Papers by Keyword: Oxidation Behavior

Abstract: The high-temperature and high-pressure oxygen-rich combustion gases often cause the high temperature gas conduit in rocket engine to suffer severe oxidation, resulting in a reduced service life. The present study deposited a dense NiAl coating on GH4202 superalloy using atmospheric plasma spraying and investigated its oxidation behavior in a high temperature and high-pressure oxygen atmosphere. The results showed that the NiAl coating presented excellent bonding with the superalloy substrate throughout tests. The uncoated GH4202 substrate was severely oxidized during high pressure oxygen atmosphere. It was found that only a continuous very thin Al₂O₃ oxide scale evolved on the NiAl coating surface and no oxidation was observed at the interface between the NiAl coating and GH4202 substrate. Moreover, no significant inner oxidation occurred to NiAl coating. Therefore, the present APS NiAl coating can provide effective protection of superalloy from oxidation at high pressure oxygen combustion gas atmosphere.

Abstract: Semi-solid processing combines the advantages of traditional forging and casting methods, so it has received much attention recently. However, the research on semi-solid behaviors of Nickel-based superalloys has been rarely reported. In order to investigate the behaviors of Nickel-based superalloy at solid and semi-solid states, oxidation experiments, isothermal treatment experiments and deformation experiments of GH4037 alloy were studied. Short-term oxidation experiments of GH4037 alloy were carried out at a solid temperature (1200 °C) and a semi-solid temperature (1360 °C). The results indicated that the oxides formed at 1200 °C were mainly composed of TiO₂, Cr₂O₃ and a small amount of spinels NiCr₂O₄, while the oxides formed at 1360 °C consisted of the spinels of NiCr₂O₄, NiWO₄ and NiMoO₄ besides TiO₂ and Cr₂O₃. Microstructure evolution of GH4037 alloy after semi-solid isothermal treatment at 1370 °C and 1380 °C was studied. The results indicated that semi-solid microstructures consisted of equiaxed solid grains and liquid phases. The average grains size and shape factor of solid grains were affected by melting mechanism and grain growth mechanism. Compression behaviors of GH4037 alloy after compressed at 1200 °C and 1360 °C were investigated. The results indicated that the flow stress of 1360 °C decreased significantly compared to that of 1200 °C. The deformation zones in the specimens were divided into three parts: the difficult deformation zone, the large deformation zone, and the free deformation zone. At 1200 °C, the deformation mechanism was plastic deformation mechanism. At 1360 °C, sliding between solid particles (SS), liquid flow (LF), flow of liquid incorporating solid particles (FLS), plastic deformation of solid particles (PDS) coexisted in the compression specimen.

Abstract: This paper aims to research the high-temperature oxidation behavior of TiC/Mo composite. Adding 5 wt.% TiC, Mo-based composite was prepared by Spark Plasma Sintering. The composite was oxidized at different temperatures (400°C, 600°C, 800°C, 1000°C and 1200°C) and times (5 min, 10 min, 20 min, 30 min and 60 min). When oxidation was at 400-1000°C for 20 minutes, the degree of oxidation intensifies with the increase of temperature, and TiO2 was observed at 1000°C. While the temperature was 1200°C, the oxidation rate gradually decreased with the increase of time. The result shows that the formation of TiO2 can inhibit the oxidation process.

Abstract: The oxidation behaviors of tantalum-tungsten alloy with 10-20% W was investigated between temperature range of 700 to 900 °C exposed in air. The kinetics of Ta-W alloy was determined by TG-DTA, the characteristics of oxides were analyzed by SEM, EDS and XRD. The oxidation tests revealed that the alloys obeyed parabolic kinetic in the initial stage, then translated in linear law. The addition of W has a good effect on the oxidation resistance of Ta-W alloys at experimental temperature. Solid solution of Ta₂O₅ form in case of oxidation product of Ta-10W, Ta-15W alloys, while the complex oxide Ta₂₂W₄O₆₇ form after Ta-20W alloy oxidized. The formation of solid solution and complex oxide impeded the volatilization. The compact oxide film protects the penetration of oxygen in the initial oxidation stage. The large compressive stresses and mismatch of the coefficient of thermal expansion between oxide scale and matrix alloys make the oxides layer be broken, which cause kinetic of oxidization obeying linear law.

Abstract: The CrN ceramic thin films were deposited using DC reactive magnetron sputtering system on silicon wafer substrate. Oxidation behavior was carried out in air at evaluated temperatures ranging from 500 °C up to 900 °C for 2 h. The structure and element composition of the films at different thermal annealing temperatures ranging were investigated by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), respectively. The oxidation activation energies of the films were calculated using Arrhenius equation. The changes in the crystal structure from CrN to Cr₂O₃ phase were investigated from XRD results. The accumulation of grains on surface was confirmed by FESEM micrographs. The cross-section analysis showed an apparent columnar feature with dense structure for the film annealed at low temperature, and becomes porous when increasing the annealing temperature. The thickness was increased from 1.43 to 2.67 μm. The EDS studies indicated the existence of Cr, N and O with different elements compositions on the deposited thin films. The oxidation activation energy for the CrN thin films is 124.4 kJ/mol.

Abstract: Si-B-C-N ceramics were synthesized by co-pyrolyzing hybrid polymeric precursors of polycarbosilane and polyborazine due to their mutual solubility. The pyrolysis behavior of Si-B-C-N precursor was analyzed by TG-DSC-FTIR-MS coupling technique. The oxidation behavior was studied through static oxidation test. Results showed that oxidation rate of Si-B-C-N multiphase ceramic was greater than that of SiC ceramic obviously, which promoted forming the liquid B2O3 or stable borosilicate glass. The generated glass state oxides acted as a protective layer which could heal the cracks and reduce oxidation rate due to lower vaporization rate and smaller oxygen diffusivity. Furthermore, Si-B-C-N multiphase ceramic shows excellent oxidation resistance and can be kept in service in a long time at 1200°C

Abstract: The oxidation of pentatitanium trisilicide (Ti₅Si₃) powder at high temperature was investigated in order to determine the suitability of this ceramic material for advanced application in an oxidation atmosphere at high temperature. Titanium silicide has been attracted for years as an engineering ceramics due to its high hardness, high melting point, and good chemical stability. The samples were oxidized from 300 to 1000 °C for 1 to 5 h in air. The mass changes were measured to estimate the oxidation resistance of the sample. The mass gain of the sample oxidized at 1000 °C for 5 h was about 26 % of the theoretical oxidation mass change. The commercial powder, Ti₅Si₃ showed an excellent oxidation resistance at 1000 °C, because the surface film of both titanium dioxide and silicon dioxide formed by oxidation acted as an oxidation resistant layer.

Abstract: This paper presents the results of a study of the oxidation behavior of NiAl produced by gel combustion synthesis calcined at two different temperatures. The objective is to compare the oxide growth rates, oxide scale composition, morphology and elemental composition of the sample powder subjected to isothermal oxidation and calcined at 1050 °C and 1300 °C for 1, 2, 4 and 10 hours by means of mass gain measurements, X-ray diffraction (XRD), field emission scanning electron microsocopy (FESEM) and energy-dispersive spectrometry (EDX) in order to investigate the reliability of the gel combustion synthesis method and evaluate the effect of calcination temperature on the oxidation behaviour of the powder. It was found that for the sample calcined at 1300°C the sample was made up mainly of metastable and stable alumina before oxidation and stable alpha alumina after oxidation whereas for the powder calcined at 1050°C the sample was mainly composed of detrimental mixed oxides before and after oxidation. Overall findings indicate that the oxidation behavior of the powder calcined at 1300°C is more protective compared to the powder calcined at 1050°C.

Abstract: Inthis investigation, the rare-earth oxide Yb₂O₃ combined with Al₂O₃served as sintering additives and SiC and B₄C powder were applied to fabricate SiC/B₄C multiphase ceramics composites by pressureless sintering. The results proved thatcombination of Al₂O₃ and Yb₂O₃ sinter additives were effective fordensification of SiC/B₄C composites. The influence of oxidation time onthe phase constitution, micro-structure and oxidation behavior of SiC/B₄C composites was investigated.Theformation of eutectic phase Yb₂Si₂O₇ phase waswrapped on the SiC surface and it reduced further oxidation of SiC particles.The oxidation kineticcurves followed a parabolic rule.

Abstract: The oxidation behavior of Fe-15Cu-10Al alloy was investigated at 700°C. Oxidation kinetics of the alloy conformed nearly to the parabolic rate law. The scales were composed mainly of alumina, plus a few nodules rich in iron. The very low oxidation rate of Fe-15Cu-10Al alloy showed that 10at.% Al level reached the critical Al content to form a complete Al₂O₃ external layer. Compared with the corresponding Fe-10Al binary alloy, the addition of 15at.% Cu played a beneficial role for the establishment of the full protective alumina layer.