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This study aims to control the oxidation resistance of Co-based deformed superalloys by adding trace elements Hf and Si.

The effects and mechanism of trace elements Hf and Si on the oxidation behavior of Co-Ni-Al-W-based forged superalloys were investigated by cyclic oxidation at 900°C.

The results show that the addition of trace elements Hf and Si does not affect the type of surface oxides of Co-Ni-based superalloys, and the oxidation layers of the alloys are TiO₂, spinel, Cr₂O₃, TaTiO₄, Al₂O₃ and TiN from outside to inside. However, the addition of elements can affect the activity of Cr and Ti elements; decrease the formation of TiO₂ and TaTiO₄ layers, which are harmful to the oxidation performance; and then improve the oxidation resistance of the alloy.

The relevant research results can not only optimize the microalloying element content of Co-Ni-Al-W-based superalloys, but also provide a new perspective for the composition optimization design of superalloys.

The aim of this paper is to study the hot corrosion behaviour of super 304H stainless steel for marine applications.

The investigation was carried out with three different combinations of salt mixture (Na₂SO₄, NaCl and V₂O₅) at two different temperatures (800 and 900°C).

The spalling and growth of oxide layer was observed more with the presence of V₂O₅ in the salt mixture at 900°C during experimentation than what was observed in 800°C. The mass change per unit area is calculated to study the corrosion kinetics and also the influence of salt mixture. Further, the samples are analysed through materials characterisation techniques using optical image, scanning electron microscope (SEM), energy dispersive X-ray (EDAX) and X-ray diffraction (XRD) analysis. The presence of V₂O₅ in the salt mixture was the most important influencing species for accelerating hot corrosion.

SEM, EDAX and XRD analysis confirmed the formation of Fe₂O₃ and Cr₂O₃ at 900°C showing contribution in corrosion protection.

This paper aims to analyse the surface evolution of pure recycled titanium subjected to isothermal and cyclic oxidation conditions using dry air as oxidant gas. It is important to mention that the cyclic oxidation behaviour of pure titanium is a process that has been barely studied.

An isothermal and cyclic oxidation reactor was built for these purposes. This installation allows the oxidation of material under the action of any atmosphere and for temperatures up to 1,200°C. For this study, the oxidation behaviour of the material was studied at 850°C and 950°C.

Oxide growth under isothermal oxidation conditions in air follows a parabolic behaviour with an activation energy of 118 kJ/mol, and the oxide phase formed on the surface of the metal was rutile. The cyclic oxidation of the material indicates that oxide is spalled from the surface following linear behaviours; this phenomenon is controlled by the thermal stresses experienced by the samples during heating and cooling cycles.

The material is obtained from the production of electrolytic copper, and during its reprocessing practices at high temperature, it was thought that it could experience some abnormal oxidation. In addition, given that pure titanium is currently used for biomedical application, some surface degree can be given by means of oxidation and subsequent spallation process situation that is found during the cyclic oxidation experiments, which could be a low-cost method to engineer a surface for these purposes.

Due to the special service environment of superalloys, this paper aims to obtain effects of temperature and Ti addition on high temperature oxidation behavior of Co-Al-W-B alloys.

Isothermal oxidation experiment of Co-Al-W-based alloys were carried out at 800°C, 900°C and 1000°C for different times (3, 5, 10, 20, 50 and 100 h) referring to the method of HB5258-2000. Oxidation weight gain curves and oxidation products were detected.

The results showed that the average oxidation rates of Co-Al-W-B alloy at 800 °C and 900 °C were 0.489 g·m⁻²·h⁻¹ and 0.888 g·m⁻²·h⁻¹, respectively, which belonged to an antioxidant grade. However, the average oxidation rate at 1000 °C was 2.068 g m⁻²·h⁻¹, belonging to the secondary oxidation resistance class. In the alloy with Ti addition, dense Ti oxides film were formed at the early oxidation stage and then gradually diffused later, which can increase the oxidation resistance of the alloys to some extent. By analyzing the oxidation products of Co-Al-W-B alloy, it was found that a dense Al₂O₃ layer could be formed when the alloy was oxidized at 800°C. The continuous Al₂O₃ layer would prevent the oxygen from further spreading and make the alloy into the stable oxidation stage. However, only a non-dense Al₂O₃ layer were observed with 900°C oxidation.

It can provide references for the composition design, preparation process optimization and protective coating selection of the γ′ phase strengthened cobalt-base superalloys.

The purpose of this paper is to investigate the oxidation behavior of Ti‐48Al‐8Cr‐2Ag (at.%) at 900°C and 1000°C for various different times.

Laboratory tests were performed to determine growth process of the oxide scale at 900°C and 1000°C for various different times with SEM/EDX, XRD and TEM.

Merely Al2O3 occurred on the Laves phase at the initial stage at 900°C, while a mixture of Al2O3+TiO2 formed at the initial stage at 1000°C. Oxidation rate of the alloy at 900°C after long‐term oxidation was higher than that at 1000°C because a dense Al2O3 scale formed on the surface at 1000°C.

The paper shows that the oxidation behavior of TiAl alloy at initial stage is the basis of the revealing mechanism of oxidation. It is necessary to further investigate the oxidation of Ti‐Al‐Cr‐Ag alloy in more detail to clearly understand its oxidation process and growth process of the oxide scale.

DISCUSSION The chromium coating thicknesses used in this work were comparable to those used commercially, being between 70 and 170 micrometres approximately. Even after oxidation for the temperatures and times stated the chromium concentrations at the metal‐oxide interface were between 20% and 60%. These concentrations fell steadily to approximately 13% over the approximate depth stated above before reducing sharply to zero at what was the ferrite‐austenite transformation boundary during the coating process. This is contrary to the structure observed in aluminized stainless steels where a complex structure is produced due to the existence of intermetallic phases. Hence during all the oxidation experiments performed the chromium level of the surface offered for oxidation was never below 13% and complete oxidative breakdown therefore did not occur, excluding spalling effects. Many workers have shown that the oxidation rate of iron‐chromium alloys initially drops sharply with increasing chromium but eventually reaches a minimum of about 20% chromium and then rises for more chromium rich alloys. From the graph of oxidation rate in pure oxygen against chromium content given by Mortimer et al., from 13% chromium to 100% chromium the oxidation rate increases by approximately 6 × 10−9 g.cm−2 sec.−1 It is reasonable to assume that for a diffusion coating the oxidation behaviour will be markedly affected by the composition at its outer surface layer and much less by the composition gradient. If oxidation was continued for sufficiently long periods the latter could affect the general availability of chromium ions for the oxidation process. Over the first 5?m the average chromium levels were between 63% and 20% for the chromised and chrome‐aluminized respectively. From the figures given by Mortimer et al the oxidation rate of the 63% chromium coating would be expected to be 0.5 × 10−9 g.cm−2 sec−1 greater than the 20% chromium coating on the chrome‐aluminized specimens at 600°C, on the basis of the chromium content alone. The results obtained here vary in this manner, hence it is reasonable to conclude that the general oxidation behaviour of the coatings will be very similar to that of pure iron‐chromium alloys containing the same chromium content as in the outer few micrometres of the respective coatings. Even though the true surface area is greater with diffusion treated specimens their oxidation rates are lower that for the corresponding pure alloys.

Nickel aluminide coatings on mild steel have been prepared by pack cementation process. The high temperature oxidation behaviour of the coatings have been studied at 750°, 800° and 850° in flowing air. The influence of different rare earth oxide addition on the oxidation rates of nickel aluminide coating on mild steel has also been investigated. The kinetic of the oxidation of nickel aluminide coating on mild steel, with or without addition of RE2O3 proceeds by a diffusion controlled mechanism as revealed by the parabolic nature of weight gain Vs time plots. At higher temperatures the oxidation rates of the nickel aluminide coatings are lowered down markedly irrespective of rare earth oxide concentration. The oxidation rates are significantly affected by the morphology of the oxide scales, in cases where the structure of oxide scales is not seriously disrupted due to decarburization, the oxidation rates are significantly reduced.

THE variation in weight gains of the binary (and ternary) iron alloys with change in the atmosphere composition clearly demonstrates the sensitivity of oxidation behaviour to conditions. In particular it can be seen from Figs. 3 and 4 that the presence of atmospheric pollutants (sulphur and nitrogen oxides, water vapour) markedly increases the oxidation rate in air. This is supported by the further marked increase in oxidation in flue gases produced by the presence of sulphur oxides. Oxidation in flue gases at 700°C is far greater than in air, Figs. 7 and 10 and Table 3. This is due to the formation of wustite which was not present in air‐formed oxide scales.

The purpose of this paper is to study the high temperature oxidation behavior of Ti and C-added FeCoCrNiMn high entropy alloys (HEAs).

Cyclic oxidation method was used to obtain the oxidation kinetic profile and oxidation rate. The microstructures of the surface and cross section of the samples after oxidation were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM).

The results show that the microstructure of the alloy mainly consisted of FCC (Face-centered Cubic Structure) main phase and carbides (M₇C₃, M₂₃C₆ and TiC). With the increase of Ti and C content, the microhardness, strength and oxidation resistance of the alloy were effectively improved. After oxidation at a constant temperature of 800 °C for 100 h, the preferential oxidation of chromium in the chromium carbide determined the early formation of dense chromium oxide layers compared to the HEAs substrate, resulting in the optimal oxidation resistance of the TC30 alloy.

More precipitated CrC can preferentially oxidize and rapidly form a dense Cr₂O₃ layer early in the oxidation, which will slow down the further oxidation of the alloy.

The purpose of this paper is to study the influence of silver on the high‐temperature oxidation behaviour of the Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga (x=0, 0.1, 0.3 and 0.5) solder alloys.

The weight gains of the studied solders are measured using thermal gravimetric analyzers (TGA) at temperatures of 250, 300, 350 and 400°C. The weight gains measured are used to compare the oxidation behaviour of the studied solders. The surfaces of the solders are also analyzed with Auger emission spectroscopy (AES) depth profiling and thin‐film X‐ray diffractometry (thin‐film XRD) to identify the elements present on the surface of the studied solders.

The TGA results show that the weight gains decrease with increasing silver content in the studied solders. It meant that increasing silver content could help improve the high‐temperature oxidation behaviour of the studied solder. AES and thin‐film XRD confirm that the formed oxide layers on the surface of the studied solder are Zn‐based oxide layers.

The findings of this paper will help provide an understanding of the effects of silver on Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solder.