Oxidation of Metals最新文献

The thermal deformation behavior of oxidation products formed on Fe–Si alloys with varying Si contents was systematically investigated using a thermal simulation testing machine during compressive deformation at temperatures ranging from 800 to 1100 °C. It is found that the higher the deformation temperature is, the better the plasticity of the oxide product is, and the better the deformation coordination between the oxidation product and the substrate, where the deformation mainly occurs in the FeO layer. The increase of Si content reduces the coordination of deformation between the oxidation product and the substrate, but it can improve the interface straightness. The crystal structure of the oxidation product determines its plastic deformation ability, and the deformation mechanism of FeO is determined by the dislocation slip and climb, and its plastic deformation ability is the best. The dislocation slip dominates the deformation mechanism of Fe₃O₄, and the deformation ability is the second, and Fe₂O₃ has basically no plastic deformation ability. Therefore, the increase of the Si content leads to the reduction of the proportion of the FeO layer in the oxidation product, which is the main reason for the decrease of the deformation coordination between the oxidation product and the substrate. As Si element forms a spinel solid solution composed of Fe₂SiO₄ with FeO and SiO₂ at the interface, it has good plastic deformation ability and can deform synchronously with the substrate, and the porous structure can effectively relieve the compressive stress during deformation, which can effectively improve the interface straightness. In addition, the increase of Si content makes the concentration of iron ions in FeO close to the substrate side lower, which causes the increase of point defect concentration to promote the dislocation climbing of FeO, and makes the steady-state plastic deformation ability of FeO close to the substrate side higher, which improves the straightness of the interface between the oxidation product and the substrate.

Propranolol is a pharmaceutical organic drug used for the treatment of high blood pressure, heart problems and anxiety diseases. The disposal of the expired drug threatens the environment, but still, it contains active components. The potentiality of the active components of the expired propranolol drug (EPD) has utilized to protect the mild steel corrosion in 1.0 M hydrochloric acid medium. Weight loss method, potentiodynamic polarization, ac-electrochemical impedance spectroscopy, scanning electron microscopy with energy disperse X-ray spectroscopy and atomic force microscopy (AFM) were used to investigate the expired propranolol drug’s capacity to defend mild steel surfaces against corrosion in 1 M HCl medium. The outcomes of the studies demonstrate that expired propranolol drug efficiently inhibits the corrosion of mild steel in 1.0 M HCl medium at various temperatures and inhibitor concentrations. The maximum inhibition efficiency obtained by the weight loss method was 89.81% at 0.01 M EPD concentration at 303 K. EPD has been determined to follow the Temkin’s adsorption isotherm model. The SEM–EDX and AFM images were indicated that the formation of protective layer on the surface of mild steel against the acid attack. Potentiodynamic polarization studies showed that the inhibition mechanism is mixed mode and predominantly cathodic control. The observed values of ∆G⁰_ads, indicated that the inhibitive effect is exothermic and spontaneous. Furthermore, the determined thermodynamic parameters suggest that the adsorption process is spontaneous.

The impacts of thermal treatment on the precipitate morphology and oxidation behavior of a dual-phase (FCC + L1₂) multi-principal element alloy (MPEA), Ni₄₅Co₁₇Cr₁₄Fe₁₂Al₇Ti₅, was studied at 1000 °C via isothermal and cyclic testing. Thermogravimetric analysis and subsequent characterization revealed that smaller precipitates had an increased capacity to form protective sub-surface oxide layers which mitigated total mass gain. The smaller-precipitate-containing samples exhibited a decrease in thickness of the primary Cr₂O₃ scale and parabolic growth rate. Mechanistically this behavior is believed to stem from the increased growth rate of initial Al₂O₃ nuclei and decreased inter-precipitate spacing which results in faster lateral diffusion and agglomeration.

The high temperature corrosion of Fe-2.25Cr-0.54Mo steel coated with WC–Co/NiCrFeSiB using a high-velocity oxy-fuel spraying technique was investigated. Coated and uncoated steel samples were tested in air and in a humidified atmosphere consisting of N₂-50%, O₂-10%, and H₂O at 750 °C for 120 h. Microstructural and phase analyses of the studied samples were performed by scanning electron microscopy equipped with energy-dispersive spectroscopy and X-ray diffraction. When compared to oxidation in air, the oxidation rate of the uncoated sample in the humidified atmosphere was faster. This occurred because there was a thicker and denser iron oxide layer at the outer subscale, and the thicker layer of inner iron oxide subscale contained chromium (Cr). Moreover, the WC–Co/NiCrFeSiB coating greatly suppressed the rates of oxidation in both the air and the humidified oxygen atmospheres. This occurred because the formation of magnetite (Fe₃O₄) was suppressed, while the protective oxides, especially nickel–chromium (Ni–Cr) spinel and chromia (Cr₂O₃) were formed during oxidation. Water vapor in the atmosphere enhanced the oxidation rate of the coated steel, with higher iron-containing oxide forming as a subscale at the outer coating.

Graphic Abstract

Thermally sprayed ceramic coatings with varied weight percentages of carbon nanotube (CNT) reinforcement were examined. AISI 1020 steel was coated with yttria-stabilized zirconia (ZrO₂ + 8% Y₂O₃) using the atmospheric plasma spraying (APS) method. The study examined the CNT dispersion in the coating microstructure and evaluated the porosity, bond strength, and corrosion resistance of the coating. In addition, the coating thicknesses were measured. The coatings were characterized using a variety of techniques, including optical microscopy, scanning electron microscopy, image analysis, bond strength testing, and corrosion analysis. According to the findings, adding CNTs to the coatings improved their mechanical characteristics, particularly their hardness and wear resistance. Notably, the best levels of hardness and wear resistance were seen in coatings with a 5 percent CNT reinforcement. Additionally, the coatings' corrosion resistance was enhanced by the inclusion of CNTs. The results of this work show that the mechanical and corrosion properties of thermally sprayed ceramic coatings can be successfully improved by the inclusion of CNTs. This means that these CNT-reinforced coatings have a lot of potential for a variety of applications, such as wear-resistant, corrosion-resistant, and thermal barrier coatings.

Thermal barrier coating (TBC) degradation has been identified as a primary problem in the case of hot corrosion via Na₂SO₄–V₂O₅ deposits. In comparison with the current top coat thickness, the current research presents a novel TBC that combines equal amounts of pure alumina (Al₂O₃) and yttria-stabilized zirconia (YSZ) with improved resistance to heat corrosion. Using the atmospheric plasma spray (APS) process, Al₂O₃ and YSZ were sprayed as a bond coat on cast iron substrates using the multilayer bond coat materials Metco 410NS and Metco 452. Utilizing a cyclic method, the hot corrosion behaviour of TBC was examined at 850 °C using a corrosive salt consisting of 45 weight percent sodium sulphate (Na₂SO₄) and 55 weight percent vanadium pentoxide (V₂O₅) powders. In increments of 100 µm, the top coat thickness ranged from 100 to 300 µm. The results indicated that a 300 µm top coat thickness will result in a greater hot corrosion resistance. The disintegrate of the TBC systems is also caused by corrosive salts like Na₂SO₄ and V₂O₅, which have the ability to dissolve the stabilizers in the zirconia coating at high temperatures.

Thermal barrier coatings (TBCs) are essential for protecting the high-temperature components in gas turbines. However, the durability of TBCs is limited, and new technologies to improve their lifetime are necessary. This study focuses on the pre-oxidation treatment of the NiCoCrAlY bond coat in TBCs to reduce the growth rate of the thermally grown oxide (TGO) and improve the TBC lifetime. The mechanism of the TGO growth rate reduction by the pre-oxidation treatment of NiCoCrAlY was investigated. Oxidation behaviors of the surface of NiCoCrAlY coating samples with or without pre-oxidation treatment were evaluated in air at 800 °C and 900 °C. In-situ X-ray diffraction (XRD) measurements and isothermal oxidation tests were performed. The obtained results revealed that the growth rate of TGO is significantly suppressed by α-Al₂O₃ layer formed by the pre-oxidation treatment. The generation of γ-Al₂O₃ and θ-Al₂O₃, which are typically formed below 900 °C, was significantly reduced by pre-oxidation. It is suggested that this reduction suppresses of the TGO growth.

Abstract

The effect of variations in Nb, Ta, and Ti concentrations in exchange for Al on the oxidation resistance of a new polycrystalline Ni-based superalloy (C19) was studied in air at 800 °C for up to 1000 h. An external scale of Ti-doped Cr₂O₃ and a sub-scale of discontinuous Al₂O₃ intrusions formed on the surface of all the studied alloys. Contrary to other reports, increasing the Nb concentration improved the oxidation performance and may have promoted the formation of a CrTaO₄ layer, thereby reducing oxygen ingress. The addition of Ta also significantly improved oxidation resistance and reduced the depth of the Al₂O₃ intrusions. Increasing the Ti concentration did not significantly affect the oxidation performance, potentially due to the relatively low Ti concentrations investigated. Several of the studied alloys with modified Ta and Ti concentrations showed regions of continuous Al₂O₃ scale formation, suggesting that the compositions are in a transition regime between Cr₂O₃-forming and Al₂O₃-forming behaviour. The findings suggested that part of the Ti content in C19 could potentially be replaced with Nb, Ta and/or other elements to further enhance oxidation resistance and other desirable properties. Overall, the insights gained could serve as a guide to optimise the composition of C19 and similar alloys for enhanced oxidation resistance.

The welding of carbon steel for boiler structures poses significant challenges that remain an open problem for researchers. Welded joints in boiler applications are subjected to harsh conditions involving exposure to both fire and water environments, complicating material sustainability. This study focuses on the unique challenges arising from the interaction of welds with chloride-rich environments. The combustion of fuel and the presence of chloride in the aqueous zone are particularly influential factors, as highlighted by research on fire side columns. The weld zone experiences severe deterioration, resulting in substantial material loss. To address this issue, the current research involved subjecting the weld material to a chloride environment, with a comprehensive evaluation of the weldment's behaviour through electrochemical corrosion studies. Material characteristics were further analysed using electron microscopy, EDS spectra, and X-ray diffractometry. The corrosion results form the basis for recommendations and suggestions aimed at enhancing the resilience of weldments in carbon steel boiler structures, offering valuable insights for the improvement of material performance in challenging operational conditions.

Abstract

In this study, a NiCoCrAlY + lanthanum zirconate multilayer thermal barrier coating was deposited on Inconel 738 through the thermal plasma spray technique. The coated samples subjected to hot corrosion testing at 900 °C for 240 h after coating them with 90 wt.% Na₂SO₄ + 5 wt.% NaCl + 5 wt.% V₂O₅. The corroded samples were evaluated using SEM, SED, XRD, microhardness and electrochemical study. The dominance of vanadium was observed in the form of LaVO₄ phase formation at the plates on the coating surface. The as-received coating sample, sample after the electrochemical test, sample after hot corrosion and hot-corroded sample after electrochemical test were tested for hardness. A significant decrease of 23.8% in hardness was measured after the electrochemical test of the corroded sample.