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1.
2.
Tatsuo Tabaru Jin-Hak Kim Kazuhisa Shobu Michiru Sakamoto Hisatoshi Hirai Shuji Hanada 《Metallurgical and Materials Transactions A》2005,36(3):617-626
Mo(Si,Al)2-base oxidation-resistant coatings for Nb-base structural materials have been studied. The coating is composed of a Mo(Si,Al)2-base Al reservoir and Al2O3 interlayer to suppress interface reactions between the Al reservoir and the substrate. To develop a suitable Al-reservoir
material, some Mo(Si0.6,Al0.4)2-HfB2 composites were prepared. Their oxidation resistance and coefficients of thermal expansion were investigated, in addition
to their chemical reactivity with the Nb substrate at high temperatures. As a result, Mo(Si0.6,Al0.4)2-20 vol pct HfB2 was selected as one of the satisfactory Al reservoirs. The introduction of a stable Al2O3 interlayer was attempted using a novel powder metallurgical process to overlay the Nb substrates with the Al reservoir, where
the Nb substrates were subjected to a slight surface oxidation prior to the coating process. The Nb specimens, which are thoroughly
coated with the Al reservoir and Al2O3 interlayer, can be successfully fabricated by this method. The coated Nb specimens are not damaged at all after prolonged
exposure in flowing Ar-20 pct O2 at 1673 K for 120 hours. Furthermore, the Al2O3 interlayer is very effective and no reactions occur at the interface. Thus, this Mo(Si,Al)2-base oxidation-resistant coating is applicable to Nb. The utility of the coating system is also confirmed for a NbSS/Nb5Si3 composite.
This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place
March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects
Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory
Metals Committee. 相似文献
3.
Ramaraghavulu Rajavaram Hyelim Kim Chi-Hoon Lee Won-Seung Cho Chi-Hwan Lee Joonho Lee 《Metallurgical and Materials Transactions B》2017,48(3):1595-1601
The effect of Al2O3 concentration on the density and structure of CaO-SiO2-Al2O3 slag was investigated at multiple Al2O3 mole percentages and at a fixed CaO/SiO2 ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al2O3 content was less than 15 mole pct, density decreased with increasing Al2O3 content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al3+ ion as a network modifier. 相似文献
4.
In-situ Al2O3/TiAl3 intermetallic matrix composites were fabricated via squeeze casting of TiO2/A356 composites heated in the temperature range from 700 °C to 780 °C for 2 hours. The phase transformation in TiO2/A356 composites employing various heat-treatment temperatures (700 °C to 780 °C) was studied by means of differential thermal
analysis (DTA), microhardness, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction
(XRD). From DTA, two exothermic peaks from 600 °C to 750 °C were found in the TiO2/A356 composites. The XRD showed that Al2O3 and TiAl3 were the primary products after heat treatment of the TiO2/A356 composite. The fabrication of in-situ Al2O3/TiAl3 composites required 33 vol pct TiO2 in Al and heat treatment in the range from 750 °C to 780 °C. The hardness (HV) of the in-situ Al2O3/TiAl3 composites (1000 HV) was superior to that of nonreacted TiO2/A356 composites (200 HV). However, the bending strength decreased from 685 MPa for TiO2/A356 composites to 250 MPa for Al2O3/TiAl3 composites. It decreased rapidly because pores occurred during the formation of Al2O3 and TiAl3. The activation energy of the formation of Al2O3 and TiAl3 from TiO2 and A356 was determined to be about 286 kJ/mole. 相似文献
5.
A magnesium-based composite with 1.1 volume percentage of nanosized Al2O3 particulates reinforcement was fabricated using an innovative disintegrated melt deposition technique followed by hot extrusion.
Al2O3 particulates with an equivalent size of 50 nm were used as reinforcement. Microstructural characterization of the materials
revealed grain refinement of magnesium matrix due to incorporation, retention, and uniform distribution of reinforcement.
Physical properties characterization revealed that the addition of nano-Al2O3 particulates as reinforcement improves the dimensional stability of pure magnesium. Mechanical properties characterization
revealed that the presence of nano-Al2O3 particulates as reinforcement leads to a significant increase in microhardness, dynamic elastic modulus, 0.2 pct yield strength
(YS), ultimate tensile strength (UTS), and ductility of pure magnesium. The results revealed that the combined tensile properties
of these materials are superior when compared to Mg reinforced with much higher volume percentage of SiC. An attempt is made
in the present study to correlate the effect of nano-Al2O3 particulates as reinforcement with the microstructural, physical, and mechanical properties of magnesium. 相似文献
6.
In the present work, the relationship between the microscopic structure and macroscopic thermophysical properties in a basic CaO-SiO2-MgO-Al2O3 quaternary system was identified using Fourier transformation infrared, Raman and 27Al magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The Raman spectra quantitatively proved that with increasing Al2O3 content, the concentrations of the symmetric units of Q0(Si) and Q2(Si) decreased, while those of the asymmetric units of Q1(Si) and Q3(Si) increased; consequently, the degree of polymerization of the networks increased, which resulted in an increase in slag viscosity. The 27Al MAS-NMR spectra demonstrated that three structural units of Al atoms, namely, AlO4, AlO5, and AlO6, mainly existed in the networks. With increasing Al2O3 content, the concentration of AlO4 slightly decreased, while those of AlO5 and AlO6 increased; overall, Al2O3 acted as a network former in the present system. The increasing Al2O3 content led to additional AlO6 and Si-NBO-Ca-NBO-Al frameworks, which replaced Si-NBO-Ca-NBO-Si in the networks (NBO: non-bridging oxygen) and induced a change in the primarily precipitated crystalline phase from Ca2MgSi2O7 and Ca2Al2SiO7 to MgAlO4. 相似文献
7.
Saeed Sheibani Abolghasem Ataie Saeed Heshmati-Manesh 《Metallurgical and Materials Transactions A》2010,41(10):2606-2612
In this article, a novel method has been used to prepare a copper matrix nanocomposite containing Cu-10 wt pct Cr-10 wt pct
Al2O3 by heat treatment of the mechanically activated Cu, Al, and Cr2O3 powder mixture. Structural evolutions were investigated using the X-ray diffraction (XRD) technique. The microstructure of
samples was examined using scanning electron microscopy (SEM). It was found that during the milling process, Cu(Al) solid
solution and Cu9Al4 phase were formed as the intermediate products, and therefore, Al activity was decreased. Hence, the reduction of Cr2O3 with Al was prevented during the ball milling stage. Further heat treatment carried out under argon atmosphere at 900 °C
for 8 hours resulted in completion of Cr2O3 reduction by Al. 相似文献
8.
In an attempt to systematize the knowledge of the heat conduction of liquid silicates, the effective thermal diffusivities
of some synthetic slags containing CaO, Al2O3, and SiO2 have been measured, using the three-layer laser-flash method on a differential scheme in the temperature range of 1625 to
1825 K. The effective thermal diffusivities measured, which are a combination of the phononic and photonic heat-transfer mechanisms,
were found to increase with increasing temperature for all the presently investigated slags. The slag compositions were chosen
in such a way that the changes in the effective thermal diffusivities would reflect the changes in the structure of the slags.
It was observed that, at a CaO/Al2O3 molar ratio of 4.42, an increase of the SiO2 content had very little effect on the effective thermal diffusivity values. On the other hand, addition of SiO2 to a slag with the CaO/Al2O3 molar ratio of 2.59 resulted in a significant increase in the effective thermal diffusivity. The addition of Al2O3 to slags with a constant CaO/SiO2 molar ratio resulted in a marked increase in the effective thermal diffusivity. Both these trends indicate that there might
be an influence of the network formation in silicate melts on the effective thermal diffusivity. 相似文献
9.
A. S. Anikeev I. V. Blinkov V. V. Ivanov A. I. Laptev V. S. Chelnokov I. Yu. Kuchina 《Russian Journal of Non-Ferrous Metals》2017,58(4):449-455
Samples of Al2O3–TiO2 coatings are fabricated by the flame spraying of a flexible cord. The influence of process parameters and composition of the sprayed material on the structure, composition, and mechanical properties of coatings is investigated. It is shown that an increase in the spraying distance and feed rate of the sprayed material leads to a decrease in their density. An increase in the concentration of the low-melting TiO2 component predetermines a decrease in the coating porosity and has no significant effect on the coating hardness. Being subjected to measuring scratching, Al2O3–TiO2 flame coatings formed with minimal porosity (Π = 3.2%) are characterized by cohesion fracture behavior and no substrate opening under an indenter load of up to 90 N. The friction factor of coatings under study varies from 0.2 to 0.78 after 2800 counterbody revolutions (44 m of the friction path). This is associated with the accumulation of fatigue cracks in the coating material and its subsequent cohesive fracture by the formation of large fragments serving as an abrasive. 相似文献
10.
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
11.
Vinay Pratap Singh Anjan Sil R. Jayaganthan 《Transactions of the Indian Institute of Metals》2012,65(1):1-12
An ever increasing demand for high-performance ceramic coatings has made it inevitable for developing techniques with precise
control over the process parameters to enable the fabrication of coatings with the desired microstructure and improved structural
properties. The literature on plasma sprayed nanostructured ceramic coatings such as of Al2O3, Cr2O3, and their composites obtained using reconstituted nano sized ceramic powders has been reviewed in this study. Ceramic coatings
due to their enhanced properties are on the verge of replacing conventional ceramic coatings used for various applications
like automotive systems, boiler components, power generation equipment, chemical process equipment, aircraft engines, pulp
and paper processing equipment, land-based and marine engine components, turbine blades etc. In such cases, the advantage
is greater longevity and reliability for realizing the improved performance of ceramic coatings. It has been observed that
the plasma sprayed nanostructured ceramic coatings show improvement in resistance to wear, erosion, corrosion, and mechanical
properties as compared to their conventional counterparts. This article reviews various aspects concerning the plasma sprayed
ceramic coatings such as (i) the present understanding of formation of plasma-spray coatings and factors affecting them, (ii)
wear performance of nanostructured Al2O3, Cr2O3 and their composite ceramic coatings in comparison to their conventional counterparts, and (iii) mechanisms of wear observed
for these coatings under various conditions of testing. 相似文献
12.
Refractive indexes for the Al2O3-Na2O-SiO2 system have been measured using an ellipsometer for a wavelength of 632.8 nm over a wide temperature range (1100 to 1800
K). Two kinds of sample were used: xAl2O3-(40-x)Na2O-60SiO2 and yAl2O3-yNa2O-(100-2y)SiO2, where x ranged between 6 and 20 mol pct and y between 12.5 and 25 mol pct. In the former samples, the temperature coefficient of refractive indexes changed from negative
to positive on increasing the concentration of Al2O3. In the latter samples, the refractive indexes increased monotonically with decreasing concentration of SiO2, and the temperature coefficient was always positive. It has been found that the temperature dependence of refractive indexes
in these melts is determined by the coefficient of thermal expansion, which would be relevant to the degree of polymerization
of the melts. In addition, the electronic polarizability of oxygen derived from the refractive indexes increased with increasing
temperature in each melt. This suggests that the basicity of the alumino-silicate melts increases as temperature increases.
The positive temperature coefficient of the electronic polarizability of oxygen can be attributed to an increase in the distance
between cation and oxygen ion due to thermal expansion. The dependence of the electronic polarizability of oxygen on the concentration
of Al2O3 has also been discussed in terms of the electronic polarizabilities of three types of oxygen contained in the melts.
This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties
& Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002. 相似文献
13.
Joo Hyun Park Dong Joon Min Hyo Seok Song 《Metallurgical and Materials Transactions B》2004,35(2):269-275
The viscosity of CaO-SiO2 (-MgO)-Al2O3 slags was measured to clarify the effects of Al2O3 and MgO on the structure and viscous flow of molten slags at high temperatures. Furthermore, the infrared spectra of the
quenched slags were analyzed to understand the structural role of Al2O3 in the polymerization or depolymerization of silicate network. The Al2O3 behaves as an amphoteric oxide with the composition of slags; that is, the alumina behaves as a network former up to about
10 mass pct Al2O3, while it acts as a network modifier, in parts, in the composition greater than 10 mass pct Al2O3. This amphoteric role of Al2O3 in the viscous flow of molten slags at the Newtonian flow region was diminished by the coexistence of MgO. The effect of
Al2O3 on the viscosity increase can be understood based on an increase in the degree of polymerization (DOP) by the incorporation
of the [AlO4]-tetrahedra into the [SiO4]-tetrahedral units, and this was confirmed by the infrared (IR) spectra of the quenched slags. The influence of alumina on
the viscosity decrease can be explained on the basis of a decrease in the DOP by the increase in the relative fraction of
the [AlO6]-octahedral units. The relative intensity of the IR bands for the [SiO4]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO4]-tetrahedra with high NBO/Si increased with increasing Al2O3 content greater than the critical point, i.e., about 10 mass pct in the present systems. The variations of the activity coefficient of slag components with composition
indirectly supported those of viscosity and structure of the aluminosilicate melts. 相似文献
14.
A. M. Patselov S. V. Gladkovskii R. D. Lavrikov I. S. Kamantsev 《Russian Metallurgy (Metally)》2015,2015(10):811-815
The static and cyclic fracture toughnesses of a Ti–Al3Ti–Al–Al3Ti laminate composite material containing at most 15 vol % intermetallic compound are studied. Composite specimens are prepared by terminating reaction sintering of titanium and aluminum foils under pressure. The fracture of the titanium layers is quasi-cleavage during cyclic crack growth and is ductile during subsequent static loading. 相似文献
15.
A thermodynamic equilibrium between the Fe-16Cr melts and the CaO-Al2O3-MgO slags at 1823 K as well as the morphology of inclusions was investigated to understand the formation behavior of the
MgO-Al2O3 spinel-type inclusions in ferritic stainless steel. The calculated and observed activities of magnesium in Fe-16Cr melts
are qualitatively in good agreement with each other, while those of aluminum in steel melts exhibit some discrepancies with
scatters. In the composition of molten steel investigated in this study, the log (X
MgO/X
Al
2O3) of the inclusions linearly increases by increasing the log [a
Mg/a
Al
2
·a
O
2
] with the slope close to unity. In addition, the relationship between the log (X
MgO/X
Al
2O3) of the inclusions and the log (a
MgO/a
Al
2O3) of the slags exhibits the linear correlation with the slope close to unity. The compositions of the inclusions are relatively
close to those of the slags, viz. the MgO-rich magnesia-spinel solid solutions were formed in the steel melts equilibrated with the highly basic slags saturated
by CaO or MgO. The spinel inclusions nearly saturated by MgO were observed in the steel melts equilibrated with the slags
doubly saturated by MgO and MgAl2O4. The spinel and the Al2O3-rich alumina-spinel solid solutions were formed in the steel melts equilibrated with the slags saturated by MgAl2O4 and MgAl2O4-CaAl2O4 phases, respectively. The apparent modification reaction of MgO to the magnesium aluminate inclusions in steel melts equilibrated
with the highly basic slags would be constituted by the following reaction steps: (1) diffusion of aluminum from bulk to the
metal/MgO interface, (2) oxidation of the aluminum to the Al3+ ions at the metal/intermediate layer interface, (3) diffusion of Al3+ ions and electrons through the intermediate layer, and (4) magnesium aluminate (MgAl2O4 spinel, for example) formation by the ionic reaction. 相似文献
16.
Ghasem Roghani Evgueni Jak Peter Hayes 《Metallurgical and Materials Transactions B》2003,34(2):173-182
Phase-equilibrium data and liquidus isotherms for the system “MnO”-CaO-(Al2O3+SiO2) at silicomanganese alloy saturation have been determined in the temperature range of 1373 to 1723 K. The results are presented
in the form of the pseudoternary sections “MnO”-CaO-(Al2O3+SiO2) with Al2O3/SiO2 weight ratios of 0.55 and 0.65. The primary-phase fields have been identified in this range of conditions. 相似文献
17.
Cu-10Cr-3Ag (wt pct) alloy with nanocrystalline Al2O3 dispersion was prepared by mechanical alloying and consolidated by high pressure sintering at different temperatures. Characterization
by X-ray diffraction and scanning electron microscopy or transmission electron microscopy shows the formation of nanocrystalline
matrix grains of about 40 nm after 25 hours of milling with nanometric (<20 nm) Al2O3 particles dispersed in it. After consolidation by high pressure sintering (8 GPa at 400 °C to 800 °C), the dispersoids retain
their ultrafine size and uniform distribution, while the alloyed matrix undergoes significant grain growth. The hardness and
wear resistance of the pellets increase significantly with the addition of nano-Al2O3 particles. The electrical conductivity of the pellets without and with nano-Al2O3 dispersion is about 30 pct IACS (international annealing copper standard) and 25 pct IACS, respectively. Thus, mechanical
alloying followed by high pressure sintering seems a potential route for developing nano-Al2O3 dispersed Cu-Cr-Ag alloy for heavy duty electrical contact. 相似文献
18.
J. L. Santos R. L. S. B. Marçal P. R. R. Jesus A. V. Gomes E. P. LimaJr. S. N. Monteiro J. B. de Campos L. H. L. Louro 《Metallurgical and Materials Transactions A》2017,48(10):4432-4440
Different amounts of LiF were added to an Al2O3-4 pct Nb2O5 basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb3O7F, but also to the absence of LiAl5O8. The preferential interaction of LiF with Nb2O5, instead of Al2O3, contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds. 相似文献
19.
In this article, the effect of CaS formation on the evolution of Al2O3-CaO inclusions in low-carbon Al-killed and Ca-treated steel during the solidification process is investigated through high-temperature
confocal scanning laser microscopy (CSLM). The inclusions started as mostly liquid-globular inclusions that did not agglomerate
with each other on the melt surface but during solidification were seen to change shape into an irregular morphology. The
shape change was found to be due to the reaction between the Al2O3-CaO inclusions with the dissolved S and Al in the melt, resulting in the formation of dense CaS shells around the inclusions.
The melt composition during solidification, estimated from the observed solid δ-front advance rate, was compared to the thermodynamic limit for CaS precipitation. The observed growth rate of the CaS shell
was found to initially increase with decreasing temperature because of the higher, solid δ-front advance rates at lower temperatures, which results in higher rates of S and Al partitioning. Once CaS had precipitated,
the inclusions were found to form agglomerates on the melt surface because of fluid flow, initially, and later, the capillary
depression. 相似文献
20.
A. R. Kamali I. Babaei Nejad M. R. Aboutalebi H. Razavizadeh 《Russian Journal of Non-Ferrous Metals》2009,50(3):246-249
Titanium Aluminide based composites with Al2O3 reinforcement can be produced via reaction of Al with TiO2. These composites are considered as low price materials for high temperature applications. In this research, the effect of
ball milling on 3TiO2/7Al system was investigated. On the basis of obtained results, ball milling for 0 to 60 h does not lead to reduction of TiO2 by Al. but reduces the temperature of exothermic reaction.
The article is published in the original. 相似文献