SST) changes in temperature gradient. The results show that the proposed MPC-based FBC-FF scheme effectively enhances the tracking and disturbance rejection performance compared to the PI-based FBC-FF control scheme with a minimum Integral Square Error (ISE) of 3.055 and Control Effort (CE) of 7.505. This experimental data-based, data-driven modelling and adaptive control research provides a new direction for automating OC-OTEC. Further, these studies will help to develop a rugged and automated upscaling OC-OTEC plant control system with proposed feasible control schemes.

Future weakening of southeastern tropical Atlantic Ocean interannual sea surface temperature variability in a global climate model

AbstractFuture changes in the southeastern tropical Atlantic interannual sea surface temperature (SST) variability in response to increasing greenhouse gas concentrations are investigated utilizing the global climate model FOCI. In that model, the Coastal Angola Benguela Area (CABA) is among the regions of the tropical Atlantic that exhibits the largest surface warming. Under the worst-case scenario of the Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5), the SST variability in the CABA decreases by about 19% in 2070–2099 relative to 1981–2010 during the model’s peak interannual variability season May–June–July (MJJ). The weakening of the MJJ interannual temperature variability spans the upper 40 m of the ocean along the Angolan and Namibian coasts. The reduction in variability appears to be related to a diminished surface-layer temperature response to thermocline-depth variations, i.e., a weaker thermocline feedback, which is linked to changes in the mean vertical temperature gradient. Despite improvements made by embedding a high-resolution nest in the ocean a significant SST bias remains, which might have implications for the results.

A laser additive manufactured metastable Ti-10V-2Fe-3Al β-titanium alloy: Microstructure, mechanical properties, and deformation mechanisms

In the present work, the deformation mechanism is investigated by tailoring the microstructure of a laser powder bed fusion (L-PBF) processed β-type Ti-10V-2Fe-3Al (Ti1023) alloy. The microstructure analysis shows columnar β grains with <001>//BD texture. The α phase appeared lath morphology after using laser power of 160 W and presented fine and intersected morphology at 200 W, and the shape of ω clusters transformed from bulk to intersected acicular with increasing laser power. The Ti1023 alloy exhibits excellent mechanical properties with a total elongation of 18 % and high yield strength above 828 MPa. The existence of α″ phase as well as {332}<113> and {112}<111> deformed twins were found in fractured microstructure at 160W, confirming the multiple deformation mechanisms consisting of dislocation slip, transformation-induced plasticity (TRIP), and twinning-induced plasticity (TWIP). By increasing the laser power, the deformation mechanisms are limited to dislocation slip. At last, the finite element analysis of the temperature and temperature gradient change reveals the underlying mechanism for microstructure evolution based on thermal history. This study provides a pathway to regulate L-PBF Ti1023 strengthening and work-hardening behavior by controlling the process parameters during the fabrication of the material.

A Millennial‐Scale Oscillation in Latitudinal Temperature Gradients Along the Western North Atlantic During the Mid‐Holocene

AbstractChanges in vegetation in North America indicate Holocene shifts in the latitudinal temperature gradient along the western margin of the North Atlantic. Tree taxa such as oak (Quercus) and birch (Betula) experienced opposing directions of change across different latitudes consistent with changes in temperature gradient steepness. Pollen‐inferred temperatures from 34 sites quantify the gradient changes and reconstruct a long‐term northward steepening in summer and southward steepening in winter. From 4.8 to 3.8 ka, an oscillation in tree distributions interrupted the long‐term trends as a steep temperature gradient developed north of 43.5°N. The shift likely limited cold outbreaks to the south, producing anomalously high summer temperatures at 42–43.5°N, and enabling a northward expansion of oak forests. The forest and temperature gradient changes appear consistent with orbital and ice sheet forcing as well as millennial variability in the North Atlantic pressure field analogous to the North Atlantic Oscillation on interannual time scales.

The Research on Ultrasonic Vibration Amplitudes in Ti6Al4V DED Additive Manufacturing

Ultrasonic-assisted Ti6Al4V Directed Energy Deposition (DED) additive manufacturing technology can improve the problem of uneven microstructure caused by laser heating and sudden cooling of the molten pool. In this paper, the numerical analysis and experimental verification methods were adopted. The influencing factors, such as the cavitations’ effect, sound flow enhancement effect, and sound flow thermal effect related to the ultrasonic assistance in the molten pool, were analyzed. After equating the energy of the ultrasound, the model of additive manufacturing was introduced in the form of a heat source. The temperature gradient changes during the solidification process of the molten pool with the addition of ultrasound assistance and the effect of ultrasonic vibration during the manufacturing process on its deposited state and microstructure of solution-aged formed parts were studied. The results showed that when the wire feeding rate is 5 mm/s and the laser scanning speed is 5 mm/s, the optimal laser power is 1000 W~1100 W, corresponding to the optimal ultrasonic amplitude of 120 μm. Then, by comparing the temperature field with the same amplitude of 0 μm (i.e., no ultrasonic vibration) and the microstructure of the formed parts, it was verified that ultrasonic vibration facilitates fluid flow in the molten pool, which could lead to a more uniform temperature distribution. This optimized approach not only enhances the understanding of the process but also contributes significantly to the advancement of related research endeavors.

Pantropical Indo-Atlantic temperature gradient modulates multi-decadal AMOC variability in models and observations

Interconnections between ocean basins are recognized as an important driver of climate variability. Recent modeling evidence suggests that the North Atlantic climate can respond to persistent warming of the tropical Indian Ocean sea surface temperature (SST) relative to the rest of the tropics (rTIO). Here, we use observational data to demonstrate that multi-decadal changes in pantropical ocean temperature gradients lead to variations of an SST-based proxy of the Atlantic Meridional Overturning Circulation (AMOC). The largest contribution to this temperature gradient-AMOC connection comes from gradients between the Indian and Atlantic Oceans. The rTIO index yields the strongest connection of this tropical temperature gradient to the AMOC. Focusing on the internally generated signal in three observational products reveals that an SST-based AMOC proxy index has closely followed low-frequency changes of rTIO temperature with about 26-year lag since 1870. Analyzing the pre-industrial control simulations of 44 CMIP6 climate models shows that the AMOC proxy index lags simulated mid-latitude AMOC variations by 4 ± 4 years. These model simulations reveal the mechanism connecting AMOC variations to pantropical ocean temperature gradients at a 27 ± 2 years lag, matching the observed time lag in 28 out of the 44 analyzed models. rTIO temperature changes affect the North Atlantic climate through atmospheric planetary waves, impacting temperature and salinity in the subpolar North Atlantic, which modifies deep convection and ultimately the AMOC. Through this mechanism, observed internal rTIO variations can serve as a multi-decadal precursor of AMOC changes with important implications for AMOC dynamics and predictability.

Influence of LaB6 inoculant on the thermodynamics within the molten pool and subsequent microstructure development and cracking behavior of laser powder bed fused TiAl-based alloys

A LaB6 particles decorated Ti48Al2Cr2Nb composite almost free of any cracks has been successfully fabricated by LPBF in this work. To better understand the role of LaB6 inoculant in LPBF-fabricated γ-TiAl alloys, the effects of LaB6 inoculant on the thermal behavior, microstructure evolution and crack sensitivity were investigated by simulation and experimental methods. Based on a single particle model, it was predicted that the addition of LaB6 particle could induce a significant change in temperature gradient G. Due to the LaB6→La2O3 in-situ transformation, the temperature field was severely perturbed, thus causing random G orientations of the matrix surrounding the particle. Furthermore, based on the multi-particle model, predictions indicated that the 0.5 wt% LaB6 inoculant led to a significant decrease of the Gmax from 1.14× 107 °C/m to 6.9 × 106 °C/m but a little influence on solidification rate R at solidified front, therefore contributing to a lower G/R and resultant larger undercooling. In this condition, fine equiaxed grains with random orientations were expected to dominate in the solidified microstructure, which got well verified by the experiments where the maximum texture index dropped from 15.06 to 2.23 and the average grain size decreased from 16.13 ± 8.52 μm to 1.52 ± 1.10 μm due to the addition of LaB6 inoculant. What's more, the LaB6 inoculant also induced an apparent reduce in crack density from 7.02 ± 1.06 mm/mm2 to 0.52 ± 0.12 mm/mm2 and a rise in relative density from 97.65 ± 0.58% to 99.88 ± 0.10%, which could be mainly attributed to grain refinement, grain purification and texture attenuation.