Papers by Keyword: Cyclic Oxidation

Abstract: The addition effect of Mn alloying element on the oxide growth behavior of 800H nickel-based alloy has been study in this paper. The alloy was experienced a cyclic oxidation at 900 °C. The cyclic oxidation test was carried out at oxidizing temperature for one hour followed by cooling at about 200 °C for 20 minutes for each cycle. The test samples were exposed to the cyclic condition up to 150 cycles. The oxidized samples of selected cycles were characterized in term of oxidation kinetic, phase analysis using x-ray diffraction (XRD) spectrometer and oxide scale morphology in plan and cross-sectional view by using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. As a results, the oxidation kinetic exhibited a weight gain pattern as the exposure cycle increase. Several protective oxide phases which are Cr₂O₃ and MnCr₂O₄ oxides were formed. In addition, continuous oxides scale was formed on the sample surface with evidence of Cr-Mn and Cr-rich oxide as detected by EDX analysis.

Abstract: In the present study, outcome of various grain size of heat treated Fe-33Ni-19Cr Ni-based superalloy at high temperature cyclic oxidation condition was investigated. The Fe-33Ni-19Cr Ni-based superalloy was experienced a series of heat treatment process at two assorted temperatures, which are 1000 °C and 1100 °C, soaking for 3 hours and then rapid cooled by water quench. The heat treatment process produced a fine and coarse grain size structure. The cyclic oxidation test was performed for both heat treated samples at 700 °C under cyclic conditions in the laboratory air for 150 cycles. The weight change was measured discontinuously at different cycles to identify the kinetics of oxidation. SEM and FESEM outfitted with EDX spectrometer were utilized to analyzed the oxidation product. As a result, the weight change increased with time, with fine grain HT1000 sample recorded lower weight gain compared to coarse grain HT1100 sample. In addition, both sample formed uniform and continuous oxide scale on the alloy surface.

Abstract: Nowadays commonly used thermal barrier coatings (TBC) are based on yttria stabilized zirconia (YSZ). Addition of mullite phase into the YSZ coating can improve resulting high temperature properties. The contribution focuses on high temperature cyclic oxidation behaviour of two TBC systems with different top coats (TC) deposited by the means of atmospheric plasma spraying. The initial mullite-YSZ powder mixture consisted of 29 vol. % of mullite and 71 vol. % of YSZ. The conventional TBC system consisted of ~ 150 µm thick NiCoCrAlYHfSi bond coat (BC) and ~ 300 µm thick YSZ top coat. The experimental mullite-YSZ (MYSZ) TBC system consisted of ~ 150 µm thick NiCoCrAlYHfSi bond coat, ~ 100 µm thick YSZ interlayer and ~ 200 µm thick mullite-YSZ top coat. The experimental TBC proved higher lifetime, durability and phase stability and also lower grow rate of thermally grown oxide (TGO) compared to conventional TBC. Lifetime, phase stability and changes in the microstructure of TBCs after the furnace cyclic oxidation test were evaluated by the means of scanning electron microscopy equipped with EDX analyzer and X-ray diffraction techniques. Oxidation kinetics of TGO was calculated based on thickness determined utilizing digital image analysis.

Abstract: Three kinds of high-strength steel plates containing (less than 0.07%, or 0.024%, or 0.057%)-Si were oxidized at 700-900 °C isothermally and cyclically in atmospheric air, and their oxidation behavior was compared. The composition of the steels significantly affected the scaling rates, thickness, and adherence of the formed scales. The most important element in terms of oxidation was Si because Si affected the oxidation rates and scale adherence much. Silicon formed quite slowly a growing SiO₂–containing scale around the scale/matrix interface. In the Si-deficient steel, quite thick oxide scales formed, and their adherence was poor. An optimum amount of Si was necessary in order to decrease the oxidation rate, and improve the scale adherence.

Abstract: The effect of rare earth element yttrium on cyclic oxidation behavior of Co-10Cr-10Al alloys in ambient atmosphere of 1 atm at 1073K was investigated. The results indicated that the addition of 0.05 at.% Y in the alloy enhanced the formation of protective oxide scales with compact smooth surface, and improved cyclic oxidation resistance of the alloy. On the contrary, the addition of 0.1-0.3 at.%Y greatly increased the oxidation rate of the alloy, with formation of a rapidly growing Co oxides layer with the porous and rough surface appearance.

Abstract: In this study, an electrodeposited alumina-forming Ni-Al composite having a nanocrystalline Ni matrix dispersing Al microparticles was produced and annealed in vacuum at 500°C for different time (3hr, 5hr and 8hr, respectively). Effect of annealing time on the microstructure, isothermal and cyclic oxidation behavior of the Ni-Al composite at 1000°C was comparably investigated. The results indicated that Al microparticles slowly dissolved into nickel grain to form an ultrafine-grained Ni₃Al/NiAl composite with micro-sized pores dispersion due to volume shrinkage. The increased distribution uniformity of Al with the increasing of annealing time favors the formation of a protective alumina layer in a short time, and then significantly reduced the isothermal oxidation rate. Besides, the reduction of pores size with the increasing of annealing time also helps the ultrafine-grained Ni₃Al/NiAl composite to grow an adherent alumina scale with increased cyclic oxidation resistance.

Abstract: The cyclic oxidation behavior of Co-10Cr-5Al alloys with and without 0.3 at% Y doped in atmosphere at 800 ^oC was investigated. The addition of 0.3 at.% Y increased the oxidation rate of the alloy and changed the oxidation mechanism. The scales grown the alloys with and without Y were both composed of an outer Co₂O₃ layer and an inner complex layer of Al₂O₃, Co₂O₃ and Cr₂O₃, except that the addition of 0.3 at% Y enhanced the adhesion of the scale. 0.3 at% Y agglomerated in local zone which accelerated the oxidation rate and was not conductive to the oxidation process of the Co-10Cr-5Al alloy.

Abstract: The oxidation behaviour of niobium and titanium enriched, heat resistant cast steel 30Ni-18Cr has been evaluated under cyclic conditions. Cyclic testing was carried out in the air, at temperature of 800, 900 and 1000°C. The alloys underwent oxidation in 5 cycle tests. Characterization of the corrosion products was performed using SEM and X-ray examinations. The cross section and the surface of tested alloys were examined. It has been found that the oxidation resistance of cast steel 30Ni-18Cr in thermal cycling is higher when niobium or especially titanium are added to chemical composition of the alloy. The formation of scale rich in titanium oxides TiO₂ was contributed to better oxidation behaviour.

Abstract: The cyclic oxidation behavior of Co-10Cr-5Al alloys in atmosphere at 700 °C was investigated. The addition of 0.3 at.% Y changed the oxidation behavior from the approximate parabolic rate law to complex mode. The scale grown on the surface of Co-10Cr-5Al cracked seriously, while the oxide scale the Y doped alloy had better adhesive property. Yttrium doped in the sample promoted the forming of continuous Al₂O₃ layer and decreased the oxidation rate of Co-10Cr-5Al alloys.

Abstract: The cyclic oxidation behavior of Co-10Cr-5Si alloys with and without Y in atmosphere at 700 °C was investigated. The addition of 0.3 at.% Y decreased the average parabolic rate constant from 4.39×10^-10 g²cm^-2s^-1 to 3.42×10^-10 g²cm^-2s^-1. The surface components with and without Y were both composed of an outer CoO and inner protective SiO₂. There were more SiO₂ formed when Y doped into the alloy. The addition of 0.3 at.% Y improved the cyclic oxidation resistance of the Co-10Cr-5Al alloy.