Oxidation of Metals最新文献

The phase composition of the pre-oxidized film on an alloy surface usually has a great influence on its corrosion resistance. In this work, the surface oxide film growth behavior in low-oxygen atmosphere at 720 °C of two 12Cr heat-resistant steels with different Mn content was studied, and their corrosion resistance in liquid lead–bismuth eutectic (LBE) with saturated oxygen at 600 °C was tested. The results indicated that the pre-oxidized film of 1.6Mn steel is mainly composed of large-size Mn–Cr spinel and Fe–Cr spinel, while that of improved 0Mn steel is mainly composed of continuous and dense Cr₂O₃ and Fe–Cr spinel. This is because Mn has a high diffusion rate in Cr₂O₃, so it can pass through the Cr₂O₃ layer and combine with O to form Mn-rich oxides, and then the Mn-rich oxides react with Cr₂O₃ to form Mn–Cr spinel. However, due to the high solubility of Mn in LBE, the Mn-rich pre-oxidized film of 1.6Mn steel will dissolve and fail quickly, so its long-term corrosion resistance in LBE is lower than that of 0Mn steel.

Hot corrosion is a severe form of industrial corrosion which occurs at high temperatures under the influence of oxidizing gases and can be prominently linked to the formation of a molten salt/ash layer over any metallic substrate. Throughout the years, several types of inhibitors and coatings have successfully been employed to reduce its devastating effects to a certain extent. In this study, two synthesized metal oxides namely Al₂O₃ and MnO₂ were used as corrosion inhibitors and XRD, FTIR analysis were carried out to assess their structural properties. Further, TGA analysis for Al₂O₃ and MnO₂ was carried out to determine thermal stability characteristics. The as-synthesized materials were further deposited as inhibitor coatings (Al₂O₃ with MnO₂ bond coating, MnO₂ coating and Al₂O₃ + 50% MnO₂ coating) on T22 boiler steel specimens. All the specimens (bare T22 and coated T22 steel) were investigated for hot corrosion studies in Na₂SO₄-60%V₂O₅ environment at the temperature of 900 °C for 50 consecutive cycles. Every cycle involved a 1-h heating step in furnace followed by 20-min cooling at room temperature. Weight gain data were collected using a digital balance. XRD and (SEM–EDS) analysis were carried out to characterize the samples after exposure to hot corrosion environment. A better resistance to hot corrosion was observed for all the different types of coatings, with Al₂O₃ + 50% MnO₂ coating representing maximum resistance. A high concentration of protective oxides such as Al₂O₃ and Cr₂O₃ present on the surface and their interaction to form dense layers on the coated samples explains the enhanced hot corrosion inhibition.

Aiming to address the Mo volatilization problem of super-austenitic stainless steel at high temperature, the S31254 steel containing B and rare earth element Y with high oxidation resistance was designed. It was observed that a synergy of B + Y can promote the formation of the dense Cr₂O₃ layer at 1050 and 1100 °C, making MoO₃ layer formation difficult. While the oxide layers of the 0B sample from top to bottom were divided into four layers: Fe-rich oxide layer, MoO₃ layer, Cr–Mn–Ni spinel oxide layer, and Cr₂O₃ layer (loose and porous), thus the undense Cr₂O₃ layer in the 0B sample can hardly inhibit MoO₃ volatilization, especially at 1100 °C. In addition, the synergistic effect of B and Y on the diffusion of Cr to the surface was calculated using first-principles calculations. The results demonstrated that both the addition of B and Y can enhance Cr diffusion to the surface, while Y can specifically promote the combination of Cr and O. Consequently, the combined presence of B and Y exhibits a more favorable synergy for improving the density of the Cr₂O₃ layer, effectively inhibiting MoO₃ formation and volatilization, thereby enhancing the oxidation resistance of S31254.

High temperature oxidation of Ni–19Fe–19Cr–5Nb alloys (based on the chemical composition of Alloy718) with different Al contents were investigated to elucidate the effect of Al on oxidation kinetics and scale formation during exposure at 800 °C in air. The experimental results indicated that the oxidation kinetics decreased with increasing Al content. The beneficial effect of Al could be attributed to be a result of the formation of γ′-Ni₃Al, which stabilizes γ′′-Ni₃(Nb,Al) and kinetically prohibits the coarsening of γ′′-Ni₃(Nb,Al) phases. Faster dissolution of finer γ′′-Ni₃(Nb,Al) precipitates due to greater γ-matrix / γ′′-Ni₃(Nb,Al) interface region in as-received Al-containing alloys could supply greater Nb flux for the formation of CrNbO₄, which promotes the formation of an exclusive Cr₂O₃ scale at the initial stage of oxidation.

Accident tolerant fuel (ATF) cladding is a new type of nuclear fuel cladding designed to improve the safety and performance of nuclear reactors. In this paper, the kinetics and degradation mechanisms during high-temperature oxidation in steam of the three most promising ATF cladding materials, i.e., chromium-coated zirconium alloys, FeCrAl alloys, and silicon carbide-based composites, are described. Each system has its own degradation mechanisms leading to different maximum survival temperatures. After providing general information and data to understand the oxidation and degradation processes, illustrative examples obtained at the Karlsruhe Institute of Technology are given for each type of cladding. The maximum temperatures at which the barrier effect of the cladding can be maintained for a reasonable period of time during nuclear accident scenarios are 1200–1300 °C for Cr-coated Zr alloys, 1400 °C for FeCrAl alloys, and 1700 °C for SiC-based composite claddings.

When a copper billet is heated in the rolling reheating furnace, certain oxides that affect the surface quality may persist on the substrate. This study investigates the effects of heating atmosphere compositions (N₂, O₂, CO₂, and H₂O) and contents on the micro-morphology and phase evolution of the copper oxides. The results revealed that O₂ is the primary factor contributing to the formation of nodules on the copper surface. The primary phase of the exfoliated oxides was CuO attached to Cu₂O, and the nodular oxides also consisted of CuO that directly adhere to copper matrix. Additionally, water vapor can increase the number of Cu₂O particles on the interface between exfoliated oxide and copper matrix, effectively reducing the number of residual nodular oxides. Finally, water vapor and its dissociation products effectively eliminated the pores within the oxide layer and at the oxide–matrix interface, while CO₂ increased the porosity within the oxide layer.

In this study, effect of Fe concentration on the high temperature oxidation and microstructural stability of Fe_x(CrAlNi)_100−x alloys (x = 25, 35, 45, 55, 65) at 1100 °C up to 168 h was investigated in air. Increasing Fe concentration decreased the molar fraction of B2 phase in as-cast alloys. However, microhardness values experienced only a 10% reduction (Fe₂₅: 517.7 ± 19 HV, Fe₆₅: 470.6 ± 22 HV) due to well-distributed B2 precipitates. After the exposures, coarsening of B2 precipitates was observed in all alloys, leading to a microhardness reduction of 20–25% after 168 h. Single-phase α-Al₂O₃ scales were formed on Fe₂₅–Fe₅₅ alloys. However, increasing Fe concentration resulted in deeper depletion zones due to reduced molar fraction and Al concentration of B2 phase. Moreover, Fe₆₅ alloy failed to develop a protective α-Al₂O₃ scale due to decreased molar phase fraction and Al concentration of B2 precipitates, along with the low Cr concentration of the A2 phase. Additionally, α-Al₂O₃ scales were highly wrinkled due to the absence of reactive elements. Absence of reactive elements also resulted in oxide spallation and seemed to intensify with the increasing Fe concentration. Possible reasons for the increased oxide spallation with the increasing Fe concentration are discussed. Nevertheless, Fe₂₅–Fe₅₅ alloys displayed oxidation properties comparable to those of lean FeCrAl alloys while also possessing enhanced mechanical properties due to B2 reinforcement.

The influence of deep cryogenic soaking of additive manufactured stainless steel 316L (SS 316L) parts on hardness and corrosion resistance is investigated. The fabrication of SS 316L was carried out using selective laser melting (SLM). A Gaussian beam for laser energy dissemination was employed in SLM process to produce SS 316L specimens characterised by distinctive curved boundaries within the melt pool, resulting in a unique grain morphology featuring semicircular melt pool boundaries and layered patterns. The deep cryogenic soaking (DCS) process treatment, conducted at an ultra-low temperature of − 196 °C for an extended duration of 120 h immersed in liquid nitrogen medium, led to a significant improvement in the microstructure. An increased amount of fine-cellular grain microstructure was achieved, with an average grain size reduced from 1.01 ± 0.5 μm to 0.78 ± 0.5 μm. X-ray diffraction (XRD) analysis revealed that the DCS treatment did not alter the crystal structures, with both SLM and DCS specimens exhibiting the presence of the FCC-austenite phase. Surface roughness analysis indicated a noteworthy reduction following DCS treatment, with a 3.23% decrease in the average surface roughness (Ra) from 9.155 μm over the SLM SS 316L surface to 8.868 μm post-DCS exposure. Moreover, the mechanical properties exhibited substantial improvement, with SLM SS 316L samples having an average microhardness value of 193.16 HV, while DCS-treated samples exhibited an average microhardness value of 222.6 HV, marking a 15.24% enhancement attributed to grain structure refinement. XRD analysis also revealed peak broadening in DCS-treated specimens, suggesting the possibility of a more refined grain structure. This fine grain structure was found to hinder ion movement, resulting in a reduction in the corrosion rate from 0.004695 to 0.003965 mm/year. Although the improvement in corrosion resistance was marginal, it underscores the potential of DCS treatment in enhancing the resistance of SS 316L to corrosion.

Calcium- and sulfur-rich deposits have been linked to failure of turbine components as a consequence of high temperature exposures (> 1000 °C). There are only limited studies on the effects of these deposits on the degradation behavior of turbine alloys. To gain further understanding of this phenomenon, a systematic study was undertaken with model binary nickel–chromium alloys. Three alloys with different chromium contents—low, medium and high—represented by Ni-5Cr, Ni-10Cr and Ni-18Cr, were exposed to CaSO₄-deposit-induced corrosion in the 900–1100 °C temperature range. At 1000 and 1100 °C, the decomposition of CaSO₄ (either by decomposition to CaO and SO₃ or by reacting with Cr₂O₃) led to the formation of calcium chromates and chromium sulfides. At the lower temperature, 900 °C, the limited decomposition of CaSO₄ allowed the formation of a continuous Cr₂O₃ scale.