Evolution Of Surface Topography Research Articles

Surface topography and subsurface structure evolution in laser micro polishing of monocrystalline silicon

Ultra-smooth silicon surfaces, crucial in short-wave optics, can be marred by surface defects and subsurface damage incurred during machining, thereby affecting the imaging quality and transmission efficiency of optical components. Laser micro-polishing emerges as a versatile and efficient technique for ultra-precision polishing. This study aims to scrutinize the surface topography and subsurface structural evolution of monocrystalline silicon wafers during laser micro-polishing experimentally and to formulate an accessible evaluation model that incorporates multiple process parameters for optimal polishing results. As laser fluence escalates, the polishing process can be divided into six regimes: bulge, coalescence, smoothness, groove, ripple, and ablation. Each regime's crystal structure evolution is analyzed using Raman spectroscopy, demonstrating a close relationship with the surface expansion preceding the melting of monocrystalline silicon. Surface roughness diminishes from 6 nm to 0.7 nm, and an optimal crystalline quality devoid of an amorphous layer, residual stress, or significant subsurface damage is achieved. Amorphous silicon, 20 μm thick, is converted into monocrystalline silicon through recrystallization, and subsurface distortions and dislocations are rectified due to silicon atom redistribution. Moreover, a mapping relationship between multiple process parameters and surface polishing effects is established. A dimensionless fluence considering multiple parameters is derived, and a predictive model for process parameter optimization to secure optimal polishing results is proposed.

Study of the Grinding Process by Friction of Cereal Grains in Stone Mills

The grinding process via friction at the micro-scale in a mill with stones is considered a variable combination of contacts, with two-body (the asperities of lower millstone in direct contact with the asperities of upper millstone) and three-body (micro-particles of ground seeds trapped between the asperities of lower and upper stones of the mill) contacts. Three elements are described: (1) the mechanical contact of the asperities of the lower and upper millstones to predict pressures on asperities by modeling; (2) tests on a millstone sample covered with grinding particles; and (3) tests on a wafer sample formed by the millstones with the grinding particles between them. This paper highlights the combined effects of the micro-scale friction via individual measurements, using an analytical model to sum these effects and validating the model by performing several experiments. An efficiency grind by friction assumes the grain’s movement and interaction between the seeds and solid surfaces, and is highlighted through theoretical and experimental studies. Topography analysis of the surface of the millstones reveals the model of microscopic frictional force. Endpoint measurements (the traces of the surface topography evolution) enable model verification in the grinding process. Thus, the results obtained in the grinding process in the stone mills via friction have practical utility through research benefits. Therefore, they allow for the improvement of quality, reliability, flexible grinding, quality control of the flours, and uniformity degree (fineness/shredding).

Effects of cyclic fatigue loads on surface topography evolution and hydro-mechanical properties in natural and artificial fracture

This work investigated permeability evolution for fluid flow through natural fractures and artificial fractures in granite and the evolution of failure surface under cyclic fatigue loads condition. We revealed and compared a clear distinction between two types of fracture surfaces before and after the test, and analyzed the evolution of fracture surface roughness and other parameters which can characterize their topography feature, as well as the relationship between fracture surface topography and permeability. The studies indicated that artificial fractures show the higher roughness and subtler variations of surface topography than those of natural fractures, however, the surface topography of natural fractures was more susceptible to cyclic fatigue loads. The initial permeability and average permeability of nature fractures were both higher than those of artificial fractures during the stress-seepage coupling test and the permeability of artificially fracture was more sensitive to normal stress changes. Moreover, the experimental results were in line with theoretical predictions and the research results can provide reference for preventing the failure of rock engineering.

Surface morphology and topography evolution of soda-lime silica glass after 1.0 MeV Si ion bombardment

Surface pattern formation on soda-lime silica glass by 1 MeV Si ion irradiation impinging at an angle of 70° with respect to the surface normal has been studied. Modification of surfaces were analyzed for total ion fluences applied between up to ions/cm2. The surface morphology and topography were studied by scanning electron microscopy (SEM), and atomic force microscopy (AFM). These surface techniques enabled the determination of roughness, characteristic wavelengths, and correlation lengths. In addition, electron dispersive spectroscopy (EDS) scans were applied on the surface topography to study the variation of the Si content on the obtained surface patterns. From the measurement of these variables, linear and non-linear regimes were established. At linear regime, the surface morphology develops from an initial flat surface giving rise to ripples for fluences up to ions/cm2. As the ion bombardment continues surface evolve into wrinkles finalizing at cellular-like structures, growing under an anomalous scaling process. The EDS scans indicate the presence of shadowing effects. The morphological changes observed can be explained in terms of a combination of thermal mass diffusion and geometrical factors during ion irradiation, including shadowing and subsequent (secondary) surface erosion effects adapted to few MeV energies.

Floating regulation and electrochemical corrosion behavior of in-situ synthesized (Nb,Ta)C by electromagnetic field under laser remelting state

Based on the aggregation phenomenon of in-situ synthesized micron-scale (Nb,Ta)C, the upward Lorentz force under the electromagnetic field (EMF) was utilized to drive the moving ceramic phase to counteract gravity and achieve surface enhancement. Also, the floating, remelting and dispersion uniformity control of multi-sized (Nb,Ta)C was realized under laser remelting (LR). The regulation mechanism of porosity, surface topography, microstructure and phase evolution by LR under EMF was emphatically revealed. A corresponding relationship between electrochemical corrosion behavior and microstructure was established. Meanwhile, the variation law of hardness between layers was also analyzed systematically. Results revealed that the stirring effect of the EMF-induced Lorentz force under LR enhanced Marangoni convection and reduced temperature gradient, which was beneficial for removing pores and micropores, thereby reducing porosity and improving surface flatness. The incompletely dissolved and tightly aligned large (Nb,Ta)C on the surface greatly increased the hardness and protected the internal microstructure from corrosion in a self-sacrificing manner.

Theoretical and experimental analysis of surface topography and surface roughness evolution in fixed abrasive double-sided planetary lapping of YAG wafers

Theoretical and experimental analysis of surface topography and surface roughness evolution in fixed abrasive double-sided planetary lapping of YAG wafers

Multiscale Wear Simulation in Textured, Lubricated Contacts

Specific surface textures may reduce the friction and increase the lifting forces in lubricated contacts. For the detrimental operating condition of mixed friction, wear is induced by the solid contact. In this study, a methodology for wear calculation in textured, lubricated contacts is presented that considers the wear-induced surface topography evolution. Based on the Reynolds differential equation, the mass-conserving cavitation model according to Jakobsson, Floberg, and Olsson (JFO), a wear-dependent asperity contact pressure curve and the wear equation according to Archard, wear in a wedge-shaped, textured lubrication gap was calculated. The results show the wear behavior of textured lubrication gaps. Based on the wear simulations, the tribological behavior of the textured surfaces compared to smooth surfaces is discussed. It is evident that textures, which improve the tribological performance in the hydrodynamic lubrication regime, are not necessarily associated with low wear values in a lubrication condition in the mixed friction regime. The analysis of the wear-dependent parameters initially showed a ‘recovery’ of the tribological system with increasing wear until the performance decreased again after a specific reversal point. This behavior is attributed to the relative position of the surface textures in the lubrication gap.

A digital close range photogrammetric observation system for measuring soil surface morphology during ongoing rainfall

Soil erosion is a hydro-geomorphic process occurring over the earth’ surface. The observation of soil surface morphology during ongoing rainfall at fine spatial and temporal scales are critical for the study of soil erosion. A digital close range photogrammetric observation system based on wireless networking technology was explored and established in this study. Through wireless networking, multi-cameras were concurrently controlled, solving the problems of synchronous acquisition of underlying digital image, big data transmission and storage. Image sensors collected data in parallel based on network command, and noise on the images such as raindrops was eliminated based on the K-means clustering algorithm by serialization technology during data acquisition. After parallel preprocessing, high density 3D point clouds and digital elevation models (DEMs) were reconstructed. The evolution of soil surface topography was dynamically monitored by instantaneous image acquisition at different time intervals during ongoing rainfall. The results showed that the measurement precision of the established system could reach a sub-millimeter level with the minimum single measurement error being 0.0069 mm. The maximum error between check point coordinates generated by photogrammetry and those generated by a Total station was 5.7 mm on the horizontal axes and 9.6 mm on the vertical axis. The temporal and spatial resolutions of the observation system were 1 min and 2 mm, respectively. Compared with a runoff sediment collection method, the average relative error of the system for estimating soil loss was 5.63%, and the accuracy of single observation was up to 99.58%. The observation methods explored in our study provided a reliable way to monitor soil erosion processes, which was also helpful to analyze the role and influence mechanism of soil erosion in surface hydrological process.

Prediction of mechanical properties and surface roughness of FGH4095 superalloy treated by laser shock peening based on XGBoost

Laser shock peening (LSP) is a novel metal surface modifying technology, which can enhance the mechanical properties of materials and extend fatigue performance of components evidently. The outstanding mechanical properties induced by LSP occurs through severe plastic deformation, which will cause the surface topography evolution. With the rapid development of artificial intelligence (AI), which provide an effective solution to solve complex problems when with limited experimental data. In this work, FGH4095 superalloy was selected as the experimental material. LSP experiments were conducted with a Q-switched Nd: YAG laser. Laser energy of 4 J, 6 J and 8 J were used with overlap rate of 30 % and 50 %. The residual stress, microhardness and surface topography of experimental samples treated by LSP was investigated. What is more, the AI method based on XGBoost was applied to predict the mechanical properties and surface roughness of FGH4095 treated by LSP. The laser energy, overlap rate, depth were set as input parameters, while the residual stress, microhardness and surface roughness were set as output parameters. The predicted results showed a great agreement with the experimental data. It can be indicated that XGBoost is a suitable method for accurately performing prediction of mechanical properties and surface roughness of materials treated by LSP.

Surface Topography Evolution of Single Crystal Silicon in Laser Polishing

Surface Topography Evolution of Single Crystal Silicon in Laser Polishing

Effects of irradiation on nano-pore phenol-formaldehyde resin infiltrated IG-110 graphite

• The PF filler in pores of IG-110 shrinks after irradiation. • The irradiated densified isostatic graphite has smaller change ratio of L a . • The irradiation behavior depends on the initial graphitization degree of graphite. Iso-molded nuclear graphite (IG-110) was infiltrated with phenol–formaldehyde (PF) resin to get the densified isostatic graphite with different bulk density (IG-110-PF, 1.86 g/cm 3 and IG-110-PF-D, 1.91 g/cm 3 ). The IG-110-PF and IG-110-PF-D samples were irradiated with 7 MeV Xe 26+ to study their surface topography and microstructure evolution. The impregnation process of PF resin affects the initial graphitization degree of graphite, which lead to the difference in irradiation behavior. Due to the irradiation-induced graphitization, the PF filler (carbonized products of PF resin infiltrated into pores) in pores of IG-110 shrinks after irradiation, which confirmed by the smaller change ratio of crystallite size along the a-axis direction (L a ) in IG-110-PF and IG-110-PF-D after irradiation than IG-110. L a of IG-110-PF-D decreased with the dose increase, resulting from the introduction of irradiation-induced in-plane defects, which is similar to IG-110.The increase in L a of PF filler in IG-110-PF and decrease of increase rate in dislocation density after irradiation with surface irradiation dose of 0.02–0.11dpa, provide supporting evidence for the change of PF filler. The difference in irradiation behavior confirms that disordered structure of PF filler and initial crystallinity play an important role in microstructure evolution.

Basic Mechanism of Surface Topography Evolution in Electron Beam Based Additive Manufacturing.

This study introduces and verifies a basic mechanism of surface topography evolution in electron beam additive manufacturing (E-PBF). A semi-analytical heat conduction model is used to examine the spatio-temporal evolution of the meltpool and segment the build surface according to the emerging persistent meltpool domains. Each persistent domain is directly compared with the corresponding melt surface, and exhibits a characteristic surface morphology and topography. The proposed underlying mechanism of topography evolution is based on different forms of material transport in each distinct persistent domain, driven by evaporation and thermocapillary convection along the temperature gradient of the emerging meltpool. This effect is shown to be responsible for the upper bound of the standard process window in E-PBF, where surface bulges form. Based on this mechanism, process strategies to prevent the formation of surface bulges for complex geometries are proposed.

Quantitative measurement of corrosion at the nanoscale by in situ spectral modulation interferometry

This research study presents a novel application of a quantitative phase microscopy technique, spectral modulation interferometry (SMI), for in situ nanoscale characterization of corrosion of an aluminum alloy in real time. SMI offers high sensitivity, rapid image acquisition, and speckle-free images; thus, real-time quantification of surface topography evolution during corrosion can be obtained accurately to evaluate the temporally- and spatially-dependent corrosion rates. With an innovative additive-manufactured fluid cell, experiments were performed in situ under flowing solution conditions. Electrochemical tests via stepwise polarization and solution chemistry through collected aliquots of outflow solution were also performed alongside the nanoscale SMI experiment to simultaneously provide a corroborating corrosion rate measurement. Based on the quantitative 3D height profiles across the corroded surface, pit formation resulting from rapid local corrosion was predominant, appearing at different times and are heterogeneously distributed across the surface. The computed time-dependent dissolution rates of aluminum also varied as the experiment proceeded, with the combination of linear and nonlinear surface normal distributions. An initial mean linear dissolution rate of [0.40 ± 0.007] μmol m−2 s−1 transitioned to a more rapid mean rate of [1.95 ± 0.035] μmol m−2 s−1, driven by the anodic polarization. Dissolution rates from the three performed methods follow similar trends and there is the visibility of linking the nanoscale in situ SMI data to the electrochemical corrosion measurements and ex situ chemical solution analysis. At the end of the corrosion period, rates of 118 μmol m−2 s−1, 71 μmol m−2 s−1, and 2.45 μmol m−2 s−1 were obtained from electrochemical measurements, ex situ solution analyses, and in situ SMI corrosion measurement, respectively. Finally, these experimental results validate the applicability of SMI for in situ nanoscale characterization of a corroding alloy surface.

Torrefaction enhanced biomass chemical-looping gasification coupled with CO2-splitting via half doped LaFe0.5M0.5O3 perovskites

In order to explore the oxidation and reduction properties of the LaFe0.5M0.5O3(M = Mn, Co, Ni, Cu) perovskites, torrefied biomass (TB) gasification and CO2 splitting were coupled as a whole chemical looping reaction, while the doped LaFe0.5M0.5O3 were prepared and employed as oxygen carriers(OCs) in the chemical looping. An proper torrefaction temperature was screened first for producing more syngas, then the effect of doped perovskites on the chemical looping reaction were evaluated via thermogravimetric analyzer and fixed-bed reactor in terms of the syngas yield and CO formation rate. The results showed that the doped perovskites exhibited higher activity in the gasification process, which promoted the conversion of TB and improved the yield of H2 and CO. Specifically, the CO yield of LaFe0.5Co0.5O3 and the H2 yield of LaFe0.5Ni0.5O3 was improved by about 4 times and 1.3 times respectively compared with original LaFeO3. Moreover, LaFe0.5Ni0.5O3 exhibited better performance in both TB gasification and the CO2 splitting reaction, and the yield of H2 and CO reached 3.71 mmol·g−1 and 1.80 mmol·g−1, respectively. Furthermore, the composition and surface topography evolution of doped perovskite were analyzed via TEM, SEM and XRD, and the results of XPS, EPR and TGA were combined to reveal the reaction mechanism.

Effect of overhanging surfaces on the evolution of substrate topography and internal defects formation in laser powder bed fusion

Overhanging (a.k.a. down-facing) surfaces are typically found in complex metal parts built with laser powder bed fusion (L-PBF). When these surfaces exceed a certain extension or inclination with respect to the build plate, they need to be supported with external structures to avoid failure and macro-geometrical errors. However, a relatively large portion of the slice gets printed directly over loose powder, thus facing a substrate with significantly different wetting and heat transfer characteristics from solid/bulk. Several quality aspects (e.g., internal defects, surface topography) can be affected by the presence of overhangs, but their evolution during the process is still a relatively unexplored field. In this work, a new strategy based on process interruption is proposed for analyzing the evolution of defects produced during the printing of down-facing surfaces. Ex-situ high-accuracy characterization equipment was used to study their effect on the evolution of printed surface topography, internal defects, melted and sintered thickness. Results show that the process gradually recovers from the disturbance introduced by the overhang, but the peculiar structure of the internal defects observed in those regions reveals that even small unsupported areas can be detrimental to the as-built quality of the part. The combined use of surface topography data and volume reconstruction also allowed developing and validating a physics-based model for predicting the evolution of surface topography and effective layer thickness in overhangs.

Surface topography in two-dimensional ultrasonic rolling 2024-T3 Al-alloy

Two-dimensional ultrasonic rolling (TDUR) is a kind of ultrasonic surface strengthening technology that can improve surface topography to enhance the service performance of parts. The surface topography evolution of the workpiece in TDUR depends on the processing parameters, the geometry, physical and mechanical parameters of the workpiece and the roller. And it also depends on the initial state of the pre-treated workpiece surface and the random vibration during processing. In order to study the process of surface topography formation of TDUR under the influence of various factors, the mechanical analysis of the residual area height of the workpiece after turning was first performed. Then the mathematical models of rolling force and penetration depth were established. Sequentially, the surface topography and surface roughness models were established based on the penetration model, the roller motion trajectory and the test results of random vibration. Finally, 2024-T3 Al-alloy was selected for simulation analysis and experimental verification of the models of the surface topography and the surface roughness. The simulation and experimental results show that TDUR can effectively improve the surface topography of the workpiece and reduce its surface roughness Rz by more than 80%. When the initial state of the workpiece surface and the random vibration of the machining process are taken into account, the error of the surface roughness prediction value is significantly reduced, compared with the models without considering both factors. So, the new developed surface topography and the surface roughness models can reflect the actual machining effect more realistically. It was also found that the surface roughness after rolling increased with the increase of initial surface roughness, but its reduction rate did not change with the change of initial surface roughness. This paper investigates the formation process of surface topography in TDUR considering the initial state of the workpiece surface, the influence of random vibration during processing and so on. And this work is important for guiding the pre-treatment process and improving the quality and efficiency of TDUR.

Compensation of mounting error in in-situ wear measurement during gear pitting test

A profilometer can be used to monitor the tooth surface topography evolution during gear pitting tests. Due to the mounting relationship variation between the instrument and the gear, the tooth profile’s measurement position deviation from its theoretical location will introduce a measurement error. In this study, the tooth profile measurement error introduced by mounting using a tactile profilometer was theoretically analysed and experimentally confirmed as a fish shape. A mounting error compensation method based on projection onto the perpendicular plane to the gear’s datum axis was proposed. The results show that the fish-shaped tooth profile measurement error can be effectively compensated, benefitting the evaluation of the gear tooth surface wear during gear pitting tests.

Evolution of Surface Topography and Microstructure in Laser Polishing of Cold Work Steel 1.2379 (AISI D2) Using Quadratic, Top-Hat Shaped Intensity Distributions.

Within the scope of this study, basic experimental research was carried out on macro-laser polishing of tool steel 1.2379 (D2) using a square intensity distribution and continuous wave laser radiation. The influence of the individual process parameters on surface topography was analyzed by a systematic investigation of a wide range of process parameters for two different, square laser beam diameters. Contrary to a typical laser polishing approach, it was shown that short interaction times (high scanning velocity and small laser beam dimensions) are required to reduce both micro-roughness and meso-roughness. A significant reduction of surface roughness of approx. 46% was achieved from Raini = 0.33 ± 0.026 µm to Ramin = 0.163 ± 0.018 µm using a focused square laser beam with an edge length of dL,E = 100 µm at a scanning velocity of vscan = 200 mm/s, a laser power PL = 60 W and n = 2 passes. However, characteristic surface features occur during laser polishing and are a direct consequence of the laser polishing process. Martensite needles in the micro-roughness region, undercuts in the meso-roughness region, and surface waviness in the macro-roughness region can dominate different regions of the resulting surface roughness spectrum. In terms of mechanical properties, average surface hardness was determined by hundreds of nano-indentation measurements and was approx. 390 ± 21 HV0.1 and particularly homogeneous over the whole laser polished surface.

Intermedial annealing process applied during the growth of quantum wells and its influence on the performance of GaN-based laser diodes.

An intermedial annealing treatment is adopted during epitaxial growth of InGaN/GaN multiple quantum well (MQW) by the metal-organic chemical vapor deposition (MOCVD), which is employed after each GaN cap layer growth is finished. Optical power, threshold current and slope efficiency of GaN-based laser diodes is improved through an appropriate intermedial annealing process. A further investigation about the influence of annealing duration on the luminescence characteristics of light-emitting diodes and the surface topography evolution of single quantum well layers is conducted through the study of electroluminescence, temperature dependent photoluminescence and atomic force microscopy. It is found that the improvement of GaN-based laser diode is attributed to reduction of nonradiative recombination centers in MQW, which is due to a better interface quality between well and barrier layers after an intermedial annealing process.

Analysis and classification of the process-induced surface topography nonuniformities during laser remelting

Surface polishing by laser remelting (SP-LRM) uses the energy of a focused laser beam to remelt the thin top layer of the workpiece material in order to improve its surface quality by 3D topography smoothing. Visual observations of the experimentally-obtained remelted laser tracks revealed that the uniformity of the LRM surface topography highly depends on the stability of the laser-material interactions and initial surface topography. Two metrics of LRM topography were proposed to assess the LRM process stability: uniformity of the laser track contour and uniformity of the middle longitudinal profile. Several sub-areas of the LRM tracks with typical topographic nonuniformities were visually selected and their nonuniformity metrics determined. Two common types of surface topography nonuniformities characterized by distinctive geometric patterns were identified: those induced by the LRM process (excessively remelted material) and those affected by the surrounding initial surface topography. The obtained results open new research avenues toward the in-process estimation of the surface topography formation and evolution via online monitoring of the LRM process stability.