High temperature oxidation behavior and mechanism of a new Ni-Co-based superalloy

A new insight into high-temperature oxidation mechanism of super-austenitic stainless steel S32654 in air

High-temperature oxidation behavior and mechanism of Inconel 625 super-alloy fabricated by selective laser melting

Microstructural evolution during exposure in air and oxidation behavior of a nickel-based superalloy

The high-temperature oxidation behavior of low-carbon steel (AISI 1015, AISI 8617, AISI 4115) was investigated over the temperature range from 600 to 1000 °C in humid air containing 25% water vapor. Mass gain of oxidation measurement was performed to study the oxidation kinetics. The microstructure, thickness, and composition of the oxide scale formed were investigated via optical microscope (OM), scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and electron probe microanalyzer (EPMA). The oxidation process was performed from 2 to 100 min. As the oxidation time increased, the trend of mass gain per unit area switched from a linear to a parabolic law, regardless of the steel grade used. As the chromium content increased, the duration of time during which the oxidation rate followed a linear relationship decreased. In the low-alloy steel with higher chromium content, the thickness of the mixed oxide layer containing Cr increased and the oxidation rate decreased at all oxidation temperatures.

Isothermal oxidation mechanism of a newly developed Nb–Ti–V–Cr–Al–W–Mo–Hf alloy at 800–1200 °C

Three studies on the oxidation behaviour of austenitic stainless steels were described in the present paper. (1) High temperature oxidation behaviour and its mechanism in austenitic stainless steels with high silicon: Sulfur contained as impurity in steel showed a harmful influence to the oxidation resistance of 19Cr-13Ni-3.5Si stainless steels. It was found that the abnormal oxidation was caused from the surroundings of MnS inclusions. (2) Effect of a small addition of yttrium on high temperature oxidation resistance of Si-containing austenitic stain less steels: The oxidation resistance of 19Cr-10Ni-1.5Si steels was improved remarkably even with only 0.01%Y addition, which is the same concentration as added for de-oxygenation. Y was enriched at the grain boundary of oxide scale and metal-oxide interface. It was suggested that Y-containing steels shoed good oxidation resistance, because the enriched Y at the grain boundary and metal-oxide interface prevented the diffusion of iron and oxygen ions through the oxide scale. (3) Effect of grain size on the oxidation behaviour of austenitic stainless steels: Type 304, 316 and 310 steels with finer grain size showed better oxidation resistance than those with coarser grain size at 850°C. The oxide scale of steels with coarser grain size easily spalled during the cooling process.

Single crystals of oilivine, (Mg0.9Fe0.1)2SiO4, have been oxidized in air at temperatures between 700° and 1100°C for times from 0.5 to 100 h. Both an internal and an external oxidation layer developed. Transmission and analytical electron microscopy observations reveal that the internal oxidation layer is composed of precipitates of magnetite plus amorphous silica, which nucleated heterogeneously on dislocations and grew in an Fedepleted matrix of olivine. Rutherford backscattering spec‐trometry (RBS) demonstrates that the thin external oxidation layer is free of Si; that is, it is made up of Mg‐Fe oxide phases. Thus, the oxidation process is primarily controlled by diffusion of Fe2+ and Mg2+ ions toward the surface with Si4+ and O2‐ remaining largely immobile. The kinetics of oxidation, as determined from RBS analyses of the external oxidation layer, are parabolic with an activation energy of 140 kJ/mol. Although this activation energy is lower than that reported for self‐diffusion of Mg in Mg2SiO4, the diffusivity calculated from the reaction rate constant is in good agreement with published values for lattice diffusion of Mg in the limited temperature range in which data overlap. However, the rate of accumulation of Fe in the external layer is more rapid than expected for lattice diffusion, indicating that the transport of Fe is dominated by short‐circuit diffusion along the precipitate complexes which decorate dislocations.

Laser additive manufacturing of CrMnFeCoNi high entropy alloy: Microstructural evolution, high-temperature oxidation behavior and mechanism

The high temperature oxidation behaviour of ferritic stainless steel SUS 430 was investigated over the temperature range from 1000 to 1150 °C in humid air containing 18% water vapour. Isothermal thermogravimetric analyses were performed to study the oxidation kinetics. The microstructure, composition and thickness of the oxide scale formed were investigated via optical microscopy (OM), X-ray diffraction and a scanning electron microscope equipped with an energy dispersive spectrometer. The results indicate that breakaway oxidation occurs at all temperatures and that its onset is accelerated by increasing temperature. The growth rate of the multilayer oxide scale follows a parabolic law with apparent activation energy of 240.69 kJ/mol, and the formation of FeO is decreased when the temperature is higher than 1120°C. The inner oxide scale, Fe-Cr spinel, grows mainly inward and internal oxidation is observed even in a short oxidation test at 1150°C for 105 s. The mechanism of high temperature oxidation of SUS 430 in humid air containing 18% water vapour is discussed.

Effect of Ta on the high temperature oxidation behavior of Mo-based bulk metallic glasses

The rehealing ability of the oxide scales on sputter-deposited Ni-based K52 nanocrystalline coatings after pitting corrosion had been studied by polarization curves in 3.5% NaCl solution. The results indicated that the oxide scales formed on the nano-coatings exhibited excellent rehealing ability after pitting corrosion, and the rehealing oxide scales still had high corrosion resistance. The rehealing ability was declined with longer immersion time in the chloride solution. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides. The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr2O3 and TiO2 and the internal oxide layer was Al2O3.

For gold alloys containing only In as a base metal, an external In2O3 layer forms uniformly on the alloy surface. However, when the alloy contains Sn and In, no external oxide layer can be detected by electron probe micro-analysis, and oxide particles composed of In2O3 and SnO2 precipitate in the alloy. For alloys containing Ni, in addition to In and Sn, the external oxide is composed of NiO; there is little development of internal oxide. For alloys containing Fe and Sn, an oxide layer of only Fe2O3 forms on the alloy surface, and the internal oxidation zone shows a band-like structure containing SnO2 and a small amount of Fe2O3.

The electrochemical behaviour of the rehealing oxide scales on the K52 nanocrystalline coatings had been studied by polarization curves. The results indicated that the oxide scales formed on the nano-coating exhibited rehealing ability after pitting corrosion, and the coating still had excellent corrosion resistance. The rehealing ability was enhanced with prolonged re-oxidation time. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides (Cr2O3, Al2O3 and TiO2). The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr2O3 and TiO2 and the internal oxide layer was Al2O3.

In order to investigate the oxidation mechanism of ferritic stainless steel during long-term oxidation at high temperature. The oxidation behavior of Fe-Cr-Ti ferritic stainless steels with 10.38 wt% Cr and 17.41 wt% Cr at 800 °C and 900 °C for 100 h was studied by a constant temperature weight gain method. The morphology and composition of the oxide film were characterized by SEM, EDS and XRD. The experimental results indicate that the oxygen element mainly diffuses inward at 800 °C for two stainless steels, and the oxide film is composed of (Cr1.3Fe0.7)O3 + MnCr2O4. When the temperature rises to 900 °C, metal element mainly diffuses outward, and Fe2O3 outer oxide layer and Fe rich Fe-Cr inner oxide layer are formed in Fe11Cr0.5Ti stainless steel; Cr2O3 + Cr rich M3O4 spinel oxide film is formed in Fe18Cr0.5Ti stainless steel, while the inner layer is composed of SiO2. The main reason for the significant decrease of oxidation resistance of Fe11Cr0.5Ti stainless steel is that the low content of Cr cannot form a Cr rich oxide layer to inhibit the outward diffusion of Fe element, and the stability of oxide film is poor to protect the matrix.

The interaction of the alloy niobium-25Titanium with air, oxygen and nitrogen I. The unusual oxidation behavior of Nb-25Ti at 1000 ° C