Structure characterization of the oxide film on FGH96 superalloy powders with various oxidation degrees

The structure of the oxide film on FGH96 alloy powders significantly influences the mechanical properties of superalloys.In this study,FGH96 alloy powders with various oxygen contents were investigated using high-resolution transmission electron microscopy and atomic probe technology to elucidate the structure evolution of the oxide film.Energy dispersive spectrometer analysis revealed the presence of two distinct components in the oxide film of the alloy powders:amorphous oxide layer covering the γ matrix and amorphous oxide particles above the carbide.The alloying elements within the oxide layer showed a laminated distribution,with Ni,Co,Cr,and Al/Ti,which was attributed to the decreasing oxygen equilibrium pressure as oxygen diffused from the surface into the γ matrix.On the other hand,Ti enrichment was observed in the oxide particles caused by the oxidation and decomposition of the carbide phase.Comparative analysis of the oxide film with oxygen contents of 140,280,and 340 ppm showed similar element distributions,while the thickness of the oxide film varies approximately at 9,14,and 30 nm,respectively.These findings provide valuable insights into the structural analysis of the oxide film on FGH96 alloy powders.

Microstructure and Oxidation Behavior of ZrB_(2)-SiC Ceramics Fabricated by Tape Casting and Reactive Melt Infiltration

ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2) and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2) phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2) oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2) is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2) particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2) increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2) in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.

Evaluation of the Oxidation Reactivity and Behavior of Exhaust Soot Particles from Diesel Engines with Different Emission Levels

The aim of this study was to investigate the oxidation reactivity and behavior of exhaust particulate matter(PM)from diesel engines.PM samples from two diesel engines(1K,CY4102)with different emission levels were collected by a thermophoretic system and a quartz filter.The oxidation reactivity,oxidation behaviors,and physicochemical properties of the PM samples were analyzed using thermogravimetric analysis(TGA),high-resolution transmission electron microscopy(HRTEM),Fourier-transform infrared spectrometry(FTIR),and Raman spectroscopy.The results showed that there was a great difference in the oxidation reactivity of soot particles emitted by the two different diesel engines.A qualitative analysis of the factors influencing oxidation reactivity showed that the nanostructure,degree of graphitization,and relative concentration of aliphatic C—H functional groups were the most important factors,whereas no significant correlation was found between the primary particle size and activation energy of the diesel soot.Based on the oxidation behavior analysis,the diesel soot particles exhibited both internal and surface oxidation modes during the oxidation process.Surface oxidation was dominant during the initial stage,and as oxidation progressed,the mode gradually changed to internal oxidation.Internal oxidation mode of soot particles from the 1K engine was significantly higher than that of CY4102.

Oxidation Behavior of La_2O_3 Oxide Dispersion Strengthened Aluminum－Diffusional Coating

NiAl-La2O3 compostite coating was prepared by Ni-La2O3 electrodeposited and pack aluminized at 1173 K on Ni-base superalloy K38. The result of oxidation in air at 1273 K for 20 h shows that the oxidation rate of NiAl-La2O3 coating is remarkably lower than that of NiAl-La2O3 free coating. The oxide film surface morphology of NiAl-La2O3 composite coating was obviously modified after oxidation. HREM study of the fine structure of aluminum oxide on the composite coating shows that La2O3 particles with diameter of 10￣40 nm were incorporated into u-Al2O3 layer. It is believed that La2O3 dispersive particles improve NiAl coating oxidation resistance by a way to influence aluminum layer microstructure and to modify cationic transfer behavior of the layer growth.

Memory Behaviors Based on ITO/Graphene Oxide/Al Structure

We investigate the memory properties of the ITO/graphene oxide/Al diodes. It is found that the devices show different memory behaviors with the diverse geometry and thickness of Al. When the thickness of the Al electrode is relatively thick, the device of the cross-point Al electrode shows a three-level memory effect, and the counterpart device of the cross-bar Al electrode exhibits a volatile static random access memory effect. When the thickness of the AI electrode is thinner, the above devices demonstrate a flash memory effect. The different memory behaviors of ITO/GO/AI diodes are ascribed to the mode and degree of reduction and oxidation of GO.

INVESTIGATION OF BEHAVIOR OF AMMONIUM SULFATE ON SURFACE OF IRON OXIDE Rong Sheng LI~*, Jing Feng CHEN, Hun YANG, Wu Yang ZHANG Dept. of Chemistry, Jilin University, Changchun 130023,

hhen ammonium sulfate-iron oxide is treated below 573 K, ammonium sulfate can spontaneously desperse on the surface of iron oxide. Simultaneously ammonium sulfate decomposes to some extent. During or after the dispersion, sulfate ion can interact with Fe atom on the surface of iron oxide to form a sort of surface sulfato complex of Fe and thus is transformed from the isolated into the bidentately bound form. Above 573 K the sulfato complex of Fe will gradually decompose with a further increase in temperature.

Oxidation behavior of Zr-containing Ti_2AlNb-based alloy at 800°C

The oxidation behavior of Ti?22Al?(27?x)Nb?xZr (x=0, 1, 6) alloys at 800 °C for exposure time up to 100 h was examined. It is shown that oxidation rate of experimental alloys obeys the parabolic kinetics. Ti?22Al?26Nb?1Zr alloy demonstrates more excellent oxidation resistance than the other two alloys. The main oxidation products are TiO2, Al2O3 and AlNbO4 phases for all these alloys. For the Ti?22Al?26Nb?1Zr alloy, Zr addition can modify the growth mechanism of oxide scale, which can effectively hinder the diffusion of oxygen. Whereas, reaction of Zr with oxygen leads to the formation of ZrO2 precipitates for the Ti?22Al?21Nb?6Zr alloy, which promotes the oxygen ingress into the substrate. Meanwhile, oxidation affected zones, including internal-oxidation layer and oxygen-enriched zone, are present beneath the outmost oxide scale. The difference in these zones is derived from the phase constitution in the starting Ti?22Al?(27?x)Nb?xZr (x=0, 1, 6) alloys.

High temperature oxidation behavior of electroconductive TiN/O′-Sialon ceramics prepared from high titania slag-based mixture

The oxidation behavior of electroconductive TiN/O′-Sialon ceramics prepared using high titania slag as main starting material was studied at 1 200-1 300 °C in air. The isothermal and non-isothermal oxidation processes were investigated by DTA-TG. Phase compositions and morphologies of the oxidized products were analyzed by XRD, SEM and EDS. The results indicate that the oxidation of TiN and O′-Sialon occurs at about 500 °C and 1 050 °C, respectively. After oxidation at 1 200-1 300 °C, a protective scale that consists of Fe2MgTi3O10, SiO2 and TiO2 is formed on the surface of the materials, which effectively prevents the oxidation process. The formation of a protective scale is relative to TiN content and apparent porosity of the samples, the amount of SiO2 and amorphous phase in the oxidation product. At the initial oxidation stage, the oxidation kinetics of the materials follows perfectly the linear law with the apparent activation energy of 1.574×105 J/mol, and at the late-mid stage, the oxidation of the samples obeys the parabolic law with the apparent activation energy of 2.693×105 J/mol. With the increase of TiN content, mass gain of the materials increases significantly.

Preparation and oxidation behavior of a novel CeO_2-modified chromizing coating

By using CeO2 particles instead of part of Al2O3 particles as filler, the CeO2 was successfully entrapped into the outer layer of the chromizing coatings on the as-deposited nanocrystalline （NC） and microcrystalline （MC） Ni films using a conventional pack-cementation method at 800 °C. For comparison, chromizing was also performed under the same condition on MC Ni film using Al2O3 as filler without CeO2 particles. SEM/EDX and TEM results indicate that the refinement of Ni grain and CeO2 entrapped into the chromizing coatings refine the grain of the chromizing coating. Oxidation at 900 °C indicates that compared with the CeO2-free chromizing coating, the CeO2-dispersed chromizing coating exhibits an increased oxidation resistance. For the CeO2-dispersed chromizing coating, the refinement of Ni grain size significantly decreases the transient-oxidation scaling rate of the chromizing coatings. Together with this, the CeO2-dispersed chromizing coating formed on NC Ni exhibits a better oxidation resistance.

Oxidation behavior of Hastelloy C-2000 superalloy at 800 °C and 1000 °C

The oxidation behavior of Hastelloy C-2000 alloy was investigated in air at 800 °C and 1000 °C for 100 h, respectively. Oxidation kinetics and oxide scales morphologies were examined by mass gain measurement, scanning electron microscopy（SEM）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The oxidation behavior of the alloy approximately follows a parabolic rate law. Moreover, annealing twins defect structure in matrix deteriorates the oxidation resistance of alloy due to the improvement of diffusion rates for alloying elements and oxygen atoms. At 800 °C, the microstructure is primarily composed of Ni O and Cr1.3Fe0.7O6 and the initial annealing twins structure is visible and Mo-rich phases are emerged to approach boundary of oxide scales. At 1000 °C, however, the morphology microstructure of oxide scales consists of oxide particle with fine Cr oxides and large Ni oxides by inlaying each other, whilst Mo-rich phases hardly appear closing to the interface of oxide scales.

Effect of Nb on plasticity and oxidation behavior of TiAlNb intermetallic compound by density functional theory

Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M （M=Ti, Al） and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAINb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%-12.5% （mole fraction）.

Oxidation Behavior of C/C-SiC Gradient Matrix Composites

Oxidation behavior of C/C-SiC gradient matrix composites and C/C composites were compared in stationary air. The results show that oxidation threshold of C-SiC materials increases with the amount of SiC particles in the codeposition matrix. Oxidation rate of C/C-SiC gradient matrix composites is significantly lower than that of C/C material. The micro-oxidation process was observed by SEM.

Structure and Oxidation Behavior of a Plasma Sprayed Yttrium Silicates Coated SiC-C/C with a Glass Outer Sealant from 1573K to 1873K

Different compositions of yttrium silicates coatings were deposited on SiC-C/C by plasma spraying and an outer borosilicate glass was applied on the yttrium silicates coatings surfaces. The structure of the multi-layer coatings was characterized by XRD and SEM analyses. High temperature oxidation behavior of the multi-layer coatings coated C/C composites was investigated. Results show that SiC/2SiO2 Y2O3/1.5SiO2 Y203/ SiO2 Y2O3/glass multi-layer coating has better high temperature oxidation resistance, protecting carbon/ carbon composites from oxidation at 1 773 K in air for 164 h with the weight loss of 1.65%. The oxidation weight loss of the coated C/C with time accorded with parabolic rule in the temperature range 1 573 K-1 873 K; and the corresponding oxidation activation energy of the coated carbon/carbon composites is 132.2 kJ/mol.

High Temperature Oxidation Behavior of La_2O_3-Mo_5Si_3/MoSi_2 Composites

The oxidation behavior of 0. 8% La2O3- Mo5Si3/MoSi2 composites at 1200℃ in air was investigated. The results reveal that the oxidation resistance of the material with 0. 8% La2O3 and Mo5Si3 is impaired. The oxidation resistance is decreased with increasing Mo5Si3 content. The mass loss follows a linear law in the initial oxidation. With oxidation time prolonging, a continuous and dense oxidation scale prevents oxygen from diffusing increasing when and leads to mass change a Mo5Si3 content is less than 30%. However, the composite shows ＂PEST＂ with the addition of 40% Mo5Si3. With increasing Mo5Si3 content, the oxidation resistance of 0.8% La2O3- Mo5Si3/MoSi2 decreases. This attributes to the poor oxidation resistance of M05Si3 and the relative density decreasing of 0. 8% La2O3-Mo5Si3/MoSi2 composite.

Fracture behavior and microstructure analysis of Al2O3–MgO–CaO castables for steel-ladle purging plugs

Three different castables based on the Al_2O_3–MgO –CaO system were prepared as steel-ladle purging plug refractories： corundum-based low-cement castable（C-LCC）, corundum-spinel-based low-cement castable（C-S-LCC）, and corundum-spinel no-cement castable（C-S-NCC）（hydratable alumina（ρ-Al_2O_3） bonded）. The fracture behavior at room temperature was tested by the method of ＂wedge-splitting＂ on samples pre-fired at different temperatures; the specific fracture energy G′f and notched tensile strength σNT were obtained from these tests. In addition, the Young＇s modulus E was measured by the method of resonance frequency of damping analysis（RFDA）. The thermal stress resistance parameter R′′′′ calculated using the values of G′f, σNT, and E was used to evaluate the thermal shock resistance of the materials. According to the microstructure analysis results, the sintering effect and the bonding type of the matrix material were different among these three castables, which explains their different fracture behaviors.

Oxidation behavior of the Fe-36Al-0.09C-0.09B-0.04Zr alloy at 1250℃

To explore and study the Fe-A1 system alloy presenting exceptional oxidation resistance at high temperature, the Fe-36Al-0.09C-0.09B-0.04Zr alloy was designed and developed. The microstructure and hardness of the backing at 1250℃were analyzed and measured. Thermodynamics and kinetics of the oxidation behavior were also analyzed by X-ray diffraction, scanning electron micros- copy, and energy-dispersive X-ray spectroscopy techniques. The results show that the microstructttre of the Fe-36Al-0.09C-0.09B-0.04Zr alloy is FeAl phase at ambient temperature and is stable at 1250℃. It displays the excellent property of oxidation resistance because the oxide film has only the Al2O3 layer, and its oxidation kinetics curve obeys the parabolic law at 1250℃. The oxidation mechanism at 1250℃ is presumed that in the early oxidation period, the alloy oxidizes to form a large number of Al2O3 and a little Fe2O3, then, the enrichment of Al caused by Fe oxidization combines with O to form Al2O3.

Effect of CaO composition on oxidation and burning behaviors of AM50 Mg alloy

Oxidation and burning behaviors were studied for CaO added AM50 Mg composites which were manufactured by conventional melting and casting processes without SF6 protective gas. CaO added AM50 Mg composites show the stable oxidation resistance, while AMS0 Mg alloys show the poor oxidation resistance. The effects of CaO addition on the burning resistance under ambient, nitrogen and dry air atmospheres were examined for CaO added AM50 Mg composites. With increasing CaO addition, the burning temperature increases under ambient, nitrogen and dry air atmospheres. The burning temperatures of small test specimen under all conditions greatly increase even by 0.3% CaO （mass fraction） addition into AM50 Mg alloys.

Influence of surface finish and annealing treatment on oxidation behavior of Ti-48Al-8Cr-2Ag alloy

The effect of surface finish and annealing treatment on the oxidation behavior of Ti-48Al-8Cr-2Ag (molar fraction, %) alloy was investigated at 900 and 1 000 ℃, respectively in air. Thermal gravimetric analysis (TGA) was conducted for the characterization of oxidation kinetics. The microstructures of oxide scales were studied by scanning electron microscopy (SEM) and transmission election microscopy (TEM) techniques. Unfavorable effect of the annealing treatment on the oxidation behavior of the coating was also investigated. The results indicate that the oxidation behavior of the alloy is influenced by surface finish and annealing treatment. The oxidation rate of ground sample is lower than that of the polished alloy at 1 000 ℃ in air. The former forms a scale of merely Al2O3, and the latter forms a scale of the mixture of Al2O3 and TiO2. Annealing can improve the formation of TiO2.

Oxidation Behavior of Fe26Cr1Mo Stainless Steel in the Presence of Ni-La_2O_3 Electrodeposited Composite Film

The oxidation behaviors of Fe26Cr1Mo with and without the Ni La 2O 3 electrodeposited composite film have been investigated by thermogravimetric analysis (TGA) and a scanning electron microscope equipped with an energy dispersive analytical X ray system(SEM/EDAX). The experimental results show that the oxide scale growing on Fe26Cr1Mo exposed at 900 ℃ spalled severely during cooling, while after the stainless steel was coated with the Ni La 2O 3 electrodeposited composite film, its high temperature cyclic oxidation resistance was significantly improved. The reason is that a La 2O 3 modified NiO scale, which has a superior adhesion to the substrate, was formed on the Fe26Cr1Mo stainless steel coated with Ni La 2O 3 composite film.