Papers by Keyword: High Temperature Oxidation

Abstract: The availability of TiC healing agent has been evaluated in low temperature self-healing behavior of Al₂O₃ based self-healing ceramics. For this purpose, some technical issues to actualize the advanced fiber-reinforced self-healing ceramics containing TiC based interlayer as healing agent were discussed. Especially, the mechanical matching between the matrix and the interlayer was focused. Moreover, the self-healing behavior of the advanced shFRC containing the optimized TiC based healing agent was investigated. As a result, 30 vol% TiC-70 vol% Al₂O₃ interlayer was confirmed to be the optimized healing agent in the self-healing ceramics, and the self-healing ceramics was found to enable to attain the perfect healing at 600°C within 10 min. And we succeeded in prototype production of fiber-reinforced self-healing ceramics for low pressure turbine blade.

Abstract: The oxidation behavior and mechanism of Ti-Cu alloys (0≤w(Cu)≤20%) in the temperature range of 1000°C～1300°C are studied by thermogravimetric analysis(TGA) combined with SEM, EDS and XRD analysis methods. The results show that the oxidation rates of Ti-Cu alloys increase sharply when the temperature rises above 1000°C. The oxidation products have a three-layer structure, from the outside to the inside, which are dense outer oxide layer of TiO₂, porous inner oxide layer of low valence oxide of Ti and Cu-enriched layer. With the increase of the temperature, the thicknesses of oxide layers of Ti-Cu alloy increase and the Cu-enriched phase increases gradually and melts. The melting Cu-enriched phase flows to the oxidation surface along the grain boundaries of the oxide layer. The high temperature oxidation resistance of Ti-Cu alloys declines with the increase of Cu content. The main reason is that more liquid Cu-enriched phase is formed and flows to the oxidation surface along the oxide grain boundaries in the Ti-Cu alloy, and Ti and O ions can diffuse more easily along the liquid Cu-enriched phase, which increases the oxidation rates.

Abstract: This present work dealt with the effect of surface roughness on the scales growth of Fe-15Cr alloy. Surface morphologies and oxidation kinetics reveal that there was no obvious influence of surface roughness on the oxide-scale growth of Fe-15Cr alloy except for the initial oxidation stage of 1 h. However, there was an obvious influence on the oxide-scale spallation and microstructure, especially under the mutual function of temperature changes and surface roughness.

Abstract: The oxidation behavior of porous nickel low-chromium alloys containing up to 1 wt%Cr oxidized in air at 1273K for 100 h was investigated. Porous-duplex scale was formed on the 1 wt%Cr pellets while single oxide layers were obtained on the 0.25 and 0.5 wt%Cr pellets. Cavities were formed underneath the NiO scales and also between both layers formed on the oxidized 1 wt%Cr pellets. Accumulation of NiCr₂O₄ was noticed at the oxide/ metal interface. The growth mechanism of the scales was explained on the basis of molecular oxygen inward migration.

Abstract: Currently, the ceramic inner container draws great attention in the field of induction heating pot. Based on the traditional roll-forming process for ceramic pot, a new kind process was proposed to fabricate ceramic inner container and synchronously embed stainless steel plate by one-step high temperature sintering. The key technology for this process is to avoid the oxidation of SUS430 stainless steel plate during the high temperature sintering for a longtime by coating a glass-ceramic layer. In this research, the glass-ceramic coating with excellent high temperature oxidation resistance was optimized. The influences of ZrO₂ content in the coating slurry on the high temperature oxidation resistance and thermal shock resistance of SUS430 stainless steel plate with glass-ceramic coating were studied. Meanwhile, the coatings were characterized by Scanning Electron Microscopy, X-ray Diffraction and Thermal Expansion Analysis. The experimental results showed that the glass-ceramic coating was smooth and had excellent thermal shock resistance when the addition of ZrO₂ reached 15wt%. The mass gain of the SUS430 stainless steel plate with glass-ceramic coating was only 0.453% after sintering at 1300°C for 10h in air atmosphere, which was less one percent than that of SUS430 stainless steel plate under the same sintering condition.

Abstract: Exhaust manifolds for diesel engines are made of high-Si ferritic nodular cast irons. It is experimentally well established that their oxidation kinetics are highly sensitive to the presence of water vapor, though the mechanism for such an effect is still controversial. In the present work, isothermal oxidation tests were performed on a SiMo nodular cast iron at 700°C and 800°C in dry and humid air for 25 and 50 hours. Other samples were oxidized for 50 h with in-situ change in H₂O content after 25 h, switching from dry air to humid air or the other way round. Samples were then analyzed using XRD, SEM-EDS and Raman spectroscopy. Thermogravimetric records clearly showed the effect of temperature and environment on oxidation and decarburization. The kinetics of these phenomena depends on silica formation at the metal-oxide interface. At both temperatures, water vapor was seen to promote internal oxidation of Si instead of its external oxidation. This leads to higher oxidation kinetics at 700°C and higher decarburization kinetics at 800°C.

Abstract: Ti (C,N)-based cermets with varying WC additions (Ti (C_0.6N_0.4)-36Ni-12Mo-1C-xWC, x = 0, 3, 6 and 9 wt%) were prepared by conventional powder metallurgy techniques. The microstructure and mechanical properties of all four Ti (C,N)-based cermets were investigated. Isothermal oxidation of all four cermets were also investigated in air at 800°C up to 100 h using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). The grains of Ti (C,N)-based cermets became more homogeneous with the increase of WC content. The TRS and fracture toughness increased with the increase of WC content and then decreased when WC content exceeded 6wt%, but hardness decreased continuously with the increase of WC content. The oxide scales formed on the surface of all four samples during the oxidation process were porous and multi-layered, consisting of NiO outerlayer and TiO₂ based innerlayer, respectively. The thickness of the oxide scales and oxidation rates increased with the increase of WC content, especially when the content of WC addition reached 9wt%. The cermet with 6wt% WC addition showed excellent mechanical properties and acceptable high temperature oxidation resistance.

Abstract: Silica sol bonded SiC castable have obvious advantages of slag resistance and thermal stress damage resistance. However, they are not widely used due to their weak oxidation resistance at high temperature. Ferro-silicon nitride is added to improve the oxidation resistance of SiC castable. The efficiency of SiC castable in the presence of different contents of ferro-silicon nitride was evaluated through sintered properties, isothermal oxidation behaviors and microstructural analysis. The results show that sample with 5wt% ferro-silicon nitride possessed good mechanical behavior after heat treatment due to its acceleration for the formation of SiC whiskers. At 1500 °C, Isothermal oxdation curve indicated that the oxidation progress performed two-stage model controlled by chemical reaction at the earlier period and diffusion at the later period. Sample with 5wt% ferro-silicon nitride present faster oxidation rate (k_c) at the earlier stage versus the contrast sample (0.025 mg·cm^-2·min^-1 vs 0.087 mg·cm^-2·min^-1), and slower oxidation rate (k_d) at the later stage (0.145 mg·cm^-2·min^-1 vs 0.137 mg·cm^-2·min^-1). After 470 min isothermal oxidation test, the weigh gain of sample with 0 wt% ferro-silicon nitride exceeded the sample with 5wt% ferro-silicon nitride.

Abstract: Stainless steels can form a protective oxide layer when exposed to a high temperature oxidising environment, this protective layer forms a diffusion barrier and slows the oxidation of the alloys in harsh environments. This characteristic has made stainless steels one of the most commonly used alloys for high temperature industrial applications. In this work, a systematic testing procedure has been used to investigate the high temperature oxidation of two commonly used grades of stainless steel, 316 and 310. Samples of each alloy have undergone isothermal testing in air at 1050°C, 1150°C and 1250°C for a range of time periods up to 8h. The oxidation kinetics were also investigated using thermo-gravimetric analysis in air at the same temperatures for 8h. The oxide layers formed on the samples were characterised using X-Ray diffraction, Scanning electron microscopy and energy dispersive spectroscopy. Information derived from oxide layer characterisation was used to explain any differences between the two alloys in terms of oxidation rate and overall alloy performance in the high temperature environment.

Abstract: Anodic current-supplying pins (ACP) made of low-carbon steel corrode intensively due to the sulfur contamination of the carbon-based Soderberg anode and iron sulfides formation in the present aluminium production technology. The aluminide coatings produced by the liquid-phase method followed by the fluoride flux treatment of the steel samples were applied for the ACP protection. The protective layer based on α-Al₂O₃ and FeAl₂O₄ was formed on the steel surface in the course of the test run in the industrial Soderberg anode during the aluminium electrolysis. The aluminized ACP wear rates calculated by the linear extrapolation of data obtained during 150 days workout were 4.0 and 5.4 cm/year for the ACP with the aluminide coating and without it, respectively. The current load on the ACP remained almost the same for the aluminized and original uncoated samples with the exception of the initial “heating” period (400-600°C).