Статті в журналах: "Grain boundary oxidation"

1

Philibert, Jean. "Grain Boundary Diffusion and Oxidation Processes." Defect and Diffusion Forum 156 (February 1998): 1–8. http://dx.doi.org/10.4028/www.scientific.net/ddf.156.1.

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2

Philibert, J. "Grain boundary diffusion and oxidation processes." Solid State Ionics 117, no. 1-2 (February 1, 1999): 7–11. http://dx.doi.org/10.1016/s0167-2738(98)00242-2.

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3

Liu, Ya, Sai Liu, Xuping Su, Haoping Peng, Jianhua Wang, and Hao Tu. "Calculation of Selective Oxidation in Grain and Grain Boundary." Journal of Phase Equilibria and Diffusion 34, no. 2 (January 12, 2013): 82–88. http://dx.doi.org/10.1007/s11669-012-0184-z.

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4

Krupp, Ulrich, V. B. Trindade, Peter Schmidt, Hans Jürgen Christ, U. Buschmann, and W. Wiechert. "The Effect of Grain-Boundary Diffusion on the Oxidation of Low-Chromium Steels." Defect and Diffusion Forum 237-240 (April 2005): 946–51. http://dx.doi.org/10.4028/www.scientific.net/ddf.237-240.946.

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Even though the oxidation behavior of steels is generally considered as to be widely understood, a closer look reveals some open questions, e.g. regarding the influence of the substrate grain size on the overall oxidation kinetics. At temperatures below 570°C the main constituent of the oxide scale formed on top of low alloy steels is magnetite. As shown by gold marker experiments it grows outward and inward at the same time, the latter exhibiting a gradual transition to the more stable spinel compound FeCr2O4. As indicated by intergranular-oxidation attack below the superficial scale, inward oxide growth seems to be driven by oxygen transport along the grain boundaries serving as fast diffusion paths. This is supported by thermogravimetric oxidation tests in air on low-Cr steels with varying grain size: The smaller the grains the higher the oxidation rate. Recently, a numerical model for the diffusive transport processes based on the finite-difference approach has been developed, which distinguishes between fast grain-boundary diffusion and bulk diffusion. Qualitatively, it is capable to predict the relationship between substrate grain size and inward oxide growth kinetics. Together with the thermodynamic tool ChemApp and in combination with a data set for the Fe-Cr-O system the mechanism-based simulation of the overall oxidation process of low-Cr steels is possible.

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5

Park, Kee Hyun, and Paul Withey. "Formation of Secondary Phases in the Boundary between Surface Defect Grains and Matrix in Third Generation Nickel-Based Single Crystal Superalloy Turbine Blades." Materials Science Forum 941 (December 2018): 766–71. http://dx.doi.org/10.4028/www.scientific.net/msf.941.766.

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Ni-based single crystal superalloy turbine blades have excellent mechanical strength and resistance to corrosion and oxidation due to a uniformly distributed gamma prime phase in a gamma matrix. However, defect grains have been often found on the surface of turbine blades after manufacturing, which can be potential sites of crack initiation. In this study, several different types of surface defect grains formed in third generation Ni-based single crystal turbine blades, such as stray grains, freckle chain grains, equiax grains, and a new grain formed in surface scale, had been investigated. The grain boundary regions were observed by high resolution electron microscopy. Although the formation mechanism of each grain defect is different, secondary phases, such as rhenium-rich particles, have been always found in each grain boundary. In addition, depending on the existence of the secondary phases as well as the size of defect grains, different microstructures were observed even in the same defect grain boundary. Finally, the observed results suggest that if there is any boundary region in a turbine blade, secondary phases, such as Re-rich particles, can be found.

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6

Yang, Y., Tomonrori Kitashima, T. Hara, Y. Hara, Yoko Yamabe-Mitarai, M. Hagiwara, and L. J. Liu. "Effect of Grain Size on Oxidation Resistance of Unalloyed Titanium." Materials Science Forum 879 (November 2016): 2187–91. http://dx.doi.org/10.4028/www.scientific.net/msf.879.2187.

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The effect of the grain size on the high-temperature oxidation resistance of unalloyed titanium was experimentally investigated using titanium samples with two different grain sizes of 219 μm and 118 μm. The weight gain during oxidation and the penetration depth of oxygen from a metal surface were larger in the small-grain-size sample compared with the large-grain-size sample. In addition, oxygen diffusion was faster in the substrate of the small-grain-size sample. These results were attributed to the grain-boundary diffusion of oxygen. A steep change in the oxygen concentration was observed at a grain boundary. Our simulation results suggested that slower oxygen diffusion into the inner grain from the surface through the grain boundary with high diffusivity can cause the observed steep change in the oxygen concentration.

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7

Alles, Aldo B., and Vernon L. Burdick. "Grain Boundary Oxidation in PTCR Barium Titanate Thermistors." Journal of the American Ceramic Society 76, no. 2 (February 1993): 401–8. http://dx.doi.org/10.1111/j.1151-2916.1993.tb03798.x.

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8

Kang, Jaewoon, and Hongsik Park. "Evaluation Method for Graphene Grain Boundary by UV/ozone-oxidation Chemical-etching Process." Journal of Sensor Science and Technology 25, no. 4 (July 31, 2016): 275–79. http://dx.doi.org/10.5369/jsst.2016.25.4.275.

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9

Fujikawa, Hisao. "Review of Several Studies on High Temperature Oxidation Behaviour and Mechanism of Austenitic Stainless Steels." Defect and Diffusion Forum 312-315 (April 2011): 1097–105. http://dx.doi.org/10.4028/www.scientific.net/ddf.312-315.1097.

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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.

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10

Li, Lv, Xiaojuan Gong, Xianjue Ye, Jianwei Teng, Yan Nie, Yunping Li, and Qian Lei. "Influence of Building Direction on the Oxidation Behavior of Inconel 718 Alloy Fabricated by Additive Manufacture of Electron Beam Melting." Materials 11, no. 12 (December 14, 2018): 2549. http://dx.doi.org/10.3390/ma11122549.

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This research was aimed at investigating the high temperature oxidation behavior of Inconel 718 superalloy fabricated by electron beam melting with the building direction of 0°, 55° and 90° deviation from the Z axis of cylindrical samples. Columnar γ-fcc phase with preferred crystal orientations was found in all specimens. With the temperature ranging from 700 to 1000 °C, the 0° sample, symbolized by the lowest grain boundary density, and largest grain size, reveals the best oxidation performance. It is concluded that the building direction has more impact on the amount of grain boundary density than crystal orientation, which determined the oxidation resistance.

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11

Parimin, Noraziana, and Esah Hamzah. "Oxidation Kinetics of Fe-Ni-Cr Alloy at 900 °C." Materials Science Forum 1010 (September 2020): 58–64. http://dx.doi.org/10.4028/www.scientific.net/msf.1010.58.

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The study of isothermal oxidation of Fe-Ni-Cr alloy was done at 900 °C for 500 hours. The effect of oxidation kinetics and oxide growth behavior on Fe-Ni-Cr alloy were investigated on heat-treated Fe-Ni-Cr alloy to understand the oxidation mechanism on different grain size of alloy. The grain size of Fe-Ni-Cr alloy was varying through heat treatment process at three different temperatures, namely 1000 °C, 1100 °C and 1200 °C for 3 hours soaking time followed by water quench. The heat-treated Fe-Ni-Cr alloy was experienced discontinuous isothermal oxidation test at 900 °C up to 500 hours exposure. The oxidation kinetics plot was calculated based on the weight change per surface area over time. The oxide surface morphology was characterized by using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. The heat treatment process recorded an increasing grain size alloy as the heat treatment temperature increase. 8H10 sample indicate the fine grain size, whereas 8H12 sample indicate the coarse grain size. The oxidation kinetics of all samples exhibit the weight gain pattern with fine grain 8H10 sample recorded the lowest weight gain compared to 8H11 and 8H12 samples. All samples were obeyed parabolic rate law indicating the oxide growth rate followed a diffusion-controlled mechanism. The oxide surface morphology of 8H10 sample displayed a continuous oxide scales with formation of grain boundary oxide along the grain boundary area. Similar oxide structure formed on 8H11 and 8H12 samples, except for the formation of crack on the grain boundary oxide on both samples. In addition, 8H12 sample also formed a porous oxide structure.

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12

Rösler, J., and S. Müller. "Protection of Ni-base superalloys against stress accelerated grain boundary oxidation (SAGBO) by grain boundary chemistry modification." Scripta Materialia 40, no. 2 (December 1998): 257–63. http://dx.doi.org/10.1016/s1359-6462(98)00375-3.

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13

Tsurekawa, Sadahiro, Tadao Watanabe, and N. Tamari. "Grain Boundary Engineering for the Control of Mechanical Properties and Oxidation-Induced Embrittlement in Silicon Carbides." Key Engineering Materials 261-263 (April 2004): 999–1004. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.999.

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Grain boundary engineering (GBE) is rapidly emerging recently as a powerful tool for achieving enhanced properties and performance in polycrystalline metallic materials. The objective of this work is to confirm the potential of GBE for enhancement in properties and performance in ceramic materials such as silicon carbide (SiC). Grain boundary microstructure in SiC could be tailored by doping with different elements (Mg, Al and P) and modifying sintering processing (hot-pressing and spark plasma sintering). FEG-SEM/OIM analyses revealed that both Al doping and SPS increased the frequency of low-energy special boundaries (Σ ≤29 ) and Mg doping enhanced grain growth. It was found that mechanical properties like microhardness depended on the grain boundary character distribution (GBCD) and the grain size. The increment in the frequency of special boundaries could yield increases in the Vickers-microhardness and the fracture stress. Furthermore, intergranular oxidation-induced brittleness in SiC was noticeably improved by increase in the frequency of special boundaries and decrease in the grain size. Thus, we have confirmed that the control of grain boundary microstructure such as grain size, GBCD and grain boundary connectivity is a key for enhancement in bulk properties and performance in ceramic materials.

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14

Brückner, W., W. Pitschke, S. Baunack, and J. Thomas. "Mechanical Stress, Grain-boundary Relaxation, and Oxidation of Sputtered CuNi(Mn) Films." Journal of Materials Research 14, no. 4 (April 1999): 1286–94. http://dx.doi.org/10.1557/jmr.1999.0175.

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This paper focuses on understanding stress development in CuNi42Mn1 thin films during annealing in Ar. In addition to stress-temperature measurements, resistance-temperature investigations and chemical and microstructural characterization by Auger electron spectroscopy, scanning and transmission electron microscopy, x-ray diffraction, and atomic force microscopy were also carried out. The films are polycrystalline with a grain size of 20 nm up to 450 °C. To explain the stress evolution above 120 °C, atomic rearrangement (excess-vacancy annihilation, grain-boundary relaxation, and shrinkage of grain-boundary voids) and oxidation were considered. Grain-boundary relaxation was found to be the dominating process up to 250–300 °C. A sharp transition from compressive to tensile stress between 300 and 380 °C is explained by the formation of a NiO surface layer due to reaction with the remaining oxygen in the Ar atmosphere. This oxidation is masking the inherent structural relaxation above 300 °C.

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15

Tan, L., Kumar Sridharan, and T. R. Allen. "Altering Corrosion Response via Grain Boundary Engineering." Materials Science Forum 595-598 (September 2008): 409–18. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.409.

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Grain boundary engineering (GBE) was employed to improve the oxide exfoliation resistance and mitigate oxide growth by optimizing the grain boundary character distribution. Studies were performed on alloys of Incoloy 800H and Inconel 617. Alloys 800H and 617 were selected due to their potential applications for the Generation IV nuclear power systems. The effect of GBE on the corrosion response was evaluated using supercritical water exposure tests and cyclic oxidation tests. The microstructure of the tested samples was analyzed by means of optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction, and gravimetry. The effects of thermal expansion mismatch and Cr volatilization on the corrosion response are discussed.

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16

Katsman, A., Hans Jürgen Grabke, L. Levin, and T. Werber. "Grain Boundary Void Formation during Oxidation of Alloys and Intermetallics." Materials Science Forum 207-209 (February 1996): 737–40. http://dx.doi.org/10.4028/www.scientific.net/msf.207-209.737.

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17

ZDANIEWSKI, WIESLAW A., and HENRY P. KIRCHNER. "Effect of Grain-Boundary Oxidation on Fracture Toughness of SiC." Journal of the American Ceramic Society 70, no. 8 (August 1987): 548–52. http://dx.doi.org/10.1111/j.1151-2916.1987.tb05703.x.

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18

Liu, H. W., and Y. Oshida. "Grain boundary oxidation and fatigue crack growth at elevated temperatures." Theoretical and Applied Fracture Mechanics 6, no. 2 (October 1986): 85–94. http://dx.doi.org/10.1016/0167-8442(86)90028-5.

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19

Park, Sang Hwan, Seon Ok Kim, Hoon Sang Oh, Sung Hoon Choa, and Taek Dong Lee. "Grain size reduction of CoCrPt-SiO2media by oxidation of RuCr intermediate layer grain boundary." physica status solidi (c) 4, no. 12 (December 2007): 4516–19. http://dx.doi.org/10.1002/pssc.200777147.

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20

Ide, Shinsuke, Yoshimasa Funakawa, Yasushi Kato, and Osamu Furukimi. "Retardation of 20%Cr Steel Oxidation with Laves Phase Precipitation." Materials Science Forum 539-543 (March 2007): 4887–90. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4887.

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A new method to improve oxidation resistance of ferritic stainless steel was studied. Increase in oxidation resistance of ferritic stainless steel with laves phase precipitation was succeeded in addition to the conventional method such as addition of rare-earth element. Ultra low carbon 20%Cr steels with various niobium content continuously oxidized at 1073-1173K in air. A mass gain with exposure at 1073K decreased with increasing niobium content and saturated more than 0.1% in niobium content. In steels contained niobium less than 0.1%, mass gain were also decreased with increase in initial ferritic grain diameter. In steels contained niobium more than 0.1%, laves phase was observed at the ferritic grain boundary by using transmission electron microscope. But then a mass gain with exposure at 1173K did not decreased with niobium content and laves phase was not observed. On the assumption that oxidation behaviors of steels contained niobium more than 0.1% obey the parabolic law, the parabolic rate constant obtained at 1173K is similar to that controlled by grain boundary diffusion, and parabolic rate constant obtained at 1073K is similar to that controlled by lattice diffusion. These results suggest that precipitation of laves phase retard growth of oxide film effectively with suppressing grain boundary diffusion of cation forming oxide film.

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21

Zhou, X. D., W. Huebner, and H. U. Anderson. "Size Effect on the Electronic Properties of Doped and Undoped Ceria." Defect and Diffusion Forum 242-244 (September 2005): 277–0. http://dx.doi.org/10.4028/www.scientific.net/ddf.242-244.277.

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The roles of grain size and chemical composition on the electronic conductivity (σ) of CeO2 are reported. In undoped high purity (99.995%) CeO2, σ increases with decreasing grain size, indicating generation of low oxidation state Ce species, Ce3+ ions, which act as the electrons. In low purity undoped CeO2, the chemical impurities act as both the acceptor dopants, as well as the components (such as Si) to form amorphous phase in the grain boundaries. In low purity (99.5%) undoped CeO2, size effects are, therefore, influenced by the presence of acceptor dopants and/or blocking grain boundary phases. In low purity undoped CeO2, the grain boundary contribution to the overall resistance decreases with increasing grain size due to dilution effects of the amorphous grain boundary phases. The intentional addition of acceptors (10%) will pin oxygen vacancies over a wide range of oxygen activity. Size effects in acceptor doped CeO2 are mainly related to the presence of grain boundary phases. In Ce0.90Gd0.10O1.95, the grain boundary contribution to total resistance increases with decreasing size, which is due to trapping of oxygen ions.

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22

Unutulmazsoy, Y., R. Merkle, D. Fischer, J. Mannhart, and J. Maier. "The oxidation kinetics of thin nickel films between 250 and 500 °C." Physical Chemistry Chemical Physics 19, no. 13 (2017): 9045–52. http://dx.doi.org/10.1039/c7cp00476a.

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23

Jepson, M. A. E., C. L. Verona, and R. L. Higginson. "Oxide Scales Grown on Stainless Steels during Simulated Reheat." Advanced Materials Research 15-17 (February 2006): 792–97. http://dx.doi.org/10.4028/www.scientific.net/amr.15-17.792.

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including, external oxide layers, internal grain boundary oxidation structures as well as many other forms of internal oxidation. During the present study, needle like grains of hematite have been observed within the top layers of a number of external oxide scales formed during simulated reheat of 316L stainless steel. It is believed that these needles are caused by the decomposition of an iron rich spinel (approximated to magnetite) along a preferred crystal direction within the spinel grains. The needles have been studied using optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD).

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24

Jia, Lichao, Peter Bogdanoff, Alejandra Ramírez, Ulrike Bloeck, Diana Stellmach, and Sebastian Fiechter. "Fe2O3Porous Film with Single Grain Layer for Photoelectrochemical Water Oxidation: Reducing of Grain Boundary Effect." Advanced Materials Interfaces 3, no. 1 (October 29, 2015): 1500434. http://dx.doi.org/10.1002/admi.201500434.

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25

Gu, H. "Quantitative Characterization of Grain Boundary Films In Si3n4 by Eels and Z-Contrast Imaging." Microscopy and Microanalysis 3, S2 (August 1997): 661–62. http://dx.doi.org/10.1017/s1431927600010199.

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High temperature mechanical properties of structural ceramics Si3N4 are controlled by ∼1 nm thick silicate amorphous films covering all grain boundaries. The composition of the film dictates the equilibrium film thickness resulted from a force balance at grain boundary. Many efforts arc brought to alter film chemistry and thickness, and this system offers ideal model materials to understand grain boundary and property relationship. Using a dedicated STEM (VG HB601) with high spatial resolution EELS analysis and high resolution Z-contrast imaging, various novel quantification data of the grain boundary in Si3N4 can be obtained. The methods described here can also be applied to other types of grain boundaries.EELS profiling was performed to acquire a full spectrum from each position at a lateral increment of 1Å across a boundary in a pure Si3N4 sample with only SiO2 impurities from surface oxidation. It gives directly elemental distributions near the boundary such as Si, N and O profiles shown in Fig. 1.

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26

Kruska, Karen, Sergio Lozano-Perez, David W. Saxey, Takumi Terachi, Takuyo Yamada, and George D. W. Smith. "Nanoscale characterisation of grain boundary oxidation in cold-worked stainless steels." Corrosion Science 63 (October 2012): 225–33. http://dx.doi.org/10.1016/j.corsci.2012.06.030.

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27

Evans, H. E., H. Y. Li, and P. Bowen. "A mechanism for stress-aided grain boundary oxidation ahead of cracks." Scripta Materialia 69, no. 2 (July 2013): 179–82. http://dx.doi.org/10.1016/j.scriptamat.2013.03.026.

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28

Zhdanov, Vladimir P. "Simulations of oxidation of metal nanoparticles with a grain boundary inside." Reaction Kinetics, Mechanisms and Catalysis 130, no. 2 (July 12, 2020): 685–97. http://dx.doi.org/10.1007/s11144-020-01818-4.

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29

Thomas, L. E., and R. E. Einziger. "Grain boundary oxidation of pressurized-water reactor spent fuel in air." Materials Characterization 28, no. 2 (March 1992): 149–56. http://dx.doi.org/10.1016/1044-5803(92)90038-j.

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30

Faria, Geraldo, Rogério Cardoso, and Paulo Moreira. "Development of an Oxidation Method for Prior Austenite Grain Boundary Revelation." Metallography, Microstructure, and Analysis 7, no. 5 (August 20, 2018): 533–41. http://dx.doi.org/10.1007/s13632-018-0470-1.

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31

Alpe´rine, S., and L. Lelait. "Microstructural Investigations of Plasma-Sprayed Yttria Partially Stabilized Zirconia TBC (In Relation to Thermomechanical Resistance and High-Temperature Oxidation Mechanisms)." Journal of Engineering for Gas Turbines and Power 116, no. 1 (January 1, 1994): 258–65. http://dx.doi.org/10.1115/1.2906802.

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This study deals with microstructural investigations of plasma-sprayed yttria partially stabilized zirconia thermal barrier coatings, performed by classical and analytical transmission electron microscopy. The aim of the study was to determine eventual relationships between coating microstructure and toughness. The ceramic/metal interface, which plays an important role during TBC thermomechanical solicitation, has also been studied. In the 6–8 wt. percent Y2O3 range, the metastable tetragonal t′ phase is observed, showing special faulted microstructural features, such as grain twinning and antiphase boundary planes. Moreover, after high-temperature annealing in air, a very fine and stable precipitation of the equilibrium cubic phase appears. It is believed that these microstructural elements could act as crack deviation sites and enhance the coatings’ intrinsic toughness. Microstructural investigations of the alumina scales grown during high-temperature annealing reveal yttrium segregation at oxide grain boundaries as well as significant quantities of zirconium inside the alumina grains. The oxide growth seems to be dominated by a classical grain boundary oxygen diffusion mechanism. The presence of zirconium inside the alumina grains suggests that Al2O3 also partially forms by chemical reduction of ZrO2 by Al.

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32

Rajasekaran, S., N. K. Udayashankar, and Jagannath Nayak. "The Effect of Aging and the Protective Coating on the Oxidation Behavior of 6061Al/SiC Composite at High Temperatures." Key Engineering Materials 462-463 (January 2011): 30–35. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.30.

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This paper analyses the effect of ageing on the oxidation behavior of 6061Al/SiC composite material at temperatures ranging from 500 to 800 K. Also aluminum coating is employed as protective coating in order to improve the oxidation resistance of the composite. SEM, EDAX, XRD and stepped oxidation measurement techniques are used to study the oxidation behavior and to characterize the composite specimens. Oxidation of the composite material without protective coatings is seen to be very rapid during the initial stages of exposure to the high temperatures but subsequently slowed down due to the formation of a protective surface layer of oxide. Among the artificially aged composites, peak aged specimens are more prone to oxidation. The oxidation was especially severe above 600 K. The interface between the matrix and reinforcement particles and the grain boundary regions of the matrix enhance this oxidation process since they provided sites for oxidation initiation. Aluminum coating on the composite obtained by DC magnetron sputtering technique, reduce the oxidation rate effectively since the interface regions between the matrix and reinforcement, grain boundary regions of the matrix are unexposed to the atmosphere. Aluminum coating provides better oxidation resistance for the artificially aged composites.

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33

Luo, Jinsong, Ligong Zhang, Haigui Yang, Nan Zhang, Yongfu Zhu, Xingyuan Liu, and Qing Jiang. "Oxidation kinetics of nanocrystalline Al thin films." Anti-Corrosion Methods and Materials 66, no. 5 (September 2, 2019): 638–43. http://dx.doi.org/10.1108/acmm-11-2018-2037.

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Purpose This paper aims to study the oxidation kinetics of the nanocrystalline Al ultrathin films. The influence of structure and composition evolution during thermal oxidation will be observed. The reason for the change in the oxidation activation energy on increasing the oxidation temperature will be discussed. Design/methodology/approach Al thin films are deposited on the silicon wafers as substrates by vacuumed thermal evaporation under the base pressure of 2 × 10−4 Pa, where the substrates are not heated. A crystalline quartz sensor is used to monitor the film thickness. The film thickness varies in the range from 30 to 100 nm. To keep the silicon substrate from oxidation during thermal oxidation of the Al film, a 50-nm gold film was deposited on the back side of silicon substrate. Isothermal oxidation studies of the Al film were carried out in air to assess the oxidation kinetics at 400-600°C. Findings The activation energy is positive and low for the low temperature oxidation, but it becomes apparently negative at higher temperatures. The oxide grains are nano-sized, and γ-Al2O3 crystals are formed at above 500°C. In light of the model by Davies, the grain boundary diffusion is believed to be the reason for the logarithmic oxidation rate rule. The negative activation energy at higher temperatures is apparent, which comes from the decline of diffusion paths due to the formation of the γ-Al2O3 crystals. Originality/value It is found that the oxidation kinetics of nanocrystalline Al thin films in air at 400-600°C follows the logarithmic law, and this logarithmic oxidation rate law is related to the grain boundary diffusion. The negative activation energies in the higher temperature range can be attributed to the formation of γ-Al2O3 crystal.

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34

Udayashankar, N. K., S. Rajasekaran, and Jagannath Nayak. "The Effect of Protective Coatings on the Oxidation Behavior of 6061Al/SiC Composite at High Temperatures." Advanced Materials Research 383-390 (November 2011): 3949–53. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.3949.

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This paper analyses the effect of protective coatings on the oxidation behavior of 6061Al/SiC composite material at temperatures ranging from 500 to 800 K. Aluminum and AlCrN coatings are employed as protective coatings in order to improve the oxidation resistance of the composite. SEM, EDAX, XRD and oxidation measurement techniques are used to study the oxidation behavior and to characterize the composite specimens. Oxidation of the composite material without protective coatings is seen to be very rapid during the initial stages of exposure to the high temperatures but subsequently slowed down due to the formation of a protective surface layer of oxide. The oxidation was especially severe above 600 K. The interface between the matrix and reinforcement particles and the grain boundary regions of intermetallic precipitates in the matrix enhance this oxidation process since they provided sites for oxidation initiation. Aluminum coating on the composite obtained by DC magnetron sputtering technique and AlCrN coating obtained by low voltage electron beam evaporation technique reduce the oxidation rate effectively since the interface regions between the matrix and reinforcement, grain boundary regions of the matrix are unexposed to the atmosphere. Aluminum coating provides better oxidation resistance for 6061 Al/SiC composites.

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35

Esa, Siti Rahmah, Ghazali Omar, Rosiyah Yahya, Noreffendy Tamaldin, Aziz Hassan, Bazura Abdul Rahim, and Wan Azli Wan Ismail. "Electron Microscopic Investigation on Nanostructure Behaviors of Thermal Oxidation Copper." Key Engineering Materials 694 (May 2016): 116–19. http://dx.doi.org/10.4028/www.scientific.net/kem.694.116.

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A copper alloy consists of 2.6% Fe, 0.15% P and 0.2% Zn with modified grain size of 500 and 750 nm were studied on their rate of diffusion at different oxidation temperature using electron microscopic imaging technique. Different oxidation temperature contributed to the variation of copper oxide particle size, surface porosity level, particle agglomeration and particle nucleation. High oxidation temperature resulted in large oxide particles formation as well as high surface porosity. The magnitude of the copper oxide growth depended on the oxidation temperature. The increase in the oxidation rate at high oxidation temperature was likely a result of faster transport of the reactants through the bulk copper due to a significant contribution from grain-boundary diffusion.

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36

Kruska, Karen, David W. Saxey, Takumi Terachi, Takuyo Yamada, Peter Chou, Olivier Calonne, Lionel Fournier, George D. W. Smith, and Sergio Lozano-Perez. "Atom-probe tomography of surface oxides and oxidized grain boundaries in alloys from nuclear reactors." MRS Proceedings 1514 (2013): 107–18. http://dx.doi.org/10.1557/opl.2013.389.

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ABSTRACTThe preparation of site-specific atom-probe tomography (APT) samples containing localized features has become possible with the use of focused ion beams (FIBs). This technique was used to achieve the analysis of surface oxides and oxidized grain boundaries in this paper. Transmission electron microscopy (TEM), providing microstructural and chemical characterization of the same features, has also been used, revealing crucial additional information.The study of grain boundary oxidation in stainless steels and nickel-based alloys is required in order to understand the mechanisms controlling stress corrosion cracking in nuclear reactors. Samples oxidized under simulated pressurized water reactor primary water conditions were used, and FIB lift-out TEM and APT specimens containing the same oxidized grain boundary were prepared and fully characterized. The results from both techniques were found fully consistent and complementary.Chromium-rich spinel oxides grew at the surface and into the bulk material, along grain boundaries. Nickel was rejected from the oxides and accumulated ahead of the oxidation front. Lithium, which was present in small quantities in the aqueous environment during oxidation, was incorporated in the oxide. All phases were accurately quantified and the effect of different experimental parameters were analysed.

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37

Schreiber, D. K., M. J. Olszta, D. W. Saxey, K. Kruska, K. L. Moore, S. Lozano-Perez, and S. M. Bruemmer. "Examinations of Oxidation and Sulfidation of Grain Boundaries in Alloy 600 Exposed to Simulated Pressurized Water Reactor Primary Water." Microscopy and Microanalysis 19, no. 3 (April 17, 2013): 676–87. http://dx.doi.org/10.1017/s1431927613000421.

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AbstractHigh-resolution characterizations of intergranular attack in alloy 600 (Ni-17Cr-9Fe) exposed to 325°C simulated pressurized water reactor primary water have been conducted using a combination of scanning electron microscopy, NanoSIMS, analytical transmission electron microscopy, and atom probe tomography. The intergranular attack exhibited a two-stage microstructure that consisted of continuous corrosion/oxidation to a depth of ~200 nm from the surface followed by discrete Cr-rich sulfides to a further depth of ~500 nm. The continuous oxidation region contained primarily nanocrystalline MO-structure oxide particles and ended at Ni-rich, Cr-depleted grain boundaries with spaced CrS precipitates. Three-dimensional characterization of the sulfidized region using site-specific atom probe tomography revealed extraordinary grain boundary composition changes, including total depletion of Cr across a several nm wide dealloyed zone as a result of grain boundary migration.

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38

Su, Yong, Shunke Zhang, Guangyan Fu, Qun Liu, and Yuanze Tang. "High-Temperature Oxidation Behavior of Fe-Si-Ce Alloys." High Temperature Materials and Processes 35, no. 2 (February 1, 2016): 177–83. http://dx.doi.org/10.1515/htmp-2014-0171.

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AbstractThe oxidation behavior of Fe-Si-Ce alloys with different Ce content at 1,173 and 1,273 K has been studied by means of optical microscope (OM), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscope (SEM). Results show that the Ce addition refines the grain size of Fe-Si alloys, and correspondingly the grain size of the oxides decreases, which increases the grain boundary concentration and promotes the short-path diffusion of the alloying elements and oxygen. During oxidation, the positive effect of the grain refinement on the oxidation behavior of the alloy is more obvious than negative effect, so the Ce addition improves the oxidation resistances of the Fe-3Si alloys. Compared to Fe-3Si-0.5Ce alloy, Fe-3Si-5.0Ce alloy has the larger mass gain for the preferential oxidation of the excessive content of Ce exceeding its beneficial effects. The rare earth Ce changes the oxidation mechanism of Fe-Si alloys. Oxygen penetrates the oxide scales and reacts preferentially with Ce-rich phases, which results in the pinning effect and improves the adhesion of the oxide scales.

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39

Strassberg, R., L. Klinger, Y. Kauffmann, and E. Rabkin. "Grain growth inhibition in thin nanocrystalline Au films by grain boundary diffusion and oxidation of Ti." Acta Materialia 61, no. 2 (January 2013): 529–39. http://dx.doi.org/10.1016/j.actamat.2012.09.076.

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40

Jones, Mark I., Kiyoshi Hirao, Hideki Hyuga та Yukihiko Yamauchi. "Effect of rare-earth species on the wear properties of α sialon and β silicon nitride ceramics under tribochemical type conditions". Journal of Materials Research 19, № 9 (вересень 2004): 2750–58. http://dx.doi.org/10.1557/jmr.2004.0357.

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The wear properties under low loads of β Si3N4 and α sialon materials sintered with different rare-earth oxide sintering additives have been studied under dry sliding conditions using block-on-ring wear tests. All the worn surfaces showed an absence of fracture and smooth surfaces with the presence of an oxygen-rich filmlike debris indicating tribochemically induced oxidation of the surfaces. Extensive grain boundary removal was observed on the worn surfaces thought to be due to adhesion between this silicate phase and the tribochemically oxidized surfaces. The resistance to such oxidation and the properties of the residual grain boundary phase are thought to be important parameters affecting the wear behavior under the present testing conditions. For both the β Si3N4 and α sialon materials, there was an increase in wear resistance with decreasing cationic radius of the rare earth, thought to be due to improved oxidation resistance, and this was more remarkable in the case of the sialon materials where the incorporation of the sintering additives into the Si3N4 structure results in a lower amount of residual boundary phase.

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41

Luo, Guo Qiang, J. Li, Dong Ming Zhang, Qiang Shen, and Lian Meng Zhang. "Densification Mechanism of SnO2 Ceramics Doped with 5.0 mol% MnO2." Key Engineering Materials 351 (October 2007): 88–92. http://dx.doi.org/10.4028/www.scientific.net/kem.351.88.

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Dense SnO2 based ceramics are widely used. In this paper, 95SnO2-5MnO2 ceramics were prepared by pressureless sintering in air at different temperatures. Phase compositions and microstructures are examined by XRD, SEM and EDX, respectively. The SEM results show that different morphologies exist at the SnO2 grain boundary of ceramic, which compose of manganese oxidation, testified by EDX. The different manganese oxides phases, found by XRD, are the source of oxygen concentration at the grain boundary during heating and oxygen dissipation when cooling. However, solid solutions of Mn, Sn and O are not observed. The density of 95SnO2-5MnO2 ceramics decreases with increasing the sintering temperature, due to the evaporation of SnO and decreasing concentration of oxygen at grain boundary in the cooling process. Densification of the ceramic is promoted with inhibiting the decomposition of SnO2 by increasing oxygen concentration in the heating process, but it is limited by the dissipation of oxygen at the grain boundary in the cooling process.

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42

Juricic, Claudia, Haroldo Pinto, Thomas Wroblewski, and Anke Pyzalla. "Dependence of Oxidation Behavior and Residual Stresses in Oxide Layers on Armco Iron Substrate Surface Condition." Materials Science Forum 524-525 (September 2006): 963–68. http://dx.doi.org/10.4028/www.scientific.net/msf.524-525.963.

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Mass gain during oxidation, texture and residual stresses in oxide layers on polycrystalline Armco iron substrates with different surface conditions are investigated using thermogravimetry microscopy and synchrotron X-rays. The mass gain during oxidation in all samples follows a parabolic law. The parabolic oxidation constant increases with increasing roughness of a mechanically ground respectively polished oxide layer. Electrolytic polishing (grain surface etching) reduces while grain boundary etching increases the parabolic oxidation constant compared to the mechanically polished sample. All oxide layers show columnar growth of the magnetite and a moderate fiber texture. The magnetite contains compressive residual stresses. Under the conditions chosen for the oxidation treatment the magnitude of these compressive residual stresses does not depend on the substrate surface condition.

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43

Li, Hua Long, Frank Czerwinski, and Jerzy A. Szpunar. "The Role of Oxide Grain Boundary Character Distribution in Nickel Oxidation Kinetics." Defect and Diffusion Forum 194-199 (April 2001): 1683–88. http://dx.doi.org/10.4028/www.scientific.net/ddf.194-199.1683.

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44

Xu, P., L. Y. Zhao, K. Sridharan, and T. R. Allen. "Oxidation behavior of grain boundary engineered alloy 690 in supercritical water environment." Journal of Nuclear Materials 422, no. 1-3 (March 2012): 143–51. http://dx.doi.org/10.1016/j.jnucmat.2011.12.022.

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45

Kogure, T., Y. Zhang, R. Levonmaa, R. Kontra, W. X. Wang, D. A. Rudman, G. J. Yurek, and J. B. Vander Sande. "Grain boundary structure of YbBa2Cu3O7−x formed by oxidation of metallic precursors." Physica C: Superconductivity 156, no. 5 (December 1988): 707–16. http://dx.doi.org/10.1016/0921-4534(88)90147-5.

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46

Ju, Jiang, Zhao Shen, Maodong Kang, Jianqiang Zhang, and Jun Wang. "On the preferential grain boundary oxidation of a Ni-Co-based superalloy." Corrosion Science 199 (May 2022): 110203. http://dx.doi.org/10.1016/j.corsci.2022.110203.

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47

Yuan, Shidan, Ye Ma, Xingyi Li, Zhen Ma, Hui Yang, and Liting Mu. "Fabrication and Microstructure of ZnO/HA Composite with In Situ Formation of Second-Phase ZnO." Materials 13, no. 18 (September 7, 2020): 3948. http://dx.doi.org/10.3390/ma13183948.

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Nanometer hydroxyapatite (n-HA) powders were synthesized by the chemical precipitation method, and a novel ZnO/HA composite, which consisted of second-phase particles with different sizes and distributions, was successfully fabricated. ZnO/HA composites were prepared by using powder sintering with different Zn contents and a prefabrication pressure of 150 MPa. Microstructure and local chemical composition were analyzed by a scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS), respectively. The phase composition and distribution of the composite were determined with electron back-scattered diffraction (EBSD) and an X-ray diffractometer (XRD), respectively. The experimental results of the XRD showed that the chemical precipitation method was a simple and efficient method to obtain high-purity n-HA powders. When the sintering temperature was lower than 1250 °C, the thermal stability of HA was not affected by the Zn in the sintering process. Due to sintering in an air atmosphere, the oxidation reaction of Zn took place in three stages, and ZnO as the second phase had two different sizes and distributions in the composites. The compressive strength of ZnO/HA composites, of which the highest was up to 332 MPa when the Zn content was 20%, was significantly improved compared with pure HA. The improvement in mechanical properties was mainly due to the distribution of fine ZnO particles among HA grains, which hindered the HA grain boundary migration and refinement of HA grains. As grain refinement increased the area of the grain boundary inside the material, both the grain boundary and second phase hindered crack development in different ways.

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Zhang, Chao, Huajie Huang, Jianan Gu, Zhiguo Du, Bin Li, Songmei Li, and Shubin Yang. "Fast Cryomediated Dynamic Equilibrium Hydrolysates towards Grain Boundary-Enriched Platinum Scaffolds for Efficient Methanol Oxidation." Research 2019 (October 13, 2019): 1–9. http://dx.doi.org/10.34133/2019/8174314.

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Although platinum nanocrystals have been considered as potential electrocatalysts for methanol oxidation reaction (MOR) in fuel cells, the large-scale practical implementation has been stagnated by their limited abundance, easy poisoning, and low durability. Here, grain boundary-enriched platinum (GB-Pt) scaffolds are produced in large scale via facilely reducing fast cryomediated dynamic equilibrium hydrolysates of platinum salts. Such plentiful platinum grain boundaries are originated from the fast fusion of short platinum nanowires during reduction of the individually and homogeneously dispersed platinum intermediates. These grain boundaries can provide abundant active sites to efficiently catalyze MOR and meanwhile enable to oxidize the adsorbed poisonous CO during the electrocatalytic process. As a consequence, the as-synthesized GB-Pt scaffolds exhibit an impressively high mass activity of 1027.1 mA mgPt−1 for MOR, much higher than that of commercial Pt/C (345.2 mA mgPt−1), as well as good stability up to 5000 cycles. We are confident that this synthetic protocol can be further extended to synthesize various grain boundary-enriched metal scaffolds with broad applications in catalysis.

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Aoyagi, Yoshiteru, and Yoshiyuki Kaji. "Crystal Plasticity Simulation Considering Oxidation along Grain Boundary and Effect of Grain Size on Stress Corrosion Cracking." MATERIALS TRANSACTIONS 53, no. 1 (2012): 161–66. http://dx.doi.org/10.2320/matertrans.md201126.

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50

Koehler, C., and G. Thomas. "Characterization of grain boundary phases in Si3N4 sintered using Y-Si-Al-O-N additives." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 1070–71. http://dx.doi.org/10.1017/s0424820100178483.

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The usefulness of silicon nitride as a high temperature ceramic can be limited by the presence of amorphous phases at the grain boundaries. Dense silicon nitride ceramics are produced using pressureless sintering of Si3N4 with Y-Si-Al-O-N additives. When these additives are left as a glassy phase at the grain boundaries and triple grain junctions, the mechanical properties at elevated temperatures are weakened due to these low viscous glasses. Post-sintering heat treatments and close compositional control can be effective in transforming the glass into crystalline phases at the grain boundaries thereby increasing the refractoriness.To optimize high temperature mechanical properties, processing must be controlled not only to fully crystallize the grain boundaries but also to avoid certain unstable secondary phases whose oxidation leads to large molar volume changes which causes possible cracking. Transmisssion electron microscopy and x-ray microanalysis (EDS) are significant methods to characterize the amorphous grain boundary pockets and to identify the crystalline grain boundary phases.

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