Papers by Keyword: Porous Coating

Abstract: A comparison was made of the properties of porous coatings obtained by ion-plasma spraying methods, 3D-coating obtained by direct laser metal deposition (DLMD), as well as a GRIPTION® and POROCOAT® coating. The influence of various methods of obtaining a porous coating on the porosity and structure of the coating, as well as the effect of thermal hydrogen treatment (THT) on the adhesion strength of the titanium coating was determined.

Abstract: Based on the flow equation of the ferromagnetic liquid lubricant for the “thin layer”, the continuity equation and the Darcy equation describing the flow of a lubricant in a porous body, the paper presents an accurate self-similar solution of the V-shaped sliding support with a porous coating of the base ring surface taking into account the rheological properties of the lubricant with ferromagnetic properties when the working gap is partially filled at the laminar flow mode. Analytical dependencies were obtained for the field of velocities and pressures in lubricating and porous layers. Besides, the main working characteristics of the studied friction pair are determined: bearing capacity and friction force. The paper provides the assessment of the influence of parameters characterizing ferromagnetic rheological properties, length of the loaded region of the Hartmann number and parameter characterizing the presence of electromagnetic field on the bearing capacity and friction force.

Abstract: The main goal of present paper is to obtain porous coatings enriched in copper by Plasma Electrolytic Oxidation on titanium and niobium as well as on NiTi and Ti6Al4V alloys. Performed SEM and EDS studies confirmed the hypothesis that it is possible to create the porous surfaces with pores, which shapes and size are different. In order to show the copper enrichment inside the surface layers, the copper-to-phosphorus ratios were used. Based on these ratios it may be concluded that average value of Cu/P is maximal for NiTi alloy after oxidation in electrolyte containing 300 g of copper nitrate in 1 liter of phosphoric acid and equals 0.26. The minimum of Cu/P ratio equaling to 0.12 was recorded for pure titanium and pure niobium treated in electrolyte containing 300 g of Cu (NO₃)₂ in 1 L H₃PO₄.

Abstract: Over the last two decades, the philosophy behind an optimal fixation of orthopaedic implants progressively evolved towards “bone-conservative” solutions and, accordingly, the researchers’ attention moved from simple mechanical fixation of the prosthesis to host bone by using screws or acrylic cement to new strategies based on a physico-chemical bond (surface modification) in order to minimize bone resection/loss and maximize tissue-implant integration. This research work explores the feasibility of a novel bioceramic single-piece acetabular cup for hip joint prosthesis that can be anchored to the patient’s pelvic bone by means of a bone-like trabecular coating (scaffold) able to promote implant osteointegration.

Abstract: A transpiration cooling system for gas turbine applications has significant benefit to reduce the amount of cooling air and to increase cooling efficiency. We had developed a porous ceramic coating deposited by plasma spraying process, which can infiltrate cooling gas, and examined about those mechanical properties. In this study, thermal cycling life of this porous ceramic coating is revealed in order to apply this technology to advanced gas turbine blade in practical use. The thermal cycling test is conducted by using the hand-made device which can heat cyclically up and down around the surface of the porous coating while infiltrating cooling gas. The number of thermal cycles up to reach the coating delamination is related with maximum exposed temperature and pressure of the cooling gas as the test condition, consequently.

Abstract: Elastic modulus of a coating is an important property for design and use of the coating. At present, many methods have been put forward to evaluate the coating elastic modulus. However, each methods has special property, which make the elastic moduli from them are different. In the study, elastic modulus of a porous Ti coating has been evaluated by three-point bending test and indentation method. The results show that the coating elastic moduli from the two different methods agree well, which can reflect the uniformity of the pore structures of the porous coating. Meanwhile, the little deviations among the different test points of indentation method could reflect the uniformity of the coating structure partly.

Abstract: NiTi alloys are widely used for bone implants due to their good mechanical properties. However, they can suffer certain disadvantages, such as leaching of toxic nickel ions and poor osteoinductive properties. A porous (Ca, P)-doped TiO2 /dense Ti double coatings on NiTi alloy with porous (Ca, P)-doped TiO2 coating as the top layer and a dense Ti coating as the interlayer should possess a very good combination of bioactivity and chemical stability. In this paper, the double coatings were formed by applying a duplex process of arc ion plating (AIP) and micro-arc oxidation (MAO). X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) have been used to investigate the microstructure and morphology of the coatings.

Abstract: In situ measurements of electrospray droplet sizes and velocities were performed by Phase Doppler Anemometry during Electrostatic Spray Deposition (ESD) of calcium phosphate (CaP) coatings. Numerous processing parameters were varied (nozzle-to-substrate distance, deposition temperature, nozzle geometry, and composition of the precursor solution), whereafter the morphological characteristics of these ESD-derived CaP coatings were correlated with measured droplet characteristics. Equal droplet sizes and velocities were measured for nozzle-to-substrate distances up to 40 mm and deposition temperatures up to 400 °C, indicating that electrospray droplets did not shrink at all during droplet flight using an involatile solvent butyl carbitol with a high boiling point (Tb = 231 °C). Nevertheless, coatings with considerably different surface morphologies were obtained under these conditions, varying from microporous structures with coalesced pore walls to morphologies revealing isolated rings on top of dense or grainy underlayers. The chemical composition of the precursor solutions and the mixing characteristics of the calcium and phosphate precursor components strongly influenced the initial droplet sizes, precipitation kinetics of the CaP solute, and subsequent coating morphology. Unique, reticular coating morphologies were deposited at a deposition rate of 3.2 µm/hour, which have a graded structure consisting of a dense underlayer, a submicron-porous intermediate layer, and a roughened toplayer revealing droplet-derived features such as isolated rings or coalesced, hollow surface pits.

Abstract: The dissolution and precipitation behavior of various porous, ESD-derived calcium phosphate coatings was investigated a) in vitro after soaking in Simulated Body Fluid (SBF) for several time periods (2, 4, 8, and 12 weeks), and b) in vivo after subcutaneous implantation in the back of goats for identical time periods. At the end of these studies, the physicochemical properties of the coated substrates were characterized by means of Scanning Electron Microscopy (SEM), XRay Diffraction (XRD), Fourier-Transform InfraRed spectroscopy (FTIR) and Energy Dispersive Spectroscopy (EDS). Moreover, part of the implants was prepared for light microscopical evaluation of the tissue response. In vitro, a highly bioactive behavior was observed for all ESD-coatings, characterized by the deposition of a thick and homogeneous carbonate hydroxyapatite precipitation layer on top of the porous coatings. Regarding the in vivo study, no adverse tissue reactions (toxic effects/inflammatory cells) were observed using light microscopy, and all coatings became surrounded by a thin, dense fibrous tissue capsule after implantation. The ESD-coatings degraded gradually at a dissolution rate depending on the specific chemical phase, thereby enabling synthesis of CaP coatings with a tailored degradation rate.