Papers by Keyword: Surface Topography

Abstract: This research investigates the effect of surface roughness, water temperature, and pH value on the wettability behaviour of copper surfaces. An electron beam physical vapour deposition technique was used to fabricate 25, 50, and 75 nm thin films of copper on the surface of copper substrates. Surface topographical analysis, of the uncoated and coated samples, was performed using an atomic force microscopy device to observe the changes in surface microstructure. A goniometer device was then employed to examine the surface wettability of the samples by obtaining the static contact angle between the liquid and the attached surface using the sessile drops technique. Waters of pH 4, 7, and 9 were employed as the contact angle testing fluids at a set of fixed temperatures that ranged from 20°C to 60°C. It was found that increasing the deposited film thickness reduces the surface roughness of the as-prepared copper surfaces and thus causing the surface wettability to diverge from its initial hydrophobic nature towards the hydrophilic behaviour region. A similar divergence behaviour was seen with the rise in temperature of water of pH 4, and 9. In contrast, the water of pH 7, when tested on the uncoated surface, ceased to reach a contact angle below 90^o. It is believed that the observed changes in surface wettability behaviour is directly linked to the liquid temperature, pH value, surface roughness, along with the Hofmeister effect between the water and the surface in contact.

Abstract: In this study, magnetic pulse welded steel/aluminum hybrid joints are investigated with the aim of optimizing the process parameters regarding the fatigue behavior. Changes in discharge current, acceleration distance, welding geometry as well as influences of surface topography and corrosion, are examined regarding fatigue life and damage mechanisms. Instrumented multiple amplitude tests combined with constant amplitude tests are carried out for assessing structure-property-relations in a resource-efficient manner. Stress-induced change in strain and alternating current potential drop measurement are well suited for reliable detection of damage initiation and estimation of the fatigue limit. Results reveal that the fatigue properties primarily depend on the imperfections of the weld seam, which are affected mostly by the discharge current and the surface topography. Corrosion shows to be a relevant factor since it decreases fatigue performance. Suitable process parameters are achieved when the fatigue strength of the weld seam lies above the weaker hybrid joint (aluminum). For S235JR and EN AW1050A-H14 (Al99.5) a suitable discharge current was found to be 349 kA at an acceleration distance of 1.5 mm.

Abstract: The selection of the relative movement mode between the friction pairs in simulated friction and wear tests is a crucial factor for the characterization and evaluation of metallic material properties. In this study, two kinds of commonly used metal materials (stainless steel 0Cr18Ni9 and aluminum alloy 2A12) were applied for the simulated friction and wear tests with four different modes of relative motion, including unidirectional, reciprocating, circular and multi-directional cross-shear. The corresponding surface topography and statistical parameters such as surface roughness Ra were obtained via OLYMPUS ultra-depth microscope. Based on the fractal theory, fractal dimension D was calculated to characterize the surface topography and the results indicate that, the fractal dimension D of the unidirectional and multi-directional cross-shear simulated friction and wear tests is the minimum and maximum respectively, which reflects that the fractal dimension D is able to characterize the complexity of the surface morphology. The fractal dimension D may be related to the intrinsic physical properties of metal materials, such as hardness and toughness, which needs to be further studied.

Abstract: An optimal surface topography for the use of an environmentally friendly lubricant was elucidated, by making a wide combination of surface roughnesses Ra and RSm representing height and frequency of surface asperity, using the wet blast treatment. A forward conical can - backward straight can extruded friction test method proposed by the present authors was used. Coulomb friction coefficient was evaluated using a calibration curve representing the relationship between the surface friction coefficient of the conical punch and the front/back extrusion height of the workpiece. It was found that the surface topography of workpiece largely affects the lubricating property when the friction coefficient is large. Especially, the surface treatment with larger Ra and smaller RSm is effective for improving the friction. Furthermore, the correlation between the friction coefficient and the proposed parameter for the surface topography Ra/RSm was shown to be better than the Ra.

Abstract: This paper study on the influence of ultrasonic vibration assisted grinding (UAG) process on surface topography and properties of C/SiC composites. Through the surface quality experiments of common grinding (CG) and UAG, the height distribution parameters and function parameters are obtained and used to analyze the characteristics of the material surface topography. The relationship between grinding process and the composites surface quality is pointed out by experimental research. The orthogonal design is employed to optimize ultrasonic parameters and grinding parameters. The optimized condition is carried out to modify the surface quality. The results show that ultrasonic vibration has a great influence on height and surface bearing properties; the surface roughness is improved by the small vibration amplitude and low frequency. The grinding depth is the key factor on surface topography modification and the feed rate is the second. According to the research, an important technical support is carried out to improve the surface performance of C/SiC composites.

Abstract: Visualization of work surface topography through simulations is very challenging task in grinding process due to the complexity of wheel-work interactions with a very high number of cutting points (grits). Kinematic mapping of abrasive grits on a three-dimensional wheel topography enables the evaluation of ground surface topography through simulations. In this paper, a method for generating the ground surface topography based on wheel specifications is presented. Abrasive grits size, abrasives volume percentage and their nature of distribution on the wheel surface are considered in the modeling and visualization of wheel topography. The simulation results of ground surface topographies prove the feasibility of the developed method.

Abstract: The topography of a surface consists of structures of different length scales. The surface roughness caused by these structures plays a decisive role in interfacial properties. Atomic Force Microscopy (AFM) can be applied to measure the surface topography with great accuracy and thus facilitates roughness quantification. Here, however, the data reduction poses a challenge. In a conventional approach, surface roughness parameters are evaluated based on averaging height differences, which leads to values dominated by the largest height differences of the surface topography. To quantify contributions of smaller structures to the roughness, a previous study presented a tunable local background correction, which eliminates structures on a larger than selected scale. Therefore, this method only considers surface structures smaller than the chosen scale. A different approach to quantify surface roughness on all length scales covered by AFM measurements uses Fourier transformation of the surface topography to calculate the power spectral density, which describes the amplitudes of different contributing spatial frequencies.In the current study, a new approach based on power spectral density is used to quantify surface roughness parameters as a function of the length scale of contributions to the surface topography. This procedure allows a comprehensive characterization of surface roughness and an intuitive comparison of different surfaces.The usefulness of this method and its compatibility to local background correction is demonstrated by analyzing several commercially available carbon fibers with and without different fiber surface treatments.

Abstract: Electrochemical process of conversion coatings formation on Zn-Ti alloy surface during one-step anodizing process was studied in NaOH and KOH electrolytes over the range of voltages (4-50 V) and constant time in order to investigate parameters for the origin of anodic zinc coating. Stainless steel was used as a counter electrode and electrolyte during the anodizing process was agitated by compressed air. Coatings microstructures and morphology were characterized by means of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Surface topography was investigated prior and after the anodizing using non-contact optical 3D profilometer. It was found that high voltage (50 V) and low concentrations of electrolyte (0.04 and 0.1 mol/L NaOH) led to origin of white coloured oxide coatings, while lower voltage (4 and 6 V) and higher concentrations of electrolyte promote the origin of black coloured oxide coatings. Concentration of electrolyte and voltage influenced the thickness of conversion coatings and its surface morphology. Moreover, the surface morphology of the coatings was also influenced by the heterogeneity of substrate alloy.

Abstract: Laser-matter interaction is commonly described regarding three main factors: laser beam, materials and environment. Conversion of absorbed energy via collision process into heat is the most important effect that occurs during laser interaction. Short-pulsed laser beam induces fast transition from the overheated liquid to a mixture of vapor and drops which allows the ablation of micrometric layers. Specific patterns can then be achieved using scanning and automation technology also called laser texturing. New materials with specific properties such as endurance life and/or lower environmental impact attract emerging technologies such as thermal spraying. However, adhesive bond strengths have to be high enough to play a key role in surface properties. A clean surface to enhance mechanical interlocking is a key element. Mechanical and physico-chemical bond strength for thick coatings elaborated by thermal spray process can then be developed using laser. The aim of the present paper is to show the potential of such emerging treatments through new results using various thermal spray processes (thermal spraying as well as cold spraying). Metal or organic materials were investigated implementing various powders.

Abstract: A crucial factor for ingrowth of permanent implants in the bone is the rapid cellular acceptance. The topographical features often follow mechanical aspects for implant stability. But several of these implants fail due to insufficient cell adhesion. Cells are able to perceive the physico-chemical properties of their surrounding and to pass these signals into the cell to modulate their adhesion structures, growth or production of extracellular matrix. However, the complex cell physiology at the material interface is not yet fully understood, particular on stochastically structured topographies resulting from industrial production. We could find out that corundum blasted titanium hampered the organization of actin filaments inside the cells, clustered adhesion components, e. g. beta-1 integrins and tensin, and the cells bridged the valleys which reduces cell-substrate contacts. These morphological changes strongly diminished the mineralization of osteoblasts. To shed light on cause and effect we reduced the physical complexity of the material surface by introduction of regular micro-structures (pillars, grooves) using deep reactive ion etching. Now it was more obvious what cells are doing on sharp edged topographies ‒ the actin filaments of our cells were clustered around the pillars. As a result the intracellular calcium signaling and the protein synthesis were impaired. Our recent findings indicated an attempted phagocytosis of the micro-pillars by osteoblasts. Therefore we conclude that implants used in orthopedic surgery should avoid any sharp-edged topographical features that could induce phagocytosis by the surrounding cells, which is an unnecessarily energy consuming process.