Papers by Keyword: Plasma Coating

Abstract: In this work, a high-entropy alloy and CrZrTiNiCu coating were synthesized by mechanical alloying. It is shown that the microhardness of the CrZrTiNiCu coating is not inferior to and in most cases exceeds the hardness of high-entropy equiatomic alloys. The wear resistance of such a coating is 3·10^-4 g/min, which also corresponds to special steels in terms of wear resistance. The high-entropy coating has a low coefficient of friction. It turns out to be antifrictional, which obviously leads to energy savings. For the first time, the surface energy, contact potential difference and work function of electrons for CrZrTiNiCu coating were determined.

Abstract: The article considers issues related to the choice of abrasive material and technology of its use for the formation of necessary roughness on the base material and necessary heat resistance of the heat-protective coating during plasma spraying. The influence of the shape and size of the abrasive on final roughness of the treated surface was studied at various angles of contact between the sprayed abrasive and the surface (angle of attack). From the condition of maximum heat resistance, the composition of the heat-resistant composite coating of the spinel type was determined, which consists of 3 layers: the 1st layer (sublayer) material is a chromium-aluminum composite and the 2nd layer of a transitional spinel-based aluminum and chromium oxide + chromium-aluminum composite and the 3rd a layer of spinel based on aluminum and chromium oxides.

Abstract: The paper presents the results of metallographic and energy-dispersive studies of a wear-resistant coating structure made from high-chromium cast iron powder in the course of integrated plasma spraying and high-energy heating by high frequency currents (HEH HFC). The problem of determining the intensity and the nature of residual stress distribution in the depth of the hardened layer is solved by the finite element method and ANSYS and SYSWELD software systems. The results of numerical simulations were checked in field experiments using X-ray and mechanical methods for residual stress measurement. An optimum mode of fusion by high-frequency heating (the source specific power q_s = (3.0 - 3.2) ∙ 10⁸ W / m2, relative velocity of parts V_d = 60 - 80 mm / sec) was determined. In doing so compressive residual voltage (σ_RS ≈ -120 ± 10 MPa) was formed in the surface layer; the coating porosity reduced and the distribution uniformity of microhardness in the depth of the hardened layer improved. It was found that after plasma spraying of the surface of the part was characterized by a sufficiently developed non-uniform topography with a maximum deviation of high-altitude performance PV = 80 - 160 μm and roughness Ra = 25 μm ± 10 μm. After thermal reflow by high-frequency heating, roughness reduced significantly (Ra = 6 μm ± 2 μm) and the homogeneity of the material improved (PV = 4 ... 10 μm).

Abstract: It is sometimes imperative to modify the characteristics of materials surface reserved for the applications requiring the particular tribological properties in order to confer them certain specific properties such as the improvement of hardness, the corrosion resistance and the wear resistance. The use of aluminium and its alloys in mechanics is limited for their certain properties related to the surface whose principal one is very bad frictions behaviour, associated with a tendency of seizing and a strong sensitivity to the effect of wear. The deposit plasma is a technique which can cure these bad behaviours. It is particularly adapted to treat superficially parts of complex geometry and of rather significant number. Our work consists to study the wear behaviour of stainless steel coatings obtained by plasma on aluminium alloy substrates. The wear tests were carried out using a pin-on-disc apparatus under dry sliding conditions. Pin specimens were 100Cr6 stainless steel, while disc specimens were 316L stainless steel coating. A study will be undertaken on the tribological behaviour of the layers and the mechanisms of wear which control them for various experimental conditions (speeds and normal force) is defined, at four sliding speeds (44, 56.5,75.4, 94.3 m/s) and force of 20N.

Abstract: Commonly made of 316L stainless steel and nitinol, metallic intravascular stents are medical devices used to scaffold a biological lumen, most often diseased arteries. While stenting procedures reduce the risk of restenosis, they do not eliminate it completely. Furthermore, other common complications observed are thrombosis, inflammation and corrosion of the stents. The corrosion of the device is induced by blood flow which provokes a degradation of its mechanical properties and leads to a high risk of release of potentially toxic metallic compounds, such as nickel-based oxides and metal ions. To lower these clinical complication rates and to prevent the corrosion of the metallic stent structure, coated stents have been developed during the last decade. Indeed, the coating is expected to improve the surface biocompatibility and corrosion resistance without compromising the stainless steel mechanical properties required for the stent implantation. The Food and Drug Administration (FDA) has already provided guidance on a series of non-clinical test protocols, methods and reports to evaluate the safety and effectiveness of intravascular stents. Properties such as the stability, durability, and adhesion of a stent coating, prior and after deployment, must be clearly assessed to demonstrate its efficiency. This study wants to evaluate the effectiveness against general and local corrosion of an ultra-thin fluorocarbon film deposited by plasma on pre-treated stainless steel. Cyclic polarization tests were used to measure the coating capacity to protect the substrate from localized corrosion and Tafel plot corrosion measurements were used to evaluate the general corrosion behaviour of uncoated and coated, flat and deformed samples.

Abstract: Plasma processing has been developed to produce selective chemistry in the inner surface of a microfluidic system. This dry process is an alternative solution to the Chemical Vapor Deposition (CVD) process that allows us to work at low temperatures thus avoiding the degradation of the substrate by heat. The present study focused on the surface modification of PDMS in order to make them more hydrophilic and capable to exhibit a high percentage of COOH functions which will provide a good asset for future cell attachment.

Abstract: This work compares the oxidation behaviour of three iron-based substrates (C40E, Invar and 304L) in CO2 industrial gas, in order to determine the conditions for producing wüstite (Fe1-xO), on the basis of kinetic and morphologic studies. For the three alloys at the beginning of the reaction, wüstite formed under 105 Pa of CO2 following a rate law          RT 220000 10.2 P e dt d( m/S) CO2 . For 304L, formation of a spinel phase chromite briefly preceded it during a first step. Magnetite appeared for long times of experiment, in the case of Invar and 304L. This can be explained by the stopping of iron outer diffusion. These results are discussed according to the literature and thermodynamic data. They open new fields for coating these alloys by plasma spray processes.

Abstract: Amorphous carbon coatings for implantable medical devices require high mechanical strength, adhesion and uniform biocompatibility response across the devices. Investigation of a-C:H properties and structure variation with thickness and substrate material provides valuable insight into requirements for device coating. A number of devices are coated and the effect of interfacial layers, film doping and the spatial variation in quality is investigated.

Abstract: Metallic intravascular stents are medical devices commonly made of 316L stainless steel or nitinol used to scaffold a biological lumen, most often diseased arteries, after balloon angioplasty. Stenting procedures reduce the risk of restenosis, but do not eliminate it completely. Indeed, restenosis remains the principal cause of clinical complications, leading to up to 30 % of failure after 3 months of implantation. During the last few years, several works have been focused on the development of an appropriate coating able to act as a carrier for specific anti-restenosis drugs. Moreover, this coating would act as an anti-corrosive barrier, thus inhibiting the release of potentially toxic ions. Actually, the main challenges in stent coatings are to synthesize a biocompatible polymer coating resistant to blood flow, wall shear stress and tensile force after the stent deployment which results in a permanent strain of up to 25%. The adhesion and chemical resistance after deployment are critical properties to investigate for the improvement of the long-term reliability of polymer coated stent. The aim of this study was to evaluate the effect of a 25% equivalent plastic deformation on chemical, mechanical and adhesion properties of Teflon-like films deposited on 316L stainless steel. These properties were studied by chemical spectroscopy and atomic force microscopy. Teflon-like films were deposited by pulsed plasma glow discharges on flat electropolished 316L stainless steel. An original method has been developed to induce the deformation, and preliminary results have showed that the 12 nm thick Teflon-like films successfully resist to deformations of up to 25%.