Facet Area Research Articles

First Principles Unveiling Equilibrium Shapes for Understanding Morphological Growth Mechanisms in Alumina Polymorphs

Understanding the morphological evolution of crystals is crucial for industrial applications and surface engineering. This study employs a multifaceted analytical approach to comprehensively analyze gibbsite, boehmite, η, γ, δ, θ, κ, and α-Al2O3. Density Functional Theory (DFT) surface energy calculations provide essential viewpoints into facet exposure and stability, enriching our comprehension of growth patterns. Using the Bravais–Friedel–Donnay–Harker (BFDH) method, a meticulous investigation into morphological properties reveals equilibrium shapes for each structure. Crucially, our models unveil the inaugural equilibrium shapes for structures previously undocumented in the literature (e.g., η, δ, θ, and κ-Al2O3). The study explores morphological growth process during phase transitions from gibbsite and boehmite to alpha alumina, emphasizing nucleation and dissolution preferences for specific facets. A grain analysis, considering bulk energy, surface area, and volume, designates α-Al2O3 as the most stable phase, offering valuable standpoints on thermodynamics and indicating a direct correlation between facet area and volume. Additionally, a comprehensive 3D surface energy mapping offers intricate visualization of facet interactions, providing valuable viewpoints into the complex relationships between surface energy, facet area, and interplanar distance. Comparisons of Fourier-transform infrared spectroscopy (FTIR) spectra, exclusively within the 200–400 cm-1 range, underscore close agreement between theoretical and experimental spectra, consistent with the expected reduction in specific surface area during polymorphic transformation.

Very high cycle fatigue properties of ultrahigh strength steels in the presence of hydrogen

The very high cycle fatigue (VHCF) properties of 2000 MPa ultrahigh strength martensitic steels after hydrogen pre-charging were investigated by means of ultrasonic fatigue tests. Results showed that the VHCF lives of the experimental steels were drastically decreased by about two orders after pre-charged with a hydrogen concentration of CH = 1.23 wppm. The experimental steel tempered at a higher temperature of 300 °C with some epsilon-carbides and a lower density of dislocations showed higher VHCF lives in the presence of hydrogen. It could be attributed to the lower hydrogen diffusion coefficient since hydrogen might accelerate fatigue crack propagation in the granular bright facet (GBF) area.

ОЦЕНКА ПЛОЩАДИ ОККЛЮЗИОННЫХ КОНТАКТОВ У ПАЦИЕНТОВ С ПАРАФУНКЦИЯМИ ЗУБОЧЕЛЮСТНОЙ СИСТЕМЫ ДО И ПОСЛЕ СПЛИНТ- ТЕРАПИИ С ПОМОЩЬЮ ЦИФРОВОГО АППАРАТА T-SCAN

Abstract. Currently, dentists in the treatment of patients are increasingly encountering manifestations of parafunctions in the dental system. Most often, this manifests itself unconsciously in the form of daytime or nighttime bruxism and clenching. However, there is no reliable easily feasible method for diagnosing parafunctions. Digital dentistry is actively developing, which opens up new opportunities for assessing occlusive contacts. One of the most functional devices in this field is the T-scan. The aim of the study was to assess the area of facets of tooth erasure in patients with parafunctions before and after the use of occlusive splints using data from a digital T-scan device. In the study, occlusal contacts were registered, the sums of the facet areas of tooth erasure at the beginning of treatment and 6 months after splint therapy were calculated from the occlusiograms obtained. The results of the study showed that at the very beginning of the study, the values of the occlusal parameters of the right and left sides in patients in the group with bruxism and clenching prevail values of the left side of the dentition. The average sum of occlusal contact areas in patients with parafunctions was 310.02 mm2 on the left and 234 mm2 on the right. Upon repeated measurement, after splint therapy, the sum of the areas of occlusal contacts was 305.1 mm2 and 289.04 mm2 on the left and right, respectively. Thus, it is proved that the sum of the areas of occlusal contacts in patients on the left side of the dentition before the use of an occlusal splint significantly prevails over those after splint therapy. Occlusal forces between both sides of the lower jaw after the treatment have become more symmetrical and are close to a uniform distribution of force. This technique allows screening and monitoring of patients with bruxism and clenching.

Enhanced piezo-catalytic performance of BaTiO3 nanorods combining highly exposed active crystalline facets and superior deformation capability: Water purification and activation mechanism

Using piezoelectric materials for advanced oxidation is a green and viable means of water purification and environmental restoration. However, unmodified piezoelectric catalysts exhibited unsatisfactory catalytic performance, which had become a bottleneck for the practical application of piezoelectric catalysis. In this work, piezoelectric responsiveness and exposed active crystal surface area were rationally coordinated by synthesizing one-dimensional BaTiO3 nanorods (BTO NRs). Enhanced piezo-responsivity enables faster free charge carriers transfer, while the highly exposed area of the (001) facets provides more active sites for piezo-catalytic reactions. Consequently, BTO NRs degraded RHB (Rhodamine B) and TC (Tetracycline) with first-order rate constants of 0.018 min−1 and 0.012 min−1, respectively, 5 times higher than BaTiO3 nanoparticles. The specific active sites on the (001) crystal plane were further investigated through a combination of DFT calculations, free radical trapping experiments, and XPS analysis. Ti4+ adsorbs and activates water molecules to generate Ti3+ and •OH, in the catalytic reaction. Afterward, Ti3+ is oxidized to Ti4+ by piezo-holes (holes driven by piezoelectric potential), while •OH is desorbed and involved in the degradation of pollutants. This research not only provides an approach to modify piezoelectric catalysts with high catalytic activity but also presents new insights into the mechanism of piezoelectric catalysis from the viewpoint of the atom level.

Exploring the solvent effect on crystal morphology of naphazoline hydrochloride: Molecular dynamic simulations and experiments

The crystal morphologies of naphazoline hydrochloride (NPZ) in vacuum and binary solvent conditions (methanol + ethyl acetate, methanol + ethanol, methanol + isopropanol and 2-moxyethanol + isopropanol) were investigated by the molecular dynamic (MD) simulation and experiments. The Hirshfeld surface (HS) analysis was employed to explore the interactions in the crystal structure of NPZ, and results revealed that H···H and H···Cl/Cl···H contacts were primary contributing interactions. The attachment energy (AE) model was utilized to simulate the crystal habit of NPZ in vacuum based on the single crystal data, resulting in the identification of six morphological crystal facets. Also, the structural characteristics of dominant crystal faces were analyzed. The crystal morphologies of NPZ in different binary solvents were predicted using the modified attachment energy (MAE) model. The simulation results indicated that the solvent adsorption processes on the crystal surfaces were exothermic, and {002} face had largest morphological importance in all solvent systems. Furthermore, the experimental morphology of NPZ obtained from the methanol + ethyl acetate system was consistent with the crystal habit predicted by MAE model, which was plate-shape. On this basis, the intermolecular interactions between solvent molecules and {002} as well as {1 1––1} facets were analyzed detailly by radial distribution function (RDF) and mean square displacement (MSD), respectively. The RDF analysis indicated that N atoms of {002} face formed hydrogen bonds with O atoms of solvent molecules, resulting in an evident change in the total facet area of this face. Moreover, MSD analysis demonstrated that the absorptions of solvent molecules on the {1 1––1} face were the main factor affecting the growth rate of this crystal surface.

Axial and bending very high cycle fatigue of completion string

Preventing or mitigating very high cycle fatigue (VHCF) damage and failure of completion string is essential for ensuring their long-term stable operation. Therefore, a comprehensive understanding of the string's fatigue performance in tension, compression, and bending over an extended service life is necessary. This study investigated the evolution, microscopic mechanisms, fracture behavior, and life prediction of VHCF damage in completion string under axial and bending conditions. It was found that the intragranular twin structures on the critical interface of VHCF source directly participate in lattice reconstruction, enhancing the grain's strain coordination ability, and increasing the proportion of facet area on the fatigue fracture surface. Based on the fracture characteristics of VHCF, the Mayer empirical formula was improved, and a novel convolutional neural network (CNN) based VHCF life prediction model was proposed. Utilizing the CNN's powerful fracture feature extraction and nonlinear modeling capabilities, the VHCF fatigue life prediction accuracy was significantly enhanced, with prediction errors all within 2 times the experimental results' error range. Based on the axial and bending VHCF fracture mechanisms of completion string and CNN, a more advanced method for predicting axial and bending VHCF life is provided, offering theoretical supports for the engineering safety service and life assessment of completion string.

A comparative study on the measurement of surface bubble size distributions in dry aqueous foams using optical methods

The measurement of bubble sizes in aqueous foams based on images of the surface is a typical method used in laboratory and industrial scales. In this article the relationship between the size distribution of the facet areas and the bubble size of wall-touching bubbles is investigated. To achieve this an invasive sampling approach is used for in-situ collection of wall-touching bubbles in dry foams, while the surface is imaged in parallel. Bubble and facet size distributions are obtained using automated image processing. It is shown that sharp peaks in the bubble size distribution will appear smoother in the facet size distribution. This results in an overestimation of polydispersity by the surface measurements. Furthermore, it is observed that the mean equivalent diameter of the facets is on average 6% smaller than the bubble diameter obtained using the sampling method. An approach proposed by Wang and Neethling (2009) gives a good approximation of the relation between facet and bubble size and can be used to reduce potential uncertainties in surface based bubble size measurements.

Structural characterization, Hirshfeld surface analysis, optical properties, and DFT study of a new copper(II) complex

The reaction of copper acetate and 4,4′-dimethoxy-2,2′-bipyridyl in ethanol afforded a novel complex, 4,4′-dimethoxy-2,2′-bipyridyl Cu(II) acetate disolvate, whose structure was determined unambiguously by single-crystal X-ray diffraction (SC-XRD) analysis. The complex was found to crystallize with a space group of P21/n and in the monoclinic system. The crystal structure shows molecular tapes arising from strong intermolecular hydrogen bonding and two molecules of water within the crystal lattice. The intermolecular interactions were studied using Hirshfeld surface analysis and the role of water molecules in stabilizing the crystal packing was explored. BFDH and attachment energy (AE) models were used in the prediction of the crystal morphology of the complex. The results of these computational studies revealed that the (10−1) face can be preserved with the most facet area due to its exceptionally slow crystal growth rate and minimal attachment energy. The DFT study of the complex shows that the complex is a direct semiconductor with an optical band gap energy of 1.8 eV. The study of the optical properties of the complex shows that it can be used in the solar cell device where the best absorption of about 6 × 104 cm−1 was shown along [001] direction with a reflectivity that does not exceed 13% along the same direction.

Clinical and Radiological Outcomes of a Comparative Study of Anterior Cervical Decompression and Fusion with Partial Pediculotomy, Partial Vertebrotomy (PPPV) Posterior Endoscopic Cervical Decompression (PECD) for Cervical Foraminal Pathology.

Background and Objectives: The purpose was to compaSre medium-term clinical and radiological outcomes of Partial Pediculotomy, Partial Vertebrotomy (PPPV) Posterior Endoscopic Cervical Decompression (PECD) surgery versus Anterior Cervical Discectomy and Fusion (ACDF) for patients with cervical disc herniations and foraminal pathologies. Materials and Methods: A prospective registry of patients who had undergone either PPPV PECD surgery or ACDF surgery for cervical disc herniation or foraminal pathologies under a single fellowship-trained spine surgeon was performed. The baseline characteristics and operative details including complications were recorded for all included patients. The clinical outcomes evaluated include VAS, MJOA, motor score, and NDI and MacNab's score. The radiological parameters in neutral-measured facet length, facet area, disc height, C2-C7 angle, neck tilt angle, T1 slope and thoracic inlet angle were also evaluated. Results: A total of 55 patients (29 PPPV PECD, 26 ACDF) were included, with mean follow-up periods of 21.9 and 32.3 months, respectively. Each cohort was noted to have a single case of surgical complication. Statistically significant changes of facet area (49.05 ± 14.50%) and facet length (52.71 ± 15.11%) were noted in the PPPV PECD group. At neutral alignment of the neck on a lateral X-ray, compared to ACDF, PPPV PECD had a statistically significant change in neck tilt angle (-11.68 ± 17.35°) and T1 slope angle (-11.69 ± 19.58°). Whilst both PPPV PECD and ACDF had significant improvements in VAS, MJOA and NDI postoperatively, PPPV PECD was found to be superior across all above scores at various follow-up timepoints compared to its ACDF counterparts. Conclusions: PPPV PECD surgery achieved a satisfactory radiological correction of neck alignment and significantly improved clinical outcomes at medium-term follow-up for our cohort of patients, highlighting its feasibility in treating patients with cervical disc herniations and foraminal pathologies.

The effect of solvent–crystal interaction on the morphology of a solvate of rifampicin

The large attachment energy (AE) of (1 0 0) and (1 −1 0) explains their vanishment. Stronger interaction with n-butanol of (0 −2 0) leads to its larger facet area than (0 2 0). The larger AE of (1 1 0) than (0 0 1) explains its faster growth rate.

The Crucial Role of Solvation Forces in the Steric Stabilization of Nanoplatelets.

The steric stability of inorganic colloidal particles in an apolar solvent is usually described in terms of the balance between three contributions: the van der Waals attraction, the free energy of mixing, and the ligand compression. However, in the case of nanoparticles, the discrete nature of the ligand shell and the solvent has to be taken into account. Cadmium selenide nanoplatelets are a special case. They combine a weak van der Waals attraction and a large facet to particle size ratio. We use coarse grained molecular dynamics simulations of nanoplatelets in octane to demonstrate that solvation forces are strong enough to induce the formation of nanoplatelet stacks and by that have a crucial impact on the steric stability. In particular, we demonstrate that for sufficiently large nanoplatelets, solvation forces are proportional to the interacting facet area, and their strength is intrinsically tied to the softness of the ligand shell.

Tooth whorl structure, growth and function in a helicoprionid chondrichthyan Karpinskiprion (nom. nov.) (Eugeneodontiformes) with a revision of the family composition

ABSTRACTRestudy of Campyloprion annectans Eastman, 1902 from North America demonstrated that neither specimen included is diagnostic at the species level; thus, the species name is a nomen dubium. Since this species was designated as the type species of the genus, this requires suppression of the generic name also. Another species earlier assigned to Campyloprion, Campyloprion ivanovi Karpinsky, 1924 is used as a type for a newly established genus Karpinskiprion Lebedev et Itano gen. nov. The composition of the family Helicoprionidae Karpinsky, 1911 is reviewed, and a new family Helicampodontidae Itano et Lebedev fam. nov. is erected. A new specimen of Karpinskiprion ivanovi (Karpinsky, 1924) recently discovered in the Volgograd Region of Russia is the most complete Karpinskiprion specimen ever found. It unambiguously demonstrates the coiled nature of these tooth whorls and presents information on their developmental stages. During organogeny, cutting blades of the crown became reshaped, and basal spurs progressively elongated, forming a grater. Whorl growth occurred by addition of new crowns to the earlier mineralised base followed by later spur growth. In contrast to consistently uniform cutting blades, spurs are often malformed and bear traces of growth interruption. Both sides of the outer coil of the tooth whorl bear lifetime wear facets. The youngest (lingual) crowns are as yet unaffected by wear. The best-preserved facets show parallel radially directed scratch marks. The upper jaw dentition of Karpinskiprion is unknown, but we suggest that the faceted areas resulted from interaction with the antagonistic dental structures here. Three possible hypotheses for this interaction are suggested: (a) two opposing whorls acted as scissor blades, moving alternately from one side to another; (b) the lower tooth whorl fitted between paired parasymphyseal tooth whorls of the opposing jaw; or (c) the lower tooth whorl fitted into a dental pavement in the upper jaw.

Facet-induced charge transfer and photocatalytic performance of an S-scheme hybrid heterojunction composed of porous g-C3N4 nanosheets and WO3 nanorods with exposed high-energy (0 0 1) facets

Crystal facet engineering has been demonstrated to be a flexible technique that significantly improves photocatalyst performance by promoting interfacial charge transfer and separation. In this study, we systematically coupled porous polymeric carbon nitride nanosheets (PCN) and WO3 nanorods with exposed (001) facets (WOAT) to fabricate a WOAT@PCN hybrid photocatalyst with improved photocatalytic properties. Importantly, the fabricated WOAT@PCN hybrid catalyst demonstrated significantly enhanced performance for the degradation of oxytetracycline and naproxen pollutants under visible light compared to PCN, WOAT, and WOST with different exposed facets. Furthermore, the hybrid catalyst demonstrated excellent stability and reusability across multiple test runs. The remarkable photodegradation performance of the hybrid catalyst is primarily attributable to the intrinsically high surface area and charge separation properties of the (001) facets of WOAT, enhanced visible light absorption, and S-scheme charge transfer at the interface, promoting photoexcited charge separation and enhancing the redox capabilities of the separated photoexcited electrons and holes. In addition, total organic carbon (TOC) analysis confirmed the efficacy of mineralization, while liquid chromatography/tandem mass spectrometry (LC/MS/MS) studies revealed the potential degradation pathways of sample pollutants. This study elucidates the systematic design of hybrid catalysts using crystal facet engineering for various photocatalytic applications.

Atomic-scale investigation on the origin of in-plane variants in L1-FePt nanoparticles embedded in a single-crystalline MgO matrix

In this work, we present an atomic-scale investigation of L10-FePt particles that are partly or fully embedded in a single-crystalline MgO matrix. Hundreds of particles in different orientations, of different sizes, and with different side contact facets are statistically and quantitatively analyzed. It is found that the presence of side contact facets does not introduce any misorientation in particles with the c axis out-of-plane (OP), even in those of small sizes. In addition, a markedly higher proportion of in-plane (IP) variants is found in smaller particles of sizes less than 10 nm, and most IP variants and the IP part in multi-variants have a large area of side contact facets or are even fully embedded. Those results can be explained by the fact that the transformation strain and interface strain jointly affect the particle orientation, and the competition between total strain energy in the film plane and in lateral planes plays a key role in determining particle orientation. Thus, a suggestion on the L10-FePt nanoparticle film production can be proposed that a moderate area of side contact facets may help keep a perfect OP orientation in the OP particles without increasing the proportion of IP variants. Additionally, our work can provide reference information on the variant orientation preference during a post-annealing process in nanoparticle films on a rough substrate or embedded in a matrix as well as in core–shell material systems.

Emotive facets of place meet urban analytics

AbstractThe lack of a well‐established and unified place theory across disciplines is decelerating its formalization, evolution, and especially its pragmatic implications and applicability. In this article, we identify research gaps in the emotive facets of place scholarship. We found that it: (1) rarely joins physical, social, and individual variables in the same model; (2) omits the immediately perceived and sensory dimensions; (3) disregards the analysis of how individual–place emotive relationships vary across time; and (4) overlooks the difficulties of reducing multifaceted emotive facets of place into geographic features. Next, we examine these research gaps through the lens of technology‐based advancements in urban analytics. Finally, we discuss the need to combine social‐oriented research and (spatial) data‐driven disciplines to enrich and expand the research area of emotive facets of place and connected disciplines.

Capping-Ligand Density on Cu Nanoparticles Determining Multi-Carbon Product Selectivity in Electrochemical CO2 Reduction

Carbon dioxide (CO2) emission from the combustion of fossil fuel causes global warming and climate change. Much attention has been paid for recycling of CO2 gas, namely converting this greenhouse gas to high-value fuels such as multi-carbon products (ethylene, ethanol, propanol, etc.). In particular, electrochemical CO2 reduction reaction (CO2RR) is one of the promising methods operated at ambient pressure and room temperature. By using gold and silver catalysts, carbon monoxide (CO) is successfully yielded with >80% Faradaic efficiency. In contrast, it is still challenging to produce multi-carbon (i.e., C2+) products. Copper (Cu) is known as the sole catalyst to yield C2+ products by affording the suitable binding energy to the intermediate of *CO (the asterisk denotes the surface adsorption). Although various synthetic methods for the preparation of Cu nanoparticles (NPs) have been developed to increase the surface area and design of the preferred facets for the CO2 reduction, the highly sensitive Cu surface in air and from contaminants resulted in variable Faradaic efficiencies for C2+ production. In particular, the capping ligands, which coat the Cu surface to stabilize the designed nanostructures, should significantly influence the catalytic efficiency and stability. However, their effects have been little studied.Here, we show the enhanced catalytic activity and stability of Cu NPs for the C2+ yield by eliminating the capping ligands.[1] The pristine Cu NPs with ~8 nm of diameter were prepared by using a capping ligand of tetradecylphosphonate (TDP). After UV-ozone treatment, the TDP ligands were eliminated in part; The phosphorous signal was attenuated, and the Cu surface was oxidized in X-ray photoelectron spectra. In addition, the carbonyl oxygen (O=C) emerged from the damaged TDP. In contrast, the carbon substrate and the surface roughness of the Cu were insignificantly changed. These UV-ozone-treated Cu NPs showed ~50% Faradaic efficiency of the C2+ conversion (FEC2+) at –0.98 V vs. RHE, which was twice as high as that of the pristine Cu NPs (~25%). In particular, the FEC2+ gradually increased as the remaining capping ligands were removed, indicating the increased catalytic sites for 3 h CO2RR. In sharp contrast, the FEC2+ from the pristine Cu NPs was consistently low despite the partial stripping of the capping ligands, suggesting the negligible formation of the C2+ active sites. For prolonged chronoamperometry tests for 20 h, these FEC2+ values were retained for both catalysts, while the size and shape of Cu catalysts were differently changed. The UV-ozone-treated ones proceeded little agglomeration and contained many grain boundaries. In contrast, the pristine Cu NPs were transformed to the cubic particles with ~100 nm size. The distinct alternations of Cu structures are closely related to the yield of the C2+ active sites, which I will discuss in this presentation.[1] J. Mater. Chem. A, 9, 11210 (2021) Figure 1

Highly porous α-MnO2 nanorods with enhanced defect accessibility for efficient catalytic ozonation of refractory pollutants

Herein we reported the first example of preparing α-MnO2 by selective acid etching from Mn-containing spinel. The defects, facet, and surface area of α-MnO2 were cooperatively engineered by an all-in-one acid etching method to enhance the defect accessibility to the reactants. The obtained highly porous α-MnO2 nanorods have rich defects of Mn3+ (24.9%) and oxygen vacancies (31.4%), mainly active crystal facets of (110), and an ultrahigh surface area of 271.1 m2/g. With α-MnO2 nanorods as the catalysts, more than 90.9% of 4-chlorophenol can be degraded within 12 min by catalytic ozonation in a wide work pH of 4.5–10.5. The experiments and DFT theory calculations reveal that α-MnO2 with (110) facet promotes the adsorption and activation of ozone directly over the defects or indirectly over H2O adsorbed on the defects. Thus, more reactive oxygen species (e.g., •OH, •O2-, 1O2, surface *O) are generated and get involved in pollutant degradation. This work provides a facile method to maximize the defect accessibility, and a deeper mechanistic study to understand the roles of the defects.

Synthesis of Magnesium Hydroxide Using Post‐Reaction Filtrate as Ammonia Carrier and Morphology Analysis

AbstractThis study proposes an advanced technology using post‐reaction filtrate as an ammonia carrier to synthesize magnesium hydroxide (MH) with small particles, which can benefit subsequent hydrothermal modification. In this work, the limitation of ammonia gas and ammonia water methods is avoided. The impact of operating parameters including MgCl2 concentration, temperature, ammonia‐to‐magnesium molar ratio, feed rate, volume of ammonia mother liquor and aging time on the magnesium yield, particle size, and morphology of MH is studied. The temperature and ammonia‐to‐magnesium molar ratio are identified as key factors affecting magnesium yield. MH with a half‐content diameter of 1.70 µm and a morphology resembling small irregular flakes is successfully synthesized at a magnesium yield of 90.06%. The predictions of idea crystal habits are also performed using Morphology and CASTEP modules with Materials Studio Software. The (0 0 1) face can be preserved with the largest facet area because of the slowest crystal growth rate and the smallest attachment energy, which exhibits that MH crystals tend to be flakes.

Effect of long-period stacking ordered structure on very high cycle fatigue properties of Mg-Gd-Y-Zn-Zr alloys

Magnesium alloys with a long-period stacking ordered (LPSO) structure usually possess excellent static strength, but their fatigue behaviors are poorly understood. This work presents the effect of the LPSO structure on the crack behaviors of Mg alloys in a very high cycle fatigue (VHCF) regime. The LPSO lamellas lead to a facet-like cracking process along the basal planes at the crack initiation site and strongly prohibit the early crack propagation by deflecting the growth direction. The stress intensity factor at the periphery of the faceted area is much higher than the conventional LPSO-free Mg alloys, contributing higher fatigue crack propagation threshold of LPSO-containing Mg alloys. Microstructure observation at the facets reveals a layer of ultrafine grains at the fracture surface due to the cyclic contact of the crack surface, which supports the numerous cyclic pressing model describing the VHCF crack initiation behavior.

Very High Cycle Fatigue Properties of 18CrNiMo7-6 Carburized Steel with Gradient Hardness Distribution

As research of the high cycle fatigue of carburized gear steel could not meet the status quo of longer and longer service lives, research of very high cycle fatigue (VHCF) performance has become the focus of current research. The VHCF properties of case-hardening steel 18CrNiMo7-6 after being carburized with gradient hardness distribution were investigated by means of ultrasonic fatigue tests. The results showed that the carburized specimens with a case hardness of 705 HV and core hardness of 530 HV showed VHCF phenomenon, and the fatigue lives continuously increased to even 109 cycles as the stress amplitude decreased to about 500 MPa. Observations of the fracture surfaces of the fatigue specimens showed that the fatigue crack initiation sites were located in the transition area with the hardness at about 580 HV. It was found that the transition area had low VHCF properties, since the core did not show VHCF phenomenon, and the case had a higher hardness. A fine microstructure was observed in the granular bright facet (GBF) area, and the stress intensity factor ΔKGBF was measured to be 3.04 MPam−1/2. The 109 cycles fatigue life was predicted based on the inclusion size, and the 1010 cycles fatigue life was 490 MPa based on the prediction model.