Use Of Surface Texturing Research Articles

STATE OF THE ART OF SURFACE TEXTURING FOR BIOTRIBOLOGY APPLICATIONS

Surface texturing can be defined as a technique that consists of creating micro cavities in the surface of a material. There are different texturing techniques such as chemical etching, electromechanical micromachining, diamond embossing, electric discharge, pellet-pressing and laser surface, the last being the most common. For years, these surface texturing techniques have been used in tribological applications because microcavities can store oils or fluids and constantly lubricate the surfaces that are subjected to wear; they can also be used to trap wear particles (debris) that would otherwise act as abrasive particles (three body abrasive wear). This literature review seeks to analyse and compare the advantages that the use of surface texturing techniques can offer in reducing the wear of prosthetic components and therefore lengthening their useful life, to provide a better quality of life to patients. The results of this review showed a growing interest in the scientific community in the use of surface texturing for biotribogical applications, using to a greater extent the Laser Surface Texturing (LST) technique and the surface pattern composed by dimples.

Special Issue on Tribology of Additive Manufacturing

Special Issue on Tribology of Additive Manufacturing

Combined Use of Surface Texturing, Plasma Nitriding and DLC Coating on Tool Steel

In cold rolling, a textured roll can be used to imprint a desired surface topography onto the sheet during rolling. This work proposes the use of diamond-like carbon (DLC) coatings to protect the surface topography of the rolls in replacement of the carcinogenic hard chrome. For that, hydrogenated amorphous carbon (a-C:H) was deposited on plasma nitrided tool steel, both for ground and textured specimens. Changes in surface topography due to DLC coating were assessed using a confocal microscope. Coating adhesion was evaluated using the method VDI 3198. The specimens were characterized using X-ray diffraction (XRD), microhardness test and scanning electron microscopy (SEM). The coating was characterized using Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). The results showed a soft multilayer coating consisting of a plasma nitrided layer for load support, a Si-rich interlayer to improve adhesion and an a-C:H top layer. DLC deposition reduced the roughness of the textured specimens. The coating resulted in relatively stable friction and good durability, with small damage and negligible wear even under dry sliding.

Understanding the role of surface textures in improving the performance of boundary additives, part I: Experimental

Tribological performance of systems in boundary lubrication is dependent on contact and lubricant conditions such as temperature, lubricant additive concentration, surface characteristics, contact pressure and additive-additive interactions. Although past parametric studies have investigated these various factors, there are limited studies on the effect of surface topography on the performance of boundary lubrication additives. This is pertinent because of the increased use of surface texturing in lubricated contacts. This study has employed laser surface texturing to achieve surfaces with different topographies. The influence of the different surface topographies on the tribological performance of a friction modifier additive, molybdenum dialkyldithiocarbamate (MoDTC), was investigated. Results show that laser-textured surfaces in some instances can offer improved friction performance compared to non-textured (polished) surfaces when working positively with a friction modifier additive. Anisotropic surfaces resulted in improved friction. The mechanism for the improved performance of the laser-textured surfaces is believed to be through the augmented local contact pressures at the asperities that accelerate additive decomposition to form protective low-friction tribofilms. This study demonstrates the feasibility of surface texturing in improving the performance of boundary additives.

Influence of contact area on the sliding friction and wear behaviour of an electrochemical jet textured Al-Si alloy

Environmental legislation continues to drive optimisation of internal combustion engines in the automotive sector in an effort to reduce harmful emissions and promote fuel efficiency. Significant frictional losses occur at the ring pack, prompting research on reducing sliding friction at the ring – liner interface through the use of surface texturing. This study assesses the influence of contact area on the friction and wear behaviour of light-weight monolithic hyper-eutectic Al-Si alloy with a textured surface generated by electrochemical jet texturing. Flat rectangular samples were prepared from a cast cylinder liner via electro-discharge machining and flat lapped to 6 µm diamond finish prior to immersion in a 1 mol solution of NaOH for 120 s to simulate the mechanical honing process. Surfaces were electrochemically jet textured using a 2.3 mol solution of NaCl and current density of 220 A/cm2. An offset array of 1.3 × 0.3 mm rectangular features at 1.2 mm spacing was created with an average depth of 39 µm. Lubricated reciprocating sliding was carried out at a stroke length of 25 mm in a bath of PAO (4 cSt) at 100 °C against a 6 mm diameter, 13 mm long 52100 steel cylinder with three different contact areas corresponding to initial contact pressures of 157, 12 and 4 MPa. Sliding frequencies were varied between 1 and 15 Hz at a load of 50 N in order to establish the influence of both the contact pressure and velocity on the friction behaviour as a function of the lubrication regime. Textured features were observed to reduce the average coefficient of friction by up to 37% via a lubricant reservoir mechanism if the counter-surface contact width was greater than the feature dimension. Increases in contact pressure prevented a micro-EHL effect due to adhesive wear rather than pressurization of textured features.

Modifying tribological performances of AISI 316 stainless steel surfaces by laser surface texturing and various solid lubricants

Severe wear is the primary failure mechanism of AISI 316 stainless steel in tribological applications. The use of surface textures is a well-known method to improve mechanical property of contact surfaces. In this paper, micro-textures were produced on the steel surface by laser ablation process. Different types of solid lubricants were filled into the micro-scale textures, including CaF2, h-BN, WS2, and graphite. Dry sliding tests were conducted to examine the tribological performance of the prepared samples. Results showed that severe plastic deformation occurred on both patterned and flat samples. The patterned sample burnished with CaF2 solid lubricants did not show any apparent decrease in average friction coefficient. Almost all h-BN solid lubricants were squeezed out of the contact area, causing a high friction coefficient. Both patterned samples burnished with WS2 or graphite solid lubricants showed a relatively low friction coefficient. The lubricating tribofilm existed on the worn area can protect the prepared samples from further wear damage. This study provides a basis for the proper selection of solid lubricants in industrial applications.

Theoretical Model for the Optimal Design of Surface Texturing on Piston Compression Ring

A Theoretical model was developed to study the potential use of surface texturing for reducing the friction between a piston ring and cylinder liner. The model can predict the load-carrying capacity and friction force of the piston compression ring from Reynolds equation. The investigation is carried out using different dimple depths as well as different dimple diameters. Micro-dimples on the piston ring were able to generate significant hydrodynamic support. Numerical results show that surface texturing can decrease the friction force and extend the load-carrying capacity. The optimum surface texturing parameters such as dimples depth and dimples diameter were found.

Combined numerical and experimental investigation of the micro-hydrodynamics of chevron-based textured patterns influencing conjunctional friction of sliding contacts

Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions. Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved micro-wedge flow. The results show good agreement between numerical predictions and experimental measurements using a precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for given conditions, dependent on the intended application under laboratory conditions. The translation of the same into practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain. This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue than that obtained under ideal laboratory conditions.

Proteins, platelets, and blood coagulation at biomaterial interfaces

Blood coagulation and platelet adhesion remain major impediments to the use of biomaterials in implantable medical devices. There is still significant controversy and question in the field regarding the role that surfaces play in this process. This manuscript addresses this topic area and reports on state of the art in the field. Particular emphasis is placed on the subject of surface engineering and surface measurements that allow for control and observation of surface-mediated biological responses in blood and test solutions. Appropriate use of surface texturing and chemical patterning methodologies allow for reduction of both blood coagulation and platelet adhesion, and new methods of surface interrogation at high resolution allow for measurement of the relevant biological factors.

Effect of laser surface modification on the micro-abrasive wear resistance of coated cemented carbide tools

The use of surface texturing on the rake face of a tool can modify the tribological phenomena present at the chip-tool interface. Many different wear mechanisms, including abrasive wear, occur at the tool during machining. The presence of hard phases in the workpiece material, as well as hard particles removed from the tool, can generate abrasive wear on the tool surfaces. The objective of this work is to study the abrasive wear resistance of micro-textured tools in comparison to conventional (commercial) cutting tools. Square cemented carbide inserts containing a three-layered coating (TiCN–Al2O3–TiN) were textured using two different linear patterns, perpendicular and parallel to the direction of the chip movement. Microabrasion and machining tests on both textured and commercial tools were carried out. Turning tests were carried out for ABNT/AISI 1050 steel under severe cutting conditions with overhead application of cutting fluid. In order to simulate the abrasive wear mechanism that can occur on the tool surface, a free ball microabrasion test was used under a suspension of silicon carbide particles and distilled water. The abrasive wear mechanisms were observed using SEM. The micro-scale abrasive wear resistance of laser micro-textured cement carbide tools was compared to untextured tools. For the turning tests, texturing increased the tool life, which was determined when the wear at the tool flank achieved a specified value. On the other hand, for the microabrasion tests, laser texturing resulted in a pronounced increase in the coating wear rate. This fact was connected to the decrease of coating hardness caused by laser texturing. Therefore, the increase of tool life in the turning tests was not related to a reduction of abrasive wear on the tool flank. Probably, it was caused by other tribological conditions that were not represented in microabrasion tests, for example: the presence of cutting fluid in the environment and elevated contact temperatures.

Macromolecular self-organized assemblies

Macromolecular assemblies can be self-organized into patterns with controllable feature sizes ranging from ∼10 Å to ∼100 μm. Smallest features are produced by organizing macromolecules into a Langmuir–Blodgett film. Using this method, we have produced quasiperiodic arrays of metal oxide islands with peroidicities as small as 9 Å. Larger (20–200 Å) extremely monodisperse features can be obtained by causing single polymer chains to self-organize into a coiled spherical ball on the surface of a substrate. By using narrow molecular weight distribution polymer chains, the standard deviation of the ball diameter can be made as small as ∼8 Å. The largest features produced come from self-organization in the assemblage of macromolecular colloidal particles (natural lithography). A wide variety of geometrical packing arrangements can be produced by controlling methods used to coat colloidal particles into a substrate. In particular, the use of surface textures to induce a form of graphoepitaxy in colloidal particle packing is discussed.