Oxidation of Metals最新文献

Degradation of coatings and structural materials due to high temperature corrosion in the presence of molten salt environment is a major concern for critical infrastructure applications to meet its commercial viability. The choice of high value coatings and structural (construction parts) materials comes with challenges, and therefore data centric approach may accelerate change in discovery and data practices. This research aims to use machine learning (ML) approach to estimate corrosion rates of materials when operated at high temperatures conditions (e.g., nuclear, geothermal, oxidation (dry/wet), solar applications) but geared towards nuclear thermochemical cycles. Published data related to materials (structural and coatings materials), their composition and manufacturing, including corrosion environment were gathered and analysed. Analysis demonstrated that random forest regression model is highly precise compared to other models. Assessment indicates that very limited sets of materials are likely to survive high temperature corrosive environment for extended period of exposure. While a higher quality and larger dataset are required to accurately predict the corrosion rate, the findings demonstrated the value of ML’s regression and data mining capabilities for corrosion data analysis. With the research gap in material selection strategies, proposed research will be critical to advancing data analytics approach exploiting their properties for high temperature corrosion applications.

Graphical Abstract

Aluminide coatings were prepared by chemical vapor deposition (CVD) method on Ni-based superalloy Mar-M247 to improve the corrosion resistance. The Na₂SO₄-induced hot corrosion behavior of Mar-M247 with and without aluminide coating was investigated at varying temperatures. The results revealed that the substrate underwent relatively mild corrosion attack at temperatures below the Na₂SO₄ melting point, but extremely severe corrosion attack above it. The aluminide coating significantly improved the corrosion resistance of the substrate, with the formation of Al₂O₃ scale during corrosion. The effects of both solid and molten Na₂SO₄ on hot corrosion resistance of Mar-M247 alloy and its aluminide coating was discussed, as well as the detrimental effect of tungsten on the substrate in ‘type I’ hot corrosion.

Ti–6Al–4V alloys manufactured by laser or electron powder bed fusion (L-PBF and E-PBF) with or without hipping treatment have different microstructures from foundry alloys. Their oxidation kinetics at high temperatures between 500 and 600 °C for durations up to 2,000 h were compared. The effect of oxidation on their room temperature tensile embrittlement was quantified. It was shown that the growth kinetics of the brittle fracture zone, of the zone with cracks at 1% strain, and of the oxygen diffusion zone were perfectly correlated. Therefore, the embrittlement was confirmed to be due to oxygen ingress below the oxide scale and the kinetics were independent of the microstructure.

The high-temperature corrosion behavior of type 310 heat-resistant steel used for superheater tubes in waste-to-energy boilers was investigated to determine the breakdown behavior of the protective Cr-rich oxide scale in the initial stages of corrosion by conducting ash-embedded corrosion tests using combustion ash collected from an actual boiler. The corrosion tests were performed in air at a specimen temperature of 460 °C and an atmospheric temperature of 685 °C. After 24 h, the specimen surfaces were entirely covered with brown corrosion products, but there was almost no mass loss. However, the corrosion mass loss increased after 60 h. After 1–12 h, the specimen surfaces were partially covered with brown corrosion products, but in other areas, the interference color or a yellow hue remained, where no breakdown had occurred. Examination of the cross-sectional microstructures of these breakdown-free areas revealed that a protective Cr-rich oxide scale was formed on the surface after 1 h of corrosion, and sodium ferrite was distributed on the surface of the Cr-rich oxide scale. Although the breakdown of the Cr-rich oxide scale was not complete, iron chloride formation occurred at the substrate subsurface under the Cr-rich oxide scale, and the latter was partially exfoliated from the substrate in SUS310S. Cl₂ gas was also generated during the formation of sodium chromate. Therefore, despite the protective nature of the Cr-rich oxide scale, partial formation of chromate may cause chloride formation on the substrate followed by exfoliation of the scale. After scale breakdown, the Cl₂ gas caused intergranular or localized internal corrosion, and when the internal corrosion had spread to some extent, the Cr-rich oxide scale was formed again. This cycle led to the corrosion of the heat-resistant steel.

Outstanding inherent environmental resistance is a precondition for the use of superalloys in high-temperature applications. Besides high Al and Cr levels, also refractory metal concentrations (W and Ta) are reported to affect protective scale formation, as these elements are expected to affect the chemical activity and also the transport of protective scale formers within the alloy. In this study, we elucidate the high-temperature oxidation behavior of 3 Co-based (Co/Ni ratio: 1.4) and 3 Ni-based (Co/Ni ratio: 0.7) superalloys differing in W and Ta levels. Time-resolved thermogravimetric analysis (TGA) in synthetic air at 1050 °C and 1150 °C for 100 h, scanning electron microscopy analysis (SEM), thermodynamic calculations using the CALPHAD software Thermo-Calc, and diffusion couple experiments were conducted to assess the impact of the Co/Ni ratio and the refractory metal content on the oxidation performance. The results indicate that a low W content (3 vs. 5 at.%) and a high Ta content (2.1 vs. 1.5 at.%) beneficially affect the oxidation resistance, as alumina scale formation is facilitated.

The present work studied the effect of the addition of SiC microfibers and their influence on interfacial adherence of NiCoCrAlY-7YSZ thermal barrier coatings (TBCs) systems. Two different coatings were fabricated (with and without the addition of SiC microfibers) and exposed to isothermal oxidation heat treatments (OHT) at 950 °C from 50 to 200 h. The microstructure and pull-off test evaluations showed that coatings reinforced with SiC possess a thinner thermally grown oxide (TGO) layer, suggesting an improvement in the oxidation resistance of these samples. In this sense, the coating with SiC also displayed better adherence resistance after 50 and 200 h of exposure. On the other hand, after the pull-off tests, reinforced samples showed a lower percentage of fracture. The above indicates that SiC microfibers enhance the interfacial adherence between the TGO and the ceramic layer (TC) by forming complex oxides resulting from the self-healing reaction mechanism.

Recently there was a new wave of research activities studying the decarburization behavior of spring steels with the main focus on the formation mechanism of a columnar ferrite layer within a certain temperature range which could not be explained by conventional decarburization theories. A new theory successfully developed recently in interpreting the oxide scale reduction mechanism on steel was then developed further and applied to interpret the observed columnar ferrite formation on spring steels. The essence of the new theory is that steel decarburization in the presence of a FeO scale on the steel surface is caused and governed by the reaction between the FeO scale and dissolved carbon in the steel, and therefore, the carbon concentration on the steel surface is determined by the FeO-steel interface equilibrium and cannot be treated as negligible within the temperature range where ferrite is able to form, because the equilibrium interface carbon concentration is in the same magnitude as the carbon solubility in ferrite. The new theory and available solutions for different decarburization scenarios using decarburization of 60Si2MnA as an example are summarized in this review. Explanations are given to interpret discrepancies between experimental observations and theoretical predictions. New areas for future research are also identified.

316LSS is used in various industrial applications, including heat exchangers, dyeing equipment, pulp and paper equipment, and marine equipment for chemicals, dyes, paper, oxalic acid, fertilizer, etc. Corrosion has always been the most serious problem across these applications. For this reason, this research specifies the features of 316LSS, the use of inhibitors for control, austenitic 316LSS research with inhibitor efficiency, the environment employed, its concentration, experimental analysis, and an emphasis on organic inhibitors for a sustainable industry. Applying thermally stable HVOF WC-10Co-4Cr powder coatings over the 316LSS can reduce this impact. The current study examines the effects of HVOF cermets powder coatings on the assessment of the 316L SS microstructure, oxidation, and corrosion behavior in a hostile situation of Na₂SO₄-88%Fe₂ (SO₄)₃ at 800 °C for up to 50 times. Every cycle lasted one hour at 800 °C for heating and twenty minutes at ambient temperature for cooling. The thermogravimetric method was used to study the hot corrosion kinetics, and it was discovered that these abide by the parabolic rate rule. The analysis of the results identified that the HVOF 86WC-10Co-4Cr sprayed coating on 316LSS has shown excellent oxidation and resistance to corrosion as compared to uncoated base metal and good coating adherence to the substrate under the tested environment.

The hot corrosion behaviors of Inconel alloys with different Cr contents (Inconel 600, 601, and 690), which are used widely in nuclear plants, were investigated in molten LiCl–Li₂O salts. The hot corrosion behaviors were studied by measuring the mass and attack depth changes, surface and cross-sectional morphologies and elemental distributions, and compositional changes at the subscale and substrate scale as well as the spalled oxide scale. At 288 h, the weight losses of Inconel 601 and Inconel 690 were approximately four and twelve times higher, respectively, than that of Inconel 600. The corrosion products of all tested alloys were Cr₂O₃, NiO, and FeCr₂O₄. Inconel 600, which exhibited a dense and continuous external corrosion layer and an internal corrosion layer with localized corrosion behavior, exhibited superior corrosion resistance compared with those of Inconel 601 and 690, which showed a spalled external corrosion layer and an internal corrosion layer with uniform corrosion behavior. Thus, the corrosion resistance of the Inconel alloys tested in the hot lithium molten salts in an oxidizing atmosphere is closely related to the contents of the primary alloying elements in the alloys. Of the various alloys analyzed in this study, Inconel 600 exhibited the highest corrosion resistance. Thus, a Cr content of 16.30 wt% or less, Ni content of at least 73.66 wt%, and Fe content considerably lower than 8.15 wt% can result in excellent corrosion resistance.

Alloys and oxidation-resistant coatings utilized in high-temperature applications can be degraded by aerosols that deposit onto surfaces during operation. Understanding how the deposit composition influences the hot corrosion mechanisms is essential to develop more durable materials. This work advances the understanding of the effect of complex oxide and sulfate deposits on the degradation of an alumina-forming FeCrAlY alloy in comparison to reactions with single-crystal sapphire. The deposit compositions were developed to systematically understand the effect of anion makeup (mixed oxides, oxide–sulfate, and sulfates) and the effect of adding Na and K salts. CaSO₄ was used as a control. The mixed oxide and oxide–sulfate deposits increased the frequency of thermally grown oxide (TGO) intrusions in FeCrAlY but did not produce a noticeable change in the sapphire. Pure CaSO₄ and mixed sulfate reacted with the TGO and sapphire to form calcium aluminates and led to roughening of the specimen–reaction product interface. The primary difference between the CaSO₄ and mixed sulfate deposits was the increased uniformity of the attack by the latter due to its tendency to melt and spread. Comparison between the change in the degradation features in the presence of CaSO₄ and mixed sulfate deposits on both types of specimens expands the current understanding of sulfate-based hot corrosion.