Papers by Keyword: High Temperature Oxidation Resistance

Abstract: In order to study the effect of spray distance on the structure and high temperature oxidation resistance of feather-columnar thermal barrier coatings, the feather-columnar ZrO₂-7wt. % Y₂O₃ (7YSZ) thermal barrier coatings were prepared at spray distances of 650 mm, 950 mm, 1100 mm, 1250 mm, and 1400 mm by plasma spray-physical vapor deposition (PS-PVD) technology. The surface roughness, micro morphology, and porosity of the sprayed 7YSZ coating were analyzed by 3D surface profiler, SEM, XRD, etc., and the impedance spectrum characteristics of the 7YSZ coating were characterized by electrochemical alternating current (AC) impedance technology. In addition, the high temperature oxidation resistance test of 7YSZ coating under different spray distances was carried out at a temperature of 1000 °C to study the influence of spray distance on the high temperature oxidation resistance of 7YSZ coating. The research results show that the surface roughness and porosity of feather-columnar 7YSZ coating increased sequentially with the increase of spray distance. At the same time, The YSZ grain boundary resistance value increased exponentially as the porosity of the coating increases. Where the spray distance was in the range of 650 mm and 1250 mm, the high temperature oxidation rate constant of the coating increased with the spray distance. However, the spray distance was greater than 1250 mm, and the spray distance had no significant effect on the high temperature oxidation resistance of the coating.

Abstract: In order to improve the high temperature oxidation resistance of exhaust pipes, the nanocomposite coatings are carried out on the surface of exhaust pipe by electrodeposition technology, and the microstructure and oxidation behavior of the nanocomposite coatings are investigated experimentally. This paper mainly focuses on the experimental work to determine the structural characteristics and oxidation resistance of nanocomposite coatings in presence of Al₂O₃ and cerium oxide CeO₂. The results show that the amount of the Al₂O₃-CeO₂ has significant influence on the structural properties of nanocomposite coatings. The surface of coating becomes more compact and smooth with the increase of the amount of the Al₂O₃ and CeO₂. Furthermore, the anti-oxidation performance of the nanocomposite coatings formed with Al₂O₃ and CeO₂ were both better than those of the composite coatings formed without Al₂O₃ and CeO₂.

Abstract: Al coating was deposited on 0Cr18Ni10Ti steel by magnetron sputtering, and then diffusing annealing at 950°C for 2h. The isothermal oxidation behaviors of the Al coating and 0Cr18Ni10Ti steel were tested at 900 °C for 24 h and 800 °C for 24 h using Thermo gravimetric analyzer. The morphology was studied by SEM, the phase composition was characterized by EDS. The result of isothermal oxidation test showed that isothermal oxidation resistance of Al coated steel is better than 0Cr18Ni10Ti steel at 900 °Cand 800 °C, due to continuous and compact Al₂O₃ scales. Al clusters of particles appears on Al coated steel during deposition. The larger particles peeling off was observed at 900°C after 18h, due to thermal and growth stresses, while no spallation appeared at 800°C for 24h.

Abstract: 0Cr18Ni10Ti stainless steel was coated by hot-dipping in a molten aluminum bath, and then diffusing annealing at 950°C for 2h. The high temperature isothermal oxidation behaviors of the hot-dipped aluminized steel and 0Cr18Ni10Ti steel were tested at 900 °C for 24h using Thermo gravimetric analyzer. The high temperature cyclic oxidation behaviors of the hot-dipped aluminized steel and 0Cr18Ni10Ti steel were tested at 900 °C for 24h using resistance furnace. The morphology was studied by SEM, the phase composition was characterized by EDS. The result of high temperature isothermal and cyclic oxidation test showed that the hot-dipped aluminum can dramatically improve the isothermal and cyclic oxidation of the 0Cr18Ni10Ti steel. The hot-dipping aluminum coating is consists of an outer layer of FeAl and an inner Iron solid solution with aluminum, after diffusion annealing at 950°C for 2 h. The Al2O3 oxide layer was formed on the hot-dipped aluminum coating during isothermal and cyclic oxidation process, which provides an additional protection for the steel from high temperature oxidation.

Abstract: The problems such as poor oxidation resistant properties at high temperatures and abated thermal storage capacities after repeated thermal cycles still exist in heat storage alloys. In order to alleviate these problems, orthogonal experiment was used to design nine Al-Si-Mg-Cu alloys in this work. An SII TG/DTA6300 differential thermal analyzer was used to determine the heat storage properties of these alloys. After integrating a series of factors, Al-12Si-2Mg-15Cu alloy was selected as the heat storage alloy. The oxidation test of this alloy at the temperature of 650 °C for 300 h was carried out, and the oxidation kinetics curve was obtained. The results showed that the oxide film was of good protection. This alloy exhibited a good thermal stability in view of the latent heat of fusion decreased 3.53%, the initial phase transition temperature decreased 0.1 °C, and terminated phase transition temperature increased 3.1 °C after 150 times of thermal cycles. The photomicrograph was used to discuss the reasons of the performance changes of this alloy.

Abstract: To remanufacture hard chromium-plated workpiece, nano-Al₂O₃/Ni-Co composite coatings and Ni-Co alloy coatings are developed using electric brush plating technology. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) are used to analyze the surface morphology, phase structure and wear properties of coatings. The surface morphology of nano-composite coating is more compact. The nano-particles are well-distributed in the coating and bounded tightly with the substrate. The hardness of composite coating is HV1027, increased approximately 38% compared with Ni-Co alloy coating, overtaking the hard chrome plating. The results of sliding wear test shows that the nano-composite coating reduces friction coefficient, increases wear resistance significantly and exceeds the chromium plating.

Abstract: Cr coatings were deposited on AISI H13 steel substrates by means of electrospark deposition (ESD). The coatings were characterized in terms of their microstructure, hardness, friction and wear behavior and high-temperature oxidation resistance. Micro-indentation and tribometer testers were employed to measure the mechanical properties of Cr coatings and AISI H13 steel. The results showed that the hardness of the coatings ranged from 600 to 660 HV, with a higher value than that of AISI H13 steel (510 HV). The coefficient of steady-state friction of the coatings against 45-carbon-steel balls ranged from 0.23 to 0.27, with a lower value than that of AISI H13 steel (0.62-0.68). The isothermal oxidation behavior of the coatings at 850°Cwas studied in comparison with AISI H13 steel substrates. The results indicated that Cr coatings substantially increase the high-temperature oxidation resistance of AISI H13 steel and the oxidation process was retarded mainly by the presence of a Cr2O3 oxide scale on the coatings at 850°C for 100 hours.

Abstract: Crack-healing effectiveness was investigated on 5 vol% nano-Ni dispersed Al₂O₃ hybrid materials. Influence of the Y or Si doping or SiC co-dispersion was also studied on the crack healing behavior. Cracks were introduced by a Vickers indentation to be a crack length of approximately 60 μm. Cracks of nano-Ni/Al₂O₃ were completely disappeared, for example, by oxidation at 1200°C for 6 h in air, Y/Si doped one and SiC co-dispersed one have similar performance of crack disappearance. Bending strength of crack-disappeared samples showed about 550 MPa and was comparable or improved with that of as-sintered one. Mechanism of crack healing was considered as filling up of cracks by NiAl₂O₄ oxidation product which is developed by outward diffusion of cations at grain boundary of Al₂O₃ matrix. Nano-Ni/Al₂O₃ with Y or Si doping or SiC co-dispersion are realized to have crack-healing effectiveness with improved high-temperature oxidation resistance.

Abstract: The aluminizing process by solid powder on the surface of GH4169 superalloy with different Y₂O₃ content and different aluminizing temperature was investigated in this paper. The results show that the crystalline phase of aluminized coating is composed of AlNi, FeNi and AlNi3, and the phase of AlNi reaches 78.1%, which indicates that aluminium atom has infiltrated into the alloy surface. Y₂O₃ can greatly improve compactness of the aluminized coating, increase thickness, surface micro-hardness and high temperature oxidation resistance of the aluminized coating. The thickness of the coating increases with the increase of temperature, but the microstructure of the aluminized samples cannot obviously divided into aluminized layer, transition layer and matrix when the aluminizing temperature is too high (980°C) or too low (920°C), and even the aluminized coating is porous and coarse at 980°C. The high temperature oxidation resistance of all the aluminized samples is improved compared to without aluminized samples. According to the microstructure, thickness, surface micro-hardness and high temperature oxidation resistance of aluminized coating, the optimal aluminizing process is 950°C×7h with 4%Y₂O₃.

Abstract: An energy-saving and high-efficient powder Al and Si codeposition process was employed on 1045 steel, the new technology was mainly based on applying direct current field (DCF) with proper parameters between the treated samples and the powder. The microstructure, thickness and the phase constituents of the coating were analyzed by OM and XRD. The high temperature oxidation resistance for a total duration of 120h and the corrosion resistance in 10% H₂SO₄ for 8h were investigated. The results showed that DCF could lower heating temperature and accelerate the diffusion rate. The phase of the coatings with DCF was composed of Al_0.7Fe₃Si_0.3 and AlFe_3. The treated samples had good high temperature oxidation resistance and corrosion resistance in 10% H₂SO₄ solution.