共查询到20条相似文献,搜索用时 11 毫秒
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Emily Eakins Doni Daniel Jayaseelan William Edward Lee 《Metallurgical and Materials Transactions A》2011,42(4):878-887
Ultra high temperature ceramics (UHTCs), including ZrB2-SiC, are designed for extreme environment applications in which temperatures exceed 2273 K (2000 °C). A key material property
of UHTCs in many applications is their resistance to oxidation. Recent research into UHTCs is described, revealing a variety
of different methods for improving the oxidation performance, which include control of starting powders, composition and size
distribution, mixing, and densification techniques. The use of additives has also been researched widely, for example, to
increase the viscosity of any liquid phase formed or provide protective refractory phases at high temperatures. SiC additions
are effective in forming protective silica but only in static environments and to ~1873 K (1600 °C). For higher temperature
applications, additions of La lead to the formation of a dense ZrO2 scale probably via liquid phase sintering. Such ceramic systems, which produce self-generating refractory oxidation barriers or dense ZrO2 scales, show the greatest promise in providing oxidation-resistant UHTCs. 相似文献
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Vedel D.V. Grigoriev O.N. Mazur P.V. Kozak I.V. 《Powder Metallurgy and Metal Ceramics》2022,60(11-12):685-697
Powder Metallurgy and Metal Ceramics - Ultrahigh-temperature hafnium diboride ceramics with additions of 15 vol.% MoSi2 or 15 vol.% SiC or a combined addition of 15 vol.% SiC and 5 vol.% WC were... 相似文献
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Sai Mahesh Yadav Kaku Asit Kumar Khanra M. J. Davidson 《Transactions of the Indian Institute of Metals》2018,71(7):1663-1668
The performance of the product components in application greatly depends on the morphological parameters and inherent capabilities of the material. In the present study, Al–ZrB2 composite is made out of powder metallurgy route. Incremental weight% (0, 2, 4 and 6 wt%) of ZrB2 were added into Al matrix to produce different composites. Composites were prepared by cold axial compaction followed by pressureless sintering at 550 °C for 1 h in controlled atmosphere (Ar gas). Hardness increased with the amount of ZrB2 in the composite. To enhance the properties further, composites were deformed at 25, 400 and 500 °C respectively. The size, shape and orientation of the grains in the deformed composites were analyzed and correlated with the mechanical properties. The mechanical adhesion of ZrB2 particle with the Al matrix was examined in different composites during different temperature conditions of deformation process. The fracture strain of the composites decreased with increase of ZrB2 in the composite. 相似文献
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Lejun Zhou Huan Li Wanlin Wang Dan Xiao Lei Zhang Jie Yu 《Metallurgical and Materials Transactions B》2018,49(5):2232-2240
The effect of Li2O content on the behavior of melting, crystallization, and molten structure for CaO-Al2O3-based mold fluxes was investigated in this article, through use of single hot thermocouple technology (SHTT), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction (XRD). The SHTT results showed that the melting temperature range of the designed mold fluxes decreases and the crystallization of mold fluxes is inhibited first and then becomes enhanced when the Li2O content increases from 1 to 6 mass pct. The FTIR and Raman spectroscopy results suggested that Li2O could release O2? ions to break the complex Al-O-Al structural unit into Al-O? structure. Meanwhile, Li2O could also stabilize the structural unit of Si-O-Al by link aluminate and Q 0 Si structure through providing Li+ ions to merge into the network and compensate for the charges between Al3+ and Si4+. Besides, the XRD results indicated that the precipitation of LiAlO2 in molten slag would enhance the crystallization behavior of mold flux when Li2O content is over 4.5 mass pct. 相似文献
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Tuncay Simsek Mustafa Baris Arun K. Chattopadhyay Sadan Ozcan Adnan Akkurt 《Transactions of the Indian Institute of Metals》2018,71(8):1885-1896
To improve mechanical properties of S2355JR carbon steel, pre-synthesized ZrB2 nanocrystals were used to coat the metal surface by laser cladding using 2000 W CO2 laser. ZrB2 nanocrystals were synthesized by mechanochemical process. The effect of laser power on the coating layers was examined for optimizing the most effective coating conditions. Microstructural studies were carried out using optical microscope, scanning electron microscope and X-ray diffraction to analyze phase structures of the coated layers. Mechanical characteristics of the laser coated layers were evaluated by studying microhardness, wear and scratch resistance properties. Maximum hardness of the coated layers was observed while cladding with 75 and 125 W laser powers, when other processing parameters and conditions were kept at optimum levels. EDS analysis of these laser cladded layers indicated the formation of complex boro-nitrides, nitrides and carbides of Zr and Fe that contributed to vast increase in hardness of the laser-clad coating on S2355JR steel. Depending upon the laser powers used, the thickness of the coated layers was found to be in the range of 15–37 µm. The wear and micro-scratch tests results revealed significant improvement in wear properties. 相似文献
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Haijuan Wang Lidong Teng Jiayun Zhang Seshadri Seetharaman 《Metallurgical and Materials Transactions B》2010,41(5):1042-1051
The oxidation mechanism of liquid Fe-V alloys with V content from 5 to 20 mass pct under different oxygen partial pressures
using CO2-O2 mixtures with CO2 varying from 80 pct to 100 pct was investigated by thermogravimetric analysis between 1823 K and 1923 K (1550 °C and 1650 °C).
The products after oxidation were identified by scanning electron microscopy energy-dispersive spectrograph and X-ray diffraction.
The results indicate that the oxidation process can be divided into the following steps: an apparent incubation period, followed
by a chemical reaction step with a transition step before the reaction, and diffusion as the last stage. At the initial stage,
a period of slow mass increase was observed that could be attributed to possible oxygen dissolution in the liquid iron-vanadium
coupled with the vaporization of V2O. The length of this period increased with increasing temperature as well as vanadium content in the melt and decreased with
increasing oxygen partial pressure of the oxidant gas. This analysis was followed by a region of chemical oxidation. The oxidation
rate increased with the increase of the O2 ratio in the CO2-O2 gas mixtures. During the final stage, the oxidation seemed to proceed with the diffusion of oxygen through the product layer
to the reaction front. The Arrhenius activation energies for chemical reaction and diffusion were calculated, and kinetic
equations for various steps were setup to describe the experimental results. The transition from one reaction mechanism to
the next was described mathematically as mixed-control equations. Thus, uniform kinetic equations have been setup that could
simulate the experimental results with good precision. 相似文献
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N. M. Barbin I. A. Sidash D. I. Terent’ev S. G. Alekseev 《Russian Metallurgy (Metally)》2018,2018(8):716-721
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The oxidation kinetics of two low-carbon steels in a flowing 17H2O-N2 gas mixture at 900 °C and the scale structures developed are examined. Similar linear and parabolic oxidation kinetics are
observed for the two steels, although some differences are observed within the first 5 minutes of oxidation and in the linear-to-parabolic
transition period. The oxidation behaviors observed in the linear kinetics stage are more consistent with published results,
exhibiting typical surface-reaction-controlled patterns. However, the observed parabolic oxidation rates are two orders of
magnitude smaller than those of iron and steel oxidation in air and oxygen as well as that predicted using Wagner’s parabolic
oxidation theory. Similar oxide scale structures are observed on the two steels for the samples oxidized for more than 15 minutes.
The surfaces of the scales exhibit pyramidal, faceted grain structures with growth ledges developed on some crystal faces
and growth pits at the peaks of the pyramidal grains. In their cross sections, the scales have a columnar structure and appear
two layered, with a thin, outer magnetite layer and an inner, growing wustite layer. The wustite grains coarsen with increased
oxidation time and develop a growth texture with preferred (111) and (110) orientations in parallel to the sample surface
after oxidation for longer than 60 minutes. Conventional oxidation theories cannot provide a satisfactory explanation of the
apparently conflicting results observed during the parabolic oxidation stage. 相似文献
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James L. Smialek 《Metallurgical and Materials Transactions A》2018,49(3):782-792
High temperature oxidation of alumina-forming MAX phases, Ti2AlC and Cr2AlC, were examined under turbine engine environments and coating configurations. Thermogravimetric furnace tests of Ti2AlC showed a rapid initial transient due to non-protective TiO2 growth. Subsequent well-behaved cubic kinetics for alumina scale growth were shown from 1273 K to 1673 K (1000 °C to 1400 °C). These possessed an activation energy of 335 kJ/mol, consistent with estimates of grain boundary diffusivity of oxygen (~375 kJ/mol). The durability of Ti2AlC under combustion conditions was demonstrated by high pressure burner rig testing at 1373 K to 1573 K (1100 °C to 1300 °C). Here good stability and cubic kinetics also applied, but produced lower weight gains due to volatile TiO(OH)2 formation in water vapor combustion gas. Excellent thermal stability was also shown for yttria-stabilized zirconia thermal barrier coatings deposited on Ti2AlC substrates in 2500-hour furnace tests at 1373 K to 1573 K (1100 °C to 1300 °C). These sustained a record 35 µm of scale as compared to 7 μm observed at failure for typical superalloy systems. In contrast, scale and TBC spallation became prevalent on Cr2AlC substrates above 1423 K (1150 °C). Cr2AlC diffusion couples with superalloys exhibited good long-term mechanical/oxidative stability at 1073 K (800 °C), as would be needed for corrosion-resistant coatings. However, diffusion zones containing a NiAl-Cr7C3 matrix with MC and M3B2 particulates were commonly formed and became extensive at 1423 K (1150 °C). 相似文献
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The Cu solubility was measured in the CaO-B2O3 and BaO-B2O3 slag systems to understand the dissolution mechanism of Cu in the slags. The Cu solubility had a linear relationship with
oxygen partial pressure in the CaO-B2O3 slag system, which corresponds with previous studies. Also, the Cu solubilities in slag decreased with increasing the slag
basicity, which value of slope was close to –0.5 in logarithmic form. From the results of experiment, the Cu dissolution mechanism
established as follows:
\textCu + \frac14\textO2 = \textCu + + \frac12\textO2 - {\text{Cu}} + \frac{1}{4}{\text{O}}_{2} = {\text{Cu}}^{ + } + \frac{1}{2}{\text{O}}^{2 - } 相似文献
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W. Kai I.F. Ren B. Barnard P.K. Liaw M.D. Demetriou W.L. Johnson 《Metallurgical and Materials Transactions A》2010,41(7):1720-1725
The oxidation behavior of both Pd43Cu27Ni10P20 bulk metallic glass (Pd4-BMG) and its amorphous foam containing 45 pct porosity (Pd4-AF) was investigated over the temperature
range of 343 K (70 °C) to 623 K (350 °C) in dry air. The results showed that virtually no oxidation occurred in the Pd4-BMG
at T < 523 K (250 °C), revealing the alloy’s favorable oxidation resistance in this temperature range. In addition, the oxidation
kinetics at T ≥ 523 K (250 °C) followed a parabolic-rate law, and the parabolic-rate constants (k
p
values) generally increased with temperature. It was found that the oxidation k
p
values of the Pd4-AF are slightly lower than those of the Pd4-BMG, indicating that the porous structure contributes to improving
the overall oxidation resistance. The scale formed on the alloys was composed exclusively of CuO at T ≥ 548 K (275 °C), whose thickness gradually increased with increasing temperature. In addition, the amorphous structure remained
unchanged at T ≤ 548 K (275 °C), while a triplex-phase structure developed after the oxidation at higher temperatures, consisting of Pd2Ni2P, Cu3P, and Pd3P. 相似文献
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Understanding the viscous behavior of copper smelting slags is essential in increasing the process efficiency and obtaining
the discrete separation between the matte and the slag. The viscosity of the FeOt-SiO2-Al2O3 copper smelting slags was measured in the current study using the rotating spindle method. The viscosity at a fixed Al2O3 concentration decreased with increasing Fe/SiO2 ratio because of the depolymerization of the molten slag by the network-modifying free oxygen ions (O2−) supplied by FeO. The Fourier transform infrared (FTIR) analyses of the slag samples with increasing Fe/SiO2 ratio revealed that the amount of large silicate sheets decreased, whereas the amount of simpler silicate structures increased.
Al2O3 additions to the ternary FeOt-SiO2-Al2O3 slag system at a fixed Fe/SiO2 ratio showed a characteristic V-shaped pattern, where initial additions decreased the viscosity, reached a minimum, and increased
subsequently with higher Al2O3 content. The effect of Al2O3 was considered to be related to the amphoteric behavior of Al2O3, where Al2O3 initially behaves as a basic oxide and changes to an acidic oxide with variation in slag composition. Furthermore, Al2O3 additions also resulted in the high temperature phase change between fayalite/hercynite and the modification of the liquidus
temperature with Al2O3 additions affecting the viscosity of the copper smelting slag. 相似文献
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H. B. Fan W. Zheng G. Y. Wang P. K. Liaw J. Shen 《Metallurgical and Materials Transactions A》2011,42(6):1524-1533
An Fe41Co7Cr15Mo14C15B6Y2 bulk metallic glass with a diameter of 5 mm was prepared with the copper-mold-casting method. The corrosion resistance of
this amorphous steel in sulfuric-acid solutions was determined by electrochemical measurements. The passive film formed on
the surface of the alloy after immersion in the 0.5-mol/l H2SO4 solution for 1 week was analyzed by X-ray photoelectron spectroscopy (XPS). Electrochemical measurements show that the corrosion
resistance of the amorphous steel in the 1 mol/l-H2SO4 solution is superior to a stainless steel (SUS 321), and is almost the same as Ti6Al4V, which shows that the amorphous steel
has an excellent corrosion resistance in sulfuric-acid solutions. As the concentration of the sulfuric-acid solutions increases
from 0.5 mol/l to 4 mol/l, the corrosion resistance of the amorphous steel decreases. The XPS result reveals that a bilayer
structure of protective film formed on the surface of the amorphous steel in a H2SO4 solution. The compositions of the inner part of the film are MoO2, Cr2O3, CoO, and FeO, and those of the outer film are MoO3, Cr(OH)3, Co(OH)2, and Fe(OH)3. 相似文献
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Hengwei Yan Jianhong Yang Wangxing Li Shazi Chen 《Metallurgical and Materials Transactions B》2011,42(5):1065-1070
KF-NaF-AlF3-based electrolyte is a promising low-temperature electrolyte for aluminum reduction. Alumina solubility in molten KF-NaF-AlF3-based electrolyte was determined as a function of the melt composition and temperature by measuring the weight loss of a
rotating corundum disk and by using a LECO RO500 oxygen analyzer (LECO Corporation, St. Joseph, MI). The investigated temperature
range is 1023 K to 1073 K (750 °C to 800 °C), and the total cryolite molar ratio (CRt = ([KF] + [NaF])/[AlF3]) is 1.3 to 1.5; the content of NaF ranges from 0 mol pct to 50 mol pct. The effect of temperature, CaF2, and LiF on alumina solubility is discussed as well. 相似文献
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