1,721,003 research outputs found
Characterization of a 17-4 PH stainless steel obtained through metal powder Hot Isostatic Pressing process for automotive application
Full text linkInfluence of atmospheric pressure plasma treatments on the oxide film and the corrosion resistance of titanium and titanium alloy
No full textIn the industrial plants, plasma is often used for cleaning and activating the surfaces and/or for the formation of different types of coatings. In the past, the plasma technology required the use of low pressures with consequent economic and technological problems. The development of plasma technologies that can work at atmospheric pressure overcomes the disadvantages of traditional vacuum operation and permits to apply this technology in a larger number of applications for example in continuous in line manufacturing. In this study, the influence of a treatment carried out with an atmospheric pressure plasma jet (APPJ) on the passive oxide films of titanium and titanium alloys and the correlation between these changes and the corrosion properties were studied. The treatments were realized on commercially pure titanium (grade 1) and a Ti6A14V (grade 5) titanium alloy using a plasma generated by air at 1.5 bar. Different process parameters were tested. In detail, the effect of the distance plasma torch-sample and of the rate of movement of the plasma torch during the treatment (useful to simulate an in line continuous process) were studied. The corrosion resistance of the samples was analyzed with potentiodynamic polarization and electrochemical impedance spectroscopy tests, using as electrolyte the Ringer solution. The effects of the treatment on the oxide layer were studied using secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The plasma treatment allowed the growth of the passive film and improved the corrosion resistance of both titanium and titanium alloy
Microstructure and corrosion properties of PEO coatings produced on am-aluminum alloys
No full textAluminum alloys are one of the main materials employed in aerospace and automotive applications. One of the problems that affect these alloys in certain application is the poor corrosion resistance that can, however, be enhanced with proper surface treatments, such as anodizing. Among these treatments, Plasma Electrolytic Oxidation (PEO) is one of the most promising and the production of PEO coatings on traditional aluminum alloy was extensively studied in literature. Recently, the production of a lot of components is going into the direction of using innovative manufacturing systems and customized components, with improved mechanical and physical properties, can be manufactured by additive manufacturing (AM) techniques. Among the AM methods, laser-based AM has an immense potential for producing fully dense metallic structures, using a variety of available metal powders and has attracted more and more attention. The resulting AM samples are characterized by different microstructures in comparison with the conventionally manufactured ones and this can cause differences also in the production of PEO coatings and other surface treatments. Objective of the present work is to produce PEO coatings on AM samples in order to increase the corrosion and wear performances of the samples. PEO coating were produced on the samples testing different parameters and the coatings were characterized, in terms of microstructure and composition, with SEM analysis. The corrosion resistance of the samples was also evaluated with electrochemical tests. The results were compared with the ones obtained on traditionally manufactured samples. PEO coatings were successfully produced on AM samples obtaining samples with good coatings thickness and improved corrosion performances compared to the untreated ones
Indurimento superficiale di leghe di titanio mediante trattamenti termici di diffusione di Ni
No full textCerium based chemical conversion coating on AZ63 magnesium alloy
No full textA CeCl3/H2O2 aqueous solution treatment is assessed for the formation of conversion coatings on a AZ63 magnesium alloy. The coating composition and morphology are examined. The conversion coating appears to consist of a thin and cracked coating with 'dry-mud' morphology with large agglomerates over cathodic intermetallic particles. The corrosion resistance in NaCl solution has been investigated. The cerium-based conversion process improves the pitting potential of the alloy. Better corrosion resistant surfaces are obtained when the samples are submitted to repeated immersions in the conversion bath for 30 s up to 180 s of total immersion time. The thickness of the cerium conversion coating rapidly grows up in the first 30 s; afterwards it remains nearly constant. An increase of both hydrogen peroxide concentration and immersion time produces a worsening of the alloy to corrosion
Structural characterization and electrocatalytic properties of Au30Zr70 amorphous alloy obtained by rapid quenching
No full textModern approaches for study of eutectoid steel oxidation and decarburization
No full textThis paper describes the results of a laboratory study into the high-temperature surface oxidation and decarburization of eutectoid steel performed using thermal gravimetric analysis which makes it possible to understand the steel surface oxidation kinetics in non-isothermal conditions as the steel specimen is continuously heated to a specified temperature. An exponential relationship is obtained between the heating temperature and the iron loss in steel. A relationship is established between the heating temperature applied and the surface oxidation rate observed in a eutectoid steel specimen. It is shown that when the temperature of the specimen is raised from 900 to 1000°С, it leads to a triple increase in the surface oxidation rate, whereas the temperature increase to 1200°С results in an eightfold increase in the surface oxidation rate. It is noted that, within the temperature range of 720-950°С, the phase transformations observed are accompanied with intensified scale formation and surface carbon depletion. Using the emission spectrometry technique, the concentration of carbon is determined in the surface layer in relation to the heating temperature and time. The results obtained indicate that eutectoid steel is subjected to an intense surface decarburization at the temperatures of 600-1200°С
Effect of microstructure and porosity of AlSi10Mg alloy produced by selective laser melting on the corrosion properties of plasma electrolytic oxidation coatings
Full text linkIn this work, PEO process was carried out on SLM samples of AlSi10Mg, characterized by different grades of porosity, in direct-current mode using high current densities and short time in a basic silicate electrolyte. For comparison, the PEO process was also performed on samples of conventional cast AlSi10Mg alloy. The microstructure and the composition of the coatings was evaluated with SEM and XPS, whereas the phase analysis was performed with XRD. The corrosion resistance was analyzed by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests. The parameters used for PEO process allowed to obtain a continuous coating on all SLM samples, but its morphology resulted strongly influenced by the initial microstructure of the substrate. The coatings more homogeneous and less porous were produced on the samples with initial lower porosity. The corrosion performances of all SLM samples improved after PEO treatment and the PEO coatings with lower porosity resulted the more corrosion resistant
Study of the effect of functionalization with inhibitors on the corrosion properties of PEO-coated additive manufactured AlSi10Mg alloy
Full text linkOn the exceptional stress corrosion cracking susceptibility of selective laser melted 316L stainless steel under the individual effect of surface residual stresses
No full textSCC and electrochemical behaviour of selective laser melted 316L stainless steel was studied under the combined effect of surface residual stresses (RS) and energy input variation. A significant correlation was found between columnar subgrains width and pore size with the electrochemical response and SCC susceptibility. There existed a critical pore size affecting local corrosion behaviour which decreased with an increase in RS magnitude. The critical RS needed for SCC occurrence was lower compared to wrought counterpart and the SCC mechanism was hypothesized as the synergistic effect of exceptional selective corrosion attack at subgrains and mechanical rupture of subgrain boundaries
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