Development Of Surface Topography Research Articles

High speed water droplet impact erosive behavior on dry and wet pulsed waterjet treated surfaces

During water droplet impact onto a dry or wet rough solid surface, several phenomena affect the surface erosion process, such as splashing, crown formation, and small droplet emission to name a few. These phenomena have been extensively studied for various simple target surface geometries. However, droplet impact studies on complex irregular and asymmetric target surface topographies resulting from a waterjet treatment have never been conducted. Furthermore, very limited reports are found on the role of target surface topography and water droplet deformation development on the resulting target stress state. In the present study, high speed droplet impingements on surfaces exhibiting coarse topographical features associated with ultrasonic pulsed waterjet treatment are modeled to understand the underlying mechanisms causing erosion. Impacts on surfaces with various roughness values and water film thicknesses are modeled using a three-dimensional coupled Eulerian–Lagrangian approach. A detailed comparative analysis of the model with experimental ultrasonic pulsed waterjet erosion features and material loss is provided. It was found that the synclastic curvature of the modeled coarse surface features increases the shock wave's strength as many compression wavelets are simultaneously emitted at each water droplet contact location with the surface, resulting in concentrated high-pressure zones. The ultrasonic pulsed waterjet treated surface features and water film thickness also greatly influence the onset of water droplet splashing, subsequent finger, secondary droplet characteristics, and crown stability. According to the numerical results, strong splashing patterns and droplet breakup are generated and create high stress zones capable of accelerating surface erosion, explaining the enhanced performance of ultrasonic pulsed waterjet process.

Surface modification and mechanical properties of laser powder bed fusion Inconel 718 after magnetic-assisted laser polishing

Industrial application of additive manufactured (AM) metal components are hindered by high rough surface. The current study focuses on instability control of laser polished molten pool on basis of magnetic-assisted technique to obtain smooth surface. Both surface topography and microstructure development of the magnetic-assisted laser polished layer has been quantitatively characterized via laser confocal scanning microscopy (LCSM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and X-ray diffractometer (XRD). Results indicate that compared to conventional laser polishing, Ra value of roughness can be further decreased by more than 98% while chemical element micro-segregation lead to more strengthen γ″ phase formation. Correspondingly, the current surface exhibits higher sub-surface microhardness, lower residual tensile stress, and better tensile property. This study demonstrates the feasibility of magnetic-assisted laser polishing on surface modification, and clarifies the mechanism of surface enhancement together with complementary multiphysics simulations of laser-magnetic-metal interactions.

Tribological behaviour and transfer layer development of self-lubricating polymer composite bearing materials under long duration dry sliding against stainless steel

Fibre-reinforced thermosets and thermoplastics containing PTFE are commonly used in marine and hydropower applications due to their self-lubricating ability in both dry and water lubricated contacts. The constant development of such composite bearings over the last decades make them even more attractive in these fields of application, due to their low maintenance cost and long service life. Their tribological performance is usually estimated by extrapolation of short, accelerated tests, which may induce risks of inaccurate or even incorrect interpretation.In this work, reciprocating dry sliding behaviour of these materials against stainless steel is investigated under typical hydropower conditions. The aim is to study the wear and friction behaviour and the development of transfer layers during long sliding tests, corresponding to years of operation. In order to mimic operational shutdowns, the tests are stopped every 20 h and the counter surfaces are examined using 3D optical interferometry and SEM to study development of surface topography and transfer layers.Test results show that the wear rates of both materials decrease significantly with time. For the thermoplastic, COF decreases with time due to accelerated material transfer observed after 80 h. In contrast, much less material transfer is observed for the fibre-reinforced thermoset, which shows its highest transfer amount after 20 h. Surface analysis indicates severe abrasive wear of the counter surface caused by the wear debris from steel and reinforcements in the material and is accompanied by simultaneous COF increase for the thermoset. Cross-sectional analysis reveals thinner transfer layers and higher wear of the steel in the middle of the wear tracks, where the sliding speed and number of load cycles are highest. These findings contribute to a more accurate interpretation of results obtained than that of short time tests regarding the tribological performance of these materials. As a direct conclusion, the selection of counter surface material can be crucial.

Staphylococcus aureus Specific Electrospun Wound Dressings: Influence of Immobilization Technique on Antibacterial Efficiency of Novel Enzybiotic.

The spread of antimicrobial resistance requires the development of novel strategies to combat superbugs. Bacteriolytic enzymes (enzybiotics) that selectively eliminate pathogenic bacteria, including resistant strains and biofilms, are attractive alternatives to antibiotics, also as a component of a new generation of antimicrobial wound dressings. AuresinePlus is a novel, engineered enzybiotic effective against Staphylococcus aureus—one of the most common pathogenic bacteria, found in infected wounds with a very high prevalence of antibiotic resistance. We took advantage of its potent lytic activity, selectivity, and safety to prepare a set of biodegradable PLGA/chitosan fibers generated by electrospinning. Our aim was to produce antimicrobial nonwovens to deliver enzybiotics directly to the infected wound and better control its release and activity. Three different methods of enzyme immobilization were tested: physical adsorption on the previously hydrolyzed surface, and covalent bonding formation using N-hydroxysuccinimide/N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (NHS/EDC) or glutaraldehyde (GA). The supramolecular structure and functional properties analysis revealed that the selected methods resulted in significant development of nanofibers surface topography resulting in an efficient enzybiotic attachment. Both physically adsorbed and covalently bound enzymes (by NHS/EDC method) exhibited prominent antibacterial activity. Here, we present the extensive comparison between methods for the effective attachment of the enzybiotic to the electrospun nonwovens to generate biomaterials effective against antibiotic-resistant strains. Our intention was to present a comprehensive proof-of-concept study for future antimicrobial wound dressing development.

Designing Supporting Structures of Passenger Ropeways of Minimum Cost Based on Modular Intermediate Towers of Discretely Variable Height

Passenger ropeways are a promising alternative for the development of public transport infrastructure in large cities. However, the construction of ropeways has a rather high cost and requires taking into account a significant number of restrictions associated with the features of the existing urban development and the placement of urban infrastructure. The main objective of this research is to develop optimization models that minimize the total cost of modular intermediate towers of a discretely variable height and a rope system due to the optimal placement and selection of the height of these towers, taking into account the features of the surface topography and urban development. The proposed modular principle for the construction of intermediate towers also enables the cost of construction to be further reduced. As a specific example, the design of a ropeway in the city of Bryansk, which has a complex terrain, is considered. The developed models are conveniently used at the initial stage of the design of the ropeway to compare the cost of various options for the location of the ropeway route in order to reduce the risk of error when choosing the least expensive option. The calculation results can serve as a guide for a preliminary assessment of the number and height of intermediate towers, their installation locations on the ground and the characteristics of the cable system.

Morphometric evolution of Everest region debris-covered glaciers

Debris-covered glaciers in the central Himalaya have now experienced several decades of sustained ice loss, manifested predominantly in glacier surface lowering. In particular, glacier surfaces of low longitudinal gradient and low ice surface velocity have developed locally complex surface topographies and undergone profound changes in supraglacial hydrology. In this study we examine the development of complex ice surface topography across six debris-covered glaciers in the Everest region over the last four decades via a new metric of glacier surface relief applied to Digital Elevation Models (DEMs). We focus in on Khumbu Glacier, and use fine spatial and temporal resolution DEMs covering a period of 28 months to quantify the contemporary contribution of ice cliff and supraglacial pond expansion to overall mass loss from stagnant areas of ice. On the broader scale, we find three common long-term changes in glacier surface topography, (1) glacier-wide expansion of high relief topography in response to ice cliff and supraglacial pond network evolution, (2) up-glacier expansion of high local relief zones that may be caused by differential sub-debris melt beneath thin debris, and (3) increase in glacier surface relief proximal to glacier termini caused by supraglacial stream incision where linked proglacial-supraglacial hydrological networks exist. Overall, we contend that these topographic measurements will be important for understanding glacier surface water storage and also the energy balance of a debris-covered glacier surface, both of which could exacerbate future ice loss and downstream meltwater supply.

A Correlative ToF-SIMS/SPM Methodology for Probing 3D Devices.

With the continuous miniaturization and increasing complexity of the devices used in nanotechnology, there is a pressing need for characterization techniques with nm-scale 3D-spatial resolution. Unfortunately, techniques like Secondary Ion Mass Spectrometry (SIMS) fail to reach the required lateral resolution. For this reason, new concepts and approaches, including the combination of different complementary techniques, have been developed in over the past years to try to overcome some of the challenges. Beyond the problem of spatial resolution in a 3D SIMS experiment, one is also faced with the impact of changes in topography during the analysis. These are quite difficult to identify because they originate from the different sputter rates of the various materials and or phases in a heterogeneous system and are notorious at the interfaces between organic and inorganic layers. As each of these materials will erode at a different velocity, accurate 3D-analysis will require means to establish a spatially resolved relation between ion bombardment time and depth. Inevitably such a nonhomogeneous erosion will lead to the development of surface topography. The impact of these effects can be overcome provided one can capture the time and spatially dependent surface erosion (velocity) with high spatial resolution during the course of a profiling experiment. Incorporating a Scanning Probe Microscope (SPM) unit which provides topography measurements with high spatial resolution, into a SIMS tool (e.g., Time of Flight (ToF) SIMS) with means to alternate between SPM and SIMS measurements, is one approach to meet that demand for complementary topographical information allowing accurate 3D chemical imaging. In this paper, the result of integrating a SPM module into a ToF-SIMS system is presented illustrating the improvements in 3D data accuracy which can be obtained when analyzing complex 3D-systems.

Finite element model for topography prediction of electrical discharge textured surfaces considering multi-discharge phenomenon

The prediction of surface topography obtained with electrical discharge texturing (EDT) process is very challenging, due to stochastic nature and complex physics in occurrence of sparks. Though there are a few models for surface texture prediction in the literature, there are still ample opportunities to improve upon by adopting more realistic assumptions and formulations for simulation. This paper presents a numerical simulation of progressive development of surface topography due to sequential application of spark discharges on an instantaneous textured surface formed by all previous spark discharges. The model incorporates major single-spark features such as, Gaussian distribution of heat flux, temperature-dependent work material properties, latent heat of melting, and operating parameter dependent variation of factors such as, cathode energy fraction, spark radius, and plasma flushing efficiency; besides the multi-spark features such as, stochastic distribution of sparks with respect to: i) location, ii) energy level, and iii) chronological order. Finite element simulation of EDT is performed in ABAQUS with the help of user-defined subroutines for the dynamic simulation of spark discharges, flagging of elements attaining evaporation temperature from further heat flux application and storage of the highest temperatures attained by each element. An evolution of surface texture through the progress of spark erosions has been studied. As EDT continues, the number of craters overlapping generally tend to increase, whereas the center-to-center distance between a crater with its nearest neighbour tends to decrease. The simulated surface textures are validated with the experimental ones using two methods: error function method and Ra distribution method, and were found to be in good agreement.

Asthenospheric buoyancy and the origin of high-relief topography along the Cascadia forearc

The forearc topography of the Cascadia subduction zone varies systematically along-strike, with high-relief in the north and south (the Olympic and Klamath ranges) separated by relatively low relief in its central region. This systematic topographic variability reflects the long-term pattern of uplift and erosion, however, the underlying cause of uplift and the mechanisms by which current topography is supported are unclear. Here, we synthesize results from seismic imaging, geodetic (decadal) and geomorphic (millennial) uplift rates, erosion rates, topographic analysis, and characteristics of the megathrust interface, with a mechanical model to infer that buoyancy in the subslab asthenosphere influences the development and longevity of Cascadia's forearc topography. The Cascadia margin can be divided into three broad segments, with the northern and southern segments characterized by rapid geodetic and geomorphic uplift rates, rapid erosion rates, high coseismic subsidence of great megathrust ruptures, shallower slab dip angles, and increased plate locking compared to the central segment. Tomographic images show low-velocity anomalies beneath the slab in the northern and southern segments, which are inferred to be regions of partial melt, resulting from localized upwellings, and regions of positive mantle buoyancy. Modeling suggests that these buoyant regions can locally increase the total shear force at the megathrust by either shallowing the slab dip — thereby increasing the area of the seismogenic zone — or increasing mechanical plate coupling along the megathrust, by increasing normal stress and/or the effective coefficient of friction. We propose that: 1) sub-slab buoyancy influences topographic development by modulating along-strike patterns of strain within the over-riding plate during the seismic cycle, 2) Permanent development of surface topography occurs due to unrecovered strain over thousands of seismic cycles, and 3) variations in Cascadia's forearc topography are laterally supported by changes in the total shear force at the megathrust interface. Using independent estimates for slab dip and plate locking, we predict the first-order variations in Cascadia forearc topography, with local maxima in the north and south as observed. Given our results, variations in subslab buoyancy may be critical to explaining forearc topography in other subduction systems.

Erosion and fuel retentions of various reduced-activation ferritic martensitic steel grades exposed to deuterium plasma

In this study the fuel retention and erosion of different reduced-activation ferritic martensitic (RAFM) steels exposed to deuterium (D) plasma were investigated. D plasma exposure was performed in a linear experimental plasma system (LEPS) with the incident ion energy between 30 and 180 eV per D, fluence from 1023 to 1025 D/m2 and sample temperature between 300 and 500 K. After D plasma exposure, erosion structure development of surface topography was observed, but no significant difference was seen among various RAFM steels within the examined conditions. W-enriched surface is formed for all investigated RAFM steels with little difference. RAFM steels exhibited similarities in D erosion and dependence on D plasma energy or fluence. Thermal desorption spectroscopy reveals in all steel samples only one broaden releasing peak from 450 to 800 K and total D inventory of 1018–1020 D/m2. Similar D retention behavior of five RAFM steels was found that it decreases with increasing incident fluence or ion energy. Moreover, different cutting treatment along rolling direction leads to different erosion structure and D releasing behaviors.

In-situ analysis of ion-induced physicochemical change of Si surface by secondary electron yield detection

We report the variation of secondary electron yield with ion fluence during 10 keV N+1 and Ar+1 ions bombardment on a Si (1 0 0) surface at normal and oblique incidence. The initial high secondary electron yield from Si surface is observed due to the native oxide layer on Si for both nitrogen and argon ion bombardment. The secondary electron yield is expected to decrease and stabilize for continue ion bombardment, which is observed for the argon ion irradiation. However, a significant variation of the electron yield with continuing nitrogen ion bombardment is observed. Ex situ measurement of ion bombarded surfaces by Atomic Force Microscope shows that the variation of secondary electron yield is correlated with the surface topography development due to ion bombardment. Also, the reaction of the projectile with target atom alters the secondary electron emission in case of N+ ion bombardment. The mean free path length of the secondary electron is estimated using the Parilis-Kishinevsky theory and the variation is presented. Real-time physicochemical changes of Si surface due to low energy ion bombardment have been probed in-situ by monitoring the secondary electron emission yield measurements.

Vibratory finishing, end phase surface topography, resolving current issues

Vibratory finishing belongs to the wider group of near ubiquitous mass finishing processes. Components are typically bulk finished in a fluidised media bed and applications vary from performance critical polishing, to cosmetic surface preparation. The established model of surface topography development has been one of initial rapid change during a ‘transient’ process phase, with subsequent slowing and a final ‘steady state’ phase in which surface character is uniform with no dependence on process duration or initial surface finish.Recent reassessment of the steady state phase has suggested that its surface roughness oscillates with process duration about a mean value and redefines it as the ‘equilibrium’ phase. Though this new model is considered to incorporate the existing model as a special case, it is argued that it represents a fundamental shift in the process mechanics. In addition, it is argued that the new findings have potential relevance to a much wider group of stochastic processes. Thus, the current paper seeks to clarify the underlying development process by investigating the nature of the end phase surface and testing these models by examining new and existing data. Results show no statistical evidence to support any periodic oscillations in the end phase surface and a number of issues with the oscillating model are noted. In addition, it is suggested that there is no clear physical mechanism to underpin the oscillating model and that the saturating model is sufficient to describe all the presented data. In conclusion a qualitative description of the end phase topography and its dynamic but temporally uniform character is given. The idea of ‘process bandwidth’ relating to the range of surface-media interactions is introduced to help describe some of the behavioural and control aspects of this stochastic process and the surface topography it produces.

Experimental analyses and numerical modeling of texture evolution and the development of surface roughness during bending of an extruded aluminum alloy using a multiscale modeling framework

Bending is an important strain path in various metal forming operations as well as vehicle crashworthiness. In the present study, the bending behavior of an extruded aluminum alloy AA6063-T6 is investigated using wrap bending tests. The focus of the work is on understanding the relationship between heterogeneous plastic deformation, strain localization, the accompanying texture evolution and the development of surface topography effects during wrap bending. In these regards, wrap bending experiments are conducted and the bendability of the as-received material is assessed. The development of micro-slip bands, shear localization and the formation of surface undulations through-thickness of the bend are analyzed using conventional metallography and scanning electron microscopy (SEM). The initial microstructure, grain size distribution and texture evolution during bending are analyzed using electron backscatter diffraction (EBSD) measurements. The surface topography of the bent specimen is analyzed using 3D laser scanning profilometry. Next, a 3D multi-scale modeling framework is used to simulate wrap bending using crystal plasticity based finite element methods (CPFEM). The simulated results for strain localization, texture evolution and surface topography development show good agreement to the corresponding experimental findings. The modeling results are further analyzed to understand the relationships between initial microstructure, strain localization and surface topography development. A set of bending simulations is also conducted using 3D synthetic microstructures to further investigate the relationship between through thickness clustering of similarly oriented grains, initial microstructure and the developed surface topography after bending. A possibility to achieve a lower surface roughness by altering the through thickness locations of similarly oriented grain clusters has been demonstrated. Lastly, it has been numerically verified that by eliminating or by reducing the tendency towards clustering of similarly oriented grains within the microstructure, a transition from a ridging to an orange peel type surface topographic behavior can be achieved.

ANALYSIS OF GEOMETRIC FEATURES OF THE 316L STEEL SURFACE AFTER DIFFERENT SURFACE TREATMENT METHODS

The paper presents the selected results of surface quality. The selected 2D and 3D surface roughness parameters are analyzed. An intensive development of various surface topography measuring techniques allows the prediction of the functional attributes of the surface and also evaluation of its quality. The measurement strategy highly influences the results of the evaluation of surface roughness. Finally, some general conclusions are given.

The topographic development and areal parametric characterization of a stratified surface polished by mass finishing

Mass finishing is amongst the most widely used finishing processes in modern manufacturing, in applications from deburring to edge radiusing and polishing. Processing objectives are varied, ranging from the cosmetic to the functionally critical. One such critical application is the hydraulically smooth polishing of aero engine component gas-washed surfaces. In this, and many other applications the drive to improve process control and finish tolerance is ever present. Considering its widespread use mass finishing has seen limited research activity, particularly with respect to surface characterization. The objectives of the current paper are to; characterise the mass finished stratified surface and its development process using areal surface parameters, provide guidance on the optimal parameters and sampling method to characterise this surface type for a given application, and detail the spatial variation in surface topography due to coupon edge shadowing. Blasted and peened square plate coupons in titanium alloy are wet (vibro) mass finished iteratively with increasing duration. Measurement fields are precisely relocated between iterations by fixturing and an image superimposition alignment technique. Surface topography development is detailed with ‘log of process duration’ plots of the ‘areal parameters for scale-limited stratified functional surfaces’, (the Sk family). Characteristic features of the Smr2 plot are seen to map out the processing of peak, core and dale regions in turn. These surface process regions also become apparent in the ‘log of process duration’ plot for Sq, where lower core and dale regions are well modelled by logarithmic functions. Surface finish (Ra or Sa) with mass finishing duration is currently predicted with an exponential model. This model is shown to be limited for the current surface type at a critical range of surface finishes. Statistical analysis provides a group of areal parameters including; Vvc, Sq, and Sdq, showing optimal discrimination for a specific range of surface finish outcomes. As a consequence of edge shadowing surface segregation is suggested for characterization purposes.

Effect of pulse duration on heat transfer and solidification development in laser-melt magnesium alloy

Compared to CW CO2 laser, Nd:YAG pulse laser is more suitable for some material processing due to higher absorptivity. However, surface ripples and microstructure inhomogeneities are main disadvantages during pulse laser melting on materials. Experiments were carried out to examine how laser melting influences surface topography and microstructure development of AZ91D Mg alloy. The laser-melt surface was characterized using Talysurf profiler, optical microscope and scanning electron microscope. Temperature distribution of molten pool was calculated from heat flow model to understand how heat transfer and fluid flow influence kinetics of rapid solidification under non-equilibrium conditions. The results implicate solidification behavior on microstructure evolution of laser-melt materials. At optimized parameters, thermally driven Marangoni flow became uniform, resulting in low height of ripples on top surface and less discrete bands in cross-sectional microstructure simultaneously, thereby improving homogeneity of microstructure in the molten pool.

Erosion study of Fe–W binary mixed layer prepared as model system for RAFM steel

Fe–W binary mixed layers were prepared as a model system for reduced-activation ferritic–martensitic (RAFM) steel for studying their dynamic erosion behavior resulting from energetic deuterium (D) irradiation. This investigation aims toward an assessment of RAFM steels as plasma-facing material. The surface composition of the model layers is modified by D irradiation. W is enriched at the surface with D irradiation fluence due to the preferential sputtering of Fe. It depends on the D impinging energy as well as the initial W fraction of the Fe–W layer. No significant development of surface topography was observed within the examined conditions. The erosion yield of a Fe–W layer is comparable to that of pure Fe in the low-fluence range and decreases with increasing D fluence. These results indicate that the dynamic change of erosion yield is significantly correlated with the surface W enrichment.

Surface properties of polyurethane powder lacquers modified with polysiloxane‐methacrylic core‐shell nanoparticles

AbstractNon‐ and core‐shell nanoparticles‐containing polyurethane‐based powder coating systems, crosslinked with allophanate bonds containing polyisocyanates were examined. The surface structure of the powder coatings were investigated with a confocal microscopy and polarized optical microscopy (POM) using reflected light. The three‐dimensional surface topography and the values of surface roughness were determined. The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior: surface free energy and gloss. These experimental results led to a better understanding of the development of surface topography and morphology and provide valuable information for the development of new polyurethane powder coating systems. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Surface structure build‐up and three‐dimensional topography of polyurethane powder coatings

AbstractNon‐ and polysilsesquioxane‐containing polyurethane‐based powder coating systems, crosslinked with allophanate bonds containing polyisocyanates were examined. The surface structure built‐up of the powder coatings were investigated at different temperatures with a polarized optical microscopy (POM) using reflected light. The three‐dimensional surface topography and the values of surface roughness were determined. The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior: surface free energy and gloss. These experimental results lead to a better understanding of the development of surface topography and morphology and provide valuable information for the development of new polyurethane powder coating systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Plasticity associated with grain boundaries during the bending of an Al–Mg–Si-based alloy

The development of surface topography with deformation reflects a range of plasticity phenomena occurring over different length scales. Surface displacement at grain boundaries occurs under bending, the displacement increasing with bending angle. This contributes to surface topography and is due to plastic deformation adjacent to the grain boundary.