Morphology Evolution Mechanism Research Articles

4D evolution of Cr23C6 precipitates in neutron-irradiated and annealed HT-UPS steel observed via synchrotron micro-computed tomography

High-temperature-ultrafine precipitate strengthened (HT-UPS) steel is a potential structural material for advanced nuclear reactors; however, its irradiation response is not well understood. This research provides insight into irradiation-induced effects, such as precipitate evolution mechanisms and four-dimensional morphological evolution, in HT-UPS steel using synchrotron micro-computed tomography. Identical specimens were characterized pre-irradiation and post-irradiation following neutron exposure up to 0.3 displacements per atom at 600 °C. Irradiation effects were also differentiated from the annealing response of precipitates. Following neutron irradiation, the average Cr23C6 precipitate size reduced, affected by the synergy of nucleation and growth, ballistic dissolution, and inverse coarsening, which was observed at fluences an order of magnitude lower than previously observed. Annealing at 600 °C for 32 h increased the average Cr23C6 precipitate size and decreased the phase fraction, attributed to precipitate coarsening. The precipitate morphology evolution and resultant mechanisms can be utilized to parameterize and validate microstructural models simulating radiation damage or annealing.Graphical abstract

Fabrication of REVO4 films via sacrificial conversion from layered rare-earth hydroxide (LRH) films: the investigation of the transition mechanism and their photoluminescence.

Rare-earth orthovanadate REVO4 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Y) films were directly synthesized within 2 hours by sacrificial conversion from electrodeposited layered rare-earth hydroxide (RE2(OH)5NO3·nH2O) films at pH ∼ 10, without subsequent heat treatment. Detailed characterization of the products was achieved by combined X-ray diffraction, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence excitation and photoluminescence. The mechanisms of phase and morphology evolution from Y2(OH)5NO3·nH2O to YVO4 were unveiled through systematic investigations into the influences of the concentration of the anion sources (Na3VO4) and the reaction temperature. The effects of lanthanide contraction on the phase structure and particle morphology of the REVO4 films were also clarified. Additionally, the photoluminescence of RE3+ activators (RE = Eu, Dy, and Eu and Dy) was elaborated with YVO4 as a representative host lattice, and the color-tunable emission and energy transfer from Dy3+ to Eu3+ were also investigated. Electrodeposition combined with a hydrothermal anion exchange technique established in this study led to the rapid synthesis of REVO4 films, and it might have wide implications for the generation of other types of inorganic functional films.

Morphology evolution and breakdown mechanism of cross‐linked polyethylene (XLPE)–silicone rubber (SiR) interface induced by silicone grease diffusion

Silicone grease (SG) is used for lubrication during cable accessory installation and can penetrate into the silicone rubber (SiR), leading to properties deterioration of the SiR. In this study, the effects of SG on the breakdown characteristics of the cross-linked polyethylene (XLPE)–SiR interface are investigated. First, the variation of the XLPE–SiR interface breakdown voltage with SG coating time is experimentally explored. The interface breakdown voltage significantly increases after SG is applied, remains stable for coating times of up to approximately 144 h and then rapidly decreases; the minimum interface breakdown voltage is lower than that without the SG coating. Next, the effects of SG on the chemical composition and surface topography of the SiR are examined by infrared spectroscopy and optical profilometry, respectively. The SG penetration does not change the functional groups of the SiR but significantly increases its surface roughness. Finally, the interface electric-field distribution after coating with SG is analysed by finite-element simulation, revealing that the residual SG at the interface distorts the interface electric field after a long coating time. The increase in the SiR surface roughness caused by SG diffusion and the interface electric-field distortion caused by the residual SG together lead to the decrease of the interface breakdown voltage.

Manipulating the film morphology evolution toward green solvent‐processed perovskite solar cells

AbstractHigh‐performance perovskite solar cells (PVSCs) with low energy consumption and green processing are highly desired, but constrained by the difficulty in morphology control and the poor understanding on morphology evolution mechanisms. To address this issue, here we studied the effect of antisolvents on the perovskite film formation. We found that both the antisolvents and the perovskite composition affect the perovskite film morphology greatly via influencing the intermediate phase, and different perovskite compositions require different antisolvents to reach the optimal morphology. This provides the opportunity to achieve high‐performance PVSCs with green antisolvent, that is, isopropanol (iPA) by changing the perovskite compositions, and leads to a power conversion efficiency (PCE) of 21.50% for PVSCs based on MA0.6FA0.4PbI3. Further, we fabricated “fully green” PVSCs with all layers prepared by green solvents, and the optimal PCE can reach 19%, which represents the highest among PVSCs with full‐green processing. This work provides insight into the perovskite morphology evolution and paves the way toward “green” processing PVSCs.

Study on dynamic behavior of water droplet impacting on super-hydrophobic surface with micro-pillar structures by VOF method

Super-hydrophobic surfaces have been widely developed due to their unique properties, such as adhesion reduction and corrosion inhibition. It is of great significance to explore droplet dynamic process when impacting on super-hydrophobic surface, which can contribute to understanding the mechanism of super-hydrophobicity, and designing self-cleaning surfaces with ultralow adhesion and excellent corrosion resistance. Herein, three-dimensional (3D) numerical model was developed to study the droplet dynamic behaviors on super-hydrophobic NiTi surface. The volume of fluid (VOF) method was carried out to track the multi-phase flow interface and then predict droplet shape evolution during the spreading, retraction, and rebounding stages. In particular, the compression- and stretch-rebounding behaviors were investigated in detail. Based on the results of numerical simulation, the emphasis was placed on the relationship between droplet shape transformation and internal velocity/pressure distribution, revealing the mechanism of droplet morphological evolution during the impingement process. Then the experimental investigations were conducted on the planar and super-hydrophobic NiTi surfaces at different impact velocities to further verify the simulation models. It is indicated that the falling droplet would directly deposit on the planar surface, while it could fully rebound off the pillar-patterned super-hydrophobic surface. Moreover, the motion mechanism of droplet impacting on super-hydrophobic surface was elaborated, which can provide an essential instruction to effectively reduce liquid adhesion and improve anticorrosion ability for the NiTi material.

Morphology evolution mechanisms and localized structural modification of repaired sites on fused silica optics processed by CO2 laser rapid ablation mitigation

In order to in-depth study the surface morphology formation mechanism and surface quality control methods of fused silica repaired sites, numerical simulation and experimental method were firstly used to analyze the process of CO2 laser rapid ablation mitigation, as well as the relationships between processing parameters, repaired angle and surface quality. Then the physical problems of the heat-affected zone, fictive temperature and structure relaxation under the irradiation of pulsed laser were studied through the mathematical model and Raman spectroscopy system. The studies found that the fixed depth morphology was formed starting from the third track’s laser scanning during the processing of fused silica by the pulsed laser that moved according to the arc trajectory. The bottom of the processed morphology presented uneven concave-convex features, which was different from the uniform topography formed by the laser linear scanning processing. The processing angle decreased as the trajectory indentation increased, while there was no clear variation law between the processed surface quality and the indentation. The thickness of the heat-affected zone characterized by the fictive temperature was consistent with the experiment, and it was proportional to the laser pulse width. The negative factors caused by the thermal effect in the laser repair process could be suppressed by reducing the laser pulse width. These studies can provide guidance for the optimization of the CO2 laser repair process and the improvement of the repaired surface quality.

Microstructure and ablation behaviour of a Cf/SiC-Al composite prepared by infiltrating Al alloy into Cf/SiC

To utilise the heat-absorption effect of sweating and sealing protection effect of the oxide layer, Al alloy was introduced into porous Cf/SiC composite using pressure-infiltration method. Microstructure, compositions, mechanical properties of the infiltrated composites were studied. The ablation properties, ablation surface morphology evolution and ablation mechanism of the Cf/SiC-Al composites were investigated for the first time. Results show that the bending strength of Cf/SiC-Al reached 349.8 MPa, which was 58.5% higher than the 220.7 MPa of Cf/SiC composite. Compared with Cf/SiC composites, linear ablation rates of Cf/SiC-Al composites decrease nearly by two orders of magnitude. It was also found that the transpiration cooling of the aluminum alloy in the composite was prior to the mechanical denudation of the Cf/SiC composite. The excellent anti-ablative properties were also attributed to self-sealing protection of ablation products, which played important roles in reducing the degree of thermochemical ablation and preventing matrix ablation.

Diffusion and mechanical properties of Ti2AlNb and TA15 interface: From experiments to molecular dynamics

The experiments and molecular dynamics simulations were employed to further understand the morphology evolution and failure mechanism of the TA15/Ti2AlNb interface. The results show that the asymmetric diffusions, caused by the difference of the diffusion coefficient and crystal structure, have played a significant role in the microstructure and mechanical properties. The diffusivity of Ti elements from TA15 was much better than those Nb and Al from Ti2AlNb base alloy owing to its higher diffusion coefficient. The macro joints are brittle fractures near the TA15 base zone, and excessive holding time will reduce the tensile strength and plasticity of the joint while increasing the temperature can enhance the strength and plasticity due to the promotion of diffusion and improvement of the microstructure. However, the nano joints are ductile failures owing to size effects. Time has little effect on the mechanical properties of nano joint, while an increase in temperature could improve the strength and plasticity. The combination of MD simulations and experiments provides new approaches for the study of deformation mechanisms and microstructure evolution.

Interface microstructure morphology and formation evolution mechanism of Al-1060/Cu-T2 composites fabricated by explosive welding method

ABSTRACT Aluminum–copper composite is an attractive candidate for electronic industry and power industry because of excellent electrical and thermal conductivity. In this work, the explosive welding technique was successfully employed to prepare the Al/Cu composite. The interface microstructure morphology was characterized using the optical microscopy (OM), field emission scanning electron microscopy (FSEM) and electron backscatter diffraction (EBSD). Meanwhile, the interface formation evolution process was simulated using smoothed particle hydrodynamics (SPH) method by ANSYS/LS-DYNA software. The experimental results indicated that the joining interface presents a typical wavy structure and formed melted zones in the vortex region. The formation of intermetallic compounds and strong texture were confirmed at the vortex region. The simulation results revealed the interface formation evolution characteristics and mechanism, and obtained a wavy joining interface, which are in good agreement with experimental results.

Simulation of the removal mechanism of thermo-oxidized layer and surface morphological evolution on TA15 alloy under nanosecond pulsed laser ablation by multiphase flow model

TA15 alloy is susceptible to form bluish-purple thermo-oxidized layer during thermal processing. It is accompanied by surface morphological defects. Laser ablation can remove the thermo-oxidized layer and modify the morphology. However, the pulse width is only a hundred nanoseconds and the spot is in the micron range. It makes the laser-matter interaction investigations extremely challenging. In this paper, a multiphase flow model is established to simulate the removal mechanism of thermo-oxidized layer and surface morphological evolution by nanosecond pulsed laser ablation with different ablation energy densities ( E ). The critical removal conditions of the thermo-oxidized layer were explored. The critical removal window of the thermo-oxidized layer was determined between 0.1 J/cm 2 and 0.35 J/cm 2 . In conjunction with thermodynamic calculations, the reasons for the minimum surface oxygen content between 3.5 J/cm 2 and 8.75 J/cm 2 were discussed. A multiphase flow model was used to analyze the formation of crater under time-dependent. Initially, the molten pool is mainly influenced by the recoil pressure and expands outward. Subsequently, the recoil pressure weakens. Instead, convection caused by surface tension and thermal buoyancy forms double vortex. Finally, depending on the low-temperature matrix, the molten pool solidifies rapidly and forms crater.

Tuning Power Ultrasound for Enhanced Performance of Thermoplastic Micro-Injection Molding: Principles, Methods, and Performances.

With the wide application of Micro-Electro-Mechanical Systems (MEMSs), especially the rapid development of wearable flexible electronics technology, the efficient production of micro-parts with thermoplastic polymers will be the core technology of the harvesting market. However, it is significantly restrained by the limitations of the traditional micro-injection-molding (MIM) process, such as replication fidelity, material utilization, and energy consumption. Currently, the increasing investigation has been focused on the ultrasonic-assisted micro-injection molding (UAMIM) and ultrasonic plasticization micro-injection molding (UPMIM), which has the advantages of new plasticization principle, high replication fidelity, and cost-effectiveness. The aim of this review is to present the latest research activities on the action mechanism of power ultrasound in various polymer micro-molding processes. At the beginning of this review, the physical changes, chemical changes, and morphological evolution mechanism of various thermoplastic polymers under different application modes of ultrasonic energy field are introduced. Subsequently, the process principles, characteristics, and latest developments of UAMIM and UPMIM are scientifically summarized. Particularly, some representative performance advantages of different polymers based on ultrasonic plasticization are further exemplified with a deeper understanding of polymer–MIM relationships. Finally, the challenges and opportunities of power ultrasound in MIM are prospected, such as the mechanism understanding and commercial application.

Research on Multi‐morphology Evolution of MoS2 in Chemical Vapor Deposition

AbstractDue to the special structure and excellent performance, the two‐dimensional mono‐layer MoS2 has received extensive attention in recent years. However, due to technical limitations, the morphology of the synthesized MoS2 is unstable. In the CVD process, at least four morphologies of MoS2 are grown on a piece of SiO2/Si substrate. Here, we discuss the reasons for the formation of different MoS2 morphologies via the experiments and the M‐CV model. Then a possible morphology evolution mechanism is proposed. Research on the relationship among the flow rate, concentration and morphology shows that in the middle of the substrate, CVD is more stable and can produce high‐quality mono‐layer MoS2 films. It provides mechanism guidance for improving the stability of CVD and generating the large‐size mono‐layer MoS2 films.

Grain morphology evolution mechanism of titanium alloy by the combination of pulsed arc and solution element during wire arc additive manufacturing

Coarse columnar grains formed during titanium alloy additive manufacturing (AM) are generally regarded as unfavorable, which trend to cause solidification defects and mechanical property anisotropy. Achieving the columnar to equiaxed transition (CET) of grain structures has been a great challenge, especially for wire arc additive manufacturing (WAAM) with the highly localized heat input and large temperature gradient. The interdependence model is widely used to explain and predict the grain size and evolution during the welding or AM process. However, the thermal undercooling and the molten pool flow which were neglect in its assumption have been found to have obvious effects on the grain morphology evolution. In this work, different deposition experiments with the combination of growth restricting solutes (boron), nucleant particles (La2O3), and pulsed arc were employed to investigate these intrinsic factors which are often neglected how to influence the grain morphology.

Morphology evolution and enhanced broadband photoresponse behavior of two-dimensional Bi2Te3 nanosheets

Bismuth telluride (Bi2Te3), as an emerging two-dimensional (2D) material, has attracted extensive attention from scientific researchers due to its excellent optoelectronic, thermoelectric properties and topological structure. However, the application research of Bi2Te3 mainly focuses on thermoelectric devices, while the research on optoelectronic devices is scarce. In this work, the morphology evolution and growth mechanism of 2D Bi2Te3 nanosheets with a thickness of 12 ± 3 nm were systematically studied by solvothermal method. Then, the Bi2Te3 nanosheets were annealed at 350 °C for 1 h and applied to self-powered photoelectrochemical-type broadband photodetectors. Compared with the as-synthesized Bi2Te3 photodetector, the photocurrent of the photodetector based on the annealed Bi2Te3 is significantly enhanced, especially enhanced by 18.3 times under near-infrared light illumination. Furthermore, the performance of annealed Bi2Te3 photodetector was systematically studied. The research results show that the photodetector not only has a broadband response from ultraviolet to near-infrared (365–850 nm) under zero bias voltage, but also obtains the highest responsivity of 6.6 mA W−1 under green light with an incident power of 10 mW cm−2. The corresponding rise time and decay time are 17 ms and 20 ms, respectively. These findings indicate that annealed Bi2Te3 nanosheets have great potential to be used as self-powered high-speed broadband photodetectors with high responsivity.

Molecular Dynamic Investigation of the Anisotropic Response of Aluminum Surface by Ions Beam Sputtering

Aluminum optics are widely used in modern optical systems because of their high specific stiffness and high reflectance. With the applied optical frequency band moving to visible, traditional processing technology cannot meet the processing precision. Ion beam sputtering (IBS) provides a highly deterministic technology for high-precision aluminum optics fabrication. However, the surface quality is deteriorated after IBS. The interaction between the bombard atoms and the surface morphology evolution mechanism are not clear, and systematic research is needed. Thus, in this paper, the IBS process for single crystal aluminum with different crystallographic orientations are studied by the molecular dynamics method. The ion beam sputter process is firstly demonstrated. Then, the variation of sputter yield of the three crystal faces is analyzed. The sputter yield difference of different crystal surfaces causes the appearance of the relief structure. Then, the gravel structure generates on the single crystal surfaces and dominates the morphology evolution. The state of the atom diffusion of the specific crystal surfaces will determine the form of the gravel structure. Furthermore, the form and distribution of subsurface damage and stress distribution of three different crystal surfaces are analyzed. Although there are great differences in defect distribution, no stress concentration was found in three workpieces, which verifies that the ion beam sputter is a stress-free machining method. The process of IBS and the mechanism of morphology evolution of aluminum are revealed. The regularity and mechanism will provide a guidance for the application of IBS in aluminum optics manufacture fields.

Hierarchical NiCo2O4 and NiCo2S4 nanomaterials as electrocatalysts for methanol oxidation reaction

In this work, Ni foam supported hierarchical NiCo2O4 nanomaterials are successfully prepared through a hydrothermal process and subsequent calcination process, then the hierarchical NiCo2O4 is converted to hierarchical NiCo2S4 through a hydrothermal anion exchange process. The hierarchical nanomaterials are constructed by a nanorod core and nanoribbons shell. The morphology evolution mechanism of the hierarchical NiCo2O4 is studied by exploratory experiments, the results show that the morphology evolution from nanorod to hierarchical nanostructure undergo a solid–solid process, and the calcination temperature is crucial for the formation of the hierarchical nanostructure. The hierarchical NiCo2O4 and NiCo2S4 nanomaterials are both used as electrocatalysts for methanol oxidation reaction in alkaline electrolyte, and the electrocatalytic activity of the NiCo2S4 is higher than that of the NiCo2O4. Cycling test shows the good stability of the NiCo2S4, and the slight loss of activity during cycling is caused by the surface oxidation of NiCo2S4 in alkaline electrolyte. This work indicate that the hierarchical NiCo2S4 is a promising non-noble metal electrocatalyst for direct methanol fuel cells.

3D flower-like NC@V2O3 constructed by nanoparticles for lithium-ion batteries

The morphology and structural engineering of V2O3 anode of lithium-ion batteries plays a significant role in improving the energy storage performance since V2O3 material suffers from tremendous volume changes, self-aggregation and intrinsic poor conductivity. In this work, we devise a novel 3D self-supporting N, C doped-V2O3 (NC@V2O3) composite, which consist of nanoparticles by adding urea to obtain 3D flower-like V2O3 microspheres precursor during the annealing process. The V2O3 microspheres self-assembled with nanosheets is fabricated by one-step solvothermal route. A possible morphological evolution mechanism of fabrication of granular NC@V2O3 is explored by SEM and TEM. As anode in Li+ batteries, NC@V2O3 material exhibits outstanding rate performance of 227 mAh g−1 at the current density of 2 A g−1 and a reversible capacity of 272 mAh g−1 at 0.1 A g−1 after 200 cycles. Such great performance is attributed to granulated NC@V2O3 architecture, which increasing the contact area of electrode-electrolyte and shortening Li+ diffusion pathway. In addition, the doped N and C atoms can create more defects, providing electrochemical active sites and electronic conduction. The achievements of this study may provide new insight into design novel architecture of V2O3 anode.

Chimerism of Carbon by Ruthenium Induces Gradient Catalysis

AbstractImproving the round‐trip efficiency and cycle life of lithium‐oxygen batteries (LOBs) through the cathode design is essential for their employment in electric vehicles. Here, a neoteric chimeric air‐cathode is proposed, in which ultra‐dispersed ruthenium (Ru) nanoparticles are partially confined by microtube walls of free‐standing carbon textiles, but petty parts of Ru with catalytic surfaces are exposed. The special chimeric structure benefits not only for preventing nanocatalysts agglomeration but also tailoring the formation/decomposition mechanisms of lithium peroxide (Li2O2) during oxygen reduction/evolution reactions. Critically, theoretical simulations disclose that the enlarged chimeric catalyst‐support interphase between the Ru and carbon matrix enhances the electron density of Ru particles and then induces a gradient Gibbs free energy of LiO2 adsorption energy at active sites, and thus fundamentally modulates the morphology evolution mechanism of finial Li2O2. In the LOBs, the chimeric electrode affords a remarkably high energy efficiency of 84.1% and long‐term cyclability (260 cycles at 300 mA g−1).

Solid-state diffusion joining of Ti6Al4V parts produced by selective laser melting: joint characteristics and bonding mechanism

This work aims to investigate the microstructure and mechanical properties of Ti6Al4V parts produced by selective laser melting (SLM) in the early stage of solid-state diffusion bonding process. A thermomechanical simulator is employed to carry out the experiment. In the experiment, three diffusion temperatures (850°C, 900°C, and 950°C) are adopted, and the pressure is kept constant. It is found that the higher diffusion temperature reduces the voids on the bonding interface and part interior, and thus it improves the mechanical properties of the joint. The diffusion bonding joints consist of criss-cross acicular α′ martensitic structure. The volume fraction of martensitic α′ decreases with the increase of bonding temperature. Finally, the underlying mechanism of morphological evolution on the diffusion plane is analyzed. The results provide insights on the bonding mechanism of SLM-produced Ti6Al4V in solid-state diffusion joining.

Tuning Polymorphs and Morphology of Microbially Induced Calcium Carbonate: Controlling Factors and Underlying Mechanisms.

Microbially precipitated calcium carbonate (CaCO3) has drawn broad attention due to its potential applications in various areas, for example, biocementation, medicine, and soil reinforcement. Sporosarcina pasteurii (S. pasteurii), formerly known as Bacillus pasteurii, has been investigated for CaCO3 biomineralization due to its high ureolytic activity. A high degree of supersaturation with respect to the presence of bacterial cell wall, extracellular polymeric substances, and organic byproducts of bacterial activity plays an important role in the formation and stabilization of CaCO3 polymorphs. Although microbially induced CaCO3 and its polymorphs have been investigated broadly, the mechanisms of polymorph selection and morphological evolution are not well understood. This study employs ex situ approaches to address the complication of biomineralization in the presence of living organisms and to elucidate how solution chemistry, bacterial activity, and precipitation kinetics alter the polymorphism and morphology of CaCO3 induced by S. pasteurii. The results indicate that in the presence of enough calcium ions and urea (as a carbonate source), the bacterial activity favors the formation and stabilization of vaterite. The morphological observations also provide valuable information on the particles’ microstructure. The morphology of calcite evolves from single crystal to polycrystalline structures, and the morphology of vaterite evolved from spherical to oval-shaped structures on increasing the organic material concentration. Specific functional groups also exert morphological control on CaCO3 polymorphs. However, the sensitivity of the calcite polymorph to the composition and orientation of these functional groups is higher compared to that of the vaterite polymorph. These findings offer important insights that can be used to constrain a set of experimental conditions for synthesizing a certain polymorph ratio for vaterite/calcite or a particular morphology of each polymorph and shed light on the crystallization and phase transformation mechanisms in such complicated bioenvironments.