Preferential Growth Research Articles

Embrittlement of notched duplex stainless steel: Role of hydrogen-assisted void growth and cleavage

The micro-degradation processes related to the ductile-brittle transition are crucial for revealing hydrogen embrittlement mechanisms. This study investigates the evolution and transition of hydrogen-assisted damages in notched duplex stainless steel using a combination of microstructural characterization, numerical simulations, and mechanistic models. The results show that the brittle area of the fracture surface increases rapidly with decreasing cathodic potential, accompanied by the fractography transition in a sequence of voids, voids mixed with quasi-cleavage, and quasi-cleavage. While hydrogen-assisted dislocation emission from the void surface and stress concentration at the phase boundary promote nanovoid growth, hydrogen-enhanced plasticity facilitates preferential void growth along the ferrite block. At higher hydrogen concentrations, ferrite cleavage cracking may originate from prolate voids and hydrogen-augmented Cottrell dislocation reactions, reducing plastic strain near the crack tip and hence diminishing the formation of vacancies as void nuclei. Previous studies have focused on the statistics of hydrogen's effect on void size. This work demonstrates the dislocation mechanism of hydrogen-assisted void growth and provides new insights into the development of micro-mechanism-based models to predict hydrogen embrittlement.

Introducing high-density growth twins in aluminum alloys by laser surface remelting via templated nucleation of grains

It is difficult to generate coherent twin boundaries in bulk Al alloys due to their high intrinsic stacking fault energy. Here, we report a strategy to induce high-density growth twins in aluminum alloys through the heterogeneous nucleation of twinned Al grains on twin-structured TiC nucleants and the preferred growth of twinned dendrites by laser surface remelting of bulk metals. The solidification structure at the surface shows a mixture of lamellar twinned dendrites with ultra-fine twin boundary spacing (∼2 μm), isolated twinned dendrites, and regular dendrites. EBSD analysis and finite element method (FEM) simulations have been used to understand the competitive growth between twinned and regular dendrites, and the solidification conditions for the preferred growth of twinned dendrites during laser remelting and subsequent rapid solidification are established. It is shown that the reduction in the ratio of temperature gradient G to solidification rate V promotes the formation of lamellar twinned dendrites. The primary trunk spacing of lamellar twinned dendrites is refined by the high thermal gradient and solidification rate. The present work paves a new way to generate high-density growth twins in additive-manufactured Al alloys.

The Influence of Varying Ar/O2 Gas Ratio with Catalyst-Free Growth by Homemade Thermal Evaporation Technique

A nanostructured zinc oxide (ZnO) with different percentages of argon and oxygen gas flow rate was deposited on a silicon wafer by a simple hot tube thermal evaporation technique. The effect of different percentages of gas flow rate on the crystal structure, surface morphology and optical properties were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and RAMAN spectroscopy, respectively. The changes of morphologies from FESEM were significant where the grown ZnO nanostructures show three different shapes which are nanotripods, nanoclusters and nanorods at 5%, 10% and 25% of oxygen gas, respectively. EDX results revealed that Zn and O elements have a major percentage in the sample indicating a composition has high purity of ZnO. XRD patterns displayed the most intense diffraction peak of ZnO at (101), which exhibited a single crystalline hexagonal structure with preferred growth orientation in the c-axis. RAMAN scattering study found that synthesized ZnO shows the high intensity of E2 mode and low intensity of E1 mode attributed to all the samples having good crystal quality containing fewer structural defects. In conclusion, the E15 sample with a 25% oxygen gas flow rate was selected as an optimum result for synthesizing a homogenous surface and high crystallinity of ZnO by using a hot tube thermal evaporation process. This work can enhance the development of ZnO production in various applications.

The mechanical anisotropy of Mg-Zn-Y alloys with columnar crystals in specific orientation

The Mg99.2Zn0.2Y0.6 alloys were prepared by directional solidification, and the effect of loading modes on mechanical anisotropy and deformation mechanism of the alloys was studied. The microstructure of the alloy is columnar crystals whose growth orientations are mainly concentrated in <112(_)0>. When the tensile load is parallel to longitudinal grain boundaries of columnar crystals, the alloy has high yield strength (232 MPa), owing to basal <a> slip with hard orientation and {101(_)1} contraction twinning with high critical resolved shear stress (CRSS), but work hardening is not obvious. When the compressive load is parallel to longitudinal grain boundaries of columnar crystals, the alloy has high compressive strength (337 MPa) and good plasticity (maximum strain, 24 %), as well as distinct work hardening, which are related to (112(_)1) [112(_)6(_)] twins and good strain compatibility of grain boundaries. When the compressive load is perpendicular to longitudinal grain boundaries, the alloy shows high plasticity (maximum strain, 31 %) because the strip-like extension twins are parallel to the longitudinal grain boundaries during deformation.

Characterization of NiCuOxNy Coatings Obtained via RF Sputtering: Structure, Morphology, and Optical Properties.

The rapid advancement of technology necessitates the continual development of versatile materials that can adapt to new electronic devices. Rare earth elements, which are scarce in nature, possess the set of properties required for use as semiconductors. Consequently, this research aims to achieve similar properties using materials that are abundant in nature and have a low commercial cost. To this end, nickel and copper were utilized to synthesize thin films of nickel-copper binary oxynitride via reactive RF sputtering. The influence of nitrogen flow on the structure, morphology, chemical composition, and optical properties of the films was investigated using various characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), as well as transmittance and absorbance measurements. The crystalline structure of the films shows that they can have preferential growth or be polycrystalline according to the nitrogen flow used during deposition and that both the oxides and oxynitrides of metals are formed. We identified unknown phases specific to this material, termed "NiCuOxNy". The morphology revealed that the grain size of the coatings was dependent on the nitrogen flow rate, with grain size decreasing as the nitrogen flow rate increased. Notably, the coatings demonstrated transparency for wavelengths exceeding 1000 nm, with an optical band gap ranging from 1.21 to 1.86 eV.

Influence of the Geometry of Cast Products on Orientation of Dendritic Crystals Growth and Formation of Hot Cracks

Influence of the Geometry of Cast Products on Orientation of Dendritic Crystals Growth and Formation of Hot Cracks

Annealing-induced transformation of structural and optical parameters of transparent γ-CuI thin films with superior thermoelectric performance

The synthesis of transparent thermoelectric materials, particularly at low processing temperature possesses a good promise for future power generation by renovating waste heat into electrical energy. The fabrication of invisible thermoelectric module is hindered by limited choices of appropriate p-type transparent thermoelectric materials so far. The present study deals with the growth and characterization of optically transparent p-type copper iodide (γ-CuI) thin films. Thermal annealing (maximum up to 200 °C) was performed to tune the electrical and optoelectronic properties for nurturing the thermoelectric performance. Annealing induced microstructural modifications instigated the preferential crystal growth by regulating the surface morphology. Low thermal conductivity is credited to strong phonon scattering leading to improved thermoelectric performance. Consequently, we attain a record Seebeck coefficient of ∼270 μV/K and power factor of ∼20 μW/(m·K2) that is almost two-order of magnitude higher as compared to conventional p-type transparent TE materials, indicating the potential of transparent γ-CuI thin films regarding its practical applicability in transparent thermoelectric devices.

Effects of annealing time on microstructural characteristics and mechanical properties of cryo-rolled CoCrFeMnNi high entropy alloys

High-entropy CoCrFeMnNi alloy was subjected to cryo-rolling with a reduction ratio of 25 % and was then annealed at 1050 °C for 5, 25, and 45 min. The results of the recrystallization textures of the various annealed samples showed the presence of similar texture components, indicating that cryo-rolling had only a limited effect on the formation of the subsequent annealing texture. The volume fractions of the different texture components similarly showed no obvious dependence on the annealing temperature. The uniformity of the recrystallization texture suggests the absence of strong preferential nucleation and growth during annealing. The cryo-rolled samples processed with different holding times exhibited a remarkable ambient temperature strength-ductility combination.

Preparation of carbon/nickel composites by magnetron sputtering and study on electromagnetic shielding effectiveness

A pure nickel film and a carbon/nickel (C/Ni) composite film were produced using radio frequency magnetron sputtering. The structure of the films was regulated by adjusting the sputtering power and the time allocation of sputtering nickel and graphite targets. Furthermore, a scanning electron microscope, an x-ray diffractometer, and a Raman spectrometer were employed for sample characterization. The results demonstrated that the thickness of the pure nickel film and C/Ni composite film with a total deposition time of 60 s was between 44.96 and 65.31 nm. The nickel film exhibited preferential growth along the crystal plane (111), and the structure of carbon materials was in the second stage of the three-stage model known as “amorphization trajectory of graphite.” The prepared films’ electromagnetic interference shielding effectiveness (EMI SE) in the X-band was investigated using a vector network analyzer. It was observed that the C/Ni composite film with a thickness of 44.96 nm demonstrated a superior EMI SE with a maximum value reaching 21 dB. The EMI SE of the C/Ni composite film can reach the same performance and even exceed that of the pure nickel film obtained at the power of 200 W for 60 s in certain frequency segments. In conclusion, the pure nickel film can be replaced by C/Ni composite film prospectively due to their excellent EMI SE along with advantages such as reduced thickness, lighter weight, and lower cost.

Impact on preferred orientation and crystal strain behavior of nanocrystal anatase-TiO2 by X-ray diffraction technique

The primary goal of this research outline is the conversion of titanium isopropoxide (TTIP) at 50.0 °C to form a high crystalline preferred oriented predominant (101) with a low crystal strain of 90.0 % anatase-TiO2 phase. With the interval of time, the peptizing agent (IP) reacts to an acidic aqueous medium and preferential growth of anatase-TiO2 has been identified. Exhaustive recombination in X-ray diffraction (XRD) analysis ensures the crystal strain, lattice volume, lattice parameters, d-spacing and crystallite size. UV–vis-NIR showed maximum absorption of 320.0 nm with 0.78 a.u. at blue shift for decreasing nano-size and smaller bandgap 3.0313 eV of larger dimensions anatase-TiO2. The preferred orientation also revealed by nanobeam diffraction (NBD) of TEM enables qualitative lattice type and highly crystal orientated predominant (101) plane 5.60 nm−1 in a diffraction pattern imposed on 200.0 kv parallel electron bean from LaB6 filament.

Rethinking growth orientation: Do ski‐resorts' strategies fit the profiles of today's alpine skiers?

AbstractThe strategy and marketing of ski resorts in the European Alps are still characterized by growth orientation and the extension of technical snow production to ensure high snow reliability. In contrast, this study hypothesizes that besides a high‐performing ski resort, winter ski vacationists have further expectations for activities during their stay varying by their skiing skill level and personal preferences. The present study surveys 1413 Alpine ski tourists to identify their daily routines, activities, and used ski resort services. The findings uncover significant differences in the activity profiles with six clearly distinguishable guest segments. The results highlight the need for custom‐tailored product development considering the complete set of winter experiences as well as pricing strategies that specifically target the identified segments. Furthermore, the findings underline that ski resort and destination managers need to include daily changes in snow and weather conditions in their strategies considering climate and demographic change.

The role of microfaceting in heteroepitaxial interfaces

We investigate the effects of microfaceting on the orientation and interface structure of fcc films on fcc substrates by molecular dynamics simulations and atomic resolution electron microscopy. For (110) substrates, the simulations reveal a misorientation between film and substrate lattices that undergoes a sudden change when interfacial facets approach the “magic size”, where a lattice dislocation minimizes the strain energy by compensating the misfit between film and substrate. For a large misfit, the angle of misorientation varies between zero and several degrees, depending on the size and sequence of microfacets. Experimental observations of interfaces in Ag/Ni near the Ni(110) orientation uncover the presence of magic-size {111} facets and show how microfaceting controls the partitioning of misfit dislocations. For facets smaller than the magic size, misfit may be compensated by partial rather than perfect dislocations. In vicinal {hhl} interfaces, made of {111} terraces separated by single-layer steps, a partial dislocation per terrace leads to film growth in the heterotwin orientation. This concept explains a range of previous results on interface structures in a variety of heteroepitaxial systems.

Comparative analysis of microstructural, compositional, and grazing incidence characteristics of oxide scale on 316L steel: SLM vs. wrought conditions

The aim of this research is to compare the oxidation behavior and characteristics of oxide scale of 316L steel produced by two methods: selective laser melting (SLM) and conventional casting and forming (wrought). To this end, the initial composition and microstructure of samples produced by those methods were first studied. Thermogravimetric analysis (TGA) and long-term isothermal oxidation tests were carried out on the samples and the oxidation kinetics were compared. The oxidized samples were then examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and grazing incidence X-ray diffraction (GIXRD). The results indicated that in the temperature range of 600 °C–900 °C, the oxidation resistance of the SLM alloy is lower than that of the wrought alloy, especially at 800 °C. This is attributed to the combined effect of: i) smaller grain size due to the rapid solidification in the SLM alloy that increases the paths of oxygen penetration, ii) lower presence of chromium and manganese elements in the oxide layer and iii) preferential growth of iron oxide in the form of hillocks on the surface. Surface and cross-section analysis of the oxide layers show that iron oxide is dominant on the surface of the SLM sample at temperatures of 600 °C and 800 °C, and at 800 °C its extended hilly growth leads to significant spallation of the oxide scale and an exponential increase in the oxidation rate. However, at 900 °C, with the formation of a continuous oxide layer containing Fe2MnO4 and CrMnO4, the oxidation rate significantly decreases in both alloys.

Lattice Matching and Microstructure of the Aromatic Amide Fatty Acid Salts Nucleating Agent on the Crystallization Behavior of Recycled Polyethylene Terephthalate.

To solve the decrease in the crystallization, mechanical and thermal properties of recycled polyethylene terephthalate (rPET) during mechanical recycling, the aromatic amide fatty acid salt nucleating agents Na-4-ClBeAmBe, Na-4-ClBeAmGl and Na-4-ClAcAmBe were synthesized and the rPET/nucleating agent blend was prepared by melting blending. The molecular structure, the thermal stability, the microstructure and the crystal structure of the nucleating agent were characterized in detail. The differential scanning calorimetry (DSC) result indicated that the addition of the nucleating agent improved the crystallization temperature and accelerated the crystallization rate of the rPET. The nucleation efficiencies (NE) of the Na-4-ClBeAmBe, Na-4-ClBeAmGl and Na-4-ClAcAmBe were increased by 87.2%, 87.3% and 41.7% compared with rPET which indicated that Na-4-ClBeAmBe and Na-4-ClBeAmGl, with their long-strip microstructures, were more conducive to promoting the nucleation of rPET. The equilibrium melting points (Tm0) of rPET/Na-4-ClBeAmBe, rPET/Na-4-ClBeAmGl and rPET/Na-4-ClAcAmBe were increased by 11.7 °C, 18.6 °C and 1.9 °C compared with rPET, which illustrated that the lower mismatch rate between rPET and Na-4-ClBeAmGl (0.8% in b-axis) caused Na-4-ClBeAmGl to be the most capable in inducing the epitaxial crystallization and orient growth along the b-axis direction of the rPET. The small angle X-ray diffraction (SAXS) result proved this conclusion. Meanwhile, the addition of Na-4-ClBeAmGl caused the clearest increase in the rPET of its flexural strength and heat-distortion temperature (HDT) at 20.4% and 46.7%.

Leveraging Inherent Structure of Tin Oxide for Efficient Carbonaceous Products Electrosynthesis

AbstractElectrochemical CO2 reduction reaction (CO2RR) holds a great potential for converting CO2 into valuable carbon‐based chemicals and fuels. A promising strategy for enhancing CO2RR performance is the deliberate structural design of electrocatalysts, which can maximize the utilization of inherent structural advantages. In this work, SnO2 nanocubes (NCs) and nanorods (NRs) are synthesized using a surface energy‐driven growth orientation method, where the stable (110) facet and the highly energetic (001) facet constitute the SnO2 nanostructures. Leveraging the inherent structural merits of different facets on SnO2, theoretical calculations reveal that the (001) facet plays a primary role in inhibiting hydrogen evolution reaction (HER), while both (110) and (001) facets are highly favorable for CO2‐to‐formate conversion under the external bias. As a result, SnO2 NCs with a higher facet ratio of (001)/(110) achieve nearly 100% selectivity for the formation of carbonaceous products during CO2RR. More importantly, a maximum partial current density of about 1 A cm−2 with a formate Faradaic efficiency (FE) of over 90% is achieved in a flow cell, distinguishing it from most of the reported Sn‐based electrocatalysts. These results highlight the strategic advantages of leveraging the inherent structure of nanomaterials for efficient CO2RR.

Художественно-педагогическая реконструкция и теоретический анализ опыта взаимоотношений «учитель – ученик» в образовательной сфере России начала ХХ в.

The study aims to determine the role of a teacher’s personality in solving moral and pedagogical problems arising in the process of teacher-student relations in the educational sphere of Russia in the early 20th century by conducting a theoretical analysis of individual documentary fiction texts by K. G. Paustovsky in the genre of documentary prose. The paper substantiates the importance of the priority spiritual and moral principles and values of Russian pedagogy and psychology as the basis of the traditional knowledge paradigm of education, actualizes their relevance in modern Russian theory and practice. The study is original in that it is the first to reveal the role of a teacher’s personality primarily as an educator and bearer of moral universal values in the traditional knowledge paradigm of education based on K. G. Paustovsky’s documentary fiction stories about the teacher-student relations in the educational sphere of Russia in the early 20th century. In addition, the paper determines the importance of a teacher’s personal self-esteem (professional reflection) and their individual threshold of tolerance and responsibility for the process of forming the personal image of pupils, humanistic qualities and psychological characteristics of students. As a result, it was found that an essential factor of success in solving moral and psychological problems in the system of teacher-student relations in both traditional and modern humanistic paradigms of education is the personality of a teacher, their “human factor”. The professional reflection of a teacher, which is their personal self-assessment manifested in psychological, creative, moral and mental abilities at an active and interactive level to influence the spiritual world of a pupil, creates conditions for the movement of the educational process towards the creative self-expression of a student’s personality. A teacher’s ability to correctly assess and take into account students’ personal and psychological characteristics ensures the formation of conditions for pupils’ personal growth, their values and worldview orientations.

VPDet: Refined region CNN for hair follicle recognition in arbitrary angle

AbstractIn response to the growing demand for hair‐loss treatments, this study introduces the vector proposal detector (VPDet), a groundbreaking solution in hair transplant robotics. VPDet, distinct from traditional approaches, addresses the complex challenges of hair follicle detection, notably the variability in hair growth orientations and the intricacies of hair clustering. The method innovatively leverages the linear nature of hair, spanning a full 360‐degree orientation spectrum. The VPDet framework, a novel two‐stage object detection system, incorporates the vector proposal network and vector align blocks. These elements are crucial in transforming conventional anchor boxes into anchor vectors, thereby generating reference vectors across various scales and angles. The vector align block, a key innovation, uniquely combines vector and adjacent feature data to align features through shared maps. The extensive experiments, conducted on the FDU_HairFollicleDataset and an extended dataset, exhibit a remarkable enhancement in model performance, with a 51.3% increase in precision and a 20.8% boost in F1 score. The results not only demonstrate VPDet's superior capability in hair follicle recognition but also its potential in posture recognition for vector‐characteristic objects. This approach represents a significant advancement in both the field of hair transplant robotics and vector‐based object detection.

Preparation of a/c-oriented YBa2Cu3O7−x homogeneous superconducting junctions via pulsed laser deposition

The growth orientation of YBa2Cu3O7−x (YBCO) is extremely sensitive to the growth atmosphere and the heat-treatment temperature. However, according to the existing literature, to obtain YBCO with preferred a-axis orientation, a buffer layer needs to be prepared on the substrate. In this work, YBCO films were grown via pulsed laser deposition, and the influence of N2 and O2 deposition atmospheres on the growth orientation of the YBCO films was studied. It was found that high-quality YBCO films with preferred c-axis orientation can be grown in O2 atmosphere, but it is difficult to grow a-axis-oriented YBCO films in O2 atmosphere without using a buffer layer; however, YBCO films with a high degree of preferred a-axis orientation can be grown in N2 atmosphere without using a buffer layer. Furthermore, an a/c-oriented homogeneous YBCO bilayer with c-axis orientation in the lower layer and a-axis orientation in the upper layer was prepared. X-ray diffraction and scanning transmission electron microscopy results show that the bilayer is epitaxial with a good a/c orientation, and the resistance–temperature curve shows the occurrence of two transitions at temperatures of 91 and 71 K. We believe that these temperatures correspond to the superconducting onset transition temperatures of YBCO in the c- and a-axis growth orientations, respectively. The superconducting current usually flows within the Cu–O plane. With its sudden change in the direction of the current at the interface, the homogeneous junction prepared in this work is expected to provide new ideas for the research of high-temperature superconducting junction devices.

Out-of-plane preferential growth of 2D molybdenum diselenide nanosheets on laser-induced periodic surface structures

In this study, we explore the morphology and orientation of molybdenum diselenide, a Van der Waals 2D material, through isothermal closed space vapor deposition on both pristine and laser-structured substrates. Laser structuring is conducted on dielectric (sapphire), semiconductor (silicon), and conductive (titanium nitride) substrates using ultrashort laser pulses, resulting in smooth topographic changes such as laser-induced periodic surface structures (LIPSS) or selective ablation. Scanning electron microscopy (SEM) reveals the pivotal role of surface structuring in the growth of out-of-plane MoSe2 nanosheets. This effect is particularly pronounced on monocrystalline substrates like sapphire and silicon, exhibiting in-plane growth on pristine substrates. Additionally, Raman spectroscopy confirms the vertical orientation of flakes on structured substrates and highlights the presence of active edge sites by demonstrating an increased abundance of deposited material. Overall, our findings emphasize the controllability of directing the growth of MoSe2 flakes through appropriate pre-treatment of the substrate, with potential applications in various fields, including Surface-Enhanced Raman Scattering (SERS). Furthermore, the scalability, reproducibility, and applicability to any substrate make ultrashort laser structuration a promising general strategy for orienting 2D materials.

Investigation of the nano and micromechanical performance of β-Ga2O3 epitaxial films on sapphire using nanoindentation

Beta-phase gallium oxide (β-Ga2O3) has attracted considerable attention because of its excellent properties as one of the emerging semiconductor materials. However, not only the fabrication of high quality β-Ga2O3 thin films on heterogeneous substrates is challenging, but there is also a lack of research pertaining to their mechanical properties. In this work, the mechanical properties of β-Ga2O3 epitaxial films of varying thicknesses on c-plane sapphire substrates fabricated via plasma enhanced chemical vapor deposition were investigated through nanoindentation and nano-scratch experiments. The β-Ga2O3 hetero-epitaxial thin films exhibit preferential orientation growth along the (−201) plane when deposited on the c-plane sapphire substrate. The elastic modulus, hardness, and fracture toughness of β-Ga2O3 films grown on sapphire substrates are 249.1 ± 14.1 GPa, 18.7 ± 0.9 GPa, and 1.822 MPa m1/2, respectively. The elastic-plastic behavior of β-Ga2O3 thin films with varying thicknesses is consistent. The critical loads for the elastic-plastic and plastic-brittle transitions are 9.4 ± 1.8 mN and 50.7 ± 2.7 mN respectively, while the scratch depths for the same are 91.8 ± 7.8 nm and 216.4 ± 10.1 nm, respectively. The critical adhesion and adhesive energy for the desquamation of the β-Ga2O3 film from the substrate are dependent on the thickness of the film. These results establish an experimental basis for understanding the mechanical behavior in the preparation and application of β-Ga2O3 thin films grown on sapphire substrates.