High Temperature Residence Time Research Articles

Influence of nonlinear heat accumulation characteristics in laser powder bed fusion (LPBF) and its effect on the shape memory bone implant

This study investigated the complex thermal accumulation characteristics and their effects in the time and spatial domains during the preparation of complex Nitinol (NiTi) alloy structures using laser powder bed fusion (LPBF) technology. The findings reveal a pronounced size dependency phenomenon when the formed dimensions fall below 2 mm. Specifically, a reduction in formed size leads to a marked surge in element loss, a heightened prevalence of internal defects, and a corresponding decline in both mechanical and functional properties. Small-sized (<0.5 mm) samples have significant thermal accumulation due to their fast heating and slow cooling rates, requiring control of heat input. Medium sized (0.5–2 mm) samples have significant temperature gradients as a result of their rapid heating and cooling rates, requiring control of high-temperature residence time. Large sized (> 2 mm) samples necessitate the insulation measures to reduce thermal stress, owing to their sluggish heating and rapid cooling characteristics. Therefore, we developed a model to evaluate the thermal history characteristics of parameters or design schemes and compensate or eliminate heat accumulation during the machining process to balance the thermal history characteristics. This model can also be combined with a thermal field detection system to develop real-time thermal management and control modules for processing. The key to eliminating size-dependency effects is to homogenize the microstructure. A single aging heat treatment (773 K for 0.5 h with air cooling) can effectively homogenize the structure and eliminate size dependence.

Study on the dynamic heating polymerization of PA MXD6: From thermal analysis to efficient polymerization

Optimizing a practical polymerization strategy for poly(m-xylylene adipamide) (PA MXD6) requires regulating the high-temperature residence time and preventing the solidification of the reaction mixture. Dynamic heating strategies have shown promise in addressing this issue. However, conventional polycondensation kinetics are not optimal for characterizing nonisothermal processes due to continuous changes in the reactant state. This study employed thermal analysis as a continuous monitoring method to comprehensively investigate the effects of pressure, temperature, and diffusion on polymerization. The results indicate that high heating rates lead to faster reaction rates, as evidenced by the evolution of the kinetic parameters throughout the reaction process. Nevertheless, excessively high heating rates increase the solidification risk. To resolve this contradiction, a low-rate heating process with pressure was developed for efficient polymerization and scale-up, resulting in superior products. This study provides new insights into polyamide polymerization and offers practical guidelines for enhancing polymerization efficiency and process stability.

Heat-balance control of friction rolling additive manufacturing based on combination of plasma preheating and instant water cooling

Friction rolling additive manufacturing (FRAM) is a solid-state additive manufacturing technology that plasticizes the feed and deposits a material using frictional heat generated by the tool head. The thermal efficiency of FRAM, which depends only on friction to generate heat, is low, and the thermal-accumulation effect of the deposition process must be addressed. An FRAM heat-balance-control method that combines plasma-arc preheating and instant water cooling (PC-FRAM) is devised in this study, and a temperature field featuring rapidly increasing and decreasing temperature is constructed around the tool head. Additionally, 2195-T87 Al-Li alloy is used as the feed material, and the effects of heating and cooling rates on the microstructure and mechanical properties are investigated. The results show that water cooling significantly improves heat accumulation during the deposition process. The cooling rate increases by 11.7 times, and the high-temperature residence time decreases by more than 50 %. The grain size of the PC-FRAM sample is the smallest, i.e., 3.77±1.03 µm, its dislocation density is the highest, and the number density of precipitates is the highest, the size of precipitates is the smallest, which shows the best precipitation-strengthening effect. The hardness test results are consistent with the precipitation distribution. The ultimate tensile strength, yield strength and elongation of the PC-FRAM samples are the highest (351±15.6 MPa, 251.3 ± 15.8 MPa and 16.25 %±1.25 %, respectively) among the samples investigated. The preheating and water-cooling-assisted deposition simultaneously increases the tensile strength and elongation of the deposited samples. The combination of preheating and instant cooling improves the deposition efficiency of FRAM and weakens the thermal-softening effect.

Microstructure and mechanical properties of AISI 410S ferritic stainless steel narrow gap weld using flux strip constraining arc welding

The achievement of high comprehensive mechanical properties in welded joints of ferritic stainless steels has attracted considerable attention in the manufacturing industry. Here, a low heat input flux strip constrained arc welding (FSCAW) was performed on a hot-rolled AISI 410S sheet. Defect free joints with a small HAZ width were obtained by one side welding both sides formation. The microstructure of HAZ consists of fine ferrite grains and a small amount of M23C6-decorated martensite due to short high-temperature residence time and rapid cooling rate, resulting in high toughness and hardness. Influenced by the stirring effect of the constraining arc and the promotion of heterogeneous grain nucleation by Ti-rich MX particles originating from the transition of alloying elements in the flux strip, the fusion zone (FZ) exhibits a unique precipitates-strengthened martensite+austensite uniform microstructure with weak martensitic texture. This translates into a simultaneous increase in impact toughness and hardness of FSCAW FZ compared to the MAG joint with a non-uniform mixed microstructure, strong martensitic texture, and large grain size. This work establishes the potential for using FSCAW welding to join ferrite stainless steels.

Does single-crystallization a feasible direction for designing Li-rich layered cathodes?

Although the synthesis technology of popular single-crystal electrode materials is mature, the large enough, greatly dispersed Li-rich single-crystal cathodes have been rarely reported. In this study, we overcome the challenge of elevated Mn-O breaking activation energy so that achieve micro-sized (∼3 μm) single-crystal Mn-Li-rich particles with extreme dispersity by regulating Li content and high temperature residence time step by step. However, the modified parameters during the sintering process severely intensify the Li/Ni mixing, leading to unavoidable dynamical hysteresis and structural damage. In addition, the long-range diffusion pathway in single-crystal Li-rich grains not only limits the effective Li⁺ transfer but also significantly weakens the kinetics of anionic redox. Hence, whether the single-crystal strategy is seriously applicable to Mn-based Li-rich cathodes remains a matter of debate, with promising outlets focusing on the enhancement of the dynamics in Li-rich cathodes.

Tailoring crystal structure and morphology of MnOx nanoparticles via electrospray-assisted flame spray pyrolysis

In this work, MnOx nanoparticles were produced by a continuous electrospray-assisted flame spray pyrolysis (EAFSP) method. In this regard, the precursor solutions containing manganese (II) nitrate hydrate (MnN) dissolved in 1-propanol precursor solutions are initially atomized into charged droplets by an electrospray in the microdripping mode. Then, the electrically charged precursor droplets enter the flame in a controlled manner without requiring a dispersion gas. The synthesis was carried out with a variation in horizontal injection locations from different heights above the burner (HAB) to control the high-temperature residence times of the charged droplets without changing the flame conditions for producing MnOx nanoparticles with tunable particle properties. Various diagnostics such as TEM, SMPS, BET, and XRD were applied for analyzing the formation of primary and agglomerated MnOx nanoparticles as well as their crystal phases with varying temperature histories. Furthermore, phase-Doppler anemometry (PDA) experiments have been conducted to track the evolution of droplet size and droplet axial velocity in the electrospray flame, allowing for the study of combustion of electrosprayed MnN droplets and the presence of µ-explosions in the flame.

Experimental and numerical analysis of friction stir additive manufacturing of 2024 aluminium alloy

With the rapid development of industrial manufacturing, additive manufacturing has attracted extensive attention in the industry since it possesses a high material utilization rate. Friction stir additive manufacturing (FSAM) is a novel solid-phase additive manufacturing method which possesses the advantage of achieving excellent mechanical properties of FSAM of aluminium alloy components. The formation characteristic of the additive zone and thermal processes in FSAM significantly determine the mechanical properties of the FSAM components. However, there is still a lack of quantitative analysis of the thermal processes in FSAM of AA2024-T4 aluminium alloy. Thus, a finite element model (FEM) of FSAM was proposed, and the element birth-death technology was employed to capture the addition of an additive layer during the FSAM process. The evolution of the thermal field in FSAM was quantitatively studied by the model. The formation characteristics and mechanical properties of the additive components were analyzed. It indicates that the volume of the additive zone increases with an increase in the tool rotation speed, while it decreases with an increase in the transverse speed during FSAM. The height and width of the hook structure decrease with an increase in the transverse speed. The tensile strength of the FSAM component first increases with the increase in the transverse speed and reaches its maximum value at the transverse speed of 90 mm/min, while further increases in the transverse speed reduce the tensile strength. The peak temperature of the first layer is the highest during the whole FSAM process. While the peak temperate of subsequent additive layers is about 475 ℃, which is lower than the first layer and remains almost constant. The maximum value of the thermal cycle decreases with an increase in the tool's transverse speed. While the high-temperature residence time increases with a decrease in the tool transverse speed. The model is validated by comparing the predicted heat-affected zone with the experimentally measured ones. It lays a solid foundation for optimizing the friction stir additive manufacturing process to improve manufacturing efficiency and enhance the performance of the built components.

Comparison of Fracture Toughness in the Coarse-Grain Heat-Affected Zone of X80 Pipelines Girth-Welded under Conventional and Ultra-Low Heat Input.

The coarse-grain heat-affected zones (CGHAZs) of X80 girth-welded steel pipelines are prone to embrittlement, which has an extremely adverse effect on their structural integrity. In the present work, the fracture behavior of the CGHAZs of X80 girth welds under the conditions of conventional and ultra-low heat input was studied. The fracture toughness of CGHAZs was evaluated using the crack tip opening displacement (CTOD) test at -10 °C, and the fracture behavior mechanism of CGHAZs were clarified by analyzing microstructural characteristics at prefabricated fatigue cracks containing fracture cloud image, scanning electron microscopy (SEM), and electron back-scatter diffraction (EBSD) figures. The results illustrate that the average fracture toughness (CTOD) value of the ultra-low heat input CGHAZ is 0.6 mm, and the dispersion of CTOD values is small, while the CTOD value of conventional heat input is only 0.04 mm. The ultra-low heat input makes the high-temperature residence time of the coarse-grained region short, reduces the proportion of prior austenite grain boundaries, and inhibits the formation of strip-like bainite and island-like M-A components. The reduction of these deleterious ductile microstructures increases the plastic reserve and deformation capacity of the CGHAZ.

A reactive force field molecular dynamics study on the inception mechanism of titanium tetraisopropoxide (TTIP) conversion to titanium clusters

We performed ReaxFF reactive molecular dynamics simulations to investigate the inception mechanism of TTIP precursor droplet conversion to Ti-containing clusters in 1000 K–2500 K with or without gaseous O2 molecules. A new Ti/C/H/O ReaxFF force field has been developed. Key intermediate titanium species and the initial decomposition pathways of TTIP are identified. The effects of temperature, O2 concentration and high-temperature residence time on the conversion of TTIP to incipient titanium clusters are investigated. Results suggest that high pyrolysis temperature does not necessarily promote the formation of incipient Ti-containing clusters, due to less stable TiO bonds at high temperatures. Ti2OxCyHz species appear earlier than TiO2 during TTIP pyrolysis, while TiO2 forms earlier than Ti2OxCyHz species and has much higher concentration with ambient O2. Decreasing high-temperature residence time boosts the formation of Ti-containing clusters by facilitating the condensation of TiO2 vapors. The growth pattern of the incipient titanium clusters is elucidated as formation of TiO bond with TiOxCyHz species or titanium clusters followed by continuous breakage of TiO or CO bonds to release hydrocarbon moieties.

Effect of Welding Heat Input on Microstructure and Impact Toughness in the Simulated CGHAZ of Low Carbon Mo-V-Ti-N-B Steel

Welding thermal cycles with heat inputs ranging from 25 to 75 kJ/cm were performed on a Gleeble 3500. The impact energy improved significantly (from 10 to 112 J), whereas the simulated coarse-grain heat-affected zone (CGHAZ) microstructure changed from lath bainite ferrite (LBF) and granular bainite ferrite (GBF) + martensite/austenite (M/A) to acicular ferrite (AF) + polygonal ferrite (PF) + M/A as the heat input increased. Simultaneously, the mean coarse precipitate sizes and the degree of V(C,N) enrichment on the precipitate surface increased, which provided favorable conditions for intragranular ferrite nucleation. The Ar3 of CGHAZ increased from 593 °C to 793 °C with increasing heat inputs; the longer high-temperature residence time inhibited the bainite transformation and promoted the ferrite transformation. As a result, acicular ferrite increased and bainite decreased in the CGHAZ. The CGHAZ microstructure was refined for the acicular ferrite segmentation of the prior austenite, and the microstructure mean equivalent diameter (MED) in the CGHAZ decreased from 7.6 µm to 4.2 µm; the densities of grain boundaries higher than 15° increased from 20.3% to 45.5% and significantly increased the impact toughness. The correlation of heat input, microstructure, and impact toughness was investigated in detail. These results may provide new ideas for the development of high welding heat input multiphase steels.

Investigation on variations of microstructures and mechanical properties along thickness direction of friction stir processed AA2014 aluminum alloy via ultra-rapid cooling

Fine-grained AA2014 aluminum alloy was innovatively achieved by cold source assisted friction stir processing (CSA-FSP) under different cooling conditions. The investigation detailedly addresses the effects of cooling capacity induced by liquid CO 2 on microstructural evolution and mechanical properties of the stirred zone (SZ) along thickness direction. The results indicated that FSP with liquid CO 2 cooling can provide fine grain structures in the upper region of SZ due to higher strain rate, higher cooling efficiency, lower deformation temperature and shorter high temperature residence time. Besides the dominant CDRX and GDRX mechanisms in the entire SZ, the additional grain refinement mechanism of DDRX in the surface region while PSN in the bottom region was partially involved. The strength and microhardness of CSA-FSP 2014 aluminum alloy were enhanced as the cooling rate increased. The ultimate tensile strength in the upper region of SZ cooled with liquid CO 2 achieved 519.7 MPa with a high elongation of 9.4%, which was 110.66% and 118.6% higher than that of the homogenized base alloy (246.7 MPa and 4.3%) due to the fine grain strengthening and second phase strengthening. The refined and retained second phase particles also can further enhance the grain refinement and dislocation accumulation effect, thus achieving an excellent combination of strength and plasticity. Meanwhile, the contribution of various strengthening mechanisms to the overall strength of CSA-FSP 2014 aluminum alloy was qualitatively evaluated • CSA-FSP can generate fine-grained SZ through higher strain rate, higher cooling efficiency, lower deformation temperature and shorter high temperature residence time. • Besides dominant CDRX and GDRX mechanisms in the entire SZ, additional grain refinement mechanism of DDRX in surface region and PSN in bottom region was partially involved. • The mechanisms of CSA-FSP on improving mechanical properties were evaluated.

Study on formation mechanism of three types of carbon nanoparticles during ethylene pyrolysis in thermal plasmas

Products of three carbon phases were synthesized by the pyrolysis of ethylene using a magnetically rotating arc under atmospheric pressure; the products thus produced were graphene nanoflakes, semi-graphite particles, and carbon nanospheres. The effects of temperature, buffer gas flow and gas type (H2 and CO2), and high temperature residence time on the morphology of the products were investigated. The results revealed that a higher temperature, proper H2 and CO2 flow, and a shorter residence time are favorable for the production of graphene with fewer layers, fewer defects, and higher purity. A suitable H/C ratio and the formation of macromolecular carbonaceous clusters are essential factors for the synthesis of semi-graphite particles. The overgrowth of graphene and the aggregation of small molecules of PAHs in the low temperature region are favorable for the formation of carbon nanospheres.

Pore Structure and Fractal Characteristic Analysis of Gasification-Coke Prepared at Different High-Temperature Residence Times.

An accurate and quantitative description of the pore structure of gasification-coke using fractal geometry could be of great significance to its industrial utilization. In this study, gasification-coke was prepared with low-quality coal blending at different high-temperature residence times to investigate the variation in the pore structure, fractal dimensions, reactivities, and their relationship. The pore structure parameters (e.g., specific surface area, pore volume, and average pore diameter) of gasification-coke were investigated by low-temperature N2 adsorption/desorption and mercury intrusion porosimetry. Fractal dimensions D1 and D2 (at relative pressures of 0–0.5 and 0.5–1, respectively) were calculated using the fractal Frenkel–Halsey–Hill model, and the fractal dimension D3 was obtained using the Menger sponge model. The results show that the pore structure systems of gasification-coke prepared at different high-temperature residence times are continuous and complete, which contributes to the gasification reaction. The variation trend of the macropore structure parameters is more complex than that of micropore and mesopore with the extension of the high-temperature residence time. It is found that D1 is linearly correlated with the micropore specific surface area, indicating that D1 is more suitable for reflecting the roughness of the micropore surface; D2 is linearly correlated with the mesopore volume and can describe the volumetric roughness of the mesopore; and D3 reflects the irregularities and surface roughness of the macropores. Gasification reactivity is closely related to the D2 value, and the reactivity of the gasification-coke may be improved if the number of mesopores is increased by controlling the high-temperature residence time or other pyrolysis conditions. The research results will provide theoretical reference for controlling the gasification reaction of gasification-coke and gasifier design.

Vpliv vnosa toplote na strukturo kompozitne prevleke na osnovi Ni, izdelane z laserskim postopkom

In this paper, Ni-based amorphous composite coatings were fabricated under different heat inputs on a mild-steel substrate using laser cladding with coaxial powder feeding. The microstructure of the coating was studied using a scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The effects of the heat inputs on the amor- phous-phase forming ability of the Ni-based alloy was investigated systematically with experimental and numerical simulation methods. The results show that there was no amorphous phase in the coating when the heat input was 131.3 J/mm. The amorphous-phase fraction increased with a decrease in the laser-cladding heat inputs from 81.3 J/mm to 50.0 J/mm. Then a 3D thermal finite-element (FE) model was built to simulate the temperature field of coaxial laser cladding at different heat inputs using the element birth and death technique. Detailed 3D transient thermal analyses were performed on temperature-dependent material properties. The proposed model was validated with the experimental results. It was found that a decrease in the heat input leads to a lower high-temperature residence time and a higher cooling rate of the melted pool. Consequently, a low heat input can be considered as a necessary condition for the formation of the amorphous phase during the laser-cladding process.

In situ observation of austenite grain growth and transformation temperature in coarse grain heat affected zone of Ce-alloyed weld metal

Laser scanning confocal microscopy (LSCM) was used to study the inhibition of austenite grain growth by the inclusions and the effect of cerium on the trend of acicular ferrite (AF) and ferrite side plate (FSP) transformation temperature in coarse grain heat affected zone (CGHAZ) of Ce-alloyed weld metals. The results showed there were lots of tiny cerium oxides and sulfides inclusions in the CGHAZ of Ce-alloyed weld metals. When the concentration of Ce was 0.021%, the volume fraction of inclusions in weld metal CGHAZ was higher and the inclusion size was smaller, therefore austenite grain size was smaller with the increase of high-temperature residence time. Cerium tended to segregate at austenite grain boundaries, so FSP transformation temperature decreased and FSP transformation was suppressed. On the contrary, AF transformation temperature increased because AF transformation was promoted in CGHAZ of the Ce-alloyed weld metal, especially when the concentration of Ce was 0.021%.

New evidence for lunar basalt metasomatism by underlying regolith

Earth-like δD values reported from lunar mare-basalt apatites have typically been interpreted to reflect the intrinsic isotopic composition of lunar-mantle water. New data indicates that some of these basalts are also characterized by having experienced a slow cooling history after their emplacement onto the lunar surface. This suggests that these basalts may have experienced metasomatism by fluxes generated during the degassing of the lunar regolith induced by the long-duration, high-temperature residence times of overlying basalts.

Synthesis of Titanium Dioxide Nanoparticles Using a Double-Slit Curved Wall-Jet Burner

ABSTRACTA novel double-slit curved wall-jet (DS-CWJ) burner was proposed and utilized for flame synthesis. This burner was comprised of double curved wall-jet nozzles with coaxial slits; the inner slit was for the delivery of titanium tetraisopropoxide (TTIP) precursor while the outer one was to supply premixed fuel/air mixture of ethylene (C2H4) or propane (C3H8). This configuration enabled rapid mixing between the precursor and reactants along the curved surface and inside the recirculation zone of the burner. Particle growth of titanium dioxide (TiO2) nanoparticles and their phases was investigated with varying equivalence ratio and Reynolds number. Flow field and flame structure were measured using particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) techniques, respectively. The nanoparticles were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and nitrogen adsorption Brunauer–Emmett–Teller (BET) for surface area analysis. The flow field consisted of a wall-jet region leading to a recirculation zone, an interaction jet region, followed by a merged-jet region. The DS-CWJ burner revealed appreciable mixing characteristics between the precursor and combustion gases near the nozzle regions, with a slight increase in the axial velocity due to the precursor injection. The precursor supply had a negligible effect on the flame structure. The burner produced a reasonably uniform size (13–18 nm) nanoparticles with a high BET surface area (>100 m2/g). The phase of TiO2 nanoparticles was mainly dependent on the equivalence ratio and fuel type, which impact flame height, heat release rate, and high temperature residence time of the precursor vapor. For ethylene flames, the anatase content increased with the equivalence ratio, whereas it decreased in the case of propane flames. The synthesized TiO2 nanoparticles exhibited high crystallinity and the anatase phase was dominant at high equivalence ratios (ϕ > 1.6) for C2H4, and at low equivalence ratios (ϕ < 1.3) for the C3H8 flame.

Effect of doping and crystallite size on the electrochemical performance of Li4Ti5O12

Defect spinel phase lithium titanate (Li4Ti5O12) has been suggested as a promising negative electrode material for next generation lithium ion batteries. Flame spray pyrolysis has been shown to be a viable fast, one-step process for synthesis of nanoparticulate Li4Ti5O12. However, due to the rapid quenching that is integral to the process the crystallite size remain very small and non-uniform.To overcome this shortcoming a vertical flow tube furnace was used to increase the high-temperature residence time. This resulted in an increase in the crystallite size and crystallinity of the product. As a result of this increase the electrochemical performance of the Li4Ti5O12 was markedly improved.Furthermore, silver doping of the Li4Ti5O12 material can be carried out simultaneously with its synthesis in the FSP process. The resulting nanosized silver particles on the surface of the Li4Ti5O12 particles further improve the electrochemical performance during high current operations.The specific capacities of these high-temperature synthesised pure and silver-doped Li4Ti5O12 nanoparticles were found to increase by up to 6% and 19%, respectively, compared to a commercial reference. Thus the technique provides a simple method for synthesising superior quality Li4Ti5O12 for battery applications.

The effect of hydrogen and oxygen contents on hydride reorientations of zirconium alloy cladding tubes

Abstract To investigate the effect of hydrogen and oxygen contents on hydride reorientations during cool-down processes, zirconium–niobium cladding tube specimens were hydrogen-charged before some specimens were oxidized, resulting in 250 ppm and 500 ppm hydrogen-charged specimens containing no oxide and an oxide thickness of 3.8 μm at each surface. The nonoxidized and oxidized hydrogen-charged specimens were heated up to 400°C and then cooled down to room temperature at cooling rates of 0.3°C/min and 8.0°C/min under a tensile hoop stress of 150 MPa. The lower hydrogen contents and the slower cooling rate generated a larger fraction of radial hydrides, a longer radial hydride length, and a lower ultimate tensile strength and plastic elongation. In addition, the oxidized specimens generated a smaller fraction of radial hydrides and a lower ultimate tensile strength and plastic elongation than the nonoxidized specimens. This may be due to: a solubility difference between room temperature and 400°C; an oxygen-induced increase in hydrogen solubility and radial hydride nucleation energy; high temperature residence time during the cool-down; or undissolved circumferential hydrides at 400°C.

Tensile hoop stress-, hydrogen content- and cooling rate-dependent hydride reorientation behaviors of Zr alloy cladding tubes

250ppm hydrogen-charged (250ppm-H) and 500ppm-H Zr alloy cladding tubes oxidized to 2.5μm at their inner and outer surfaces were employed to examine the effect of tensile hoop stress, hydrogen content, cooling rate and oxygen content on the radial hydride precipitation behaviors during cool-down processes. The oxidized cladding tube specimens were heated up to 400°C and then cooled down to room temperature at cooling rates of 0.3, 2.0 or 8.0°C/min under tensile hoop stresses of 80, 100 or 150MPa. The amount of the radial hydrides precipitated and their growth during the cool-down processes were found to be strongly dependent upon the hydrogen content, tensile hoop stress, cooling rate and oxygen content. The lower hydrogen content, the higher tensile hoop stress, the slower cooling rate and the lower oxygen content generated the larger fraction of radial hydrides and the longer radial hydride length. These phenomena may be explained by the solubility difference between room temperature and 400°C, the effect of tensile hoop stress on the radial hydride nucleation energy, cooling-rate-dependent hydrogen super-saturation and high temperature residence time, and the effect of undissolved circumferential hydrides on the radial hydride precipitation.