Temperature-dependent Growth Research Articles

Ammonia-free quasi-atmospheric MOCVD of InN/Al2O3 (0001)

We demonstrate ammonia-free quasi-atmospheric metal–organic chemical vapor deposition (AFQA-MOCVD) of InN grown on c-plane sapphire (Al2O3) substrate using high-density nitrogen (N2) microstrip-line microwave plasma. Dependence of growth temperature (Tg) and N2 plasma power on structural properties were examined. Increasing Tg and N2 plasma power markedly improved surface morphology of InN. An atomically smooth surface with layer-by-layer growth mode was realized at Tg of 750 °C under N2 plasma power of 80 W. Fully strain-relaxed InN was grown on in-plane crystal rotation by 30° with respect to the Al2O3 (0001). N-polar InN on Al2O3 (0001) was revealed by scanning transmission electron microscopy. AFQA-MOCVD enables to expand growth windows by increasing Tg and V/III ratio compared to the standard MOCVD using NH3.

Temperature Dependent Growth of Ytterbium Oxide as Gate Dielectric on Silicon Substrate Via Combination of Nitrogen and Oxygen Ambient

The ongoing trend towards downsizing silicon (Si)-based metal-oxide semiconductor (MOS) devices has led to constraints on the silicon dioxide (SiO2) gate dielectric due to increased leakage current through the thin SiO2. In this study, ytterbium oxide (Yb2O3) as a high dielectric constant (k) gate oxide material was deposited on a Si substrate and subjected to annealing at different temperatures ranging from 400 to 1000oC in a nitrogen-oxygen-nitrogen ambient atmosphere. The successful formation of Yb2O3 was verified using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and ultraviolet-visible (UV-VIS) spectroscopy. The FTIR analysis indicated that Yb2O3 gate dielectrics post-annealing exhibited Yb-O bonding due to oxygen diffusion, as well as N-O bonding and NO3-bonding, demonstrating the formation of a nitrogen barrier at the interface to hinder oxygen diffusion. The optical band gap values of Yb2O3 gate dielectrics post-annealing ranged from 3.092 eV to 3.267 eV. Notably, the Yb2O3 gate dielectric annealed at 800 °C showed no breakdown within the 0–3 V range across all samples. The acquisition of a high k value of 19.40 and a low effective oxide charge (Qeff) of 5.32 x 1011 cm-2, along with the superior I-V characteristics, suggest that the Yb2O3 gate dielectric annealed at 800oC has the potential to be employed for next generation MOS applications.

First individual-based model to study the impact of temperature on Sakura shrimp larvae development: Integrating experimental insights

The decline in marine resources, exemplified by the Sakura shrimp (Lucensosergia lucens), highlights the pressing need for aquaculture solutions. This study pioneers the development of the first individual-based model (IBM) to explore the impact of temperature on Sakura shrimp larvae development. By integrating novel experimental data on the effect of temperature on larvae development and survival, and individual variability, our model provides insights crucial for informed artificial rearing practices. In our breeding experiments, larvae were successfully raised to the third protozoa stage, with development time and survival rates showing high sensitivity to water temperature. Notably, embryonic development times exhibited significant variations across temperature conditions, with durations of 3 days at 14 °C, 2 days at 18 °C, and 1.3 days at 26 °C. However, none of the individuals reached adulthood, highlighting the complexity of larval development under different thermal regimes. Our individual-based model, integrating experimental data and insights from Omori's (1971) work, revealed the Ratkowsky et al. (1983) equation as the most suitable representation of temperature-dependent larval growth. Similarly, the Gaussian equation emerged as the optimal choice for capturing temperature-dependent survival patterns. Notably, the model predicted an optimal larval temperature of 24 °C. By scrutinizing these patterns, our model not only elucidates the temperature-dependent dynamics of Sakura shrimp larval development but also provides a valuable framework for optimizing artificial rearing practices. Moving forward, future iterations of the model should incorporate considerations of salinity and environmental effects on hatching success to further refine our understanding of Sakura shrimp aquaculture.

Deep Blue CsPbBr3 Quantum Wires with Tailored Shapes.

Low-dimension metal halide perovskites are attractive for bandgap tunable optoelectronic materials. Among them, 1-D CsPbBr3 quantum wires (QWs) are emerging as promising deep-blue luminescent material. However, the growth dynamics of 1-D perovskite QWs are intricate, making the study and control of 1-D QWs highly challenging. In this study, a strategy for controlling both the length and width of the CsPbBr3 QWs was realized. The temperature-dependent isotropic growth mechanism was revealed and employed as the main tool for the oriented growth of 1-D CsPbBr3 QWs for various aspect ratios. Our results pave the way for the controlled synthesis of ultrasmall perovskite nanocrystals.

Temperature Dependent Growth Kinetics of Pd Nanocrystals: Insights from Liquid Cell Transmission Electron Microscopy.

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

Some like it hot: adaptation to the urban heat island in common dandelion

Abstract The Urban Heat Island Effect (UHIE) is a globally consistent pressure on biological species living in cities. Adaptation to the UHIE may be necessary for urban wild flora to persist in cities, but experimental evidence is scarce. Here, we report evidence of adaptive evolution in a perennial plant species in response to the UHIE. We collected seeds from common dandelion (Taraxacum officinale) individuals along an urban–rural gradient in the city of Amsterdam (The Netherlands). In common-environment greenhouse experiments, we assessed the effect of elevated temperatures on plant growth and the effect of vernalization treatments on flowering phenology. We found that urban plants accumulate more biomass at higher temperatures and require shorter vernalization periods, corresponding to milder winters, to induce flowering compared to rural plants. Differentiation was also observed between different intra-urban subhabitats, with park plants displaying a higher vernalization requirement than street plants. Our results show genetic differentiation between urban and rural dandelions in temperature-dependent growth and phenology, consistent with adaptive divergence in response to the UHIE. Adaptation to the UHIE may be a potential explanation for the persistence of dandelions in urban environments.

Temperature-dependent development and population growth of the invasive pest Cassida vittata vill. In sugar beet crops

The sugar beet flea beetle, Cassida vittata Vill. is an invasive pest that significantly damages sugar beet crops in Morocco by affecting the leaves. To gain a deeper understanding of how temperature influences the development and reproduction of C. vittata and to facilitate its population management, laboratory-based experiments were conducted. Individuals were subjected to a range of constant temperatures spanning from 15 °C to 36 °C. The most extended lifespans for both adult females and males were recorded at 30 °C, with respective longevities of 62.8 and 62.5 days. The highest likelihood of eggs maturing into the adult stage occurred at 25 °C, with survival rates of 39.0% for females and 37.5% for males. Preadult survival rates displayed significant variability with temperature, with the highest survivorship observed at 25 °C (76.5%). The maximum average number of offspring produced per female reached 225.1 eggs at 25 °C. Daily reproduction, maximum total fecundity, and maximum daily fecundity were also notably higher at 25 °C. The population growth parameters exhibited their most favorable values at 25 °C, with r (0.0933 d−1), and R0 (87.15 offspring per female) being highest at this temperature. The temperature thresholds for the complete pre-adult stage (1st instar larva to adult) were estimated to be 9.4 °C for females and 9.0 °C for males. The thermal constants from the 1st instar larva to the adult stage were calculated to be 526.3 and 476.2 DD, respectively. These findings indicate that the most favorable temperature range for the population growth of this invasive pest falls between 25 °C and 30 °C.

Temperature dependence of pollen germination and tube growth in conifers relates to their distribution along an elevational gradient in Washington State, USA.

Pollen germination and tube growth are essential processes for successful fertilization. They are among the most temperature-vulnerable stages and subsequently affect seed production and determine population persistence and species distribution under climate change. Our study aims to investigate intra- and inter-specific variations in the temperature dependence of pollen germination and tube length growth and to explore how these variations differ for pollen from elevational gradients. We focused on three conifer species, Pinus contorta, Picea engelmannii, and Pinus ponderosa, with pollen collected from 350 to 2200m elevation in Washington State, USA. We conducted pollen viability tests at temperatures from 5 to 40°C in 5°C intervals. After testing for four days, we took images of these samples under a microscope to monitor pollen germination percentage (GP) and tube length (TL). We applied the Gamma function to describe the temperature dependence of GP and TL and estimated key parameters, including the optimal temperature for GP (Topt_GP) and TL (Topt_TL). Results showed that pollen from three species and different elevations within a species have different GP, TL, Topt_GP, and Topt_TL. The population with a higher Topt_GP would also have a higher Topt_TL, while Topt_TL was generally higher than Topt_GP, i.e., a positive but not one-to-one relationship. However, only Pinus contorta showed that populations from higher elevations have lower Topt_GP and Topt_TL and vice versa. The variability in GP increased at extreme temperatures, whereas the variability in TL was greatest near Topt_TL. Our study demonstrates the temperature dependences of three conifers across a wide range of temperatures. Pollen germination and tube growth are highly sensitive to temperature conditions and vary among species and elevations, affecting their reproduction success during warming. Our findings can provide valuable insights to advance our understanding of how conifer pollen responds to rising temperatures.

Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2

Transition metal silicides represented by MoSi2 have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2 oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2 at temperatures of 1000 °C–1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2 underwent high-temperature selective oxidation reactions at 1000 °C–1200 °C, forming MoO2 and SiO2 oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2 and the phase transformation of SiO2, a continuous Mo5Si3 layer with a thickness of approximately 47 μm was formed at the SiO2–MoSi2 interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2 and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3 layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2 coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3 during the high-temperature oxidation of MoSi2 coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.

Bloom dynamics under the effects of periodic driving forces

Phytoplankton bloom received considerable attention for many decades. Different approaches have been used to explain the bloom phenomena. In this paper, we study a Nutrient–Phytoplankton–Zooplankton (NPZ) model consisting of a periodic driving force in the growth rate of phytoplankton due to solar radiation and analyse the dynamics of the corresponding autonomous and non-autonomous systems in different parametric regions. Then we introduce a novel aspect to extend the model by incorporating another periodic driving force into the growth term of the phytoplankton due to sea surface temperature (SST), a key point of innovation. Temperature dependency of the maximum growth rate (μmax) of the phytoplankton is modelled by the well-known Q10 formulation: μmax=μ0∗(Q10)T/10, where μ0 is maximum growth at 0oC. Stability conditions for all three equilibrium points are expressed in terms of the new parameter ρ2, which appears due to the incorporation of periodic driving forces. System dynamics is explored through a detailed bifurcation analysis, both mathematically and numerically, with respect to the light and temperature dependent phytoplankton growth response. Bloom phenomenon is explained by the saddle point bloom mechanism even when the co-existing equilibrium point does not exist for some values of ρ2. Solar radiation and SST are modelled using sinusoidal functions constructed from satellite data. Our results of the proposed model describe the initiation of the phytoplankton bloom better than an existing model for the region 25–35° W, 40–45° N of the North Atlantic Ocean. An improvement of 14 days (approximately) is observed in the bloom initiation time. The rate of change method (ROC) is applied to predict the bloom initiation.

Modeling insect growth regulators for pest management.

Insect growth regulators (IGRs) have been developed as effective control measures against harmful insect pests to disrupt their normal development. This study is to propose a mathematical model to evaluate the cost-effectiveness of IGRs for pest management. The key features of the model include the temperature-dependent growth of insects and realistic impulsive IGRs releasing strategies. The impulsive releases are carefully modeled by counting the number of implements during an insect's temperature-dependent development duration, which introduces a surviving probability determined by a product of terms corresponding to each release. Dynamical behavior of the model is illustrated through dynamical system analysis and a threshold-type result is established in terms of the net reproduction number. Further numerical simulations are performed to quantitatively evaluate the effectiveness of IGRs to control populations of harmful insect pests. It is interesting to observe that the time-changing environment plays an important role in determining an optimal pest control scheme with appropriate release frequencies and time instants.

Temperature-dependent bubble growth under synergistic interactions of hydrogen and helium in tungsten

A novel theoretical model based on modified diffusion rate equations is proposed to simulate the retention of hydrogen isotopes and the dynamics of bubble growth in tungsten (W) when exposed to simultaneous hydrogen (H) and helium (He) plasma irradiations. Simulation is conducted to assess the influence of temperature as well as simultaneous H and He irradiation at an increasing fluence. Not only to develop a holistic understanding but also to substantiate simulation findings about synergy between H and He plasma irradiation, a W sample is exposed sequentially to H and He plasma at 873 K using the large-power material irradiation experimental system. The topographical changes in the W sample are investigated using atomic force microscopy (AFM) after each plasma irradiation exposure sequence. Simulation results reveal that the ability of a bubble containing both H and He to trap adjacent H/He atoms is primarily governed by their individual partial pressure within the bubble. Furthermore, at elevated temperatures, the synergy between H and He significantly enhances the retention of H isotopes in W. AFM micrographs of the W sample exposed to both H and He plasma irradiation show a severely damaged and locally delaminated layer, absent in the sample exposed only to either H or He, conclusively establishing evidence of synergy between H and He irradiation effects. The average bubble radius computed using the model aligns excellently with experimentally determined values obtained through SEM/AFM analysis. The robustness of the proposed model is also assessed by comparing bubble radius and H isotopes retention at various temperatures with experimental data reported in the literature.

Processing temperature-dependent nucleation and growth behaviors of polypropylene nucleated by a bisamide nucleating agent

It has been widely reported that the processing temperature significantly influenced the effectiveness of a β-nucleating agent (β-NA) in polypropylene (PP) and thus leads to variations in the final relative content of β-phase (kβ). To comprehensively understand the changing kβ with processing temperature, PP nucleated by a bisamide β-NA, N,N′-dicyclohexylterephthalamide (DCHT), was heating-treated at different temperatures (Tf) in the range of 200–250 °C, and the impact of Tf on the nucleation and subsequent growth behaviors of the α- and β-phases were separately investigated. Under low Tf, DCHT induced a high relative density of β-nuclei to α-nuclei (Nβ/Nα) with high total nucleation density (N), and both the α- and β-phases grew competitively until the crystallization ended. Under middle Tf, the Nβ/Nα became low with middle N induced by DCHT, and the faster-growing phase dominated the subsequent growth process. Under high Tf, there was a middle Nβ/Nα with low N, and the faster-growing phase became more dominant during the growth process. Based on the observed morphology of DCHT, the decreasing N with Tf could be associated with the specific surface area, the varying Nβ/Nα could be attributed to the variations in both the energy barrier and the surface area of β-nucleation under diverse DCHT morphologies, and the varying growth behavior was probably associated with the outer surface shape of diverse DCHT morphologies. Combining the thorough analysis of the changing nucleation and growth behaviors with Tf, a possible mechanism was proposed to explain the effect of processing temperature on the final polymorphic composition.

Geographic variation in larval cold tolerance and exposure across the invasion front of a widely established forest insect.

Under global climate change, high and low temperature extremes can drive shifts in species distributions. Across the range of a species, thermal tolerance is based on acclimatization, plasticity, and may undergo selection, shaping resilience to temperature stress. In this study, we measured variation in cold temperature tolerance of early instar larvae of an invasive forest insect, Lymantria dispar dispar L. (Lepidoptera: Erebidae), using populations sourced from a range of climates within the current introduced range in the Eastern United States. We tested for population differences in chill coma recovery (CCR) by measuring recovery time following a period of exposure to a nonlethal cold temperature in 2 cold exposure experiments. A 3rd experiment quantified growth responses after CCR to evaluate sublethal effects. Our results indicate that cold tolerance is linked to regional climate, with individuals from populations sourced from colder climates recovering faster from chill coma. While this geographic gradient is seen in many species, detecting this pattern is notable for an introduced species founded from a single point-source introduction. We demonstrate that the cold temperatures used in our experiments occur in nature during cold spells after spring egg hatch, but impacts to growth and survival appear low. We expect that population differences in cold temperature performance manifest more from differences in temperature-dependent growth than acute exposure. Evaluating intraspecific variation in cold tolerance increases our understanding of the role of climatic gradients on the physiology of an invasive species, and contributes to tools for predicting further expansion.

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

The Impact of Gravity Waves on the Evolution of Tropical Anvil Cirrus Microphysical Properties

AbstractAnvil cirrus generated by deep convection covers large fractions of the tropics and has important impacts on the Earth's radiation budget and climate. In situ measurements made with high‐altitude aircraft indicate a rapid transition in ice crystal size distributions and habits as anvil cirrus ages. We use numerical simulations to investigate the impact of high‐frequency gravity waves on the evolution of anvil cirrus microphysical properties. The impacts of both monochromatic gravity waves and ubiquitous stochastic mesoscale temperature fluctuations are simulated. In both cases, the interplay between wave‐driven temperature fluctuations, deposition growth/sublimation, and sedimentation causes accelerated removal of both small ice crystals (diameters less than about 10 μm) and large crystals (diameters larger than ≈30 μm). These changes are consistent with the observed evolution of anvil cirrus microphysical properties. The Kelvin effect (higher saturation vapor pressure over curved surfaces) is a critical factor in the anvil evolution, driving mass transfer from small to large ice crystals. The wave‐driven decrease in ice concentration is much faster for typical anvil cirrus detrained at ≃11.5–12.5 km than for less frequent anvils at 15.5–17.5 km because of the strong temperature dependence of deposition growth and sublimation rates. The simulations also show that waves, along with the Kelvin effect, drive growth of mid‐sized (5–20 μm) ice crystals, which is consistent with the observed transition to bullet rosette habits in aging anvil cirrus. We conclude that high‐frequency gravity waves, which are generally not resolved in large‐scale models, likely have important impacts on anvil cirrus microphysical properties and lifetimes.

Structural and surface characterizations of 2D β-In2Se3/3D β-Ga2O3 heterostructures grown on c-Sapphire substrates by molecular beam epitaxy

Integrating two-dimensional (2D) layered materials with wide bandgap β-Ga2O3 has unveiled impressive opportunities for exploring novel physics and device concepts. This study presents the epitaxial growth of 2D β-In2Se3/3D β-Ga2O3 heterostructures on c-Sapphire substrates by plasma-assisted molecular beam epitaxy. Firstly, we employed a temperature-dependent two-step growth process to deposit Ga2O3 and obtained a phase-pure (2¯01)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\overline{2 }01)$$\\end{document} β-Ga2O3 film on c-Sapphire. Interestingly, the in-situ reflective high-energy electron diffraction (RHEED) patterns observed from this heterostructure revealed the in-plane ‘b’ lattice constant of β-Ga2O3 ~ 3.038Å. In the next stage, for the first time, 2D In2Se3 layers were epitaxially realized on 3D β-Ga2O3 under varying substrate temperatures (Tsub) and Se/In flux ratios (RVI/III). The deposited layers exhibited (00l) oriented β-In2Se3 on (2¯01)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\overline{2 }01)$$\\end{document} β-Ga2O3/c-Sapphire with the epitaxial relationship of [112¯0]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$[11\\overline{2 }0]$$\\end{document} β-In2Se3 || [010] β-Ga2O3 and [101¯0]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$[10\\overline{1 }0]$$\\end{document} β-In2Se3 || [102] β-Ga2O3 as observed from the RHEED patterns. Also, the in-plane ‘a’ lattice constant of β-In2Se3 was determined to be ~ 4.027Å. The single-phase β-In2Se3 layers with improved structural and surface quality were achieved at a Tsub ~ 280 °C and RVI/III ~ 18. The microstructural and detailed elemental analysis further confirmed the epitaxy of 2D layered β-In2Se3 on 3D β-Ga2O3, a consequence of the quasi-van der Waals epitaxy. Furthermore, the β-Ga2O3 with an optical bandgap (Eg) of ~ 5.04 eV (deep ultraviolet) when integrated with 2D β-In2Se3, Eg ~ 1.43eV (near infra-red) can reveal potential applications in the optoelectronic field.

Comparative study of bacterial load and organoleptic quality changes between lean fish and fatty fish in fresh, iced and non-iced state under laboratory condition

The study conducted in the laboratory conditions of Sylhet Sadar Upazila compared the bacterial load and organoleptic quality changes in lean fish (Oreochromis niloticus) and fatty fish (Pangasianodon hypophthalmus) across fresh, iced, and non-iced states. Preservation times of 6- and 8-hours intervals were examined, focusing on organoleptic quality changes and Total Viable Count (TVC). The evaluation of defect points and fish grading revealed that all fresh and iced Tilapia and Pangas samples were in excellent condition (Grade A) at 0, 6, and 8 hours, while non-iced samples at 6- and 8-hours intervals were in acceptable condition (Grade B). Notably, non-iced Pangas exhibited higher defect points than non-iced Tilapia at the same intervals. The bacterial load varied, with the highest observed in non-iced Pangas at an 8-hour interval in May and the lowest in iced Tilapia at a 6-hour interval in April. Compliance with International Commission on Microbiological Specifications for Foods (ICMSF) standards was noted in both fish types across all states. The temperature dependence of bacterial growth was evident, with the highest bacterial load at 35 ℃ in May and the lowest at 24 ℃ in April. Overall, the study suggests that fresh Tilapia and Pangas, whether iced or non-iced at 6- and 8-hour intervals, meet ICMSF standards, ensuring their safety for consumption and potential export.

Temperature-dependent void nucleation and growth in single-crystal and nanocrystalline iron at extreme strain rates: atomistic insights

In this paper, we use molecular dynamics simulation with the embedded atomic method to perform triaxial deformation experiments on single-crystal and nanocrystalline iron at a strain rate of 5×10−9 s−1 and investigate the temperature effect on the void nucleation and growth process. We also evaluate the applicability of the Nucleation And Growth (NAG) model for single-crystal iron. The results indicate that the maximum tensile stress of both single-crystal and nanocrystalline iron decreases as temperature increases, with a reduction of 35.9% for single-crystal iron and 36.2% for nanocrystalline iron from 100 K to 1100 K. It is demonstrated that void nucleation and growth is more favored at high temperature. The void nucleation and growth process in single-crystal iron under high strain rate follows the NAG model. We analyze the sensitivity of the NAG parameters at different temperatures and find that the void nucleation and growth threshold of single-crystal iron is much higher than that of low carbon steel. The results can provide insights for developing fracture models of iron at extremely high strain rate and describing the dynamic damage at continuum length scales.

Prediction of temperature-dependent nucleation and growth rates from crystallization-related heat release.

We propose a method for determining the time and, therefore, temperature-dependent relative nucleation and growth rates during crystallization. We do so by linking the partial differential equationgoverning the time dynamics of the crystal size distribution to kinetic (Avrami) parameters describing heat release. This approach is tested in silico by nucleating and growing diffusion limited aggregates with time-varying morphology and growth rates unhindered by impingement. The associated heat release is analyzed, showing that nucleation and growth rates could be extracted with high fidelity.