Grain Size Research Articles

Effects of Li concentration in the precursor solution on NiO thin films deposited using electrostatic spray deposition

Abstract Undoped and Li-added NiO thin films were deposited using electrostatic spray deposition (ESD) techniques. Initially, the NiO thin films displayed minimal contamination, predominantly C and H. The NiO thin films exhibited a flat surface morphology comprising grains of uniform size, approximately 20–30 nm in diameter, and reliable crystal growth, with a full width at half maximum of approximately 0.30 in X-ray diffraction analysis. Moreover, the NiO/ZnO diode demonstrated superior properties when a 5 at. % Li concentration solution was incorporated. The rectification ratio reached approximately 2.3 × 10³ at ± 1.0 V, with an ideality factor of 1.9. Additionally, the NiO/ZnO diodes exhibited remarkable photovoltaic properties even without detailed optimization. These findings underscore the potential of ESD in advancing semiconductor thin-film technology, thereby paving the way for more cost-effective and scalable production methods.

The rotational disruption of porous dust aggregates from ab initio kinematic calculations

The size of dust grains in the interstellar medium follows a distribution where most of the dust mass is made up of smaller grains. However, the redistribution from larger grains towards smaller sizes, especially by means of rotational disruption, is still poorly understood. We aim to study the dynamics of porous grain aggregates undergoing an accelerated rotation, namely, a spin-up process that rapidly increases the angular velocity of the aggregate. In particular, we aim to determine the deformation of the grains and the maximal angular velocity up to the rotational disruption event by caused by centrifugal forces. We precalculated the porous grain aggregate by means of ballistic aggregation analogous to the interstellar dust as input for subsequent numerical simulations. We performed three-dimensional (3D) N-body simulations, mimicking the radiative torque spin-up process up to the point where the grain aggregates become rotationally disrupted. Our simulations results are in agreement with theoretical models predicting a characteristic angular velocity, $ disr $, on the order of $ rad\ $, where grains become rotationally disrupted. In contrast to theoretical predictions, we show that for large porous grain aggregates ($ nm $), the $ disr $ values do not strictly decline. Instead, they reach a lower asymptotic value. Hence, such grains can withstand an accelerated rotation more efficiently up to a factor of 10 because the displacement of mass by centrifugal forces and the subsequent mechanical deformation supports the buildup of new connections within the aggregate. Furthermore, we report that the rapid rotation of grains deforms an ensemble with initially 50:50 prolate and oblate shapes, respectively, preferentially into oblate shapes. Finally, we present a best-fit formula to predict the average rotational disruption of an ensemble of porous dust aggregates dependent on the internal grain structure, total number of monomers, and applied material properties.

Effect of Deposition Temperature on Zn Interstitials and Oxygen Vacancies in RF-Sputtered ZnO Thin Films and Thin Film-Transistors

ZnO thin films were deposited using RF sputtering by varying the argon:oxygen gas flow rates and substrate temperatures. Structural, optical and electrical characterization of ZnO thin films were systematically carried out using X-Ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy, X-Ray photoelectron spectroscopy (XPS) and Hall measurements. Film deposited at room temperature and annealed at 300 °C exhibited low O2 incorporation with localized defects and a high percentage of Zn interstitials. A large crystalline size and fewer grain boundaries resulted in a high Hall mobility of 46.09 cm2/V-s Deposition at higher substrate temperatures resulted in improvement in O2 incorporation through the annihilation of localized defects and decrease in oxygen vacancies and Zn interstitials. Urbach tails within the bandgap were identified using the absorption spectrum and compared with the % defects from XPS. Bottom-gate thin-film transistors were subsequently fabricated on a SiO2/p-Si substrate using the combination of RF sputtering, wet etching and photolithography. Variation in the substrate temperature showed performance enhancement in terms of the leakage current, threshold voltage, sub-threshold swing and ION/IOFF ratio. Thin-film transistor (TFT) devices deposited at 300 °C resulted in an O2-rich surface through chemisorption, which led to a reduction in the leakage current of up to 10−12 A and a 10-fold reduction in the sub-threshold swing (SS) from 30 V to 2.8 V. Further TFT optimization was carried out by reducing the ZnO thickness to 50 nm, which resulted in a field-effect mobility of 1.1 cm2/V-s and ION/IOFF ratio of 105.

Back propagation neural network model for controlling artificial rocks petrophysical properties during manufacturing process

Artificial rocks are increasingly used in experiments, and it is important to make artificial rocks’ petrophysical properties similar to real rocks to obtain more valuable results. The effect of widely used five factors, grain size (GS), grain size distribution (GSD), mass fraction of cementing agent (MC), pressing pressure (PP), and pressing time (PT), on artificial rock petrophysical properties are analyzed. Three factors, GS, MC, and PP, which are suitable for establishing a quantitative model are opted. The relationships of 80 rock plugs’ petrophysical properties and manufacturing factors are studied, which indicates MC and PP are negatively correlated with porosity and permeability, and GS has a significant effect on permeability but little effect on porosity. Furthermore, a novel back propagation (BP) neural network model is proposed, which can be used to determine factor values during artificial rock manufacturing process. A series of artificial core plugs are manufactured relying on manufacturing factor values calculated by the BP neural network model, and their petrophysical properties are tested and compared with design petrophysical properties value to verify the model. Verification results show that comprehensive average error of porosity and permeability of artificial rock, including calculating error and manufacturing error, is 2.38 and 18.68%, respectively.

The adverse effect of grain refinement on hydrogen embrittlement in a high Mn austenitic steel

This study presents a novel observation wherein the reduction in grain size (GS) from 20 μm to 1 μm in austenitic steel adversely affects hydrogen embrittlement (HE). The findings indicate an increase in total absorbed hydrogen with grain refinement when subjected to cathodic hydrogen charging. The results demonstrate that even with grain refinement to 1 μm, the primary mode of hydrogen damage remains intergranular, with a significant increase in relative elongation loss (REL%). This phenomenon is attributed to the early nucleation of intergranular hydrogen-induced cracks (HICs) and the accelerated propagation rates of HICs, leading to local stress increments and rapid alloy failure. The accelerated development of HICs is ascribed to the impact of grain refinement on intensified normal stress exerted on grain boundary planes, as well as the suppression of ε-martensite and its positive effect on crack arresting. Besides the enhanced degradation rate of the hydrogen-affected area (HAA) due to grain refinement, the higher ratio of HAA to the entire cross-sectional area was identified as a crucial factor contributing to rapid failure and the inverse effect of grain refinement on HE resistance.

Austenite grain growth in tailored cooling rate experiment designed by numerical simulation for peritectic steel

The heat transfer model for steel solidification in Al2O3 crucial and permanent mold by finite element method was developed and validated by temperature measurement. The multi-gradient operation was novelly designed, and the tailored cooling rate in range of 0.1–10 °C/s was obtained at the target location. The simulation aided experiment with the large-sized samples was carried out, and the local cooling rate was verified by secondary dendrite arm spacing. The size of austenite grain decreases slightly as cooling rate increases from 0.15 °C/s to 0.31 °C/s, and then increases dramatically in the range of 0.31–0.48 °C/s, finally decreases with cooling rate increasing further to 9.76 °C/s. The relationship between austenite grain size and cooling rate was logarithmically regressed in the range of 0.48–9.76 °C/s, in which the kinetic equations on basis of cooling experiment and continuously cast slab can also work. However, the grain size decrease in 0.15–0.31 °C/s and then increase in 0.31–0.48 °C/s cannot be described. Based on the mechanism of peritectic solidification, the austenite grain growth is mainly controlled by diffusion at a low cooling rate smaller than 0.31 °C/s, and the final grain size is less than 1.0 mm. At a medium cooling rate between 0.48 and 3.60 °C/s, austenite grain growth is accelerated by the energy stored during massive type peritectic transformation previously, and the grain size is between 1.7 and 2.9 mm. At high cooling rate larger than 9.76 °C/s, austenite grains grow to about 0.9 mm in columnar shape. The time for grain growth is not adequate, although addition energy storage by massive transformation can also occur. The critical cooling rate for the onset of massive type peritectic transformation in the large-sized sample is between 0.31 and 0.48 °C/s. The growth velocity in the isothermal experiment is much smaller than that in continuous cooling process, confirming that the austenite grain evolution is significantly affected by previous peritectic solidification.

Directed energy deposition combined with interlayer remelting for improving NiTi wear resistance by grain refinement

Directed energy deposition of NiTi coatings has received much attention, however, its performance is difficult to meet the increasing requirements in the engineering field. In order to refine the grains to improve wear resistance, a novel interlayer remelting method for fabricating NiTi alloys by directed energy deposition is proposed in this study. The influence of laser interlayer remelting parameters on lattice structure, phase transformation behavior, microstructure, crystallographic evolution, and microhardness was thoroughly analysed in comparison. Good formability is demonstrated after interlayer remelting, while the high energy density leads to microstructure refinement and eutectic regions are observed between dendrites. The grain size decreases with increasing remelting speed, which is due to the faster cooling rate having a greater degree of subcooling with more nucleation points. The faster interlayer remelting speed shows a higher microhardness (586 HV0.2) with higher wear resistance, which is attributed to its finer grain size and significant grain boundary strengthening. Reciprocating sliding wear experiments show that the wear resistance is improved after interlayer remelting, especially at a load of 30 N, the specific wear rate is 1.35 * 10−4mm3/Nm, which is only 47 % of that of the untreated sample. This study proposes a technique to achieve synergistic enhancement of microhardness and sliding wear properties of reinforced coatings, which provides a theoretical basis for the application of NiTi coatings in engineering and extends the field of additive manufacturing.

Charging effects on Rosetta dust measurements

ABSTRACT Dust particles released from comet 67P/Churyumov-Gerasimenko collect electrostatic charges. Their motion is influenced by the electric fields induced by the flow of the solar wind and by the charging of the Rosetta spacecraft itself. Dust grains with sufficiently low tensile strength might even be destroyed en route from the nucleus to Rosetta. A simple model of the plasma environment is discussed here to enable simultaneously following the charging and the dynamics of dust particles as a function of the heliocentric distance of the comet, the distance between Rosetta and the nucleus, the asymmetry in gas production between the northern and southern hemispheres of the nucleus, the amplitude and timing of ultraviolet flares, and the possible outbursts intermittently increasing the production rate of the comet. The electrostatic disruption, and the combination of attractive and repulsive forces between the dust grains and Rosetta might significantly alter the conclusions about the size and spatial distributions of dust grains released from 67P/Churyumov-Gerasimenko. These calculations are presented to help assess the effects of dust and spacecraft charging in the analysis and interpretation of dust measurements by Rosetta.

Does long-term radiation exposure in Chornobyl impact the reproductive structures of Nuphar lutea (Linné) Smith?

The 1986 Chornobyl Nuclear Power Plant accident caused radioactive contamination of water bodies within the Pripyat River floodplain, resulting in the accumulation of radionuclides by macrophytes, which are fundamental species in water ecosystems. Yellow water lily Nuphar lutea (L.) Smith., a macrophyte playing a significant role in the formation of vegetation cover in aquatic ecosystems, is commonly considered as a bioindicator of water pollution. In this study, we investigate the potential of N. lutea as an indicator of radionuclide contamination in water bodies, particularly through changes in its reproductive structures, such as pollen viability, morphology of pollen grains, seeds, and fruits. Our findings reveal that pollen viability remains stable at total absorbed dose rates below 14.4 μGy/h, with only 1–4% of sterile grains. However, beyond this threshold the percentage of sterile grains increases nearly fivefold, pointing to high internal plant exposure to 90Sr. A similar trend was observed in the allometry and size of pollen grains, where small and flattened grains are formed in the reservoir with the highest external radiation dose rate (≥14.4 μGy/h). On the other hand, while morphometric parameters of fruits are influenced by radiation, their variation appears to be the result of a combination of physicochemical factors and the trophic status of a water body. Our research highlights the adverse impact of long-term radiation exposure on the male reproductive system of N. lutea and shows the potential of using the pollen grains sterility as an indicators of heavily radionuclide-contaminated water bodies. Additionally, we observed gradual changes in a pollen allometric length-to-width coefficient as the radiation dose level increases.

Investigating the mechanical properties and corrosion resistance of extruded Mg-1Zn-xCaO (x=0, 0.5, 1.0 wt%) materials

The effect of nano-CaO content on the microstructure, mechanical properties, and in vitro degradation performance of extruded Mg-1Zn alloys was investigated to enhance the strength and corrosion resistance of biodegradable materials for medical implants. The results showed that the addition of CaO nanoparticles effectively refined the size of dynamic recrystallization grains in the extruded composites. During the extrusion process, Ca2Mg6Zn3 and Mg2Ca phases precipitated in the Mg-1Zn-0.5CaO and Mg-1Zn-1CaO composites, respectively. As the CaO content increased, the basal texture strength was elevated from 3.97 for the Mg-1Zn alloy to 12.05 for the Mg-1Zn-1CaO composite. Benefiting from the combined mechanisms of grain refinement, dislocation strengthening, and precipitation strengthening, the yield strength of the materials was fortified with an increase in CaO content. During the short immersion time, the matrix of the extruded Mg-1Zn-0.5CaO composite was preferentially corroded, resulting in the formation of a dense corrosion product layer that impeded the transport of ions in the electrolyte solution, thereby exhibiting the lowest annual corrosion rate. With an increase in the immersion time, galvanic corrosion destroyed the protective film, leading to a slightly higher corrosion rate in the extruded Mg-1Zn-0.5CaO composite compared to the Mg-1Zn alloy. The substantial nano-Mg2Ca phase particles were preferentially degraded, causing severe pitting corrosion in the extruded Mg-1Zn-1CaO composite, which exhibited the highest degradation rate. The extruded Mg-1Zn-0.5CaO composite exhibited superior overall properties; its yield strength, elongation, and annual corrosion rate after immersion (21 d) were 334.9 MPa, 8.9 %, and 1.06 mm/y, respectively.

Achieving high strength and ductility of Al-Zn-Mg-Cu alloys via laser shock peening and spray forming

In order to further enhance the strength and ductility of ultra-high strength aluminum alloys, the laser shock peening technology was applied to ultra-high strength Al-Zn-Mg-Cu alloy. The ultimate tensile strength, elongation and hardness can reach to 751 MPa, 11 % and 208.3 HV by combining spray forming, secondary extrusion, solid solution, retrogression and reaging as well as laser shock peening. The high strength and hardness of the alloys is mainly attributed to the fine-grained layer on surface as well as new grain boundaries, dislocation cells and high-density dislocations introduced by laser shock peening, uniform nano-sized strengthening phases with high density precipitated during heat treatments. The excellent ductility of the alloys is mainly ascribed to multiple structures including fine-grained layer on surface and slip lines inside different grains introduced by laser shock peening, smaller size of fibrous grains and Al7Cu2Fe phase produced by secondary extrusion and spray forming. The aging treatment after laser shock peening can lead to the annihilation of high-density dislocations as well as significantly promote the formation of stable and coarse η phase, which can greatly reduce the strength of the studied alloys.

Towards high stiffness and ductility-The Mg-Al-Y alloy design through machine learning

In traditional trial-and-error method, enhancing the Young's modulus of magnesium alloys while maintaining a favorable ductility has consistently been a challenge. It is a need to explore more efficient and expedited methods to design magnesium alloys with high modulus and ductility. In this study, machine learning (ML) and assisted microstructure control methods are used to design high modulus magnesium alloys. Six key features that influence stiffness and ductility have been extracted in this ML model based on abundant data from literature sources. As a result, predictive models for Young's modulus and elongation are established, with errors less than 2.4% and 4.5% through XGBoost machine learning model, respectively. Within the given range of six features, the magnesium alloys can be fabricated with the Young's modulus exceeding 50 GPa and an elongation surpassing 6%. As a validation, Mg-Al-Y alloys were experimentally prepared to meet the criteria of six features, achieving Young's modulus of 51.5 GPa, and the elongation of 7%. Moreover, the SHapley Additive exPlanation (SHAP) is introduced to boost the model interpretability. This indicates that balancing the volume fraction of reinforcement, the most important feature, is key to achieve Mg-Al-Y alloys with high Young's modulus and favorable elongation through the two models. Enhancing reinforcement dispersion and reducing the size of reinforcement and grain can further improve the elongation of high-stiffness Mg alloy.

Cermet coatings obtained by electric spark alloying to increase service life of dental instruments

The article presents the results of our study of protective cermet coatings obtained by the method of electric spark alloying on a dental instrument (excavator) using SHS (self-propagating high-temperature synthesis) electrodes based on TiC-NiCr. The influence of discharge energy during electric spark alloying on the roughness, thickness, and proportion of the TiC carbide phase in the cermet coating has been established. It has been shown that during electric spark alloying, the material of the used SHS electrode and the surface of the substrate melt, their convective mixing occurs, and during crystallization, coatings are formed that consist of a strengthening phase TiC and iron-based solid solutions: Fe9.64Ti0.36, F1.88C0.12, and Cr-Ni-Fe-C. It has been found that the maximum size of TiC grains is formed on the surface of the cermet coating, and as they approach the substrate, their size decreases to less than 10 nm. It has been found that the microhardness of the surface of the resulting cermet coatings increased to 6.2 times compared to the microhardness of the original metal base, which was 2 GPa. The results of scanning electron microscopy and energy dispersive analysis of the surface of samples with and without cermet coating before and after corrosion tests are presented. The influence of disinfectants (2 and 100 % Trilox, Wendelin, MegaDes-ortho) on the corrosion resistance of samples with and without developed protective cermet coatings at room and elevated temperatures up to 50 °C and their exposure for 120 h has been established.

Copper-coordinated nanomedicine for the concurrent treatment of lung cancer through the induction of cuproptosis and apoptosis

The resistance of tumor cells to apoptosis often leads to chemoresistance and treatment failure in clinic. In this study, we have developed a Cu2+-coordinated lignosulfonate (CLS) /doxorubicin (DOX) biological complex (referred to as LCD) with the aim of overcoming cellular resistance to apoptosis for combined lung cancer therapy. The copper complexes modified by CLS exhibit significant water solubility and excellent in vivo biocompatibility. The proportion of copper in the composite is simultaneously increased. Due to the coordination and π-π stacking effects, the self-assembled LCD exhibits nanometer-scale particle size, a narrow and homogeneous grain distribution, as well as excellent dispersion stability. Furthermore, LCD has the potential to disassemble in the presence of high levels of glutathione (GSH) and low pH, leading to effective drug release. Cu2+-mediated cuproptosis can lead to the down-regulation of FDX1 and DLAT protein expression by reducing mitochondrial membrane potential, resulting in non-apoptotic programmed cell death (PCD) regardless of cellular resistance to apoptosis. Moreover, the released DOX not only exhibits a preference for localizing in the cell nucleus to induce apoptosis for combined chemotherapy, but also generates a substantial amount of H2O2. This H2O2 further produces ROS to induce apoptosis through Fenton reaction with Cu2+. LCD demonstrates significant superiority over monotherapy in inhibiting tumor growth while minimizing systemic toxicity through the combined action of cuproptosis and apoptosis. This study may provide a potential avenue for the advancement of self-delivery nanomedicine to overcome resistance to apoptosis in tumor therapy.

Dust Survival in Galactic Winds

We present a suite of high-resolution numerical simulations to study the evolution and survival of dust in hot galactic winds. We implement a novel dust framework in the Cholla hydrodynamics code and use wind tunnel simulations of cool, dusty clouds to understand how thermal sputtering affects the dust content of galactic winds. Our simulations illustrate how various regimes of cloud evolution impact dust survival, dependent on cloud size, wind properties, and dust grain size. We find that significant amounts of dust can survive in winds in all scenarios, even without shielding from the cool phase of outflows. We present an analytic framework that explains this result, along with an analysis of the impact of cloud evolution on the total fraction of dust survival. Using these results, we estimate that 60% of 0.1 μm dust that enters a starburst-driven wind could survive to populate both the hot and cool phases of the halo, based on a simulated distribution of cloud properties. We also investigate how these conclusions depend on grain size, exploring grains from 0.1 μm to 10 Å. Under most circumstances, grains smaller than 0.01 μm cannot withstand hot-phase exposure, suggesting that the small grains observed in the circumgalactic medium (CGM) are either formed in situ due to the shattering of larger grains, or must be carried there in the cool phase of outflows. Finally, we show that the dust-to-gas ratio of clouds declines as a function of distance from the galaxy due to cloud–wind mixing and condensation. These results provide an explanation for the vast amounts of dust observed in the CGMs of galaxies and beyond.

Bayesian statistical analysis reveals spatial heterogeneity in Cyclone Thane deposits from Southeast India

Modern and geological records of storm sedimentary deposits preserved on siliciclastic coastlines are important archives to evaluate the past and current magnitude and impacts of.storms. Examination of modern storm deposits also offers the opportunity to evaluate the similarities and differences between storm and other coastal overwash processes and hazards.We examined the stratigraphy and sedimentary characteristics of the 31st December 2012 Cyclone Thane and underlying coastal units from 14 pits from six sites from the coastal zone of Tamil Nadu Province, southeast India. We analysed the grain size parameters, grain shape, and heavy mineral proportions of each deposit in high resolution and examined the sedimentary structures of each unit. For the first time, we use Bayesian factors to quantitatively evaluate the similarities and differences between the storm sedimentary deposits and other co-located coastal sedimentary deposits. At several sites, the storm deposits differ in several parameters from the underlying coastal deposits, but at some locations, distinguishing between different depositional units cannot be achieved. In comparing the storm deposits from the different sites, mean grain size results in the most coherent pattern with closely located sites having similar mean grain size, and more southerly sites being finer grained. The other measured parameters show a far less coherent pattern with adjacent sites often preserving larger differences than more distal sites attesting to very local hydrodynamic variations during sediment deposition. As with the sedimentary parameters, the sedimentary structures formed during sediment deposition preserved at each site are highly variable. To date, the presence of terminal foresets at the landward edge of washover fans remains the only diagnostic feature of storm deposition, but that this feature is not ubiquitous across all storm deposits. Our findings demonstrate the spatially heterogeneous nature of storm sediment deposition and the challenges of identifying storm deposits in coastal siliciclastic sequences. The use of Bayesian statistical approaches also offers a robust method for evaluating and discriminating between coastal sediment deposits that has many advantages over traditional frequentist approaches. This method can easily be applied to other sedimentary depositional environments.

Structural and Optical Characterization of Cu2Se0.8S0.2 Thin Films Deposited by Thermal Evaporation

Abstract A simple cost thermal evaporation deposition technique was used to prepare of Cu2SeS thin films on the substrates made of glass at RT with thickness ( 500 + − 20 ) nm . Structural, and optical properties of these films were investigated. The films were structurally characterized using X-ray diffraction XRD analyses, the film samples were morphologically characterized using atomic force microscopy (AFM), and optical UV-Vis spectroscopy was also to characterize the samples. The films have been treated at deferent temperatures (403, 453 &503) K for 1 hour, X-ray diffraction (XRD-with wavelength 1.54 A) study the structure properties of this films suggest a cubic structure and have prominent (111) orientation. AFM analysis, it is evident that Cu2SeS film is polycrystalline in nature, and that crystallite size and average grain size for films after annealing were increasing. The optical absorption coefficient (α) of the film was evaluated using absorbance spectra in the wavelength range (400-1100) nm. The direct band gap of about 2.2 eV, decrease by increasing annealing temperature, The structure and the optical characteristics of these films may have practical applications in renewable energy.

Effects of clay grains on the shear properties of unsaturated loess and microscopic mechanism

Different clay grains affect the structural strength of loess through the cementation of skeletal particles. This study investigates both clay-clay grains and quartz-clay grains. Clay-clay grains mixed loess (CM-L) and quartz-clay grains loess (Q-L) samples were prepared, and their unsaturated shear properties analyzed. X-ray diffractometry (XRD) analysis was conducted to determine the types and proportions of clay grains. Ball mill grinding and laser particle size analysis were employed to ensure comparable sizes of clay grains, while mercury intrusion porosimetry (MIP) tests confirmed similar pore characteristics. Scanning electron microscope (SEM) and unsaturated triaxial consolidation and drainage tests explored the impact of different clay grains on loess shear characteristics, assessing both microscopic and macroscopic performance. The results indicate that CM-L loess exhibits higher cohesion and a lower internal friction angle at the same matric suction level. The cohesion and internal friction angle of both CM-L and Q-L loess exhibit a linear relationship within the range of 50–200 kPa matrix suction. The cohesive force ranges for CM-L and Q-L loess are 60.31–80.07 kPa and 43.01–69.60 kPa, respectively, while the ranges for internal friction angles are 19.95°-19.59° and 25.91°-25.06°, respectively. Compared to Q-L loess, CM-L loess exhibits an average difference in cohesion of 23.18 kPa and in internal friction angle of -5.72°. The microscopic variation in shear strength can be attributed to the “fish scale-like” interlocking state between clay-clay grains and the “tower-like” scattering arrangement of quartz-clay grains. In conclusion, the effect of different clay-grain types on the shear strength of loess varies significantly. The present study elucidates the relationship between the influence of different clay grains on the mechanical properties of loess and their microscopic structural characteristics, thereby providing crucial data for investigating the microscopic effects on the structural strength of loess.

Вплив хімічного складу та температури гартування на розмір зерна аустеніту та твердість інструментальної сталі

Alloying elements and impurities influence ambiguously on the factors that determine the process of the austenite structure formation. This does not make it possible to qualitatively predict the direction of their influence on the change of austenite grain dispersion during austenitizing heating and the hardness of tool steel. To date, there is no information on mathematical models that reliably describe the influence of chemical composition and quenching temperature on the specified characteristics of tool steels. The influence of the chemical composition and quenching temperature on the austenite grain size and the hardness of tool steels was studied, with the development of mathematical models of such influence with the determination of the effectiveness of these factors. It was established that the size of the austenite grain and the hardness of the quenched tool steel are mainly determined by the nature and quantity of alloying elements, the degree of distortion of the crystal lattice and the quenching temperature. The main influence on the austenite grain size of tool steels is the quenching temperature and the quantity of carbon, molybdenum and tungsten in the steel. An increase in the heating temperature leads to growth, and the quantity of elements - to the dispersion of the austenite grain. According to the increase in the specific efficiency of the influence of 1% alloying element on the decreasing of the austenite grain size, they can be arranged in the following sequence: W, Mo, C, and the efficiency of their relative influence is, respectively, 1 : 1.4 : 6.7. The hardness of tool steel is mainly determined by the content of carbon, silicon, tungsten and molybdenum in the steel and the degree of distortion of the crystal lattice by them, as well as the quenching temperature. The evaluation of the effectiveness of the factors showed that the influence of carbon is 26%, tungsten – 22%, molybdenum – 20%, tempering temperature – 17% and silicon – 15%. The obtained regression equations can be used by scientists for further research and by practitioners in the selection of materials for making tools. Keywords: steel, chemical composition, temperature, quenching, grain, austenite, hardness

Microstructural evolution and dynamic mechanical behavior of PM 2195 Al-Li alloy with resistance to shear instability in high strain rate deformation

The risk of adiabatic shear instability is common in traditional alloys covering high-strength steels, copper alloys and aluminum alloys during high strain rate deformation. However, the research on shear instability of 2195 Al-Li alloy prepared by powder metallurgy (PM) at high strain rates is still blank. The purpose is to explore its microstructure evolution and dynamic compression behavior. In this work, the 2195 Al-Li alloy prepared by PM amazingly demonstrates excellent resistance to shear instability at high strain rates during Split-Hopkinson pressure bar (SHPB) experiment. The microstructural evolution of grains and T1 (Al2CuLi) precipitate phase, and dynamic compression behavior of PM 2195 Al-Li alloy at various strain rates from 3000 s−1 to 9000 s−1 are investigated in detail employing correlative electron-backscatter diffraction (EBSD) and transmission electron microscopy (TEM). During high strain rate deformation, the alloy undergoes grain fragmentation and rotation, increasing dislocation density around the grains. When the strain rate is from 3000 s−1 to 7500 s−1, the Kernel Average Misorientation (KAM) value increases, indicating intensified localized strain. At a strain rate of 9000 s−1, a small number of grains are surrounded by nanocrystals (around 200 nm) that undergo stress release, while the average size of micrometer-sized grains is 0.81 μm. As the strain rate increases, the T1 phases in the alloy extends, vibrates, and fractures before dissolving in the matrix, while high-rate deformation promotes dislocation entanglement and defects, leading to the decomposition or ordering of precipitated phases through rapid plastic deformation. By virtue of energy dissipation strategy via the formation of nanocrystallines and dislocation behavior induced by the dissolution of T1 phases, the "positive-positive" effect is observed. The PM 2195 Al-Li alloy undergoes no shear failure even at the strain rate of 9000 s−1, showing great prospects in future applications in dynamic-loading conditions.