Showing papers on "Surface roughness published in 2007"

Selective laser melting of biocompatible metals for rapid manufacturing of medical parts

Abstract: Purpose – This paper seeks to investigate the possibility of producing medical or dental parts by selective laser melting (SLM). Rapid Manufacturing could be very suitable for these applications due to their complex geometry, low volume and strong individualization.Design/methodology/approach – The SLM‐process has been optimized and fully characterized for two biocompatible metal alloys: Ti‐6Al‐4V and Co‐Cr‐Mo. Mechanical and chemical properties were tested and geometrical feasibility, including process accuracy and surface roughness, was discussed by benchmark studies. By developing a procedure to fabricate frameworks for complex dental prostheses, the potential of SLM as a medical manufacturing technique has been proved.Findings – Optimized SLM parameters lead to part densities up to 99.98 percent for titanium. Strength and stiffness, corrosion behavior, and process accuracy fulfil requirements for medical or dental parts. Surface roughness analyses show some limitations of the SLM process. Dental frame...

Making waves: Kinetic processes controlling surface evolution during low energy ion sputtering

Abstract: When collimated beams of low energy ions are used to bombard materials, the surface often develops a periodic pattern or “ripple” structure. Different types of patterns are observed to develop under different conditions, with characteristic features that depend on the substrate material, the ion beam parameters, and the processing conditions. Because the patterns develop spontaneously, without applying any external mask or template, their formation is the expression of a dynamic balance among fundamental surface kinetic processes, e.g., erosion of material from the surface, ion-induced defect creation, and defect-mediated evolution of the surface morphology. In recent years, a comprehensive picture of the different kinetic mechanisms that control the different types of patterns that form has begun to emerge. In this article, we provide a review of different mechanisms that have been proposed and how they fit together in terms of the kinetic regimes in which they dominate. These are grouped into regions of behavior dominated by the directionality of the ion beam, the crystallinity of the surface, the barriers to surface roughening, and nonlinear effects. In sections devoted to each type of behavior, we relate experimental observations of patterning in these regimes to predictions of continuum models and to computer simulations. A comparison between theory and experiment is used to highlight strengths and weaknesses in our understanding. We also discuss the patterning behavior that falls outside the scope of the current understanding and opportunities for advancement.

UV-Driven Reversible Switching of a Roselike Vanadium Oxide Film between Superhydrophobicity and Superhydrophilicity

Abstract: We report the fabrication of a roselike nanostructured vanadium oxide (V2O5) film with photoinduced surface wettability switching by carrying out the drop-casting of a suspension of V2O5 particles synthesized with the sol−gel method. Although a pure V2O5 film is slightly hydrophilic, the addition of alkylamine renders the nanostructured V2O5 film superhydrophobic owing to the intercalation of alkyl chains between the V2O5 layers. UV exposure switches the wettability of the V2O5 surface to superhydrophilic with a water contact angle of almost 0°, and storage in the dark reconverts the irradiated surface back to its initial superhydrophobic state. This extraordinary wetting transition is ascribed to the cooperation between the photosensitivity of V2O5 and the surface roughness of its nanostructure, which has submicron- to micron-scale apertures. Our approach provides not only the possibility of producing large homogeneous or patterned surfaces with tunable wettability, but also potential uses in catalysts, ...

Water wetting transition parameters of perfluorinated substrates with periodically distributed flat-top microscale obstacles.

Abstract: Superhydrophobicity is obtained on photolithographically structured silicon surfaces consisting of flat-top pillars after a perfluorosilanization treatment. Systematic static contact angle measurements were carried out on these surfaces as a function of pillar parameters that geometrically determine the surface roughness, including pillar height, diameter, top perimeter, overall filling factor, and disposition. In line with thermodynamics models, two regimes of static contact angles are observed varying each parameter independently: the "Cassie" regime, in which the water drop sits suspended on top of the pillars (referred to as composite), corresponding to experimental contact angles greater than 140-150 degrees, and the "Wenzel" regime, in which water completely wets the asperities (referred to as wetted), corresponding to lower experimental contact angles. A transition between the Cassie and Wenzel regimes corresponds to a set of well-defined parameters. By smoothly depositing water drops on the surfaces, this transition is observed for surface parameter values far from the calculated ones for the thermodynamic transition, therefore offering evidence for the existence of metastable composite states. For all studied parameters, the position of the experimental transition correlates well with a rough estimation of the energy barrier to be overcome from a composite metastable state in order to reach the thermodynamically favored Wenzel state. This energy barrier is estimated as the surface energy variation between the Cassie state and the hypothetical composite state with complete filling of the surface asperities by water, keeping the contact angle constant.

Cell and protein compatibility of parylene-C surfaces.

Abstract: Parylene-C, which is traditionally used to coat implantable devices, has emerged as a promising material to generate miniaturized devices due to its unique mechanical properties and inertness. In this paper we compared the surface properties and cell and protein compatibility of parylene-C relative to other commonly used BioMEMS materials. We evaluated the surface hydrophobicity and roughness of parylene-C and compared these results to those of tissue culture-treated polystyrene, poly(dimethylsiloxane) (PDMS), and glass. We also treated parylene-C and PDMS with air plasma, and coated the surfaces with fibronectin to demonstrate that biochemical treatments modify the surface properties of parylene-C. Although plasma treatment caused both parylene-C and PDMS to become hydrophilic, only parylene-C substrates retained their hydrophilic properties over time. Furthermore, parylene-C substrates display a higher degree of nanoscale surface roughness (>20 nm) than the other substrates. We also examined the level of BSA and IgG protein adsorption on various surfaces and found that surface plasma treatment decreased the degree of protein adsorption on both PDMS and parylene-C substrates. After testing the degree of cell adhesion and spreading of two mammalian cell types, NIH-3T3 fibroblasts and AML-12 hepatocytes, we found that the adhesion of both cell types to surface-treated parylene-C variants were comparable to standard tissue culture substrates, such as polystyrene. Overall, these results indicate that parylene-C, along with its surface-treated variants, could potentially be a useful material for fabricating cell-based microdevices.

An experimental investigation of micro-machinability of copper 101 using tungsten carbide micro-endmills

Abstract: This paper presents an experimental investigation of micromachinability during micromilling of oxygen-free high conductivity (OFHC), commercially pure copper 101 using tungsten carbide micro-endmills. The forces, surface roughness, tool wear, and burr formation are analyzed under varying cutting speeds ( 40 , 80 , and 120 m/min) and feed rates ( 0.75 , 1.5 , 3 and 6 μ m / flute ). The experiments included full-immersion cutting with 254 μ m micro-endmills with an axial depth of cut of 30 μ m . The variation of forces, surface roughness, and burr formation with wear progression is also studied. It was seen that the minimum chip thickness and associated ploughing/indentation effects induce erratic variations to micromilling forces at feed rates in the vicinity of edge radius of the micro-endmills. At larger feed rates, the micromilling forces resemble those of conventional milling in the presence of tool-tip runout. The surface roughness was observed to be nearly constant at feed rates up to 3 μ m / flute , and to increase with feed rate for larger feed rates. Unlike conventional milling, greatest tool wear was experienced at the lowest feed rate and lowest speed, and the lowest wear was seen at the highest feed rate. The main mechanism of wear was concluded to be attrition wear in its most basic form, whereby the tungsten–carbide grains on the cutting edges were dislodged from the cobalt matrix. The smallest top burrs were experienced at 40 m/min surface speed at higher feed rates. The lowest feed rate of 0.75 μ m / flute resulted in large burrs at any speed. Progressing wear was seen to induce an increase in forces, a reduction in surface roughness, and a strong increase in burr formation.

Evaluation of surface characteristics of dental composites using profilometry, scanning electron, atomic force microscopy and gloss-meter

Abstract: The aim of this in vitro investigation was to compare various roughness and topography measurement methods to characterize the surface quality in several types of resin composites. The initial surface quality of several resin composites was compared. The materials evaluated were of three categories: i) hybrid: TPH Spectrum; ii) reinforced microfill: Micronew and iii) microhybrid: Synergy Duo, Esthet-X, Point.4 and Palfique Estelite. Three Groups of identical disk-shaped specimens (10 × 1.5 mm) were prepared from each material (n = 6) and polished with Soflex discs. Macro-roughness (Ra) was measured with Group 1 by 2-D profilometry. Atomic Force Microscopy (AFM) gave 3-D images and micro-roughness (Ra) of Group 2. Surface optical gloss at 60∘ was determined for Group 3. Specimens of each material were also studied by scanning electron microscopy. Macro-Ra values (μm) ranged from 0.30 to 0.56. Micro-Ra values ranged from 0.03 to 0.14 and they differed from macro-Ra values in ranking order. Percentage Gloss values ranged from 30.6 to 70.1%. The results revealed that micro-roughness showed a high correlation with gloss values (r = 0.93), whilst macro-roughness did not (r = 0.62). Moreover, the AFM method showed higher capability to distinguish surface roughness compared with the 2-D profilometry and to reveal more detailed definition of surface texture than the examination under SEM.

The effect of viewpoint on perceived visual roughness.

Abstract: In previous work, we examined how the apparent roughness of a textured surface changed with direction of illumination. We found that observers exhibited systematic failures of roughness constancy across illumination conditions for triangular-faceted surfaces where physical roughness was defined as the variance of facet heights. These failures could be due, in part, to cues in the scene that confound changes in surface roughness with changes in illumination. These cues include the following: (1) the proportion of the surface in shadow, (2) mean luminance of the nonshadowed portion, (3) the standard deviation of the luminance of the nonshadowed portion, and (4) texture contrast. If the visual system relied on such "pseudocues" to roughness, then it would systematically misestimate surface roughness with changes in illumination much as our observers did despite the availability of depth cues such as binocular disparity. Here, we investigate observers' judgments of roughness when illumination direction and surface orientation are fixed and the observers' viewpoint with respect to the surface changes. We find a similar pattern of results. Observers exhibited patterned failures of roughness constancy with change in viewpoint, and an appreciable part of their failures could be accounted for by the same pseudocues. While the human visual system exhibits some degree of roughness constancy, our results lead to the conclusion that it does not always select the correct cues for a given visual task.

A surface roughness prediction model for hard turning process

Abstract: An experimental investigation was conducted to determine the effects of cutting conditions and tool geometry on the surface roughness in the finish hard turning of the bearing steel (AISI 52100). Mixed ceramic inserts made up of aluminium oxide and titanium carbonitride (SNGA), having different nose radius and different effective rake angles, were used as the cutting tools. This study shows that the feed is the dominant factor determining the surface finish followed by nose radius and cutting velocity. Though, the effect of the effective rake angle on the surface finish is less, the interaction effects of nose radius and effective rake angle are considerably significant. Mathematical models for the surface roughness were developed by using the response surface methodology.

Multiscale friction mechanisms and hierarchical surfaces in nano- and bio-tribology

Abstract: Various mechanisms of solid–solid and solid–liquid friction are studied in this review, and their relation to the surface roughness hierarchy is discussed. For ideal solid bodies with conservative forces acting between them, there would be no friction. Different deviations from the ideal state, such as the surface roughness, contamination and chemical heterogeneity, bulk material deformation and non-conservative adhesive bonds, lead to energy dissipation. Most heterogeneities involved into various dry friction mechanisms are associated with small ratios of magnitudes and of characteristic lengths of the forces at the interface and in the bulk. This small ratio leads to an almost linear dependence of the friction force upon load (the Coulomb law). However, the heterogeneities lead also to non-linear and multiscale effects. Mapping of dry friction mechanisms is proposed based upon the characteristic length parameters. It is discussed also how hierarchical friction mechanisms lead to biological hierarchical surfaces with reduced or increased adhesion and friction. Current advances in nano- and bio-tribology reveal a growing number of hierarchical (multiscale) surfaces. From the lotus leaf and gecko foot to self-affine and textured engineering surfaces, the hierarchy plays a fundamental role in frictional energy dissipation.

Design of a superhydrophobic surface using woven structures.

Abstract: The relationship between surface tension and roughness is reviewed. The Cassie-Baxter model is restated in its original form, which better describes the most general cases of surface roughness. Using mechanical and chemical surface modification of nylon 6,6 woven fabric, an artificial superhydrophobic surface was prepared. A plain woven fabric mimicking the Lotus leaf was created by further grafting 1H,1H-perfluorooctylamine or octadecylamine to poly(acrylic acid) chains which had previously been grafted onto a nylon 6,6 woven fabric surface. Water contact angles as high as 168 degrees were achieved. Good agreement between the predictions based on the original Cassie-Baxter model and experiments was obtained. The version of the Cassie-Baxter model in current use could not be applied to this problem since the surface area fractions in this form is valid only when the liquid is in contact with a flat, porous surface. The angle at which a water droplet rolls off the surface has also been used to define a superhydrophobic surface. It is shown that the roll-off angle is highly dependent on droplet size. The roll-off angles of these superhydrophobic surfaces were less than 5 degrees when a 0.5 mL water droplet was applied.

Laser polishing of parts built up by selective laser sintering

Abstract: In this work, a surface finish method for parts built-up by selective laser sintering (SLS) is presented One of the main drawbacks of the SLS technique is the high surface roughness of resulting parts Therefore, parts have to be polished to be valid for operation conditions Polishing processes are usually based on manual abrasive techniques However, in the present paper, a surface polishing method based on laser irradiation is presented The laser beam melts a microscopic layer on the surface, which re-solidifies under shielding gas protective conditions, resulting in a smoother surface Laser-polishing tests for lines, planar surfaces and inclined planes have been performed, with satisfactory results in all the cases The experimental tests were carried out on sintered test parts with an initial roughness of 75–78 μm Ra The tested material is a commercial alloy denominated LaserForm ST-100©, composed by sintered stainless steel and infiltrated bronze that it is used mainly for the constitution of injection moulds Experimental results present final surface roughness below 149 μm Ra, which represent an 801% reduction of the mean roughness Finally, a complete analysis of test probes and its metallurgical composition is presented Considering that the material presents a non-homogeneous structure, the polished surfaces present slightly higher hardness values and are more homogeneous than the initial ones Thus, polished surfaces do not present any heat affected zone or cracks, which could cause failure during the part operation

Nanostructured mesoporous nickel oxide thin films

Abstract: Nanostructured nickel oxide thin films were prepared by the pulsed laser ablation technique. The effects of annealing on the structural, morphological, electrical and optical properties are discussed. Phase imaging was used to examine the surface contaminants, adhesion and hardness and height imaging to evaluate the height profile of the films. Morphological investigations using atomic force microscopy and scanning electron microscopy indicate a strong influence of the annealing process on the surface roughness and particle size. A self-assembly of nanocrystals agglomerating together to form an island-like structure is observed in films annealed at 773 K. X-ray diffraction and x-ray photoelectron spectroscopy investigations indicate the presence of Ni2O3 in the as-deposited films. A transformation to cubic NiO with growth along (111) and (200) planes with increase of annealing temperature is also observed.

A negative permeability material at red light

Abstract: A negative permeability in a periodic array of pairs of thin silver strips is demonstrated experimentally for two distinct samples. The effect of the strip surface roughness on negative permeability is evaluated. The first sample, Sample A, is fabricated of thinner strips with a root mean square roughness of 7 nm, while Sample B is made of thicker strips with 3-nm roughness. The real part of permeability, mu', is -1 at a wavelength of 770 nm in Sample A and -1.7 at 725 nm in Sample B. Relative to prototypes simulated with ideal strips, larger strip roughness acts to decrease |mu| by a factor of 7.8 in Sample A versus a factor of 2.4 decrease for Sample B.

Cutting temperature, tool wear, surface roughness and dimensional deviation in turning AISI-4037 steel under cryogenic condition

Abstract: Machining of steel inherently generates high cutting temperature, which not only reduces tool life but also impairs the product quality. Conventional cutting fluids are ineffective in controlling the high cutting temperature and rapid tool wear. Further, they also deteriorate the working environment and lead to general environmental pollution. Cryogenic cooling is an environment friendly clean technology for desirable control of cutting temperature. The present work deals with experimental investigation in the role of cryogenic cooling by liquid nitrogen jet on cutting temperature, tool wear, surface finish and dimensional deviation in turning of AISI-4037 steel at industrial speed-feed combination by coated carbide insert. The results have been compared with dry machining and machining with soluble oil as coolant. The results of the present work indicate substantial benefit of cryogenic cooling on tool life, surface finish and dimensional deviation. This may be attributed mainly to the reduction in cutting zone temperature and favorable change in the chip–tool interaction. Further it was evident that machining with soluble oil cooling failed to provide any significant improvement in tool life, rather surface finish deteriorated.

Characterizing arid region alluvial fan surface roughness with airborne laser swath mapping digital topographic data

Abstract: [1] Range-front alluvial fan deposition in arid environments is episodic and results in multiple fan surfaces and ages. These distinct landforms are often defined by descriptions of their surface morphology, desert varnish accumulation, clast rubification, desert pavement formation, soil development, and stratigraphy. Although quantifying surface roughness differences between alluvial fan units has proven to be difficult in the past, high-resolution airborne laser swath mapping (ALSM) digital topographic data are now providing researchers with an opportunity to study topography in unprecedented detail. Here we use ALSM data to calculate surface roughness on two alluvial fans in northern Death Valley, California. We define surface roughness as the standard deviation of slope in a 5-m by 5-m moving window. Comparison of surface roughness values between mapped fan surfaces shows that each unit is statistically unique at the 99% confidence level. Furthermore, there is an obvious smoothing trend from the presently active channel to a deposit with cosmogenic 10Be and 36Cl surface exposure ages of ∼70 ka. Beyond 70 ka, alluvial landforms become progressively rougher with age. These data suggest that alluvial fans in arid regions smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces.

Examination of a critical roughness height for outer layer similarity

Abstract: The existence of a critical roughness height for outer layer similarity between smooth and rough wall turbulent boundary layers is investigated. Results are presented for boundary layer measurements on flat plates covered with sandgrain and woven mesh with the ratio of the boundary layer thickness to roughness height (δ∕k) varying from 16 to 110 at Reθ=7.3×103–13×103. In all cases tested, the layer directly modified by the roughness (the roughness sublayer) is confined to a region <5k or <3ks from the wall (where ks is the equivalent sandgrain roughness height). In the larger roughness cases, this region of turbulence modification extends into the outer flow. However, beyond 5k or 3ks from the wall, similarity in the turbulence quantities is observed between the smooth and rough wall boundary layers. These results indicate that a critical roughness height, where the roughness begins to affect most or all of the boundary layer, does not exist. Instead, the outer flow is only gradually modified with increas...