Papers by Keyword: Oxidation Resistance

Abstract: A novel aqueous plasma electrolysis applied for depositing a uniform and continuous Al₂O₃/Y₂O₃ ceramic coating on each fiber within a carbon fiber bundle are reported in this study. All equally spaced tungsten wires generated plasma arc, where the plasma was overlapped, excluded and extruded each other, finally a cylindrical plasma arc zone was formed, promoting the full coverage of the coating on each fiber. The Al₂O₃/Y₂O₃ coating protected the carbon fiber from oxidation above 850^oC. Similarly, the coating significantly improved the oxidation resistance of the carbon fiber with the mass loss of ~5% after isothermal oxidation in N₂ atmosphere at 800°C for 30 min, compared to ~14% of bare carbon fiber. By the movement of the T300 carbon fiber bundle, 1500 m coated carbon fiber bundle with the high-quality Al₂O₃/Y₂O₃ coating deposited on each fiber was successfully realized. It is believed that the novel aqueous plasma electrolysis will find a wide range of applications in modifying the interface of the carbon fiber reinforced composites. The present investigation will also open up a new horizon for preparing a protective coating on each fiber within two/three-dimensional carbon fiber fabric.

Abstract: The Inconel 600 alloy relies on high temperature strength and aggressive environment resistance for main pipes and heat exchangers for power plant. Through high energy laser beam surface treatment, upgrade oxidation performance and design based accident prevention, the durable Inconel 600 alloy is realized. At the same time, the chemical diffusion and high energy beam welding are used for wearness enhancement and chemical oxidation. It is suggested that, the laser surface treatment and hydrogen effect are accurately selected for abrasive wear resistance and high temperature oxidation, repectively. As a result, the lifespan of Inconel 600 alloy increases, the pitting concentration and cracks formation are prevented effectively.

Abstract: In this paper, coated ZrSiO₄-ZrB₂ powder was prepared by sol-gel method. The ZrSiO₄ coating can improve the oxidation resistance of ZrB₂ at high temperature. The effect of N (n_ZrSiO4/n_ZrB2), sintering temperature, holding time and catalytic hydrolysis condition of tetraethoxysilane (TEOS) on coated ZrSiO₄-ZrB₂ powder was discussed. The modern testing techniques such as XRD, SEM and TG-DSC were used to analyze the crystal phase compositions, microstructures and the oxidation resistance property. The results of experiments showed that the oxidation resistance of coated ZrSiO₄-ZrB₂ powder was excellent when N is 0.7, and TEOS is alkaline-catalyzed hydrolyzed.

Abstract: Ti₃SiC₂ and three different kinds of Ti₃SiC₂ matrix composites (Ti₃SiC₂/SiC, Ti₃SiC₂/Al₂O₃ and Ti₃SiC₂/MgAl₂O₄) were fabricated by reactive hot pressing method. The oxidation resistance of four kinds of materials at 1373 K-1773 K was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the main oxidation products of Ti₃SiC₂ were rutile and cristobalite. The oxidation layers were composed of two layers, the outer was consisted of TiO₂, and the inner was a two-phase mixture of TiO₂ and SiO₂. A large number of pores existed in oxide layers which leading to a poor oxidation resistance. For Ti₃SiC₂ matrix composites, rutile grains in oxidation layers were refined due to the introduction of the second phase. The volume expansion caused by reactions between Al₂O₃ (or MgAl₂O₄) and TiO₂ could close pores and improve the densification of oxide layers, which further improve the oxidation resistance of Ti₃SiC₂/Al₂O₃ and Ti₃SiC₂/MgAl₂O₄. As for the oxidation of Ti₃SiC₂/SiC, the SiO₂ content in oxidation layers was increased from the oxidation of SiC. The dense SiO₂ layer acted as a protective film which could prevent the inward diffusion of oxygen. Moreover, liquid phase under high temperature could also fill the pores in oxidation layers. Thus, Ti₃SiC₂/SiC composite had the best oxidation resistance among three Ti₃SiC₂ matrix composites.

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: Dense ZrB2-SiC composites were fabricated by high pressure and high temperature sintering(HPHT) at 1500 oC for 3 min under a pressure of 5 GPa. The vickers’ hardness of ZrB2-SiC composite is 25 GPa. The flexural strength of the ZrB2-SiC composite is 300 MPa with the amount of SiC increased to 30wt.%, which increased after the composites oxidized at high temperature. The generated glass phase like SiO2 sealed pores and cracks on the surface of the ZrB2-SiC composite to increase the mechanical properties of the ZrB2-SiC composite. After oxdized at 1500oC for 45 mins, the dense oxidized film formed on the surface of ZrB2-SiC composites to improve the resistance oxi dation of ZrB2 ceramics.

Abstract: To protect carbon fiber-reinforced SiC (C/SiC) composites against oxidation,mullite coating was prepared on C/SiC composites by dip-coating method with high solid content Al₂O₃-SiO₂ sol as raw materials. X-ray diffraction and scanning electron microscopy were employed to analyze the phase and microstructure of the coating. The results show that the as-prepared coating is SiO₂-rich, monolithic and well bonded with substrate without penetrating crack, giving rise to good oxidation-resistance. After soaked at 1400°C for 30min under static air, the coated C/SiC composites possess 87% of original flexural strength. As a result of sealing and filling of cracks and pores by viscous SiO₂ in coating, the coated C/SiC composites exhibit improved oxidation resistance at 1500°C and 1600°C. There is no change in flexural strength after oxidized at 1500°C and 1600°C for 30min, respectively. Nevertheless, the carbothermal reduction between viscous SiO₂ and free carbon in C/SiC substrate would occur obviously when oxidation temperature was elevated or oxidation time was prolonged, leading to local foaming in coating and decreasing in oxidation resistance.

Abstract: Graphite is one of the most important material for the reactor core and fuel elements of high temperature gas-cooled reactor (HTR). Improving the oxidation resistance of graphite is very essential for the research of new fuel elements and the development of HTR. In this study, a gradient SiC layer of 500~700 μm was prepared on matrix graphite spheres by a two-step pack cementation, and the outer SiO₂ layer prepared by the high-temperature oxidation process. The phases, microstructure, bonding strength and oxidation resistance of SiC/SiO₂ coated matrix graphite spheres were investigated. The SiC/SiO₂ coated matrix graphite spheres were carried on rapid thermal shocking tests from 1773 K to room temperature for 50 times without any cracks. The SiC/SiO₂ coated matrix graphite spheres exhibits excellent anti-oxidation properties. No obvious weight loss was found after isothermal oxidation in air at 1273 K for 50 h and the weight gain was less than 1% at 1773 K in air for 50 h due to the oxidation of SiC layer.

Abstract: The high temperature oxidation phenomenon will occur on the tool-workpiece contact area when machining the superalloy. Two kinds of cemented carbide tools (YG6X, YG8) are selected, the coated carbide tool and coated ceramic tool which are suitable for machining superalloy are selected. The resistance furnace is used for heating tool material, and the oxidation resistance experiments are carried out. The results show that: WC which is included in the cemented carbide tool is oxidized to WO₃ and the Co is oxidized to Co₃O₄, Ti which is included in the coated carbide tool is oxidized to TiO₂. The grain of the tool is smaller, the oxidation resistance is better. The oxidation resistant of coated carbide tool is better than the non-coated tools. The coated ceramic tool is not substantially oxidized in high temperature situation. The merits order of the oxidation resistant properties is that: coated ceramic tool>coated carbide tool > YG6X>YG8.

Abstract: The present research work has an aim to modify microstructure and oxidation behavior of Hastelloy X, a solid solution nickel base alloy, by both aluminium and titanium additions by mean of arc melting process. The Hastelloy X was added both Al and Ti (50:50) for 2% 4% and 6% by weight and casted by vacuum arc melting furnace. Then all received specimens were performed heat treatment, which consist of solutioning treatment at 1175°C for 4 hours and aging temperatures for 760°C, 800°C and 845°C for 24 hours. From the obtained results, it was found that the amount of both Al and Ti additions as well as precipitation aging temperature provided significant effect on both final microstructure and oxidation behaviors at 900°C and 1000°C. Widmanstatten type of microstructure was found in many case. Intermetallic phase formation of molybdenum and chromium was also found in all cases by element mapping. This phase should be γ’-phase. Both aluminium and titanium additions could not provide beneficial effect on oxidation resistance tests at temperature of 900°C and 1000°C. However, with 4%wt. of both aluminium and titanium addition, it resulted in slightly increasing of oxidation resistance at temperature of 1000°C