Nitrocarburized coating by plasma electrolytic saturation, PEN/C coatings, have been proposed to increase the corrosion and wear resistance of steel by using a process of low-temperature hydrostatic plasma. The objective of this work is to analyse the wear and corrosion resistance of PEN/C coatings on SAE 1045 steel, using the electrochemical slurry erosion wear test (ESEWT). This test allows the evaluation of the simultaneous effect of erosion wear and electrochemical behaviour on this coating. Thus, it was possible to evaluate the erosive and corrosive effect and the synergy of these phenomena on the PEN/C coated SAE 1045 mass loss rates. ESEWT tests were performed at different times and under different electrochemical conditions: under cathodic protection and open circuit potential (OCP). The PEN/C coating increased the corrosion resistance of SAE 1045. Synergy between the erosive wear and corrosion was the main factor in the mass loss rates of both analysed systems. The synergistic mechanism of the substrate occurred by removing the corrosion product and by activating the surface generated by the erosive process of the particles. The synergistic mechanism of the PEN/C coating occurred with the removal of inherent surface irregularities through the erosive process, combined with localized corrosion. saturation PENC PEN C lowtemperature low temperature 104 ESEWT. . (ESEWT) Thus conditions OCP. OCP (OCP) systems particles 10 (ESEWT (OCP 1

For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N2-H2 gas mixtures, containing 5, 24, and 76 vol.% N2. Samples were characterized concerning the resulting roughness, microstructure, compound layer’s phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe2-3(C)N content in the compound layer decreases. A γ’-Fe4N monophasic compound layer was achieved at 5 vol.% N2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N2 in the gas mixture as higher amounts of γ’-Fe4N were formed. The 76 vol.% N2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ’-Fe4N and ε-Fe2-3(C)N) with a predominant content of ε-Fe2-3(C)N.

In this study, the sliding wear of a DIN 18MnCrSiMo6-4 continuous cooling bainitic steel plasma nitrided with a nitrogen rich gas composition was investigated. To evaluate the influence of processing time and temperature on mechanical and microstructural characteristics of nitrided layer, the samples were nitrided at 400, 450, 500 and 550 °C for 3, 6 and 9 h. The produced nitrided layers were characterized concerning the microstructure, phase composition, microhardness and surface roughness. The samples were tested by ball-on-flat reciprocating dry sliding for friction coefficient and wear analysis. The tests were stopped after a given damage criteria involving the rapid growth of the friction coefficients and wear. The correlation of the different treatment parameters and resulting case depths and surface hardness with sliding distance at the time of microcracks formation or delamination of the surface layer was evaluated statistically by the analysis of variance (ANOVA). The plasma nitrided samples at 550 °C showed better wear performances in the ball-on-flat tests than the other groups investigated, since these samples have a thicker compound layer and diffusion zone higher than the other conditions investigated. In general, the beginning wear is slower because of the hardest region of the compound layer.

RESUMO Os novos aços bainíticos de resfriamento contínuo (CCBS) são uma excelente alternativa quando se requer elevada dureza, tenacidade e resistência à fadiga. Contudo, estima-se que a taxa de desgaste dos CCBS seja insuficiente para aplicação em componentes com alta solicitação mecânica, sendo necessário aprimorar suas propriedades de superfície. O objetivo deste estudo é o de analisar os efeitos da nitretação a plasma sobre à microestrutura e propriedades de desgaste do aço bainítico de resfriamento contínuo DIN18MnCrSiMo6-4. Portanto, tratamentos com duração de 6 horas foram conduzidos com pressão de 3 mbar, mistura gasosa composta por 76% N2 + 24% H2, e temperaturas de 400, 450, 500 e 550 °C, respectivamente. As amostras foram analisadas através de microscopia eletrônica de varredura, difração de raios-X, microdureza e ensaios de desgaste por deslizamento recíproco. Nas condições investigadas, foi possível obter uma camada de compostos e atingir um aumento de até 393% na dureza superficial, entretanto, o uso de temperaturas mais elevadas durante os tratamentos favoreceu a formação de camadas mais profundas. Em todas as amostras nitretadas, constatou-se a formação predominante da fase de nitretos ε-Fe2-3N e, em menor quantidade, da fase de nitretos γ’-Fe4N. Nos ensaios de deslizamento recíproco houve diminuição do desgaste das amostras nitretadas na temperatura de 550°C.

ABSTRACT The new continuous cooling bainitic steels (CCBS) are an excellent alternative when high hardness, toughness and fatigue resistance are required. However, it is estimated that the wear rate of the CCBS is insufficient for application in highly mechanical loaded components, being necessary to improve the surface properties. The objective of this study is to analyze the effects of plasma nitriding on the microstructure and wear properties of DIN18MnCrSiMo6-4 continuous cooling bainitic steel. Therefore, treatments lasting 6 hours were conducted with a pressure of 3 mbar, a gas mixture composed of 76% N2 + 24% H2, and a temperature of 400, 450, 500 and 550 °C, respectively. The samples were analyzed by scanning electron microscopy, X-ray diffraction, microhardness and reciprocal sliding wear tests. Under the conditions investigated, it was possible to obtain a compound layer and to achieve an increase of up to 393% in surface hardness, however, the use of higher processing temperatures favored the extension of the depth layer. In all the nitrided samples, the major presence of ε-Fe2-3N nitrides phase was observed, and the γ'-Fe4N phase content was smaller. In the reciprocal sliding tests, there was a decrease in the wear of nitrided samples at temperature of 550 °C.

Abstract Previous studies showed the formation of new phases affecting the electrical properties of LSC thin films deposited on stainless steel substrates, which are commonly tested for ITSOFC and SOEC interconnects. A 4.3 μm thick La0.6Sr0.4CoO3 coating was deposited on AISI430 steel by spray pyrolysis, followed by heat treatment (800°C/2h) and an oxidation in air (800°C/96h). The La0.6Sr0.4CoO3 phase interacted with the metallic substrate and formed SrCrO4, causing degradation of the perovskite into La0.9Sr0.1CoO3. An EDS mapping showed Sr and Cr enrichment in the coating/substrate interface. TG analysis indicated a lower mass gain for the coated substrate. The total ASR at 800°C of the interconnect before and after oxidation was 3.23 Ω.cm2 and 3.98 Ω.cm2, respectively. The Ea underwent very small variation, remaining around 0.24 eV (T≤300°C) and 0.65 eV (T≥400°C). The reaction of Cr from the substrate and Sr from LSC seems to have impaired the performance of the interconnect.

ABSTRACT In this work, sol-gel/dip-coating process for obtaining yttria stabilized zirconia (YSZ, ZrO2–8% Y2O3) films deposited onto LSM-YSZ (lanthanum strontium manganite (LSM, La0.7Sr0.3MnO3) mixed with YSZ) with different proportions (20/80, 50/50, 80/20) was investigated. The films were deposited on substrate varying the number of layers deposited. LSM powders were obtained by the combustion method using metal nitrates and urea and YSZ was commercial. LSM-YSZ composite powders were obtained by the solid state method, through ball-milling of a mixture of LSM-YSZ (mass ratio) powder for 4 h with 500 rpm using ZrO2 balls as milling media. For LSM-YSZ substrate a study of sintering temperature was performed, where the optimum sintering temperature for each LSM-YSZ studied proportion was obtained. According to our results, it was found that 1100 ºC is the optimum sintering temperature for 20/80, 950 ºC is the optimum sintering temperature for 50/50 and 900 ºC is the optimum sintering temperature for 80/20 because of the good phase formation. The films were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The films showed LSM, YSZ, SrZrO3 and La2O3 phases. Crack-free, homogeneous and well adhered films were obtained with a thickness between 3 and 38 µm. In this work, YSZ films with appropriate thickness were obtained for application as SOFC electrolyte.

The growth of titanium dioxide nanotubes (TiO2) via anodization process depends on the controlling parameters such as applied potential, anodization time, and electrolyte composition. In the present work, the Taguchi method was applied to evaluate statistically the influence of the anodization parameters on the morphology of anodized TiO2 films. Mixture of ethylene-glycol and glycerol was used as an electrolyte and the settings of the experimental design were parameterized on the basis of four important anodization factors consisting of chemical pretreatment, amount of fluoride, water content and applied potential. Samples were characterized by XRD and FEG-SEM. Based on 4 variables at 3 different settings, full factorial plan requires 34 = 81 tests. In this work the experiment was designed on the basis of an L9 (34) orthogonal array (4 variables, 3 levels, 9 tests). The optimum conditions were found on the basis of smaller-is-better and larger-is-better analyses. The signal-to-noise ratio was employed to find optimal process parameters levels and to analyze the influence of these parameters on the tubular length, internal and external diameters and formation of nanograss on the film surface. Hence, it is clearly shown that the performance of TiO2 nanotubes can be evaluated by the Taguchi method.

Nanotexturing processes that focus on enhancing the bone-implant contact, such as electropolishing, have been proposed. The aim of this work was to evaluate the influence of Ti6Al4V surface morphology on human embryonic stem cell-derived mesenchymal progenitor (hESCs-MP) growth. Three surface treatments were used in this study: mechanically polished samples and two types of electropolished samples that were treated for 4 min and 12 min, respectively. The systems were characterized by atomic force microscopy, contact profilometry, X-ray diffraction, and wettability. Each system was submitted to a cell culture containing hESCs-MP cells for 14 days, and the resultant cell growth on each system was then evaluated. The results indicated that surfaces with higher nanometric and micrometric roughnesses experienced greater hESCs-MP cell growth in osteogenic media. The same behavior was not observed for cell growth in non-osteogenic media due to the absence of dexamethasone, which is responsible for controlling protein adsorption on the surface.

Abstract Coatings developed through sol-gel method is presented as an interesting replacement to chromium coating. Sol-gel method present advantages as high purity and excellent distribution of the components. The objective of this work is to synthesize and characterize a film obtained by sol-gel route. The film was prepared with 3-(trimethoxysilylpropyl) methacrylate (TMSPMA), tetraethoxysilane (TEOS) and cerium nitrate, using water and ethanol as solvents. Polyethyleneglycol (PEG) plasticizer was added at four different concentrations. The sol was characterized by techniques of viscosity, thermogravimetric analysis (TGA), X-ray diffraction (XRD) nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FT-IR). The results showed that tetrafunctional alkoxides condensation was retarded by the plasticizer, forming a compact film. The film with 20 g.L-1 of PEG showed the best electrochemical behavior.

The evolution of TiO2 nanotubular morphology, synthesized in a mixture of fluorinated ethylene glycol and glycerol electrolyte, was studied as a function of the anodization time. The samples were characterized by FEG-SEM, XRD, XPS, UV-Vis and EIS. The formation of single-or double-walled TiO2 nanotube structure can be efficiently controlled by the anodization time. For anodization times less than 30 minutes, a compact oxide layer is formed, followed by double-walled nanotube formation up to 120 minutes and single-walled nanotubes up to 240 minutes. XPS analyses show that the samples obtained with short anodization time have a high carbon content and oxygenated surface species compared to the longer-time anodized sample; however, binding energy peaks for Ti 2p remained invariant. The performances of TiO2 nanotubular photoelectrodes were evaluated in photoelectrochemical water splitting where TiO2 nanotubes anodized for 120 minutes presented the best performance that was related to their optimal morphology and charge transportation.

The fluoride use for anodizing electrolytes has been primarily responsible for the formation of nanoporous oxides at valve metals, except aluminum, since it causes a dissolution process. This study presents the formation of an oxide model according to the following anodizing parameters: 100 V, 12.73 mA/cm2, room temperature and the niobium samples anodized in niobium oxalate and oxalic acid electrolytes without and with the addition of HF for 5, 30 and 60 min. The anodized samples were analyzed morphologically by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and the hydrophobicity of the samples was assessed by the sessile drop method. The presence of fluor in the niobium oxalate electrolyte formed oxides with lower a dissolution and a low hydrophobicity compared to the one formed in oxalic acid was attributed to the incorporation of niobium and oxalate ions. Thereby, the model proposed in this paper showed that during anodization the migration of the fluoride ion into the oxide occurs at high speed, which results in the formation of microcones, leading to the formation of discrete layers of porous oxide.

DIN 1.4110 martensitic stainless steel is largely used in the cutlery industry due to its high corrosion resistance associated with high mechanical resistance. However, when this material works under corrosion and wear conditions at the same time, their synergistic effect can accelerate the degradation process of the alloy. Cryogenic heat treatments have been proposed to improve the dimensional stability and mechanical properties, since they minimize the amount of retained austenite. The aim of this work is to study the effect of deep cryogenic heat treatment at -80 ºC and at -196 ºC on the corrosion resistance and tribocorrosion behavior of DIN 1.4110 martensitic stainless steel. The microstructure, hardness, corrosion resistance and tribocorrosion behavior were evaluated. Although the heat-treated samples presented higher hardness and lower corrosion current density (icorr) compared to samples in spheroidized condition, their material removal under tribocorrosion conditions increased, which demonstrated the synergy between corrosion and wear.

AbstractSeveral studies regarding superficial treatments of Nitinol (NiTi) shape-memory have been developed aiming to the improve corrosion resistance and to block the Ni release to adjacent tissues. The necessary heat treatment to achieve the shape memory effect normally occurs at temperatures between 500 and 600 °C. However, titanium oxide (TiO2) is formed on the NiTi surface during the shape memory process heat treatment. In this work the effects of the heat treatment time on the surface characteristics of the formed NiTi oxide, at temperatures that promote the shape-memory (530 and 570 °C), were evaluated. The TiO2 layers which were obtained were evaluated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscope (SEM), thermogravimetric analysis (TGA), wettability and roughness. The results show that by increasing the exposure time at the temperature of 570 °C the formation of a thicker oxide is promoted, with less superficial roughness and of a hydrophobic nature. According to the literature, these characteristics indicate that the obtained oxide layer has properties that accelerat the osseointegration process.

Ferritic stainless steels are used in specific applications where corrosion resistance, oxidation resistance and a high mechanical resistance are required. Shot peening is a process applied to add residual compression stresses in metallic surfaces with the intent of improving the material when exposed to corrosion due to stress and fatigue. Some studies about the effect of the shot peening process on the fatigue resistance, bending fatigue behavior, and residual surface stress in the ferritic stainless steels have been performed. However, the effect of the shot peening process on the corrosion and oxidation resistance of the stainless steel is not well known. In this context, the purpose of this study is to evaluate the effect of the shot peening process on these superficial properties of ferritic AISI430 stainless steel. The obtained results showed that the ferritic AISI430 stainless steel samples treated with shot peening presented a significant modification on the surface morphology and an important decrease of oxidation and corrosion resistance, evidencing that the shot peening process compromises the chemical and physical properties of the surface.

In improving the corrosion and hardness proprieties of ferritic stainless steel, the use of protective coatings becomes an interesting alternative. In this study, a carbon layer was deposited on AISI 430 by electrodeposition using N,N-dimethylformamide with the addition of an organic dopant as the electrolyte. The AISI 430 stainless steel was pretreated by anodization aiming to optimize the film anchoring. The obtained films were characterized by atomic force microscopy, by scanning electron microscopy and by optical interferometry. The microstructural characterization of the films was obtained by Raman Spectroscopy. The corrosion resistance was evaluated by open circuit potential and by potentiodynamic polarization. The friction test and the scratch test were performed to evaluate the mechanical properties. The Raman spectroscopy showed the presence of an amorphous carbon film. The films improved the corrosion resistance of stainless steel. In addition, on the wear analysis the coating showed a good adhesion on the substrate.