Oxidation of Metals最新文献

This study investigates the influence of separate and combined addition of 5 vol.% TiC and/or WC on the isothermal oxidation behaviour of ZrB₂–20 vol.% SiC composites consolidated by a spark plasma sintering route. The oxidation performance of the composites was evaluated in the temperature range of 1500–1600 °C in air for up to 4 h. Following oxidation, the samples were subjected to a detailed characterization of the microstructure, micro-composition, phase aggregate, and oxide scale growth kinetics. The thermodynamic feasibility of probable reactions and the phase stability of Zr–B–O, Zr–Si–O, Ti–B–O, Ti–C–O, Ti–W–O, and W–C–O systems were examined by dedicated software. While addition of TiC or WC was found to result in protective oxide scale formation, the highest oxidation resistance in terms of reduced mass gain and oxide layer thickness was offered by ZrB₂–20SiC–2.5TiC–2.5WC (vol.%) composite at 1500–1600 °C in air.

The corrosion behavior of the aluminum-alloyed austenitic steels Fe-18Ni-12Cr-2.9Al and Fe-18Ni-12Cr-2.3Al-Nb-C was investigated at 700 °C in static Pb for 1000 h as a function of the concentration of dissolved oxygen in the liquid metal. In Pb with ~ 5 × 10^–9 mass % dissolved oxygen, both steels showed dissolution. Depth of corrosion averaged 67 (± 18) µm and 78 (± 25) µm for Fe-18Ni-12Cr-2.3Al-Nb-C and Fe-18Ni-12Cr-2.9Al, respectively. In Pb with higher oxidation potential of 2 × 10^–6 mass %O, both steels showed protective and accelerated oxidation. The protective thin oxide film (≤ 1 µm) was composed of outermost Fe-rich, intermediate Cr-rich and inner Al-rich sublayers. The thicker oxide scale was of irregular thickness (2 ÷ 30 µm) and consisted of Fe–Cr mixed oxide with Ni-rich metallic inclusions.

The modern turbines aimed to work at enhanced efficiencies demand the use of a novel high-performance thermal barrier coating (TBC) which may be susceptible to multiple failure modes. Specifically, ingestion of calcium–magnesium–alumino–silicate (CMAS) or volcanic ash (VA) at elevated temperatures induce accelerated deterioration of conventional yttria-stabilized zirconia (YSZ) TBCs. The ability to form an impervious and rapidly crystallizing rare earth-based apatite layer upon interaction with CMAS/VA salt favors the choice of rare earth zirconates (REZs) as novel TBCs. Among diverse REZs, Yb₂Zr₂O₇ (YbZ) exhibits ideal TBC characteristics. A detailed insight into YbZ coating characteristics and performance is vitally needed to qualify these materials for TBC applications. Accordingly, in this study indigenously developed YbZ and commercial YSZ were deposited by air plasma spraying. Subsequently, the VA infiltration resistance of deposited coatings was comprehensively compared up to 1350 °C. The SEM analysis of VA-infiltrated YSZ and YbZ coatings revealed the thickness of the infiltration zone and the corresponding mechanism. YbZ coatings displayed significantly better VA infiltration resistance attributed to forming an impervious Yb-apatite-based arresting layer and pinning the further seepage of the VA salt front. Besides, VA rapidly infiltrated YSZ coatings, which failed to form an arresting layer. Overall, the study provides essential insights and thrust in developing next-generation TBCs.

Graphical Abstract

The oxidation performance of CoCrFe₂Ni_0.5 HEA borided through a powder-pack boriding process was investigated at 900 °C for 120 h. The boriding process at 900 °C for 6 h resulted in the formation of a two-zone structure: the outmost part contained a Ni₂Si layer and the inner part consisted of a MB/M₂B layer. The borided alloy displayed better oxidation resistance with the least oxidation rate constant value of 0.0383 (mgⁿ cm⁻²ⁿ h⁻¹). Moreover, this alloy rendered a continuous oxide layer that was denser, more compact, and contained fewer defects, which confirmed the improvement in oxidation resistance. The Ni₂Si layer plus the boride layer was responsible for the enhanced oxidation performance of borided alloy.

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.