Surface Formation Mechanism Research Articles

Atomistic understanding on the surface formation mechanism of nanoscale scratches along different crystal orientations of silicon carbide

Single crystal silicon carbide has been widely used in many fields due to its excellent physical and chemical properties. However, these special properties of silicon carbide can lead to surface defects and subsurface damage in precision machining processes. In this research, high-speed scratching experiments and molecular dynamics simulations were used to study the surface formation mechanism of nanoscale scratches along the [1-210] and [1-100] crystal orientations of silicon carbide. For both the simulations and experiments, different scratching crystal orientations result in the formation of different amorphous patterns. The angle between the scratching orientation [1-210] and the amorphous pattern is 60°, while the angle between scratching orientation [1-100] and the amorphous pattern is 30°. The stress concentration during the scratching process along the orientations [1-210] and [1-100] is mainly located at the two edges and one edge of the amorphous patterns, respectively. The amorphous patterns along the < 1-210 > directions on the (0001) plane are caused by dislocations and slips on the {10-10} plane. This study reveals the material deformation mechanism and removal mechanism of silicon carbide along different crystal orientations scratching, providing theoretical guidance for the nanoscale machining of silicon carbide.

Achievement of ductile-regime removal in fabricating Gaussian curved microstructure processed by micro ball-end milling on soft-brittle KDP surface

Laser-induced damage points (known as defects) would seriously reduce the service life of large-aperture KDP optics in high-power laser devices. The ball-end milling procedure is recognized as an efficient method for creating a Gaussian mitigation pit (GMP) to restore the optical transmission performance of functional KDP crystals by removing defects. Nevertheless, achieving smooth and flawless Gaussian curved microstructures is a massive challenge for soft-brittle KDP crystals. Herein, a judging criterion of the ductile-regime machining for the GMP is developed by the models of uncut chip thickness (UCT) and critical milling depth. Simultaneously, the obtained judging criterion can be validated by the microstructure fabrication experiments. Besides, considering the spindle vibration, plowing effect, and machined surface texture, the influence of spindle speed (n), feed rate (f), and tool mark interval (d) on the surface formation mechanism of the GMP is analyzed, respectively. It can be discovered that the n of up to 60,000 r/min can lead to severe velocity fluctuation of the motion system, increasing the UCT and causing brittle fractures on the KDP surface. A low f can result in an undesirable plowing phenomenon, and a large number of crystal materials are accumulated in the up-cut process. Once the f reaches 72 mm/min, the tool path would fluctuate significantly, resulting in poor GMP surface texture. When the d exceeds 15 μm, the surface quality of the GMP can no longer meet the engineering requirements of the Ra ≤ 50 nm. Moreover, the optimized processing parameters of the microstructure fabrication are 47,800 r/min in the n, 30 mm/min in the f, and 5 μm in the d. This study can provide crucial guidance for obtaining the ultra-smooth and defect-free GMP processed in the ductile regime, which would resultantly possess significant theoretical importance and practical value in enhancing the optical properties of flawed KDP crystals.

A reexamination of the relationship between β to α crystal transition and the surface crater formation in biaxially oriented polypropylene film

The formation mechanism of the crater-like surface of biaxially oriented polypropylene (BOPP) film remains controversial. To clarify this issue, in this work, three isotactic polypropylene (iPP) samples with different tacticities are selected to prepare BOPP films. It is shown that the relative β crystal content (kβ) in the cast sheet increases with tacticity. The β crystal transforms to the α crystal when stretched at 145 °C along the machine direction. For all the samples, rough surfaces are obtained even if the kβ value of the cast sheet is very low (kβ < 0.1). The arithmetic mean roughness (Ra) of the BOPP films increases with the increase of the kβ in the cast sheet. While higher kβ in the iPP cast sheet contributes to a higher Ra value, the β crystallites hinder the enlargement of roughening rings, and cause surface defects (cavitation), which are detrimental to applications. Our results indicate that the β crystal in the cast sheet is not essential for the crater formation and a higher β crystal content is not always beneficial for BOPP capacitor films.

A novel process of chemical-mechanical fluid-solid coupling polishing with high-quality and high-efficiency for turbine blisk

Turbine blisk is the core part of an aero-engine, which is characterized by its complex blade profile, resulting in the difficulty of its polishing. In this study, a novel process of chemical-mechanical fluid-solid coupling polishing was proposed to achieve high-quality and high-efficiency polishing for the blisk. Analyzed the principle of chemical-mechanical fluid-solid coupling polishing process of the blisk with the material of K418 nickel-based alloy. Then, established the material removal theoretical model of the process, and investigated the influence law of process parameters on the blisk surface force state to obtain the optimal parameters by using FLUENT fluid simulation. Moreover, simulated the abrasive particle trajectory to reveal the formation mechanism of the blisk surface with high-quality and high-efficiency. Furtherly, experiment shows that the novel process can effectively improve the blisk surface quality, and the surface roughness Ra decreased from 3.151 μm to 0.779 μm. This method provides a novel solution for precision polishing of the complex structural parts.

In-situ ellipsometric study of WO3–x dielectric permittivity during gasochromic colouration

The complex dielectric permittivity of tungsten oxide at all stages of its colouration in a hydrogen-rich atmosphere was retrieved from measured VIS-NIR ellipsometric spectra of WO3/Pd bilayer. The retrieval was done by fitting the spectra with the Cody-Lorentz dispersion model, and, for optical absorption features, two Gaussian functions were added. The band gap edge, the Gaussian center energies, amplitudes, spectral widths and integrals were traced as the redox reaction progressed. Analysis of obtained data provides insight into mechanism of surface and bulk oxygen vacancies formation. We discuss these peculiarities in detail and show how they do affect the optical constants of WO3–x and potential sensors’ response rates.

The effects of the angle between the indenter edge and the scratch direction on the scratch characteristics of Ti–6Al–4V alloy

Ti–6Al–4V alloy has become a crucial raw material in aerospace and other industries owing to its exceptional mechanical properties. However, it is also a typical difficult-to-machine material, and its removal process and mechanism have been widely investigated by scratch testing. Nevertheless, the inherent non-rotational symmetry of the Vickers indenter introduces a crucial parameter, i.e., the angle λ between the indenter edge and the scratch direction, which affects not only the mechanical response of materials but also its surface formation mechanism during scratch. This study systematically characterized the micro/nano scratch characteristics of Ti–6Al–4V alloy under three typical angles λ (0°, 22.5°, 45°) as well as various normal forces and scratch speeds. The coefficient of friction (COF), scratch depth, scratch width, residual scratch morphology, and specific scratch energy were comparatively analyzed. Finite element simulations confirmed that the direction of material flow changed with the change in angle λ. The corresponding deformation mechanisms during scratch were discussed accordingly. The results revealed a significant influence of the angle λ on the scratch behaviors and surface quality of Ti–6Al–4V alloy.

Formation mechanism and properties of superhydrophobic surface of ship plate steel

Superhydrophobic surface of ship plate steel was constructed by chemical etching and low surface energy modification. Formation mechanism and properties of the superhydrophobic surface were investigated through SEM, FT-IR, electrochemical analysis and anti-icing evaluation. Corrosion and dissolution of ferrite creates a high-roughness surface with a micro-nano composite structure, and a monomolecular layer of low surface energy material covers steel surface through chelation coordination of stearic acid and Fe, which endows ship plate steel surface with superhydrophobicity. Compared with bare steel, the superhydrophobic surface shows high corrosion resistance, while 75.2% of surface icing is prevented, achieving the purpose of anti-water, anti-icing and corrosion resistance of ship plate steel. In addtion, the simple and cost-effective preparation technique is conducive to large-scale industrial applications in the future.

Surface microtopography evolution of monocrystalline silicon in chemical mechanical polishing

Chemical mechanical polishing (CMP) is a widely utilized technique for achieving ultra-smooth surfaces, yet a comprehensive understanding of the surface microtopography evolution remains elusive due to the intricate chemical and mechanical interactions inherent in chemical mechanical polishing. Accordingly, this study explores the evolution law of different spatial frequency features of surface microtopography of monocrystalline silicon by analyzing the changes in the power spectral density (PSD) curve. More importantly, the evolution mechanism of the chemical mechanical polishing surface micromorphology is revealed through the analysis of the power spectral density under different mechanical and chemical conditions. The results emphasize the noticeable impact of both mechanical and chemical actions on the evolution of different spatial frequency features in surface microtopography. The mechanical action of a large particle, less likely to contact the valley region with a small curvature radius, enhances the smoothing speed of high-spatial frequency roughness. Moreover, the mechanical action of polishing pad demonstrates a greater efficiency in smoothing mid-spatial frequency roughness when utilizing a hard pad. This is attributed to the limited impact of pad hardness on the removal depth of single particles within the reaction layer, rendering it less significant for high-spatial frequency roughness. Upon elevating the chemical reaction rate, a notable acceleration in the reduction of roughness in both mid- and high-spatial frequency regions is observed. Furthermore, insights derived from molecular dynamics (MD) simulations of monocrystalline silicon and quartz glass show that the manner of surface atom removal, whether through single atom removal or cluster removal, exerts a significant effect on the final high-spatial frequency components of the power spectral density. This study contributes valuable insights into the intricate formation mechanism of a smooth surface in chemical mechanical polishing.

Enhancement of SrTiO3 photocatalytic efficiency by Al doping: Answers from the structure, morphology and electronic properties contributions

Our study focuses on disclosing the mechanisms standing behind the improved photocatalytic performance of SrTiO3, where Al modification of the perovskite structure boosts the photocatalytic O2 evolution activity of the Al:SrTiO3 system. By adapting the synthesis method that produces well-crystallized materials with low defect density and employing surface modification techniques, we aim to enhance the photocatalytic efficiency of SrTiO3via Al2O3 nanoceramic oxide doping at concentrations ranging from 0 to 10% and further examining of the relationship between doping process and the changes in the electronic and crystalline structure of SrTiO3. The prepared Al-based SrTiO3 perovskite samples (Al3%:SrTiO3, Al7%:SrTiO3, Al10%:SrTiO3) were thoroughly characterized to understand their structural, electronic, and morphological properties. Complementary X-ray techniques were employed to assess the stoichiometry (X-ray photoelectron spectroscopy - XPS), local environment, and chemical state (X-ray absorption spectroscopy - XAS in both total electron yield (TEY) and fluorescence yield (TFY). The comprehensive characterization enables us to understand the changes in the electronic properties and morphological features of the modified samples elucidating the surface formation mechanism while providing insights into the structural modifications induced by Al doping in the SrTiO3 perovskite lattice. Our findings give new perspectives for the development of Al-modified SrTiO3 perovskite materials with enhanced photocatalytic performance providing rich insights into the optimization of photocatalytic processes for applications in environmental remediation and sustainable energy production.

A theoretical and experimental investigation on the surface formation mechanism in elliptical vibration cutting of single crystal magnesium fluoride

Manufacturing precise microstructures on magnesium fluoride surface remains challenging due to its brittleness and anisotropy. This study investigates the surface formation mechanism in ductile machining of single crystal magnesium fluoride and explores the feasibility of fabricating sophisticated microstructures on magnesium fluoride surfaces by applying elliptical vibration cutting technology. We conducted a systematic study on the ductile-brittle transition behavior, material removal mechanism, and fabrication performance of microstructures through theoretical analysis and cutting experiments. A theoretical model that takes into account the elliptical trajectory's orientation angle has been established to determine the evolution of instantaneous uncut chip thickness and the characteristic nominal depth of cut in one cycle during elliptical vibration cutting. By comprehensively examining the influence of the elliptical trajectory, determined by vibration amplitudes, orientation angle, and nominal cutting speed, on the dynamic behaviour of the ductile-brittle transition, we verified the proposed theoretical model with convincing experimental results. Larger critical depth of cut for ductile-brittle transition and smaller cutting forces achieved by EVC contribute to the improved ductile machinability of MgF2. With optimal vibration parameters, the critical depth of cut increases by 56 times compared to ordinary cutting. Theoretical findings regarding plastic deformation parameters and cleavage fracture parameters align well with experimental observations, providing a more comprehensive understanding of the anisotropy influence on damage evolution during the surface formation in elliptical vibration cutting of magnesium fluoride. Furthermore, leveraging our fundamental understanding of material removal and surface formation mechanisms, we successfully generated bi-sinusoidal arrays on magnesium fluoride surfaces with exceptional accuracy (machining error < 1.5%) and high efficiency (machining time < 121.5 min) by applying elliptical vibration cutting.

The Formation Process and Mechanism of the 3D Porous Network on the Sulfonated PEEK Surface.

A three-dimensional (3D) porous network can be prepared on the PEEK surface by sulfonation with enhanced osseointegration and antibacterial properties. However, few studies have been conducted on the formation mechanism of a 3D porous network. In this work, the surface and cross-sectional morphologies, chemical compositions, functional groups, surface wettability, and crystalline states of sulfonated PEEK were investigated at different sulfonation times and coagulant concentrations. The results show that the number of nodular structures and broken fibers on the sulfonated PEEK surface as well as the size of macrovoids in the cross sections increase with increasing sulfonation times when water is used as a coagulant. In contrast, dilute sulfuric acid as a coagulant can inhibit the formation of surface porous structures and macrovoids in the cross sections. Moreover, all of the sulfonated PEEK samples have the same chemical compositions but exhibit better hydrophilicity as the number of microsized pores decreases. It is proposed that non-solvent-induced phase separation (NIPS) occurs during the sulfonation process, and the formation mechanism of surface and cross-sectional morphologies is discussed. Furthermore, it is assumed that the air is trapped in the microsized pores, leaving the surface of the 3D porous network in the Cassie-wetting state. All of these preliminary results throw light on the nature of the sulfonation process and may guide further modification of the structures of sulfonated PEEK.

Anisotropic etching behavior and topography formation mechanism of silicon solar cell surface textured by atmospheric plasma

Atmospheric plasma etching (APE) has been used to texture Si surfaces due to anisotropic material removal capability. Controlling features and size of the light-trapping structure are keys to improving the reflection performance of silicon (Si) solar cells, which need to fully understand the interfacial etching behavior and the microscopic topography formation mechanism of the Si surface. In this study, microwave plasma with a temperature below 100 °C is employed to investigate the dependence of microstructure evolution on the O/F atom ratios in plasma. The results show that as the O/F atom ratios increase, the microstructure of the Si surface changes from square opening pits to spherical opening pits. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy analyses indicate that the exciting F atoms dominate the orientation-selective etching process, causing the formation of square opening pits. The CFx and C2 radicals induce the generation of the Si interface reactive layer, resulting in the occurrence of amorphous layers and termination of the non ⟨111⟩-crystal face in APE. The exciting O atoms preferentially occupy the active site of Si surfaces, causing the isotropic etching and then the formation of spherical opening pits. In addition, the richer O atoms will weaken the anisotropic etching ability of F atoms, resulting in the etched surface trends’ flattening. The insight into anisotropic etching behavior and topography formation mechanism of the silicon surface textured by atmospheric plasma is valuable for developing a new texturing approach to silicon solar cells.

Compositional aspect and mechanism of surface formation of spray-dried microparticles with surface-active rice protein hydrolysates

Flavourzyme enzymatically hydrolyzed rice protein isolate to different degrees of hydrolysis (DH, 2, 6, and 10%) to stabilize formulated linseed oil emulsions with different protein concentrations (0.5, 1.0, and 1.5%). The emulsions were spray dried, and the microstructure, surface composition by X-ray photoelectron spectroscopy (XPS), and oxidative stability of the resultant microparticles were investigated. The physicochemical properties of powders were also evaluated. DH and protein concentration did not affect solubility, hygroscopicity, wetting time, and particle size. However, a strong and positive correlation was found between DH and oxidative stability. The lowest peroxide value (2.48–1.99 meq/kg oil) was found from the powder formulated with protein hydrolysate (DH 10%) and 1.5% of protein concentration during the entire storage study. Fluorescence optical microscopy and atomic force microscopies also allowed identifying the effects of these variables on oxidative stability. Through XPS analysis, it was possible to observe that higher DH favored the surface accumulation of proteins at the powder surface. The protein content on the particle surface (9.8%) was overrepresented compared with the bulk composition (1.5%). These results showed that the degree of hydrolysis exerted an influence on the distribution of components and the percentage of protein on the powder surface.

Investigation on micro-milling of cemented carbide with ball nose and corner radius diamond-coated end mills

Micro-milling of cemented carbides is a challenging task due to their high hardness, low toughness and high wear resistance. Ensuring good surface quality and dimensional accuracy is crucial for extending parts service life, which in turn enhances economical and environmental sustainability. This paper is mainly focused on evaluating surface formation mechanisms, scale effects, fracture behaviour and chip formation using distinct cemented carbide micro-milling tools with multi-layer diamond HF-CVD. In order to achieve higher precision and more efficient micro-milling operations on WC-15Co and WC-10Co, a systematic experimental approach has been carried out. The influence of cutting parameters, achievable surface quality and defects occurrence were thoroughly examined. Experimental results evidence the influence of operational conditions on the chip formation of cemented carbides as well as an important impact of the utilized cutting tool. Micro-pits, cracks, thin ploughing layer and fractured workpiece edges are amongst the observed surface damage mechanisms. A ductile cutting regime of the high-hardness composite material is confirmed, exhibited by the plastic deformation even when small depths of cut are considered.

Study on surface formation mechanism of multiple abrasive particles under ultrasound

ABSTRACT The mechanism of material removal under ultrasonic vibration has not been elucidated, which is not conducive to its promotion and application in the field of machining. Previous research on the mechanism of material removal was mainly conducted through grinding experiments with a single abrasive particle. The interference effect of abrasive particles on the surface has been ignored, and it is obvious that this research method has shortcomings. In this study, tangential ultrasonic vibration assisted grinding (TUVAG) and radial ultrasonic vibration assisted grinding (RUVAG) experiments were conducted on multiple abrasive particles to reveal basic principles of material removal and surface formation. Three tools with multiple abrasive particle arrangements were specially designed. The debris and groove morphology were analyzed and compared with conventional grinding (CG). This research work explains the surface formation mechanism under different forms of ultrasonic vibration and has reference significance for efficient and high-quality machining of difficult-to-cut materials.

Study on the surface formation mechanism and theoretical model of brittle surface roughness in turning machinable ceramics

Study on the surface formation mechanism and theoretical model of brittle surface roughness in turning machinable ceramics

Laser patterning captured in real-time: surface modifications of multilayer thin-films under nanosecond laser heating.

Controlled wrinkle formation has attracted intensive research interest as a means to modify surface properties. However, most of the currently explored methods rely on mechanically stretching polymer substrates with hard surface coatings, and the application of these methods to different materials is limited. Here, for the first time, we demonstrate laser-assisted periodic wrinkle formation on silicon nitride (SiN) membranes that are coated with titanium (Ti)/nickel (Ni) multilayers. Corrugated surface formation mechanism, as well as grain nucleation and growth, are studied using ultrafast transmission electron microscopy (UTEM). Periodic wrinkling and patterning of multilayers on thin SiN membranes are induced by a nanosecond pulsed laser, and the deformation of the film is captured by single-shot imaging. The investigated structures revealed periodic wrinkling of the membrane and corrugated surface formation on both sides of the film. The findings of this work could allow laser-irradiation-based fast fabrication of corrugated films with tailored properties.

Surface topology, electrophysical properties and formation mechanism of tin(ii) sulfide thin films

Surface topology, electrophysical properties and formation mechanism of tin(ii) sulfide thin films

Scratch-induced surface formation mechanism in C/SiC composites

Due to the extremely complex composition of C/SiC composites, their material removal mechanisms are significantly different from those of conventional single-phase ceramic materials. Therefore, the grinding removal mechanism of C/SiC composites must be investigated so that the components based on these composites can be machined efficiently and with low damage. In this paper, nano-scratch experiments with various cutting depths are carried out along different fiber orientations to simulate the material removal process in grinding and theoretically clarify the damage failure mechanism based on different cutting thicknesses. According to the assessment of surface and subsurface morphology of the various constituents in the scratch grooves regarding different fiber orientations, the multiple brittle breakage modes and surface integrity of carbon fiber are revealed. Green’s function is applied to establish a half-space anisotropic analytic elastic stress field considering the microstructural characteristics of material, and the crack nucleation and propagation principles during micro brittle fracture regime for nano-scratch experiment are elucidated based on the fracture mechanics and the maximum principal stress criterion. The formation mechanism of machined surface morphology in macro brittle removal process is investigated under the crack deflection effect at the weak interface and based on the elastic foundation beam theory. The related findings can provide a reasonable reference framework for optimizing the grinding technology, material and tool design regarding C/SiC composites.

Insight into surface formation mechanism during ultrasonic elliptical vibration cutting of tungsten alloy by scratching experiment and molecular dynamics

Insight into surface formation mechanism during ultrasonic elliptical vibration cutting of tungsten alloy by scratching experiment and molecular dynamics