Nucleation mechanisms of dynamic recrystallization in Inconel 625 superalloy deformed with different strain rates

The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s?1. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decrease and then increase with increasing strain rate. Meanwhile, the nucleation mechanism of DRX is closely related to the deformation strain rate due to the deformation thermal effect. The discontinuous DRX (DDRX) with bulging of original grain boundaries is the primary nucleation mechanism of DRX, while the continuous DRX (CDRX) with progressive subgrain rotation acts as a secondary nucleation mechanism. The twinning formation can activate the nucleation of DRX. The effects of bulging of original grain boundaries and twinning formation are firstly gradually weakened and then strengthened with the increasing strain rate due to the deformation thermal effect. On the contrary, the effect of subgrain rotation is firstly gradually strengthened and then weakened with the increasing strain rate.

Analysis of the Fractal Growth Characteristics and Nucleation Mechanism of Phosphogypsum-based Materials

Phosphogypsum-based materials (PBM) were synthesized with varied phase compositions of phosphogypsum,portland cement and fly ash.Effects of fractal growth characteristics on physicochemical properties,pore structure,compressive strength,as well as the hydration behaviour and mineralogical conversion of mortars were examined by a multitechnological approach,including mercury intrusion porosimetry,rietved phase analysis,thremal analysis,calorimetry and Fourier transforminfrared spectroscopy analysis.Expermental results indicate that the specimens cured with mosite resulted in higher strength and lower porosity compared with those cured in the drying chamber.In addition,a more complicated course of the aluminate and silicate reactions during the hydration process has been published,with the hydration products mainly consisting of calcium silicate hydrate (C-S-H),portlandite,ettringite,hemicarbonate,monocarboaluminate,calcite,quartz,a mixed AFm passed with carbonate,and hydroxide.After all,the nucleation process is a reaction that can be defined as a solid,liquid and gaseous phases that goes through the four stages of materialization mixing and modification,i e,hydration of low calcium content,secondary hydration,high calcium condensation and geoplymensation,respectively.The rupture,recombination,polymerization reactions of Si-O,Ca-O,Al-O bonds contribute to the nucleation mechanism that serves as the formation of C-S-H in hydration products.

STUDY OF THE NUCLEATION MECHANISM OF α-Al GRAINS AFTER ADDITION OF Al-Ti-B MASTER ALLOYS

Nucleation sites of α-Al grains after addition of an Al-Ti-B master alloy into pure aluminium have been investigated using EPMA. The results show that either TiAl3 or boride particales can nucleate α-Al grains. But the number of TiAl3 nucleants is reduced with the holding time prolonged and the boride-nuclei are increasing gradually. Based on these results, a new refining method, adding molten Al-Ti-B into commercially pure aluminium, which has a quicker and better refining efficiency is presented.

Cerium oxide inclusion nucleation mechanism based on classical nucleation theory and two-step nucleation

It is challenging to assess the mechanism responsible for the nucleation of inclusions in metals at high temperatures.The present work therefore systematically investigates the nucleation of cerium oxide inclusions according to classical nucleation theory and a two-step nucleation mechanism.The nucleation rates and nucleation radii of these inclusions are obtained,and the results demonstrate a considerable difference between theoretical and experimental values.On the basis of a two-step nucleation mechanism,(CeO_(2))_(n) and(Ce_(2)O_(3))_(n)(n=1-6)clusters were constructed and the thermodynamic properties of both these clusters and of cerium oxide nanoparticles were analyzed.In addition,the entropies and heat capacity changes of cerium oxides were determined using first principles calculations and are found to be consistent with literature data.The present data indicate that the cerium oxide inclusion nucleation pathway can be summarized as[Ce]+[O]→(CeO_(2))n/(Ce_(2)O_(3))_(n)→(Ce_(2)O_(3))_(n)→(Ce_(2)O_(3))_(2)→core(Ce_(2)O_(3)crystal)-shell((Ce_(2)O_(3))_(2) cluster)nanoparticles→(Ce_(2)O_(3))bulk.

Nucleation mechanisms of dynamic recrystallization for G3 alloy during hot compression

Dynamic recrystallization （DRX） mechanisms of a nickel-based corrosion-resistant alloy, G3, were investigated by hot compression tests with temperatures from 1050 to 1200 ℃ and strain rates from 0.1 to 5.0 s-1. Deformation microstructure was observed at the strain from 0.05 to 0.75 by electron backscatter diffraction （EBSD） and transmission electron microscope （TEM）. Work hardening rate curves were calculated to analyze the effect of deformation parameters on the nucleation process. Results indicate that strain-induced grain boundary migration is the principal mechanism of DRX. Large annealing twins promote nucleation by accumulating dis- locations and fragmenting into cell blocks. Continuous dynamic recrystallization is also detected to be an effective supplement mechanism, especially at low temperature and high strain rate.

Altering polythiophene derivative substrates to explore the mechanism of heterogeneous lithium nucleation for dendrite-free lithium metal anodes

Lithium metal batteries(LMBs)possess outstanding theoretical energy density and have attracted widespread attention as the next generation of energy storage devices for various crucial applications.However,the commercialization of LMBs has to simultaneously overcome numerous challenges,such as inferior Coulombic efficiency and cycling performance,high self-discharge,and complicated interfacial reactions.It has traditionally been an enormous challenge about the uniform deposition of lithium on the surface of current collector to relieve the formation of lithium dendrites.In this study,a novel efficient strategy of plating uniform lithiophilic polythiophene derivatives substrates on Cu foils was developed and the nucleation mechanism of Li ions on polythiophene derivatives substrates was further explored.We first explored the interaction between polythiophene derivatives substrates and Li ions by firstprinciples calculations,and found shorter side chains of polythiophene derivatives can enhance the adsorption energy and promote the diffusion rate of Li ions.Polythiophene derivatives substrates have a large number of dispersive lipophilic sites and Li ions diffusion channels in the main chain,which can effectively regulate the nucleation and growth stages of Li ions deposition.We further found polythiophene derivatives with different side chains can induce the electrodeposition of Li ions with different morphology,while the polythiophene derivatives with the shortest side chains can contribute to the most excellent cycle efficiency,resulting in a uniform lithium deposition with less lithium dendritic growth experimentally.

Electrodeposited PtNi nanoparticles towards oxygen reduction reaction:A study on nucleation and growth mechanism

In this work,highly monodispersed Pt-Ni alloy nanoparticles were directly deposited on carbon substrate through a facile electrodeposition strategy in the solvent system of N,N-dimethylformamide(DMF).A series of carbon supported Pt-Ni alloy electrocatalysts were synthesized under different applied electrode potentials.Among all as-obtained samples,the Pt-Ni/C electrocatalyst deposited at-1.73 V exhibits the optimal specific activity up to 1.850 mA cm^(-2)at 0.9 V vs.RHE,which is 6.85 times higher than that of the commercial Pt/C.Comprehensive physiochemical characterizations and computational evaluations via density functional theory were conducted to unveil the nucleation and growth mechanism of PtNi alloy formation.Compared to the aqueous solution,DMF solvent molecule must not be neglected in avoiding particle agglomeration and synthesis of monodispersed nanoparticles.During the alloy co-deposition process,Ni sites produced through the reduction of Ni(Ⅱ)precursor not only facilitates Pt-Ni alloy crystal nucleation but also in favor of further Pt reduction on the Ni-inserted Pt surface.As for the deposition potential,it adjusts the final particle size.This work provides a hopeful extended Pt-based catalyst layer production strategy for proton exchange membrane fuel cells and a new idea for the nucleation and growth mechanism exploration for electrodeposited Pt alloy.

Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys

Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.

Investigation of Coercivity Mechanism for Nd-Fe-B Magnets Prepared by Combination of Strip-Casting with Hydrogen Decrepitation Techniques

The coercivity mechanism of Nd Fe B magnets prepared by combination of strip casting with hydrogen decrepitation techniques was investigated. The microstructure of (Nd 0.935 Dy 0.065 ) 14.5 Fe 79.4 B 6.1 magnet was observed. The average grain size is about 6～12 μm. The magnetizing field dependence of the hardmagnetic properties for the (Nd 0.935 Dy 0.065 ) 14.5 Fe 79.4 B 6.1 and the temperature dependence of the coercivity for the Nd 14.5 Fe 79.4 B 6.1 were investigated. Results show that the coercivity for magnets prepared by the combination of strip casting with hydrogen decrepitation techniques is controlled by the nucleation mechanism.

Mechanism and Inhibition of Grain Coarsening of Al-Mg-Si Alloy in Hot Forming

A high-Ti 6061 alloy was rolled with strains up to 0. 8 - 2. 0 and at 350 - 550 ℃ . Microstructures that developed during deformation and subsequent solution heat treatment (SHT) were observed by using optical and transmission electron microscopy. Microstructure evolution during SHT depends mainly on the initial rolling temperature,and it was found that the higher this temperature is,the coarser the grains are. After rolling at 400 ℃ ,well-defined cells and subgrains were formed, which induced further sites for recrystallization nucleation during subsequent SHT. The recrystallization mechanism was found to be subgrain rotation,with a final grain size smaller than 200 μm. Increasing the rolling temperature to 500 ℃ results in a low density of dislocations distributed uniformly in the deformed matrix and fewer nucleation sites during subsequent SHT. The recrystallization mechanism is grain boundary bulging,while the final grain size approaches several millimeters. Finally,a hot forming process of high-Ti 6061 alloy for inhibiting grain coarsening was proposed,and verified by experiments.

Theoretical investigation of lithium ions’ nucleation performance on metal-doped Cu surfaces

Lithium metal batteries(LMBs)of an ultrahigh theoretical energy density have attracted lots of attentions for a wide range of practical applications.However,there are still numerous challenges in LMBs system,such as poor cycling performance,complicated interfacial reactions,low Coulombic efficiency,and uncontrollable lithium dendrites.Understanding Li^+ions’nucleation mechanism is essential to tackle the uncontrolled growth of lithium dendrites.However,the nucleation behavior of Li+ions is interfered by the structural complexities of existing substrates during the reduplicative plating/stripping process and the rational mechanism of uniform nucleation of Li^+ions has not been clearly understood from the theoretical point of view.In our work,first-principles theoretical calculations are carried out to investigate the Li^+ions nucleation performance on metal-doped Cu surfaces(MDCSs)and the key descriptors that determines the properties of various MDCSs are systematically summarized.It is found that the introduction of heterogeneous doping Ag and Zn atoms will induce a gradient adsorption energy on MDCSs,and such gradient deposition sites can reduce the diffusion barriers and accelerate the diffusion rates of Li+ions dynamically.By maneuvering the Li+ions nucleation on MDCSs,a dendrite-free lithium metal anode can be achieved without the use of porous matrixes and complex synthesis process,which can be attributed to suppress the uncontrollable lithium dendrites for realizing the high-efficiency LMBs.

Effects of PVP on the preparation and growth mechanism of monodispersed Ni nanoparticles

Monodispersed Ni nanoparticles were successfully prepared by chemical reduction with hydrazine hydrate in ethylene glycol. The effect of the amount of polyvinylpyrrolidone （PVP-K30） on the preparation of Ni nanoparticles was investigated. X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and high resolution transmission electron microscopy （HRTEM） were employed to characterize the nickel powders. The average nickel particle size can be controlled from 103 nm to 46 ran with increasing the mass ratio of PVP to NiCl2·6H2O. The particles are spherical in shape and are not agglomerated. A possible extensive mechanism of nickel nanoparticle formation has been suggested.

Investigation of the coercivity mechanism for Nd-Fe-B based magnets prepared by a new technique of strip casting

The coercivity mechanism of Nd-Fe-B based magnets prepared by a new techniqueof strip casting was investigated. Different from the traditional magnets, α-Fe phases aredifficult to be found in Nd-Fe-B magnets prepared by strip casting. Meanwhile, the rich-Nd phasesoccur not only near the grain boundaries of main phases, but also within the main-phase grains.Investigation on the magnetizing field dependence of the coercivity for the(Nd_(0.935)Dy_(0.065))_(14.5)Fe_(79.4)B_(6.1) magnet and the temperature dependence of thecoercivity for the Nd_(14.5)Fe_(79.4)B_(6.1) magnet hav been done. Results show that coercivitiesfor strip casting magnets are controlled by the nucleation mechanism.

Identification of Different Cobalt Nucleation on Glassy Carbon

The nucleation mechanisms of cobalt from sulfate solutions were studied by utilizing the electrochemical technique, chronoamperometry. It was found that the recorded current-time transients introduced from 1.0 mol/L CoSO4 solution were complexes with unusual shapes. All characteristic features were identified as separate process. The instantaneous or progressive nucleation with 2D or 3D growth exists during the cobalt deposition, depending on the applied potentials.

Electrodeposition behavior of bright nickel in air and water-stable betaine·HCl-ethylene glycol ionic liquid

The electrodeposition behaviors of nickel on glassy carbon（GC） and carbon steel（CS） electrodes were investigated in the14.3%-85.7%（mole fraction） betaine.HCl ethylene glycol（EG） ionic liquid using cyclic voltammetry and chronoamperometry.The results indicated that the reduction of Ni（Ⅱ） on CS electrode via a diffusion-controlled quasi-reversible process was much more facile and easier than that occurred on GC electrode,which followed a diffusion-controlled three-dimensional instantaneous nucleation and growth.Scanning electron microscopy was used to observe that the deposit was dense and contained fine crystallites with average size of（80±4） nm.Energy dispersive spectrometer analysis showed that the obtained deposit was metallic nickel.X-ray diffraction spectroscopy indicated that（111） plane was the most preferred crystal orientation.The nickel deposit was luminous and bright,and had good adhesion with the CS substrate.

Effect of welding speed on microstructure and mechanical properties of Al−Mg−Mn−Zr−Ti alloy sheet during friction stir welding

Effects of welding speed on the microstructure evolution in the stir zone(SZ)and mechanical properties of the friction stir welding(FSW)joints were studied by OM,XRD,SEM,TEM,EBSD and tensile testing.Compared with the base metal(BM),an obviously fine dynamic recrystallization(DRX)microstructure occurs in the SZ and the DRX grain size decreases from 5.6 to 4.4μm with the increasing of welding speed.Fine DRX microstructure is mainly achieved by continuous dynamic recrystallization(CDRX)mechanism,strain induced boundary migration(SIBM)mechanism and particle stimulated nucleation(PSN)mechanism.Meanwhile,the geometric coalescence and the Burke−Turnbull mechanism are the main DRX grain growth mechanisms.Among all the welding speeds,the joint welded at rotation speed of 1500 r/min and welding speed of 75 mm/min has the greatest tensile properties,i.e.ultimate tensile strength(UTS)of(509±2)MPa,yield strength(YS)of(282±4)MPa,elongation(El)of(23±1)%,and the joint efficiency of 73%.

STUDY ON THE POLYMERIZATION KINETICS AND STABILITY OF P(UA)/MMA MICROEMULSION

Urethane acrylate anionomer (APUA) as a kind of new type polymerizable emulsifier was synthesized using 2,4-toluene diisocyanate (TDI), polypropylene glycol (PPG), 2-hydroxyethyl methacrylate (HEMA) and dimethylolpropionic acid (DMPA). The critical micelle concentration (CMC) of APUA was measured by the methods of conductance and surface tension. The comparative studies between polymerizable emulsifier AUPA and conventional emulsifier sodium dodecyl sulfate (SDS) were carried out in the emulsion polymerization of methyl methacrylate (MMA). Polymerization kinetics, stability, size and morphology of the latex particles were investigated. It was found that in APUA both water soluble initiator potassium persulfate (KPS) and oil soluble initiator 2,2'-azobisisobutyronitrile (AlBN) can start the reaction of MMA, and the polymerization rate and yield were very high. On using AlBN as an initiator, the conversion-time behavior of MMA with APUA as emulsifier was different to that of SDS as emulsifier, signifying a different nucleation mechanism of the polymer latex particle. The average size of the two kinds of particles is about 50 nm. The particle size decreases with increasing emulsifier concentration. On using KPS as the initiator, APUA as emulsifier, cross-linking hydrogel of PMMA would be formed, but SDS was used as emulsifier and the hydrogel of PMMA was not present.

Evolution of Goss texture in thin-walled copper tube at different heat treatment temperatures

The evolution of microstructure,textures,and mechanical properties of thin-walled copper tube during heat treatment was investigated using EBSD technique and tensile test.The results show that the initial deformation textures of pre-drawn thin-walled copper tube are mainly composed of Copper and Y components,while with the increase of temperatures,the textures are transformed into a strong Goss texture gradually.The high-resolution microstructural characterizations indicate that the new Goss recrystallized grains nucleate and grow up within the deformed Copper grains and Y grains in different mechanisms,respectively.The tensile strength of the thin-walled copper tube decreases gradually with the increase of the temperature,while the elongation increases first and then decreases sharply due to the action of grain sizes and texture components.

Ferronickel preparation using Ni-Fe co-deposition process

Nucleation mechanism and technological process for Ni-Fe co-deposition with a relatively high Fe^(2+)concentration surrounded were described,and the effects of Fe^(2+) concentration,solution pH,temperature,and sodium dodecyl sulfonate concentration were investigated.Electrochemical experiments demonstrate that iron's electrodeposition plays a leading role in the Ni-Fe co-deposition process,and the co-deposition nucleation mechanism accords with a progressive nucleation.Temperature increase does favor in increasing nickel content in the ferronickel(Ni-Fe co-deposition products),while Fe^(2+) concentration increase does not.When solution pH is higher than 3.5,nickel content in the ferronickel decreases with pH because of the hydrolysis of Fe^(2+).With the current density of 180 A/m^2,Na_2SO_4 concentration of 100 g/L and Ni^(2+) concentration of 60 g/L,a smooth ferronickel deposit containing 96.21% Ni can be obtained under the conditions of temperature of 60 °C,Fe^(2+) concentration of 0.3 g/L,solution pH of 3 and sodium dodecyl sulfonate concentration of 40 mg/L.

Size, phase-controlled synthesis,the nucleation and growth mechanisms of NaYF_4:Yb/Er nanocrystals

Near-monodisperse NaYF4：Yb/Er nanoparticles（NPs） with controlled size, phases（α,β） and shapes（sphere, and hexagonal plate） were synthesized by adjusting the NaF to RE（RE = Y, Yb, Er） ratios, the reaction temperature and time in the hot surfactant solutions（oleic acid, 1-octadecene） from the improved one-pot thermal decomposition metal trifluoroacetate, and the precursors were prepared via hydrothermal route. The growth kinetics of β-NaYF4 NPs includes several stages： nucleation, growth of aNaYF4, Ostwald ripening, size shrinkage and growth. The results prove that the temperatures are preferred to the phase transformation compared with the NaF content when other experimental conditions are unchanged. Our work will further facilitate the comprehension of the nucleation and growth mechanisms of the NPs, and provide guidance for their controlled synthesis.