Papers by Keyword: Oxidation Behavior

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Authors: Tsuyoshi Aoki, Hidenori Hatta, Koji Goto, H. Fukuda
Authors: Rabindra Mahapatra, M. Ashraf Imam, C.S. Lei, C.R. Feng
Abstract: The isothermal oxidation behavior and thermal stability of a cobalt base alloy was investigated up to a period of 312 hr in air from 1000 to 1200°C. A comparison of oxidation behavior of this alloy with a conventional nickel-base superalloy (Inconel 713C) has been conducted in detail. This experimental alloy oxidizes by forming layers of Al2O3, Cr2O3, TiO2, CoO and traces of SiO2 with WO2 oxides on the surface of the specimen in contact with air. Scanning electron microscopy (SEM) was used to study the microstructure, morphology and compositions of oxides formed after the exposure. Thermal stability of the alloy after extended periods of exposures to air at 1000, 1100 and 1200°C was studied using transmission electron microscopy (TEM).
Authors: Hong Hua Zhang, Jun Huai Xiang, Xian Chao Xu, Chu Wang
Abstract: Kinetics and products of oxidation behavior of binary Co-10Al, Co-10Si and Co-10Cr alloys at 0.1Mpa oxygen at 973 and 1073K were analyzed and compared. The investigations show that CoO doesn't provide protective properties at high temperatures. Among the three alloy components, Co-10Cr has better oxidation resistance at 973K, while Co-10Al has at 1073K, and the causes are given. In addition, the schematic model of scale growth process is presented.
Authors: Alexander Donchev, Michael Schütze
Authors: P. Pérez, J. Ruiz-Chica, G. Garcés, P. Adeva
Authors: Jin Xia Song, Ya Fang Han, Cheng Bo Xiao
Abstract: The effect of ion implantation of yttrium on the oxidation behavior of Ni3Al base alloy IC6 at 1100°C was investigated by SEM/EDS, TEM and XRD methods. The results indicated that after Y ion implantation, the surface of IC6 alloy changed from large column crystals to fine distributed nano-crystals, and the density of dislocations in distorted region increased with the implanted ions dose, which can act as high-diffusivity path and oxide core. Comparing to un-implanted IC6 alloy, Y-implantation increased the oxidation rate of IC6 alloy in initial 25 h at 1100°C, but decreased the maximum weight gain and the oxidation rate in final period. Moreover, the oxide scales of Y-implanted IC6 alloy were more continuous and compact due to the benefit effect of yttrium, and had better coherence to substrate through reduction of oxide grain size resulting in oxide scale plasticity improvement. Hence the proper amount of implanted Y could improve the oxidation resistance of IC6 alloy at 1100°C in air slightly.
Authors: Shu Qi Guo
Abstract: In this study, oxidation behavior of ZrB2-MoSi2-SiC composite was investigated in the hot-pressed 5-20 vol% SiC-containing ZrB2-20 vol% MoSi2-based composites which were exposed to dry air between 1100°C and 1500°C up to 10 hours. The effects of SiC additive on the oxidation behavior were assessed. Experimental results showed that the weight gain due to oxidation exposure in air increased with increasing exposure temperature and exposure time. Parabolic oxidation behavior was observed for all the compositions composites. On the other hand, the weight gain decreased with increasing amount of SiC added. The addition of SiC improved the oxidation resistance of the composites, and the improvement was enhanced with increasing amount of SiC added. In addition, X-ray diffraction was used to identify major crystalline phases present in both the as-received and the post-oxidized composites. The oxidized sample surface was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The microstructure of the post-oxidized composites consisted of two characteristic regions: oxidized reactive region and unreactive bulk material region. Furthermore, the oxidized reactive region divided into an outermost dense silica-rich scale layer and oxidized reactive mixture layer. The improvement of the oxidation resistance due to the addition of SiC is associated with the presence of the thicker dense outermost scale layer which inhibited inward diffusion of oxygen through it.
Authors: F. Pedraza, Jean Luc Grosseau-Poussard, J.F. Dinhut, J. Balmain, G. Bonnet
Abstract: Nitriding by low energy high flux processing has been carried out at about 400°C in fcc metal substrates (pure Ni, Ni-20Cr model alloy and a conventional AISI 304L stainless steel). The gradual ingress of this element into the structures will be shown to depend markedly on the chemical composition of the substrate. The associated expansion of the fcc lattices and surface roughness will be discussed in this work with the support of X-ray diffraction, atomic force, scanning and transmission electron microscopy techniques. In light of the resulting composition, microstructures and thickness of nitrided layers, some preliminary results of their behaviour under isothermal oxidation conditions at high temperatures will be discussed. The high temperatures will provoke decomposition of the expanded austenite into a conventional gamma phase and some chromium nitrides. Trapping of chromium therefore shall explain a reduction of the high temperature oxidation resistance against the untreated substrates.
Authors: Xiao Fei Ding, Yi Tan, Yong Shen, Fu Gang Wang, Jenn Ming Yang
Abstract: Three types of Ti-Al-Nb ternary alloys are obtained by arc-melting and heat treatment, which are γ-TiAl single phase alloy, γ-TiAl + α2-Ti3Al duplex phase alloy, and γ-TiAl +α2-Ti3Al +Nb2Al multiple phase alloy. The phase stability is studied using optical microscope, X-ray diffractometer and electron probe microanalyzer. The oxidation behavior of three Ti-Al-Nb ternary alloys with different microstructures was investigated at 1273K using interrupted oxidation test in air. The compression test was carried out at 298K-1373K. The oxidation resistance of Ti-Al-Nb ternary alloy at high temperature was found to be better than that of the binary Ti-Al alloy. Among the three Ti-Al-Nb ternary alloys, the two-phase alloy with γ+α2 has the best oxidation resistance and mechanical properties. The existence of α2 could enhance the oxidation resistance of the alloy at high temperature. On the contrary, the presence of Nb-enriched phase such as Nb2Al would decrease the oxidation resistance at elevated temperature due to the formation of Nb2O5, which would accelerate the exfoliation of oxide.
Authors: Kyeong Hwan Choe, Sang Mok Lee, Kyong Whoan Lee
Abstract: High temperature oxidation behavior of Si-Mo ferritic ductile cast iron was investigated in the point of the effect of chromium and vanadium addition. The addition of Cr promoted the formation of as-cast pearlite around carbide which exists in cell boundary, which was eliminated during annealing process. The addition of vanadium promoted the precipitation of tiny carbide and reduced the grain size of ferrite. As the test temperature increased, the change of volume increased, on the other hand, the change of weight decreased above 1173K. In the case of Cr added specimen, the change of weight decreased with the increase of test temperature because of the presence of Cr oxide layer. The vanadium added specimens showed higher increase in the weight and volume change. The oxide layer of vanadium added specimen had very porous structure and showed severe internal oxidation. It is due to the catastrophic oxidation characteristic of vanadium alloyed ferrous alloy.
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