Nanocrystalline Grains Research Articles

Supersaturated Antisolvent-Assisted Crystallization for Highly Efficient Inorganic Perovskite Light-Emitting Diodes.

We introduced a strategy to form nanocrystalline CsPbBr3 perovskite films with high luminescence and stability, inhibiting crystal growth using a CsBr supersaturated antisolvent during the antisolvent-assisted crystallization process. We devised this strategy because the supersaturated antisolvent has a higher CsBr concentration over its solubility limit in the saturated antisolvent and consequently will form the smaller perovskite nanocrystalline grains due to the quick precipitation of the CsBr. Here, the CsBr is chosen as a model inorganic antisolvent additive for a crystal growth inhibitor and a passivator. Consequently, we have achieved a nanocrystalline CsPbBr3 film with an average grain size of ∼39 nm by the CsBr supersaturated antisolvent-assisted crystallization process, which is about 41% smaller than the average grain size of the control sample. Hence, the perovskite thin film exhibited a much higher photoluminescence quantum yield than the control film. The maximum current efficiency (CEmax) and the maximum external quantum efficiency (EQEmax) of the corresponding CsPbBr3 perovskite light-emitting diodes (PeLEDs) were approximately twice higher (CEmax of 94.64 cd A-1 and EQEmax of 22.93%) than those of the control device. Simultaneously, the inclusion of CsBr additives played a multifunctional role in diminishing the leakage current of PeLEDs and enhancing their operational lifetime.

A model of thermodynamic stabilization of nanocrystalline grain boundaries in alloy systems

Nanocrystalline (NC) materials are intrinsically unstable against grain growth. Significant research efforts have been dedicated to suppressing the grain growth by solute segregation, including the pursuit of a special NC structure that minimizes the total free energy and completely eliminates the driving force for grain growth. This fully stabilized state has been predicted theoretically and by simulations but is yet to be confirmed experimentally. To better understand the nature of the full stabilization, we propose a simple two-dimensional model capturing the coupled processes of grain boundary (GB) migration and solute diffusion. Kinetic Monte Carlo simulations based on this model reproduce the fully stabilized polycrystalline state and link it to the condition of zero GB free energy. The simulations demonstrate the emergence of a fully stabilized state by the divergence of capillary wave amplitudes on planar GBs and by fragmentation of a large grain into a stable ensemble of smaller grains. The role of solute diffusion in the full stabilization is examined. Possible extensions of the model are discussed.

Tailoring microstructure in a soft-magnetic Fe-based amorphous-nanocrystalline alloy for high resistivity according to electrical percolation threshold

Superior soft-magnetic materials are necessary for the development of modern magnetic devices with energy-saving and high-power density requirements. However, improving the magnetism by nanocrystallization always brings about the sacrifice of resistivity, presenting a common trade-off in Fe-based amorphous-nanocrystalline alloys. Here, the comprehensive merits of both superior soft-magnetic properties (high saturation magnetization of 1.81 T and low coercivity of 3.8 A/m) and high resistivity of 117.2 μΩ·cm were obtained by precisely tailoring amorphous-nanocrystalline microstructure close to electrical percolation threshold for a Fe82.5B12P2C1Cu0.5Co2 amorphous alloy. The soft-magnetic properties are attributed to the low magnetic anisotropy stemming from high nuclei number density and ultrafine nanocrystalline grains of 9.2 nm. The high resistivity is associated with the electrical percolation behavior with a nanocrystalline volume threshold of 14.8 % in the composite alloy. The results provide an effective strategy to overcome the trade-off in traditional amorphous-nanocrystalline alloys, significant for applications in high-frequency, high-power, and energy-saving devices.

Twin inheritance effect of thermomechanical-processing NiTiCu shape memory alloy

NiTiCu shape memory alloy undergoes thermomechanical processing which deals with local canning compression followed by annealing at 300, 450 and 600 °C, respectively. In particular, formation of twins is dependent upon size of grains. In the case of annealing at 300 °C, nanocrystalline NiTiCu specimen is fabricated, where a small number of nanotwins are observed and the smaller nanocrystalline grains contributes to suppressing the formation of twins. In addition, twin inheritance effect of NiTiCu shape memory alloy is revealed during thermomechanical processing which deals with local canning compression followed by annealing at 450 and 600 °C, respectively. {112} B2 austenite twin, (001) B19′ martensite twin and (100) B19′ martensite twin are found in NiTiCu specimen annealed at 450 °C. In addition to (001) B19′ martensite twin, {114} B2 austenite twin appears in NiTiCu sample annealed at 600 °C. Formation of {114} twin results from transformation of 201̄ B19′ martensite twin during reverse martensite transformation, whereas formation of {112} twin stems from transformation of {113} B19′ martensite twin during reverse martensite transformation. During subsequent martensite transformation, {114} and {112} twins are so stable that they are unable to be transformed into the corresponding 201̄ and {113} twins.

Interdiffusion behaviors and mechanical properties of Zr–Hf system

In this work, Zr–Hf diffusion couples were firstly prepared by Spark Plasma Sintering (SPS) method and the diffusion behavior and mechanical properties of the Zr–Hf system in temperatures range from 1300 to 1600 °C were investigated in detail. The microstructure characterization by SEM and TEM reveals that Zr–Hf diffusion zone form some amorphous and nanocrystalline grains in local area. Then the hardness and Young's modulus of the Zr–Hf system in the diffusion zone were tested and the results show that the hardness and Young's modulus of the alloy system was enhanced by solid solution Hf element, and the maximum hardness and Young's modulus in the diffusion zone reached to 10.74GPa and 203.5GPa, respectively. Finally, based on the profiles of Electron probe microanalysis (EPMA), the interdiffusion coefficient is composition-dependent. The value calculated by Sauer-Freise method is between 10−13 m2/s and 10−11 m2/s, which indicating that SPS diffusion annealing significantly enhances the diffusion rate of the Zr–Hf system. Meanwhile, the current direction has negligible effect on the diffusion of Zr–Hf system and the interdiffusion coefficient decreases slowly with increasing Hf concentration. The diffusion activation energy Q and the frequency factor D0 of the Zr–Hf binary system in this experiment ranges from 196 to 215 kJ/mol and 3.9 × 10−6 to 6.8 × 10−5 m2/s, respectively.

Improving Electrical Conductivity of LiFePO4 through Advanced Synthesis and Multidoping Techniques

Extensive research has been conducted to enhance the electrical conductivity of LiFePO4. Several techniques, including doping with metal cations, synthesizing nanocrystalline grains, and carbon coating, have been employed [1]. Recent advances in material synthesis have revolutionized LiFePO4, such as depositing conductive carbon coatings on active material particles and exploring surface doping techniques. These advanced approaches have significantly improved the mass transfer rate [2]. High-capacity LiFePO4 materials close to the theoretical specific capacitance have been obtained.Efforts are currently underway to improve the electronic and ionic conductivity of LiFePO4 to enhance its efficiency. However, before it can be widely used, the material's low electronic conductivity and suboptimal performance in high-speed regimes must be overcome. Doping with supervalent cations is an effective method for narrowing the energy gap and increasing the electrical conductivity of LiFePO4 [3]. Additionally, the synthesis of nanocrystalline grains and the deposition of conductive carbon coatings on the particle surface contribute to an increase in mass transfer rate, removing critical performance limitations of LiFePO4. Reducing the size of LiFePO4 to the nanoscale has been identified as a strategic method to shorten the diffusion length of Li-ions and accelerate electron-conducting pathways during charging and discharging cycles, ultimately improving the overall performance of the material.This work compares the doping process of LiFePO4 cathode material using two methods: solid-phase synthesis in a planetary ball mill and spray pyrolysis in an inert gas atmosphere. The studies on the synthesis and modification of LiFePO4 have significant potential to overcome existing limitations and unlock its full potential for integration into high energy density batteries. The above multidoping methods enable the production of doped LiFePO4 materials with specific capacitance approaching theoretical values. Acknowledgments This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP19677233).

Investigation of the growth kinetics of Streptococcus mutans bacteria on Zr-C coating surfaces deposited on 316L stainless steel substrates

The conducted research aims to describe the kinetics of Streptococcus mutans bacteria growth on the surface of Zr-C coatings with varying carbon content deposited on 316L medical-grade stainless steel substrates.The coatings were deposited using the MS PVD (Magnetron Sputtering Physical Vapour Deposition) technique at a constant temperature of 400C. Varying carbon contents in the coatings were achieved by changing the flow rate of acetylene during the process. The dynamics of bacteria growth cultivated at 37C were examined on the surface of the coatings for incubation times ranging from 0 to 72 hours. Generalised logistic functions were utilised for the mathematical description of the obtained results.The produced coatings exhibited varying carbon content, determining the structural composition ranging from a mixture of metallic Zr and ZrC through stoichiometric zirconium carbide to nanocrystalline grains of ZrC in an amorphous carbon matrix. The obtained results unequivocally demonstrate that in the case of ZrC coatings, the carbon content influences both the bacterial growth rate during the proliferation phase and the final population of bacteria.In the conducted research on bacterial population dynamics, only a single strain of Streptococcus mutans was considered, and the mathematical description was limited to reaching a pseudo-steady state by the population.The proposed model can successfully be adapted to describe the dynamics of other individual strains of bacteria dwelling on metallic surfaces as well as coatings.The proposed model can serve as a tool for studying, among other things, inflexion points of logistic curves, which are considered as the boundary between the dominance of anabolic and catabolic processes in the bacterial population.

On the fatigue crack growth behavior of nanocrystalline CrMnFeCoNi

The fatigue crack growth (FCG) behavior of the equimolar CrMnFeCoNi Cantor-alloy in the nanocrystalline grain size regime has been explored with special focus on the influence of specimen orientation and the effect of additional heat-treatments. For the synthesis severe plastic deformation using high-pressure torsion (HPT) was used. The results were critically discussed regarding the impact of grain size on the FCG-behavior and compared to a conventional 316L stainless steel in the nanocrystalline state: The reduction of grain size in the Cantor alloy from the micrometer to the nanometer regime invokes crack growth rates being about one order of magnitude higher paired with significantly lower threshold values. Furthermore, the sensitivity of thresholds and crack growth rates in the Paris regime on the applied load ratio in the NC material state is also profoundly reduced. This can be explained based on a diminishing contribution of crack closure effects, especially roughness induced closure. Even though the chemical composition differs distinctively, the crack growth rates and fatigue threshold values of the nanocrystalline Cantor alloy and the stainless steel are comparable with the latter being slightly lower for the CrMnFeCoNi alloy. Moreover, the extent of anisotropy is more pronounced than for 316L. Heat-treatment leading in the NC-Cantor alloy to an increasing hardness, has also an effect on the FCG-rate and depends on the specimen orientation. In addition, an unusual self-annealing behavior affecting the FCG behavior of the Cantor alloy was found.

“Yb modification of bismuth Ferrite: Unveiling Optical, Dielectric, and electrochemical properties for advanced applications”

This study explores the detailed impact of Yb3+ substitutional doping on the structural, optical, dielectric, and electrochemical characteristics of bismuth ferrite. Rigorous structural analysis conducted via X-ray diffraction confirmed the formation of a rhombohedral distorted perovskite structure, within the R3C space group. The investigation of crystallite size showed a reducing trend as Yb3+ content increased. Morphological studies revealed the presence of finely dispersed nanocrystalline grains, exhibiting particle size within the range from 281 to 197 nm. Raman spectroscopy unveiled notable phonon mode shifts towards higher wavenumbers, correlating with increased Yb3+ doping concentrations. Additionally, a discernible reduction in bandgap energy, from 2.15 to 1.98 eV, was observed with increasing doping levels. An improved dielectric response was observed with Yb3+ doping. Electrochemical assessments, employing cyclic voltammetry and galvanostatic charge–discharge techniques, revealed the superior electrochemical performance of the 30 % Yb-doped bismuth ferrite-modified electrode, demonstrating a specific capacitance of 575 Fg−1 at a scan rate of 10 mVs−1. These findings underscore the tailored engineering of Yb-doped bismuth ferrite nanoparticles, positioning them as promising candidates for the next generation of supercapacitor devices.

Mechanism of thermal exposure on the mechanical properties of microtextured Ti60 alloys

In this study, the mechanism of thermal exposure on the mechanical properties of two Ti60 alloys with different micro-texture regions (MTRs) was systematically investigated through macro- and microstructural characterization. It was found that when the alloy was exposed to prolonged thermal exposure at 600 °C for 100 h, the strength of the no-MTR samples increased significantly and the plasticity decreased sharply. In contrast, the MTR samples showed a sharp decrease in strength and plasticity due to the transmissibility of dislocation slip and crack propagation, resulting in the formation of a continuous brittle cleavage plane on the fracture. Meanwhile, the oxide film formed on the surface promotes the formation of early cracks and cleavage planes, and the oxide film serves as the location of surface crack nuclei and creates a notch effect leading to premature fracture of the alloy. It is further found that the oxide film is mainly composed of alternating nanocrystalline grains of Al2O3 and TiO2, and there is an oxygen-rich layer of Ti3O near the matrix, and these nano-oxides increased the brittleness of the oxide film. The strengthening and embrittlement mechanism of the alloy was revealed based on the deformation characteristics, i.e. the plasticity reduction was attributed to the formation of the oxide film and precipitation of the α2 phase on the surface, whereas the inhomogeneous distribution of the α2 phase in the interior led to the formation of microcracks in the interior. The precipitation of (Ti, Zr)6Si3 phase at grain boundaries hinders the dislocation motion and leads to a significant increase in the strength of No-MTR alloys. This study reveals the effects of interactions between MTRs, oxide films and precipitated phases on the thermal exposure properties of Ti60 alloys, providing theoretical support for the stability of titanium alloy properties at elevated temperatures.

Dual-phase competitive behavior in N-type Sn–Bi–Te thermoelectric films achieving high thermoelectric performance

The dual-phase competitive behavior is introduced as an effective strategy to optimize the physical and chemical properties of N-type Bi2Te3 thermoelectric (TE) materials. Controllable SnTe-embedded Bi2Te3 nanocomposites can be synthesized with the addition of excessive Sn into Bi2Te3 by tuning the crystallization behavior under proper thermal heating temperature. Notably, the precipitation temperature of Bi2Te3 increases from 473 ​K for Sn20.9(Bi2Te3)79.1 to 573 ​K for Sn34.4(Bi2Te3)65.6, expanding the controllable temperature span for the presence of SnTe phase. The second-phase nanoprecipitate SnTe can improve electrical conductivity by competing with the Bi2Te3 phase, achieving an increase of four orders of magnitude at the critical temperature of ∼500 ​K. Simultaneously, it increases the interfacial energy filtration effect between nanocrystalline grains, decoupling electrical parameters between conductivity and Seebeck coefficient. Consequently, the high power factor of ∼147 ​μW/mK2 at 650 ​K for optimized Sn26.6(Bi2Te3)73.4 films can be obtained, which is more than twice that of the pure Bi2Te3 material. Our work demonstrates a new physical mechanism to unravel the complicated structure-property relationship by dual-phase competitive behavior during phase transition. This study fills the gap in knowledge on the effects of the SnTe phase regarding the Bi2Te3 system and provides guidance for the innovative design of high-performing inorganic thermoelectrics.

Microstructure evolution and mechanical properties of Cu–9Ni–6Sn alloy during continuous cold deformation process

A Cu–9Ni–6Sn alloy bar with pronounced axial columnar grains and a diameter of 10.5 mm was fabricated by using directional solidification technology, which was directly cold-drawn into a superfine alloy wire with a diameter of 40 μm without intermediate annealing. The strength and microstructure evolutions of the Cu–9Ni–6Sn alloy during the cold drawing were studied. The results indicate that twinning is more likely to occur in fiber structures ranging from 60 to 120 nm. A dual-fiber structure consisting of <111> and <100> orientations formed after cold-drawing. Unexpectedly, a large number of deformation twins were discovered within the <111> fibrous texture and later transformed into detwinning structures, disrupting the axial fibrous texture. The generation of deformation twinning primarily results from Ni and Sn elements disrupting crystal symmetry and reducing stacking fault energy of the alloy and the formation of <111> texture. The combined effects of detwinning structures and dislocation wall induced work-softening of the alloy, enabling high-strain processing and ultimately yielding nanocrystalline grains, i.e., the Cu–9Ni–6Sn alloy underwent cold drawing with a high train of 11.23 and obtained an average grain size of ∼38 nm, which exhibited a tensile strength of 1453 MPa.

Unveiling the microstructure and promising electrochemical performance of heavily phosphorus-doped diamond electrodes

The challenge of doping synthetic diamond with phosphorus stems from the atomic size mismatch between phosphorus and carbon atoms, which previously hindered achieving high phosphorus doping levels. This limitation delayed the exploration of phosphorus-doped diamond (PDD) in electrochemical applications, where it holds potential as a novel and appealing electrode material because PDD uniquely combines diamond's exceptional properties with phosphorus atoms inducing n-type conductivity. In this study, heavily doped PDD electrodes were successfully developed using chemical vapour deposition, followed by comprehensive microstructural and electrochemical characterisations. The influence of phosphorus doping, manipulated via high phosphine gas concentration or time-dependant precursor gas flow control, on the PDD properties was thoroughly examined. PDD layers grown at higher phosphine concentrations demonstrated enhanced phosphorus incorporation, leading to a higher prevalence of fine nano-crystalline diamond grains and non-diamond carbon components, while also slowing the growth rate. Notably, a distinct PDD sample produced under dynamic gas flow with lower phosphine concentration revealed larger grain sizes, increased effective deposition rate, and improved phosphorus levels compared to its counterpart synthesized under static conditions. Cyclic voltammetry in a 1 mol L−1 KCl solution revealed a low double-layer capacitance (<11 µF cm−2) in all as-grown PDD electrodes. However, significant differences between the samples emerged during the experiments conducted with redox probes [Ru(NH3)6]3+/2+ and [Fe(CN)6]3−/4−. Particularly, higher phosphorus content promoted well-developed voltammograms, significantly reduced peak-to-peak separation values, faster electron transfer rates, and increased peak currents. Furthermore, the possibility of using heavily P-doped diamond electrodes for the detection of two organic analytes, dopamine and ascorbic acid, was successfully manifested. All in all, the as-grown, highly P-doped diamond electrodes proved their ability, first time ever, to record well-defined signals of both inorganic redox probes and complex organic compounds, unravelling their potential in electroanalysis and sensor development and broadening the scope of PDD utilisation.

Effects of highly-textured and untextured polycrystalline layers on deformation mechanisms in amorphous submicron-layered materials

Amorphous alloys have high strength, but softening can lead to room temperature brittleness, limiting their applications. Typically, soft means low hardness and yield strength, and the lower the yield stress, the higher the fracture toughness. Two amorphous/crystalline multilayer samples with submicron single layer thickness were prepared. The crystalline layer of one sample is composed of highly-textured (111) nanocrystalline grains, and the other sample is untextured. Indentation experiments proved that the samples were plastically deformed, while the amorphous layer did not form shear bands with decreased layer thickness. The thickness reduction of the amorphous layer in the sample with highly-textured crystalline layers is greater than in the sample with untextured crystalline layers. The strain-hardening ability of the textured crystalline layer is higher, while the corresponding amorphous layer is deformed more severely with free volume annihilation and greater flow with more compact atoms. The amorphous layer corresponding to the untextured crystalline layer absorbs dislocations, and activates shear transformation zones (STZs), increasing the free volume near the interface. The annihilation of the free volume is less than the sample with highly-textured crystalline layers.

Nanocrystalline SmCo12 main-phase alloys with V-doping: Structure stability and magnetic performance

The intermetallic compounds based on the tetragonal ThMn12 prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properties. However, the trade-off between the phase stability and the magnetic performance is often encountered in the ThMn12-type magnets. This work was focused on the effects of V doping and nanostructuring on the phase stability and magnetic properties of ThMn12-type Sm-Co-based magnets. Novel SmCo12-based nanocrystalline alloys with the SmCo12 main phase were prepared for the first time. The prepared alloys from the optimal design achieved obviously higher coercivity than the isotropic SmFe12-based alloys, together with comparable performance of other magnetic features. The enhancement in the coercivity was ascribed to the pinning of domain walls by the nanocrystalline grain boundaries and stacking faults. First-principles calculations and magnetic structure analysis disclosed that V substitution can stabilize the SmCo12 lattice and elevate its magnetocrystalline anisotropy. This study provides a new approach to developing stabilized metastable structured rare-earth-lean alloys with high magnetic performance.

Mechanical and electrochemical properties of (MoNbTaTiZr)1-xNx high-entropy nitride coatings

High-entropy materials possess high hardness and strong wear resistance, yet the key bottleneck for their practical applications is the poor corrosion resistance in harsh environments. In this work, the high-entropy nitride (HEN) coatings of (MoNbTaTiZr)1-xNx (x = 0–0.47) were fabricated using a hybrid direct current magnetron sputtering technique. The research focus was dedicated to the effect of nitrogen content on the microstructure, mechanical and electrochemical properties. The results showed that the as-deposited coatings exhibited a typical body-centered cubic (BCC) structure without nitrogen, while the amorphous matrix with face-centered cubic (FCC) nanocrystalline grain was observed at x = 0.17. Further increasing x in the range of 0.35–0.47 caused the appearance of polycrystalline FCC phase in structure. Compared with the MoNbTaTiZr metallic coating, the coating containing nitrogen favored the high hardness around 13.7–32.4 GPa, accompanied by excellent tolerance both against elastic and plastic deformation. Furthermore, such N-containing coatings yielded a low corrosion current density of about 10−8–10−7 A/cm2 and high electrochemical impedance of 106 Ω·cm2 in 3.5 wt.% NaCl solution, indicating the superior corrosion resistance. The reason for the enhanced electrochemical behavior could be ascribed to the spontaneous formation of protective passive layers over the coating surface, which consisted of the dominated multi-elemental oxides in chemical stability. Particularly, noted that the (MoNbTaTiZr)0.83N0.17 coating displayed the highest hardness of 32.4 ± 2.6 GPa and H/E ratio at 0.09, together with remarkable corrosion resistance, proposing the strongest capability for harsh-environmental applications required both good anti-wear and anti-corrosion performance.

Strengthening and precipitation hardening mechanisms of surface-mechanically treated 17-4PH stainless steel

Achieving ultra-high strength without sacrificing too much ductility is the focus of attention in nanostructured materials. Here, the strengthening mechanism and property enhancement of surface-mechanically treated 17-4PH stainless steel (SS17-4PH) were investigated. Our findings show that a grain refinement and elongated lath-like martensitic grain (~ 50 nm thick) could be produced after surface treatment. The grain size remains in the nanoscale, and random crystallographic orientations with the presence of nanocrystallites characterize the nanocrystalline grains formed on the treated sample. This contributes to the property enhancement with a yield strength of about 901 MPa and a reduced elongation to failure of about 17%. The atom probe tomography (APT) characterization unveiled the emergence of high-density precipitate (Cu-rich) at the material surface, with a number density of about 2.6255 × 1024 m−3 and an average radius of 2.22 nm. Besides, the dislocation activities caused by SMAT result in the gradual breakdown of precipitates into smaller sizes and final dissolution in the matrix, increasing the number of nucleation sites and leading to more grain refinement processes. The grain boundary, dislocation densities, and the Cu-rich precipitate greatly influence the strengthening mechanism of surface-treated SS17-4PH.

Molybdenum-Doped ZnO Thin Films Obtained by Spray Pyrolysis.

A batch of ZnO thin films, pure and doped with molybdenum (up to 2 mol %), were prepared using the spray pyrolysis technique on glass and silicon substrates. The effect of molybdenum concentration on the morphology, structure and optical properties of the films was investigated. X-ray diffraction (XRD) results show a wurtzite polycrystalline crystal structure. The average crystallite size increases from 30 to 80 nm with increasing molybdenum content. Scanning electron microscopy (SEM) images demonstrate a smooth and homogeneous surface with densely spaced nanocrystalline grains. The number of nuclei increases, growing over the entire surface of the substrate with uniform grains, when the molybdenum concentration is increased to 2 mol %. The estimated root mean square (RMS) roughness values for the undoped and doped with 1 mol % and 2 mol % of ZnO thin films, defined by atomic force microscopy (AFM), are 6.12, 23.54 and 23.83 nm, respectively. The increase in Mo concentration contributes to the increase in film transmittance.

New insights into the immobilisation of Ce(IV) in Portland cement: Properties, hydration, microstructure and occurrence status of Ce

The immobilisation mechanism of Pu(IV) by Portland cement-based material is not well understood. This study aims to reveal the immobilisation mechanism and occurrence status of Ce(IV) (chemical analogue of Pu(IV)) in Portland cement paste. The addition of Ce(NO3)4 first slightly retarded then accelerated the early-age hydration of Portland cement, thereby resulting in an increase of compressive strength by 29 %. The main contributor to immobilisation of Ce is Portland cement rather than zeolite. The hydration products were not altered by Ce(NO3)4 addition, whereas the hydration degree and mean chain length of C-(Al/Ce)-S-H increased. Over 99.99 % of Ce was immobilised by synthesised C-S-H. A analysis of the synthesised C-S-H confirmed the formation of C-Ce-S-H, where Ce tetrahedra took the bridging site of silicate chain of C-Ce-S-H. Nano-crystalline CeO2 grains were identified, which intermixed with C-Ce-S-H. Approximately 90 % of Ce were immobilised by C-Ce-S-H, and the rest exist as nano-crystalline CeO2 grains.

Study on the mechanical properties and deformation mechanism of copper with different volume fractions of gradient structure

In this study, ultrasonic rolling process (USRP) were performed on the rolled copper samples (with an initial grain size of 11.4 μm) to obtain the gradient structure (GS), which comprises nanocrystalline layer (NL), deformed layer (DL), and center layer (CL). The different GS layer (NL and DL) volume fractions of samples were obtained by performing different passes of USRP after rolling, and the effect of the GS layer volume fractions on the mechanical properties was further studied. The morphology and structure of (unrolled, rolled and rolled + USRP) samples were characterized by electron backscattering diffraction (EBSD) and transmission electron microscope (TEM). In-situ tensile testing was used to investigate the tensile deformation behavior of the GS sample. The results show that the rolled + USRP (12 passes) sample with the thickest GS layer (volume fraction of 42%) has the greatest strength (yield strength (YS) 262 MPa and ultimate tensile strength (UTS) 325 MPa). The fine grains, dislocations and textures jointly strengthen the GS sample by increasing the force required for dislocation slip, and their contribution to YS is 51.3%, 44.4% and 4.3%, respectively. In addition, the nanocrystalline grains of GS layer make microcracks evenly distributed and hard to gather, to efficiently hinder cracks propagation and result in good ductility of GS samples. This study provides an effective method to obtain GS materials with good comprehensive properties and a deeper understanding of their deformation behavior and strengthening mechanism.