Comparing Wettability and Frictional Performance of Laser Micro-machined Discrete and Continuous Textures
01 Jan 2021-pp 185-192
TL;DR: In this paper, Dimple and cross-hatch textures are fabricated using laser surface texturing (LST) technique to compare the wettability and coefficient of friction (CoF) of discrete and continuous texture under bio-lubricated condition.
Abstract: TiAl4V is used widely in aerospace and biomedical application due to its high specific strength and good bio-compatibility. Its poor tribological performance restricts usage for hip implant articulation. Various surface characteristics such as surface roughness and wettability affect the tribological behaviour of Ti6Al4V sliding. Surface texturing is the recent technique to modify the surface features and improve the wettability. This study aims to compare the wettability and coefficient of friction (CoF) of discrete and continuous texture under bio-lubricated condition. Dimple and crosshatch textures are fabricated using laser surface texturing (LST) technique. The geometrical parameters such as depth, pitch and area density have been kept the same. Wettability associated with both the textures are analysed by measuring surface contact angles using goniometer. Further, friction behaviour is evaluated for all the textured and non-textured surfaces under biological environment using reciprocating pin-on-disc tribometer. Results show a significant reduction in contact angle for crosshatch texture compared to dimple and non-textured surface. Also, both the texture reduced the friction by 24% compared to non-textured surface.
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TL;DR: In this paper , oriented crosshatch textures were fabricated over Ti6Al4V surface using Nd:YAG laser and the effect of heat treatment over DLC coating morphology, adhesion strength and surface characteristics was analyzed.
Abstract: Superior surface characteristics, tribological performance and adhesion strength are critical for DLC coated surface in hip implant. Incorporating laser surface texturing and heat treatment before DLC deposition can improve surface properties by inducing oxygen diffusion and phase formation. Therefore, oriented crosshatch textures were fabricated over Ti6Al4V surface using Nd:YAG laser. Textured surface was heat treated followed by DLC coating deposition with Cr interlayer. Effect of heat treatment over DLC coating morphology, adhesion strength and surface characteristics was analyzed. Phase formation and bonding behavior at the coating interlayer were characterized and correlated with adhesion strength. Bio-tribological performance of modified surface was evaluated under elliptical sliding contact to replicate hip implant articulation. Increased surface roughness, better wettability and enhanced graphitic characteristics were associated with DLC coating with prior heat treatment. With heat treatment, Cr2O3 and TiO2 phase formation with superior bonding at interlayer demonstrated improved adhesion strength including deformation resistance. Textured, heat treated and DLC coated surface showed relatively increased compressive residual stress with HF1 quality adhesion. The synergic effect of surface texturing and DLC coating achieved lowest friction. Qualitative wear analysis using Raman spectroscopy reveals beneficial effect of heat treatment before DLC coating for long term hip implant application.
9 citations
TL;DR: In this paper , the authors investigated the role of laser scanning and post heat treatment in improving the oxygen diffusion depth and overall surface characteristics of Ti6Al4V surface and found that the combination of LST and heat treatment improves rutile phase fraction, surface hardness and adhesion.
Abstract: The combination of laser surface texturing and heat treatment process was barely investigated in the past, particularly for improved surface characteristics of Ti6Al4V. Hereby, the important role of laser scanning and post heat treatment in improving the oxygen diffusion depth and overall surface characteristics was analyzed. Polished Ti6Al4V surface was scanned using Nd:YAG nanosecond laser and analyzed for the oxygen pickup, phase change and hardness variation. The laser textured surface was heat treated to grow oxide coating over textured surface. In comparison with heat treated surface, the synergic effect of laser scanning and heat treatment improved the surface hardness by 15% and raised the TiO 2 rutile phase fraction from 0.36 to 0.73. The dual engineered Ti6Al4V surface was found to have superior HF1 quality adhesion strength along with the presence of low magnitude tensile residual stress. The increase in oxygen diffusion depth, diffusion coefficient and TiO 2 rutile phase fraction due to synergic effect of laser scanning and heat treatment were associated to the Ti 2 O 3 and C doping assisted anatase to rutile transformation mechanism. • Laser scanning is responsible for oxygen and carbon pickup and forms Ti2O3 phase at the Ti6Al4V surface. • Combination of LST and heat treatment improves rutile phase fraction, surface hardness and adhesion. • Oxygen diffusion depth and diffusion coefficient increase using laser texturing with heat treatment process. • Anatase to rutile transformation is prominent mechanism in laser textured with heat treated Ti6Al4V surface.
6 citations
2 citations
TL;DR: In this paper , the authors combined the laser surface texturing technology and heat treatment process to fabricate a dual surface engineered Ti6Al4V consisting of micro-groove crosshatch pattern texture covered with hard TiO 2 oxide coating to reduce friction and improve the wear resistance at the bio-lubricated interface.
Abstract: This study combines the laser surface texturing technology and heat treatment process to fabricate a dual surface engineered Ti6Al4V consisting of micro-groove crosshatch pattern texture covered with hard TiO 2 oxide coating to reduced friction and improve the wear resistance at the bio-lubricated interface. Crosshatch texture with 25 μm width, 5 μm depth at 25% area density were fabricated using nanosecond Nd:YAG laser over Ti6Al4V surface and then heat treated at 600 °C for 48 hours. XRD result showed rutile TiO 2 phase formation along with the presence of anatase TiO 2 , Al 2 O 3 and Ti 3 O minor phases whereas, the surface hardness was increased to 1538±41 HV. Bio-tribology experiments were carried out for 45 and 90 o oriented micro-groove crosshatch textures, with and without heat treatment, under partially replicating hip implant articulation. Results demonstrated 60% friction reduction corresponding to the 45 o oriented crosshatch texture with heat treatment. Further, the worn-out surface morphology showed reduced wear damage and good wear debris entrapment inside the micro-grooves.
1 citations
TL;DR: In this article , thermal oxidation was performed on micro-blasted Ti6Al4V surfaces for 24 and 48 hours and the electrochemical performance was evaluated using FESEM, EDS, XRD, AFM, and Goniometer.
Abstract: Ti6Al4V alloy is widely used for orthopaedic applications due to its excellent osteointegration, good biocompatibility, great strength-to-weight ratio, and comparable elasticity with bone. However, when this alloy is exposed for long-term in the body fluid, it releases the corrosion products of metals and metal oxides. The released particles react with the surrounding tissue and cause an adverse local tissue reaction (ALTR) which leads to pseudotumor formation, osteolysis (bone degradation). Thus, corrosion is a critical parameter for bio-implants and in this study to minimize corrosion, thermal oxidation was performed on micro-blasted Ti6Al4V surfaces for 24 and 48 h. Surface morphology, phase analysis, surface roughness, and wettability of all types of samples were evaluated using FESEM, EDS, XRD, AFM, and Goniometer. The electrochemical performance was studied in 0.9 wt% NaCl. The combined mechanical and thermal process increases surface roughness and improves the hydrophilic nature of the Ti6Al4V surface by 67 %. The formation of metastable Ti2O3 during micro-blasting and further transformation of anatase and rutile TiO2 during thermal oxidation increases the intensity of anatase and rutile TiO2 formed on the surface and enhances corrosion resistance. Overall, micro-blasting with 48-h thermal oxidation showed 2 times higher corrosion resistance and reduced corrosion rate by almost 50 % as compared with the untreated Ti6Al4V.
References
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TL;DR: In this paper, the effect of partially laser surface textured piston rings on the fuel consumption and exhaust gas composition of a compression-ignition IC engine was evaluated with a Ford Transit naturally aspirated 2500 cm3 engine at a wide range of engine speeds under near-half load conditions.
379 citations
TL;DR: It is demonstrated that the results of investigations aiming at technological applications can also provide insights into biophysical phenomena and techniques for reducing wall shear stresses and for controlling boundary-layer separation are described.
Abstract: A survey is given on fluid-dynamic effects caused by the structure and properties of biological surfaces. It is demonstrated that the results of investigations aiming at technological applications can also provide insights into biophysical phenomena. Techniques are described both for reducing wall shear stresses and for controlling boundary-layer separation. (a) Wall shear stress reduction was investigated experimentally for various riblet surfaces including a shark skin replica. The latter consists of 800 plastic model scales with compliant anchoring. Hairy surfaces are also considered, and surfaces in which the no-slip condition is modified. Self-cleaning surfaces such as that of lotus leaves represent an interesting option to avoid fluid-dynamic deterioration by the agglomeration of dirt. An example of technological implementation is discussed for riblets in long-range commercial aircraft. (b) Separation control is also an important issue in biology. After a few brief comments on vortex generators, the mechanism of separation control by bird feathers is described in detail. Self-activated movable flaps (= artificial bird feathers) represent a high-lift system enhancing the maximum lift of airfoils by about 20%. This is achieved without perceivable deleterious effects under cruise conditions. Finally, flight experiments on an aircraft with laminar wing and movable flaps are presented.
378 citations
TL;DR: The pressure distribution between the cartilaginous surfaces in the human hip joint was measured using pressure-sensitive film, indicating that the cartilage did not, to any great extent, distribute the applied load.
Abstract: The pressure distribution between the cartilaginous surfaces in the human hip joint was measured using pressure-sensitive film. Five cadaveric hip joints (aged between 58 and 87 years) were measured at three positions and loads, representing three instants in the stance phase of the walking cycle. The pressure distribution was not uniform, indicating that the cartilage did not, to any great extent, distribute the applied load. The maximum pressures recorded were about 10 MN/m2. The anterosuperior surface of the cartilage was identified as an area of high pressure.
277 citations
TL;DR: In this paper, a critical review of surface texturing over the past decades is presented, highlighting design, optimization and fabrication of surface texture, and their effects on tribological performance in terms of friction and load bearing capacity under different lubrication regimes.
Abstract: Surface texturing is a surface modification approach, resulting in an improvement in tribological performance such as friction and wear resistance. Surface texturing can be performed either as a protruded or recessed asperity, with the latter being more popular due to advantages in terms of micro-lubrication and ease of manufacturing. There are a number of ways of material preparation for surface texturing, with the laser surface texturing being the most popular because of its flexibility and high accuracy. The performance of textured surface depends on the geometrical characteristics of the surface texture and the operating condition of the bearing components. In hydrodynamic and mixed lubrication, microcavity in negative surface texture acts as a reservoir for fluid lubricant, while in boundary lubrication, it traps wear particles to reduce further abrasion. In the past, tremendous amount of research effort has been put into the study of surface texturing, with an aim to investigate the underlying effect of surface texturing on tribological performance. This paper presents a critical review of research and development on surface texturing over the past decades, highlighting design, optimization and fabrication of surface texture, and their effects on tribological performance in terms of friction and load bearing capacity under different lubrication regimes. Numerical modelling approaches involving Reynolds and Navier–Stokes equations employed to understand and determine the tribological behaviour are discussed and compared with respect to experimental investigations. Thin film coatings on textured surface have been found to be a promising means to further reduce friction and increase wear life.
212 citations
TL;DR: In this paper, a finite element model was developed to study the hydrodynamic effect of micro-pores generated by laser surface texturing (LST) in a circumferential gas seal.
Abstract: A theoretical finite-element model was developed to study the hydrodynamic effect of micro-pores generated by laser surface texturing (LST) in a circumferential gas seal. The seal is represented by two non-contacting annular surfaces of a rotating shaft and a stationary ring. The micro-pores of spherical segment shape are distributed uniformly over one of the annular surfaces. The hydrodynamic dimensionless pressure distribution in the uniform clearance between the annular surfaces is obtained from a solution of the Reynolds equation for compressible viscous gas in a laminar flow. Results of a parametric study along with a numerical example for a specific circumferential seal demonstrate a substantial hydrodynamic effect that can raise the opening average pressure in the seal clearance above the ambient one by up to 50 percent. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001
137 citations