Papers by Keyword: Oxidation Resistance

Abstract: Polyphenylene sulfide (PPS) fiber is widely used in the fields of high-temperature filtration, protective clothing, electronics, automobile, and aircrafts sectors relying on its excellent heat and chemical resistance. However, PPS fiber is easily oxidized under high temperature, which vastly restricts its applications. In this study, using the copper nanoparticles loaded halloysite nanotubes (HNTs@Cu) as a nanofiller, we prepared a PPS composite fiber with improved oxidation resistance. The successful loading of copper nanoparticles into HNTs was demonstrated through TEM and elemental analysis. The crystallinity, orientation, thermal and mechanical properties of PPS nanocomposite fibers were investigated via DSC, XRD, WXRD, TGA and mechanical test. While the mechanical performance of the composite fibers was slightly decreased, the thermal stability was improved when comparing to the neat PPS fiber. The composite fiber with 1.0 wt.% loading of HNTs@Cu showed an over 100% retention rate of breaking strength after thermal oxidative aging, suggesting an improvement in oxidation resistance of PPS fiber. This work provides an effective and accessible method for improving the thermal stability and oxidation resistance of PPS fibers, which thereby helps to extend the applications of PPS fibers in high temperature environment.

Abstract: The aim of this investigation was to study the influence of Nb-enriched powder mixtures on structure and oxidation resistance of protective layers based on Ni-based self-fluxing alloy, produced by non-vacuum electron beam cladding technique on low-carbon steel substrates. The oxidation resistance of coatings was studied by thermogravimetric analysis (TGA). The samples held at 900°C for two hours in air atmosphere. TGA results indicate that the highest oxidation resistance has the material, obtained by cladding of pure Ni-based self-fluxing alloy. Samples, produced by cladding of Ni-based self-fluxing alloy in combination with Nb-enriched powder mixtures demonstrate lower level of oxidation resistance. Structure of the coatings was characterized by optical and scanning electron microscopy combined with electron microprobe analysis as well as X-ray diffraction.

Abstract: Basic titanium alloys are successfully used in modern aviation GTE (gas turbine engine). They are used for parts of a compressor and partly in low pressure part of turbine (intermetallic Ti-Al alloys) due to their high specific strength and at the same time low density, high corrosion resistance but can be used only up to 700 °C. The paper deals with the results of heat resistance testing at 750 °C of Ti-Al-(X)+N based thin ion-plasm multilayers coatings, with different priority of monolayers- intermetallic, conglomerate or nitride for gas turbine engine (GTE) blades from titanium alloys. All coatings showed high resistance during the test, with a maximum efficiency 42.8 of coating with a priority of conglomerate after 30 hours of testing.

Abstract: The objective of the present investigation is to study the oxidation resistance of SiO₂/SiC coating on carbon fiber by electrolytic plasma spraying. The SiO₂/SiC coating can be easily prepared within several tens seconds through this approach. The effect of spraying parameters (fixed point 5s and spray 5 times at the speed of 20mm/s) on the microstructure and oxidation resistance properties of coatings was discussed in this paper. Scanning electronmicroscopy (SEM), energy dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and DTG have been used to characterize the SiO2/SiC coatings. It was demonstrated that fixed-point spray 5s has better density and oxidation resistance coating, and the oxidation resistance increased by 12% compared with spray 5 times at the speed of 20mm/s. The fixed-point spray 5s coating was mainly composed of SiO₂ and SiC. The SiO₂ relative content was 72.6% and the SiC relative content was 27.4%.

Abstract: With the objective of partial and total replacement of nickel by nitrogen in austenitic exhausted valve steel X45CrNiW18-9, a program of work with series of experimental heats was designed. Experimental heats were carried out in 10 Kg. induction furnace under nitrogen pressure. The chemical composition of produced stainless steels was determined. The produced automotive steel grades were forged. The nitrogen contents were determined. The produced forged stainless steels were subjected to solution treatment at 1050 °C for 1 hour, followed by water cooling. Isothermal oxidation test is used to detect the behavior of new grades at different temperatures in air for solution treated stainless steels. The mass gain was measured for samples exposed to air at temperatures (500 °C, 600 °C, 700 °C, 800°C) for different time intervals, up to 1000 hrs. The oxide layer thickness for two selected steels was investigated by using optical microscope. XRD was used to detect types of oxides which are formed during oxidation process at 800 °C for 1000 hrs for represented investigated exhausted valve steels. Scanning Electron Microscope was used to make scan steels surface, after heating at 500 °C and 800 °C for l000hr. The mechanism of the oxidation of developed steels was investigated. It was found controlled by diffusion mechanism and the kinetic of oxidation process is parabolic. Oxidation rate of the investigated stainless steels for times, up to 8 h and between 200 andl000 h, at all investigated temperatures (500 °C - 800 °C), is parabolic and the oxidation is diffusion controlled. While in the time region 10 to 200 h, it obeys combined mechanisms. Partial replacement of nickel, by nitrogen, improves the oxidation resistance in air at temperature range 500°C - 800°C.

Abstract: In this study, Si and SiC powder with a critical particle size ranged from 0.1 to 0.4mm was added into MgO-C refractory as antioxidants. At 1200°C in air atmosphere, oxidation weight losses of cylindrical specimens with additives were measured and the effective diffusion coefficient of oxygen in refractories was calculated from the results. Thus, the effects of antioxidants particle size on the oxidation resistance were researched. The result shows that the particle size of antioxidant has a considerable influence on oxidation resistance of material. The oxidation resistance of MgO-C refractories increased at first as the critical particle size of Si powder increased from 0.1 to 0.2mm and then decreased as the critical particle size increased up to 0.4mm, while the oxidation resistance of MgO-C refractories decreased as the critical particle size of SiC additives increased from 0.1 to 0.4mm. The minimum effective diffusion coefficients of oxygen in MgO-C refractories added by Si and SiC were 10.90 and 14.09cm²/min, individually.

Abstract: ZrB₂-SiC-WSi₂ (labeled as ZSW) coating and ZrB₂-SiC (labeled as ZS) coating were fabricated by vacuum plasma spray technique. The microstructure and composition of as-sprayed coating were detected through X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray energy dispersive spectrometry (EDS). Oxidation behaviors and microstructure evolution of these coatings were evaluated at 1500 °C in air and compared with ZrB₂-SiC coating. The results showed that the addition of WSi₂ improved the oxidation resistance of the ZrB₂-SiC coating. There was more liquid formed on the ZSW coating surface. Some bubbles were also observed on the coating surface, which might be resulted from gas formation. It can be concluded that the amount of WSi₂ had great influence on its function in ZrB₂-SiC system.

Abstract: This paper focusses on the development of materials for exhaust gas components. The present work will focus on a ferritic SiMo-cast iron to create an economic alternative to the austenitic D5S. Aluminum and silicon are essential for this material development because they increase the transformation temperature. They also improve the durability of the protective oxide layer. Additionally, aluminum improves the high temperature mechanical properties by precipitation of a kappa-phase. The ferritic SiMoAl cast iron shows very good oxidation resistance and also mechanical properties.

Abstract: Zr-20Ti-5Al (at. %) alloy used as substrates for Si-Y₂O₃ co-deposition experiments was prepared by firstly vacuum non-consumable arc melting and then high frequency induction skull melting. The results showed that Y modified silicide coating prepared at 1250 °C for 4 h possessed a double-layer structure, mainly consisting of a thick (Zr, Ti)Si₂ outer layer and a 15 mm thick (Zr, Ti)Si inner layer. Meanwhile, the growth rate of ZrSi₂ phase changed with temperature, while the growth rate of ZrSi did not vary significantly with temperature. The growth of the coating as well as the two layers followed parabolic laws, and the co-deposition process was controlled by diffusion. ZrSi₂ was not appropriate as oxidation-resistant coatings to protect Nb based alloy from oxidation due to the lack of the formation of good quality glassy SiO₂ layer in the scale.

Abstract: Cr₃C₂-Ni cermets exhibit high hardness and excellent corrosion, oxidation, abrasive and erosion resistance. However, nickel is toxic and carcinogen and because of that great efforts were made to displace or replace nickel in the composition of cermets. Therefore, in the present research chromium carbide-based cermets with FeCr-type ferritic binder was fabricated and investigated. Composites were sintered at different conditions: vacuum and spark plasma sintering. Spark plasma sintered cermets demonstrated acceptable structure and mechanical characteristics. Chemical composition of chromium carbide-based iron alloy bonded cermets was analyzed by energy-dispersive X-ray spectroscopy and structural analysis was carried out using X-ray diffraction. Sintered cermet consists of two main phases: α-Fe and (Cr,Fe)₇C₃ complex dicarbide. Mechanical characterizations – hardness and fracture toughness – was performed. Also oxidation rates were determined.