Oxidation of Metals最新文献

The mechanism of oxide scale exfoliation from P92 steel during formation in CO₂ under over-temperature conditions at 650 ℃ was studied by the experiments, thermodynamics, and molecular dynamics. A duplex oxide scale with an inner FeCr₂O₄ scale and an outer Fe₃O₄ scale was formed on P92 steel, in which honeycomb pores were observed in Fe₃O₄ oxides. The honeycomb pore size and CO gas generation rate on P92 steel showed maximum values after 80 min. The exfoliation of Fe₃O₄ oxide scale was divided into two stages based on the deposition of carbon in the honeycomb pores.

High temperature corrosion and slag deposition significantly reduce the thermal efficiency and lifespan of biomass-fired boilers. Surface modification with protective coatings can enhance boiler performance and prevent commercial losses due to maintenance and damage. This review focuses on the development of corrosion-resistant coatings (CRCs) and anti-slagging coatings (ASCs) over the past decade. CRCs are explored through thermal spray processes that include arc spray, atmospheric plasma spray (APS), high-velocity oxygen fuel (HVOF), detonation gun (D-gun™), and cold spray. Studies on alloys, ceramics, and ceramic–metal composites are summarised, highlighting the high temperature corrosion prevention mechanisms and discussing new coating materials. ASCs are reviewed in the context of advancements via thermal spray and slurry spray methods. The mechanisms for slag reduction, testing methods to evaluate ASC effectiveness, and the necessary architecture for preventing slag deposition are examined. A lab-based rig simulating fly ash deposition onto water-cooled coating coupons for anti-slagging investigations is also presented. Further research is needed to develop and evaluate materials for ASCs effectively.

Graphical Abstract

The 304HCu stainless steel is a candidate material for superheater and reheater tubes in advanced ultra-supercritical power plants due to its excellent creep and oxidation resistance. However, these operating conditions involve exposure to steam at high pressure and temperature on the steam-side and hot coal-ash products on the fireside. In this study, the role of grain boundary character distribution (GBCD) on oxidation and fireside corrosion behavior of 304HCu steel is investigated. The GBCD was modified through grain boundary engineering (GBE) via optimized strain-annealing treatment on the as-received (AR) specimen. The air oxidation, steam oxidation (pressure ~ 243 bar) and fireside corrosion studies were conducted at 973 K for up to 1000 h, in custom-designed setups precisely simulating the operating conditions. Following GBE, the grain size (excluding twins) and coincident site lattice boundary (Σ ≤ 29) fraction increased from 21 ± 1 to 60 ± 12 μm and from 62 ± 4 to 74 ± 3%, respectively, resulting in disruption of the random high angle grain boundary networks through the introduction of twins. Evaluation of oxidation behavior revealed that the GBE specimens have lower oxidation resistance (i.e., higher weight gain and oxide scale thickness) in both air and steam, while the same specimen displayed improved fireside corrosion resistance (lower percolation depth) as compared to the AR specimen. From a detailed analysis of the oxidation/fireside corrosion products and cross-sectional microstructures of the oxide layers, the above responses could be correlated with the GBCD and grain size, and the possible mechanisms operative during the air/steam oxidation and fireside corrosion are also presented.

Graphical Abstract

Chemical-looping combustion (CLC) of biomass has the potential to facilitate negative CO₂ emission in heat and power production when combined with a carbon capture technique. However, typical biomass contains alkali metals and chlorine compounds, such as potassium chloride, which can lead to corrosion of heat-transfer surfaces in the reactors. The combined influence of potassium chloride, hydrochloric acid, and oxygen on the corrosion of five typical heat-transfer materials, which are potential candidates for use in the fuel reactor in a CLC process, was studied using one-week laboratory-scale experiments. The results suggested that potassium chloride, especially in the presence of HCl and O₂, greatly affects the corrosion of lower-alloyed heat-transfer materials. The outcome of this study can provide valuable information for selecting suitable heat-transfer materials for CLC.

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.

Paralinear oxidation models provide a description of parabolic scale growth combined with linear loss, as might occur for scales forming volatile oxide, hydroxide, chloride, or fluoride scales. Classic weight change exhibits an initial parabolic oxygen gain, a maximum (ΔW_max at t_max), then a linear loss. The magnitude of these features is determined by the parabolic growth rate, k_p, the linear volatility rate, k_v, and the stoichiometric constant of the reaction, S (fixed by the atomic weights and stoichiometry of the reaction). Model curves were generated (at constant k_p and k_v) to show that, for typical oxides, increases in S only moderately decrease ΔW_max and t_max, but directly increase the rate of mass loss. Universal oxidative behavior can be produced using normalized ½ k_p/k_v weight and ½ k_p/k_v² time constants. Furthermore, it is shown that, on average, k_p ≈ 4.1 (ΔW_max)²/t_max and k_v ≈ 1.2 (ΔW_max)/t_max. These relations apply for a broad spectrum of scale molecular weights, ranging from low mass SiO₂ to high mass Ta₂O₅ oxides. Oxidation of carbides and nitrides may release C and N elements and thus increase the effective S_eff, with concomitant effects on the paralinear curves.

The need for advanced materials that can meet application requirements at ultra-high temperatures in oxidizing environments is an area of active research. One challenge facing the high temperature materials community is the ability to conduct controlled ultra-high temperature oxidation tests with minimal to no contamination or reaction with the chamber. A unique resistive heating system (RHS) capable of achieving ultra-high temperatures (> 1700 °C) to enable such experimentation is described. A concern of such a system is the potential presence of thermal gradients in directions not reflective of actual material applications, e.g., the hottest region being in the center of the sample. Experimental results from the oxidation of ZrB₂ specimens at nominal temperatures of 1500°, 1700° and 1800 °C in low pO₂ (0.1–1% O₂ in Ar) environments are presented. Specimen thermal gradients generated during oxidation were evaluated using finite element analysis models. Thermal gradients on the order of the uncertainty in temperature measurements were calculated, confirming the RHS suitability for conducting ultra-high temperature oxidation exposures on ultra-high temperature ceramics.

The quest for high-entropy alloys (HEAs) with superior resistance against oxidation at elevated temperatures is one of the urgent problems in materials society, since HEAs are candidates for coating machinery parts operating in aggressive conditions (such as turbine blades, turbojet and jet engines, etc.). In this study, the effect of minor platinum alloying on the microstructure, phase composition and high-temperature oxidation resistance of Al_0.5CoCrFeNiCuPt_0.3 HEA was studied. It was demonstrated that platinum does not precipitate as an intermetallic phases; rather, it dissolves in the solid solution phases. High-temperature oxidation tests were carried out in a muffle furnace at 900 °C and 1000 °C for 50 h in air. It was found out that platinum alloying significantly increases oxidation resistance of Al_0.5CoCrFeNiCuPt_0.3 HEA at elevated temperatures with specific weight change of 0.139 mg/cm² and 0.238 mg/cm² after 50 h of isothermal exposure to 900 °C and 1000 °C, respectively. A dense oxide layer, mainly composed of Al₂O₃, without defects and pores protected the surface of the alloy.

The isothermal and cyclic oxidation behavior of a multi-principal element (MPE) TiNbCr alloy at 800–1000 °C in air was studied and compared to Co-based alloy 188. The phase constitution of the MPE alloy consisted of a Nb-rich body-centered cubic (BCC) matrix and Cr-rich Laves precipitates. While isothermal tests conducted at 800 °C led to the formation of a complex mixture of Nb, Ti and Cr oxides, tests at 900 and 1000 °C resulted in the formation of an innermost Cr₂O₃-rich scale layer which provided improved oxidation resistance. However, for all exposure temperatures, the scaling kinetics of the alloy were linear and therefore deemed non-protective. In contrast, alloy 188 exhibited parabolic scaling kinetics and smaller mass gain per area than the MPE alloy. The similarity between isothermal and cyclic test results for the MPE alloy confirmed that the scale does not offer much protection. Additionally, for all tests, there was extensive internal oxidation and nitridation.

La₂Ce₂O₇ (LC) has been identified as a promising thermal barrier coating (TBC) for use up to 1250 °C. In this study, a TBC system was deposited on grit-blasted Inconel 738 using atmospheric plasma spraying (APS) with NiCrAlY as the bond coat, followed by YSZ, and then LC as the top layer. The coatings were exposed to a mixture of molten Na₂SO₄ (45 wt.%) and V₂O₅ (55 wt.%) at 950 °C for hot corrosion. On the top LC layer, LaVO₄, CeVO₄ and CeO_{(1.66–2.00)} formed as hot corrosion products after 4 h exposure. A reaction between YSZ and the corrosion products could not be observed due to the absence of YVO₄. The hot corrosion mechanism of the LC-based TBC is also discussed in this study.