Initial Surface Topography Research Articles

Control of surface ripple amplitude in ion beam sputtered polycrystalline cobalt films

We have grown both polycrystalline and partially textured cobalt films by magnetron sputter deposition in the range of thickness (50–200nm). Kinetic roughening of the growing film leads to a controlled rms surface roughness values (1–6nm) increasing with the as-grown film thickness. Ion erosion of a low energy 1keV Ar+ beam at glancing incidence (80°) on the cobalt film changes the surface morphology to a ripple pattern of nanometric wavelength. The wavelength evolution at relatively low fluency is strongly dependent on the initial surface topography (a wavelength selection mechanism hereby confirmed in polycrystalline rough surfaces and based on the shadowing instability). At sufficiently large fluency, the ripple wavelength steadily increases on a coarsening regime and does not recall the virgin surface morphology. Remarkably, the use of a rough virgin surface makes the ripple amplitude in the final pattern can be controllably increased without affecting the ripple wavelength.

Crystal plasticity based analysis of localized necking in aluminum tube under internal pressure

The finite element method is used to numerically simulate localized necking in aluminum alloy tube under internal pressure. The measured electron backscatter diffraction (EBSD) data are directly incorporated into the finite element model and the constitutive response at an integration point is described by the single crystal plasticity theory. The tube is assumed sufficiently long, so that length changes as well as the end effects can be ignored and a plane strain analysis can be performed. Localized necking is assumed to be associated with surface instability, the onset of unstable thinning. It is demonstrated that such a surface instability/necking is the natural outcome of the present approach, and an artificial initial imperfection required by other approaches is not necessary in the present analysis. The effects of spatial grain orientation distribution, material strain rate sensitivity, work hardening, and initial surface topography on necking are discussed. It is found that localized necking depends strongly on both the initial texture and its spatial orientation distribution, while the initial surface topography has a negligible effect on necking.

Experimental study of real roughness attenuation in concentrated contacts

The understanding of the processes involved in the in-contact deformation of surface roughness represents one of key factors in increasing lubrication capabilities of highly loaded machine components. Two main approaches have been developed in an effort to understand the changes of initial surface topography within highly loaded contacts to provide detailed information about lubrication film thickness and pressure distribution in the vicinity of roughness features. The first approach considers the real surface topography while the other uses the simplified topography features. Numerical solutions based on measured topography data can provide the film thickness and pressure distribution around asperities of realistic scale; nevertheless, obtained results are typically limited to the specific topography configuration measured from a very small area of rubbing surface. That is why some researchers have considered harmonic features of various wavelength and amplitudes to explain the behaviour of real roughness. This study is focused on the experimental validation of an approach based on Fourier decomposition of the surface roughness into harmonic components. Two optical measurement techniques—phase shifting interferometry and thin film colorimetric interferometry are combined to provide the undeformed surface topography and film thickness data within the elastohydrodynamic contact formed between a smooth disk and a ball having a real rough surface. The results obtained under pure rolling conditions not only confirmed the general principle that roughness deformation is component dependent and that long wavelengths deform more than short wavelengths, also the observed deformation for different components agreed well with the data predicted by the theory.

Influence of the abrasive particles size in the micro-abrasion wear tests of TiAlSiN thin coatings

Ball rotating micro-abrasion tribometers are commonly used to carry out wear tests on thin hard coatings. In these tests, different kinds of abrasives were used, as alumina (Al 2O 3), silicon carbide (SiC) or diamond. In each kind of abrasive, several particle sizes can be used. Some studies were developed in order to evaluate the influence of the abrasive particle shape in the micro-abrasion process. Nevertheless, the particle size was not well correlated with the material removed amount and wear mechanisms. In this work, slurry of SiC abrasive in distilled water was used, with three different particles size. Initial surface topography was accessed by atomic force microscopy (AFM). Coating hardness measurements were performed with a micro-hardness tester. In order to evaluate the wear behaviour, a TiAlSiN thin hard film was used. The micro-abrasion tests were carried out with some different durations. The abrasive effect of the SiC particles was observed by scanning electron microscopy (SEM) both in the films (hard material) as in the substrate (soft material), after coating perforation. Wear grooves and removed material rate were compared and discussed.

The influence of initial surface topography on tribological performance of the wheel/rail interface during rolling/sliding conditions

The influence of surface roughness in a rail/wheel contact has been a concern for railway owners since the introduction of ‘rail grinding’ as a maintenance strategy. Presently, there are no well-defined guidelines regarding the surface topographies of ground rails and re-turned wheels. There is thus a need to establish scientific guidelines regarding the surface topographies for the rails and wheels in order to minimize grinding costs/time and to improve rail/wheel performance. This study is aimed at investigating the influence of surface topographies of wheels and rails on running-in behaviour, wear, friction, and the resultant surface damage through experimental simulation in the laboratory. A two-disc rolling/sliding test machine has been used in this experimental work. Two different roughness values were produced on both the rail and wheel test specimens. A design of experiment approach has been used to conduct experiments and to analyse the results. The results show that the surface roughness values of the specimens in some material pairs do influence wear, friction, and resulting surface damage.

AFM tip-induced ripple pattern on AIII-BV semiconductor surfaces

Modification of c(8x2) InSb(0 0 1) surface induced by prolonged scanning with an atomic force microscope tip has been investigated. The experiment performed with loads of few tens of nanoNewtons resulted in creation of ripples perpendicular to the fast scan direction. It was found that terrace edges are acting as initial instabilities leading to development of the ripple pattern. As a result, information about initial surface topography is preserved in the ripple amplitude, even so the final height of the ripples and their periodicity are determined by the tip curvature.

Film-forming capability in rough surface EHL investigated using contact resistance

Highly loaded machine elements such as gears and cams have a non-smooth surface topography that is created during manufacturing. It is well known that the film-building properties of such surfaces may be different from those that are perfectly smooth. The capability to form a separating film may also be altered in time due to run-in phenomena. In this study, a smooth steel ball was loaded against rough steel discs and run under pure rolling as well as sliding conditions. Several different steel surfaces were tested under nominal EHL conditions, where the contact was monitored by means of its electrical resistance and capacitance. Each surface was first run in for 15 min, followed by a sweep-in speed determining the lift-off curve. Electrical contact measurements were continuously conducted during run in as well as lift-off. Fully formulated gear oil and its base fluid were used as test lubricants. Results show that run in of a surface seems to be a competition between conformation of surface topography and tribofilm formation. At the tested conditions, the formation of a tribofilm is dependent on the initial surface topography and is created rapidly causing less metal–metal contact. This film also seems to effectively prohibit changes in surface topography causing less structural run in than expected.

The initial surface composition and topography modulate sphingomyelinase-driven sphingomyelin to ceramide conversion in lipid monolayers

Changes of the initial composition and topography of mixed monolayers of Sphingomyelin and Ceramide modulate the degradation of Sphingomyelin by Bacillus cereus Sphingomyelinase. The presence of initial lateral phase boundary due to coexisting condensed and expanded phase domains favors the precatalytic steps of the reaction. The amount and quality of the domain lateral interface, defined by the type of boundary undulation, appears as a modulatory supramolecular code which regulates the catalytic efficiency of the enzyme. The long range domain lattice structuring is determined by the Sphingomyelinase activity.

Effects of spatial grain orientation distribution and initial surface topography on sheet metal necking

The finite element method is used to numerically simulate localized necking in AA6111-T4 under stretching. The measured EBSD data (grain orientations and their spatial distributions) are directly incorporated into the finite element model and the constitutive response at an integration point is described by the single crystal plasticity theory. We assume that localized necking is associated with surface instability, the onset of unstable growth in surface roughening. It is demonstrated that such a surface instability/necking is the natural outcome of the present approach, and the artificial initial imperfection necessitated by the macroscopic M–K approach [Marciniak and Kuczynski (1967). Int. J. Mech. Sci. 9, 609–620] is not relevant in the present analysis. The effects of spatial orientation distribution, material strain rate sensitivity, texture evolution, and initial surface topography on necking are discussed. It is found that localized necking depends strongly on both the initial texture and its spatial orientation distribution. It is also demonstrated that the initial surface topography has only a small influence on necking.

Statistical analysis of the significance of site topography and erosion history on erosion rates on intertidal shore platforms, Kaikoura Peninsula, South Island, New Zealand

Sites with five periods of consecutive measurements from the Kaikoura Peninsula data were used to assess the influence of erosional history and surface topography upon subsequent erosion rates. Analysis of multilevel models suggests that initial erosion rates and initial surface topography have a significant, but decreasing influence upon subsequent erosion rates. Surface topography and erosion rates immediately prior to each measurement period have a consistent positive and negative relationship respectively to erosion rates in the subsequent measurement periods. These data suggest that there is a short-term memory influencing erosion rates at any specific measurement period. Use of traversing microerosion meter data may, however, not be the most appropriate means of analysing the causes of the variance of erosion at the intra-site scale.

潤滑摩耗特性に及ぼす試験片の初期表面形状の影響(OS9-2 摩擦・摩耗)

潤滑摩耗特性に及ぼす試験片の初期表面形状の影響(OS9-2 摩擦・摩耗)

Initial surface topography changes during divalent dissolution of silicon electrodes

The changes of the surface topography of float zone (FZ) n-Si(1 1 1) upon conditioning of the electrodes at potentials slightly anodic of the rest potential are monitored with atomic force microscopy (AFM) in the contact mode. The influence of the composition of the used 0.1 and 0.2 M NH 4F electrolyte at pH 4, of the potential and of the charge passed on the topography is investigated. The dissolution charges Q diss ranged from 0.28 to 10.6 mC cm −2 corresponding to ∼0.5 and ∼21 bilayers (BL), respectively. The root mean square roughness R q changes from R q=0.2 nm for the H-terminated surface to 2.9 nm for a charge passed of 10.6 mC cm −2 at an electrode potential of 0.1 V positive of the rest potential. The evaluation of height, deflection and line scan AFM data shows pitting to originate at edges of 〈1 1 2〉 oriented steps which separate atomically smooth terraces. Upon increased dissolution charge, island-type smooth and rather circular features form. Only for the highest Q diss, these islands are beginning to show corrosion. An exponential relation between R q and Q diss is found by evaluation of the three-dimensional roughness. The slope, i.e. the increase of ln R q with Q diss depends on the composition of the electrolyte and is higher for the 0.1 M NH 4F solution. From these data, a branching of the dissolution reaction between charge going into terrace removal or pit formation is obtained. Synchrotron radiation photoelectron spectroscopy (SRPES) is used to identify chemical products of the dissolution process. Comparison of data obtained at 0.15 V anodic of the electrode rest potential with an elaborate model of Gerischer and coworkers (which, however, only describes terrace dissolution) yields partial agreement with the predictions.

Interaction of sedimenting spheres with multiple surface roughness scales

The interaction of a pair of spherical particles of different densities and/or sizes with microscopic surface roughness sedimenting due to gravity in a viscous fluid is analysed by theory and experiment. The surface topography is modelled as a combination of small uniformly distributed bumps of uniform height and larger bumps that are more sparsely distributed. The existence of these surface asperities allows the spheres to physically contact each other, so that both hydrodynamic and solid-contact forces are important. When the angle between the line of centres and vertical is small, the spheres may rotate as a rigid body because they are not able to roll up and over a large bump. As this angle increases, however, the heavy sphere rolls and slips past the lighter sphere, and the separation between the nominal surfaces of the spheres varies between the heights of the small and large asperities. When considering many encounters, there is a distribution of nominal separations at each angle due to the distribution of initial conditions and surface topography. The average nominal separation generally increases with increasing angle between the line of centres and vertical because the normal component of gravity, which drives the spheres close together after an encounter with a large bump lifts them apart, decreases as this angle increases.

The strength of the lunar lithosphere

A self-gravitating, elastic, spherical thick shell model is used to derive the present state of the lateral variations of density and stress differences within the lunar lithosphere. The model is allowed to deform under the load of an initial surface topography and internal density distribution, such that the resulting deformed body gives rise to the observed surface topography and gravity specified by the spherical harmonics of degree up to 70. Two main models are considered, Model A and Model B, with elastic lithospheres of thickness 300 and 210 km, respectively. Model A displays density perturbations of generally less than ±200 kg/m 3 within the crustal layers, reducing rapidly to less than ±20 kg/m 3 at the base of the lithosphere. The density perturbations in Model B are similar in the crust and marginally higher at the base of the lithosphere. The major stress differences in the mantle are associated with the mascon basins and are found to reach maximums of 8–10 MPa within the lower lithosphere (150–270 km) of Model A and maximums of 12–16 MPa at 150 to 180 km depth for Model B. A moderate correlation exists between the modeled stress distributions and shallow moonquake epicenters. However, the overall results of this study imply that other remnant stresses, due to processes other than density perturbations, exist and play a critical role in the large shallow moonquakes.

Lateral control of self-assembled island nucleation by focused-ion-beam micropatterning

We demonstrate that the nucleation sites of nanoscale, self-assembled Ge islands on Si(001) can be controlled by patterning the Si surface in situ with a focused ion beam. At low doses of 6000 Ga+ ions per <100 nm spot, the selective growth is achieved without modifying the initial surface topography. At larger doses, topographic effects produced by sputtering and redeposition control the selective nucleation sites. Islands grown on irradiated spots are smaller with higher aspect ratio than islands grown on clean Si(001), suggesting a strong surfactant effect of Ga.

Erosion of aluminium-based claddings on steel by sand in water

This paper describes the slurry erosion of a range of HVOF deposited aluminium-based claddings on steel by sand in water. Coatings, approximately 300μm thick, of commercially pure aluminium, eutectic aluminium/silicon alloy (12%) and of a novel composite incorporating alumina in this alloy have been tested, both as sprayed and as ground to remove surface roughness as far as possible. Angular silica sand of mean diameter 235μm was used at a concentration of 2.5% in tapwater at impingement angles of 90° and 30° and a jet velocity of 27m/s. Mass loss data and surface structure, as shown by electron microscopy and profilometry, are related to the test conditions, initial surface topography, material hardness and microstructure, especially porosity. They are discussed in terms of the mechanisms of erosion that occur in the different materials, with reference to microcutting and plastic deformation of the surface and to the effects of the alumina inclusions. The consequences of poor flow-out, leading to significant residual porosity of the composite cladding are discussed.

A Study of the Dependence of the Functional Properties of the Cylinder Liner Surface Layer on the Operating Conditions

The paper presents results of the measurements of the surface roughness and physical properties of the outer layer of honed cylinders. The results of wear measurement of the cylinders and piston rings mating with them during running-in and during automotive engine operation under artificially increased dustiness conditions are presented and analysed. Interdependences among the state of the cylinder liner outer layer and operating parameters of the engines after running-in are also analysed. Additionally, the honed cylinder liners were used as specimens in wear resistance tests performed in the presence of lubricating oil with some amount of grinding particles. The results of the measurements of specimen and counter-specimen wear, as well as friction force and temperature at the friction surfaces during the test, are also presented and analysed. It was found that abrasive wear resistance of the honed cylinder liner depends on the operating conditions. During engine operation under increased dustiness conditions cylinder wear intensity depends mainly on the initial surface topography. Under conditions of low relative speed, low temperature and constant load, cylinder wear resistance in the case of large wear values depends on physical properties of the surface layer. However, when the amount of wear is smaller than the initial surface height, cylinder wear intensity in two studied cases depends mainly on its surface topography.

Effect of surface finish on fatigue strength

The components surfaces used in lubrication, friction and wear vary in their initial surface topography according to the particular use involved. In practice a real component from a machine or structure will generally have various surface finishes and different fatigue strengths. The usual stand by which various surface conditions are judged is the polished laboratory specimen. Irregular and rough surfaces generally exhibit interior fatigue properties. The present study represents a neat investigation which is carried out to correlate the various surface finish parameters with the endurance fatigue strength of a commercial aluminium alloy. The flow strain in both horizontal and vertical directions is monitored using two attached transducers during the testing of specimens grouped according to their surface finish features. Accordingly, the fatigue initiation life as interpreted from the generated flow curves is correlated with the surface finish parameters. Results indicate a great effect for all surface finish parameters. It leads to a significant correlation between the fatigue initiation life, final separation life and the fatigue endurance limit. Implementing the regression analysis leads to exponential correlations between the number of cycles for initiation of microcracks and applied cyclic stress, also between total life and alternating stress. Moreover, polynomial equations have been developed to relate the endurance stress to the various surface finish parameters.

A study on the functional properties of honed cylinders surface during running-in

The hypothetical possibilities of effects of surface topography of honed cylinders on their wear resistance during running-in are presented in this paper. In order to confirm theoretical considerations, experimental investigations were conducted. The cylinders tested had various surface topographies as a result of honing by abrasive tools of different design. The results of wear measurements of the cylinders during running-in of an automotive gasoline engine are presented and analysed. Some connections between the initial cylinder surface topography and the selected engine operating parameters after running-in are also studied.

An in-situ scanning tunneling microscopy study of electrochemically induced “hex” ↔ (1 × 1) transitions on Au(100) electrodes

The “hex” ↔ (1 × 1) transitions on Au(100) electrodes immersed into sulfuric acid solutions were investigated from an atomic up to a micrometer scale by in-situ scanning tunneling microscopy. Directly after immersion freshly flame annealed Au(100) crystals are completely covered by a well-ordered “hex” reconstruction, comparable to that observed in UHV. The dependence of this initial surface topography on the sample pretreatment is demonstrated. Domains of parallel running modulation rows, which are the main feature of the reconstructed phase, can have spatial extensions of several micrometers. The potential-induced lifting of the reconstruction starts at the termination of these rows at step edges and domain boundaries. It proceeds by a quasi-one-dimensional growth along the rows, the speed of which is a function of potential. Due to the ~ 25% higher density of the reconstructed surface layer, Au atoms are expelled to the surface during the transition. They form monoatomic islands of isotropic shape, which grow by a ripening process. The reverse (1 × 1)→ “hex” transition proceeds by nucleation and growth of reconstruction domains originating at step edges. A detailed analysis of the mechanisms and interactions of both transitions reveals the importance of surface defects in the kinetic behavior of the phase transition.