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1.
Austenitic Fe-18Cr-20Ni-1.5Mn alloys containing 0, 0.6, and 1.5 wt.% Si were produced both by conventional and rapid solidification processing. The cyclic oxidation resistance of these alloys was studied at 900°C in a SO
2-O
2
gas mixture to elucidate the role of alloy microstructure and Si content on oxidation properties in bioxidant atmospheres. All the large-grained, conventionally processed alloys exhibited breakaway oxidation during cyclic oxidation due to their poor rehealing characteristics. The rapidly solidified, fine-grained alloys that contained less than 1.5 wt.% Si exhibited very protective oxidation behavior. There was considerable evidence of sulfur penetration through the protective chromia scale. The rapidly solidified alloys that contained 1.5 wt.% Si underwent repeated scale spallation that led to breakaway oxidation behavior. The scale spallation was attributed to the formation of an extensive silica sublayer in the presence of sulfur in the atmosphere. 相似文献
2.
A study has been undertaken of the oxidation behavior of Fe-26 wt.% Cr-1 wt.% Al and Fe-26 wt.% Cr-1 wt.% Si at 800° and 1000°C in oxygen, in order to determine the usefulness of the two tertiary elements in facilitating the development of the Cr2O3 external scale. The research has also permitted a comparison of the modes of internal oxidation of these elements, with a view to ascertaining the ease of establishment of the tertiary element oxides as healing layers at the scale/alloy interface. It has been shown that aluminum is the more effective addition in this respect, due to formation of a higher population density of internal oxide nuclei in the early stages. However, in the 1% Al alloy, the precipitates penetrate inward, to considerable depths, as continuous platelets, making development of a complete healing layer difficult. In practice, a higher aluminum concentration is necessary for the closely spaced precipitates to coalesce to form the healing layer, but the process then occurs rapidly. The initial internal oxide nuclei in the 1% Si alloy have a much smaller population density and are restricted to a location very close to the surface. Thus, a healing layer can be established, but the large interparticle spacing makes this a very slow process. Even at a higher silicon concentration, it takes a significant period to be completed. The effects are discussed and accounted for, particularly in terms of the relative stabilities of the various oxides. 相似文献
3.
The oxidation of Cu-Si alloys (containing up to 4.75 wt. % Si) in
=0.01 atm from 800 to 1000°C has been investigated using thermogravimetry and other techniques. A 0.04% Si alloy followed a parabolic oxidation law with a rate similar to that of pure Cu. As the Si concentration increased the rate decreased and became irregular owing to SiO2 particles or flakes at the alloy-scale interface. It is considered that sintering of SiO2 particles and rupture of the sinter because of contraction during sintering are responsible for the irregular kinetics. A SiO2 layer forms directly on the 4.75% Si alloy which oxidizes uniformly. The SiO2 was always amorphous. In pure CO2 a similar pattern of amorphous SiO2 particles, flakes, and layers occurs. 相似文献
4.
An investigation of the oxidation of nickel-silicon alloys has been carried out in order to ascertain the mode of development of partially or fully protective SiO2 layers. The addition of 1% Si has little effect on the oxidation rate of nickel at 1000°C but is sufficient for partial-healing layers of amorphous SiO2 to be established. These layers are incorporated into the inner part of the duplex NiO scale but do not react with the oxide to form a double oxide. Increasing the silicon concentration to 4% or 7% facilitates the development of apparently continuous amorphous SiO2 layers at the base of the NiO scale, resulting in reduced rates of oxidation. However, these layers develop imperfections, possibly microcracks resulting from oxide growth stresses, and are unable to prevent some continued transport of Ni2+ ions into the NiO scale and oxygen into the alloy, particularly for Ni-4% Si. Although the formation of SiO2-healing layers can reduce the rate of oxidation of nickel, they provide planes of weakness that result in considerable damage under the differential thermal contraction stresses during cooling. In particular, severe scale spalling occurs for Ni-4% Si and Ni-7% Si as failure occurs coherently within the SiO2 layer. 相似文献
5.
Effect of grain size reduction on high temperature oxidation of binary two-phase alloys 总被引:4,自引:0,他引:4
1 INTRODUCTIONMetallicmaterialsforhightemperatureapplica tionsoftencontainmorethanone phase ,andele mentsAl,CrandSiaremainlyintroducedtoimprovetheirmechanical properties ,suchasstrengthandcreepresistance .Thecorrosionresistanceoftheseal loysdependsontheira… 相似文献
6.
Jeffrey W. Fergus 《Oxidation of Metals》1997,48(3-4):201-214
In a recent study, CO2 has been reported to enhance the oxidation rate of binary titanium-aluminum alloys. The detrimental effect of CO2 was not, however, observed in a ternary alloy containing niobium. In this paper, possible explanations for these observations are examined. First, results from the literature regarding the effects of niobium in improving the resistance of titanium-aluminum alloys are briefly reviewed. Second, a thermodynamic analysis which offers a possible explanation for the beneficial effect of niobium in eliminating the CO2-enhanced oxidation of titanium-aluminum alloys is presented. 相似文献
7.
1 INTRODUCTIONTheoxidationofunalloyedcopperandnickelhasalreadybeenstudiedindetail.Whilethehigh tem peratureoxidationofCu Nialloys ,alsostudiedanumberoftimestodate[13] ,isanexampleofarela tivelysimpleclassofscalingofbinaryalloysbyasin gleoxidant,becausethemetalsformacontinuousse riesofsolidsolutions ,whiletheiroxides ,CuO ,Cu2 OandNiO ,exhibitsmallmutualsolubilitiesandshowsignificantdifferencesinthethermodynamicstabilityandparabolicgrowthrates .Thus ,copper richalloysformexternalscales… 相似文献
8.
Experiments were carried out to evaluate the effect of solute elements on grain refinement in aluminum based hypoeutectic alloys. Grain sizes of the as-cast structures were measured. The measured grain sizes were plotted vs. the undercooling parameter, P, the growth restriction factor, Q, and the solidification interval, ΔT, of the alloys. The results indicated that grain sizes decrease monotonically with increasing ΔT over the whole range of the hypoeutectic compositions whereas the relationships between the grain size and P or Q are “V” type curves. 相似文献
9.
Effect of NaCl vapor on the oxidation of Ni-Cr alloys 总被引:1,自引:0,他引:1
Ni-Cr alloys are known for their resistance to high temperature oxidation. The kinetics of scale formation and the nature of the scale in these alloys are affected by NaCl liquid or vapor. There have been a few investigations dealing with the influence of NaCl on long-time exposure. But the nature of reaction at short times can provide information on the initiation of such attack. In this investigation, Ni-Cr alloys with Cr varying from 0 to 25 wt% were exposed to NaCl vapor at 850°C for a few minutes. The surface chemistry of these alloys along with the unattached ones was analyzed by Auger electron spectroscopy. The nature of scale and the distribution of chlorine was found to vary with the Cr content in the alloys, which has a direct bearing on the rate of oxidation of these alloys in NaCl vapor. 相似文献
10.
The effect of alloy grain size on the transient oxidation behavior of an alumina-forming alloy 总被引:5,自引:0,他引:5
In the early stages of alloy oxidation, diffusion of solute through the metal to the surface is important in determining the composition of the oxide scale that forms during the transient stage. Rapid solute diffusion to the interface will promote the formation of a protective scale, thereby suppressing the formation of base-metal oxide. The effect of alloy grain size on the formation of the transient oxide scale has been studied using a very fine grained NiCrAlY alloy produced by plasma spraying. The long-term oxidation behavior of this alloy was found to be independent of the grain size of the underlying alloy. However, the short-term, transient oxidation rate was found to decrease with decreasing alloy grain size. This is attributed to the rapid grain boundary transport of Al and Cr to the oxide/metal interface which promoted the formation of Cr2O3 and Al2O3. 相似文献
11.
Oxidation studies were carried out in oxygen at 800°C, on a series of pure binary iron-based alloys with between 1.9 and 9.8 wt. % aluminum. The results are presented in conjunction with the existing literature and these permit the development of a classification of scale morphologies based on alloy composition. Alloys with less than about 2.4 wt. % aluminum form bulky stratified scales composed of Fe2O3 and Fe3O4 with FeAl2O4 and Al2O3 at the scale-metal interface. Alloys with between 2.4 and 6.9 wt. % form an external Al2O3 scale but this is interspersed with iron oxide nodules that penetrate the alloy substrate. Only alloys with greater than 6.9 wt. % aluminum form completely protective Al2O3 scales. Models based on oxide nucleation are presented for the growth of bulky scales and also the iron oxide nodules. 相似文献
12.
Compositional changes in the alloy beneath scales have been examined for the oxidation of Ni-27.4%Cr and Ni-40.2% Cr in 1 atm oxygen in the temperature range 1073–1473°K. Calculations of the rate of approach of the interfacial alloy composition to a constant value are compared with experimental data. Theoretical chromium depletion profiles obtained using both a finite difference analysis and an analytical expression are shown to be essentially equivalent and in good agreement with experimental measurements. The consequences of alloy depletion for the scaling behavior, when the protective scale is ruptured, are discussed. 相似文献
13.
The oxidation of an austenitic Fe-16.7% Mn-2.1% Ni-6.6% Si (by weight) alloy in SO2 in the temperature range 600–900°C is described. The corrosion products formed on this alloy in this environment below 800°C consist only of oxides, rather than a mixture of oxides and sulfides as is observed for unalloyed Fe or Mn. The kinetics of oxidation of the alloy in SO2 in this temperature range are similar to those in O2. It is proposed that these characteristics result from the presence of a thin silicate layer near the scale-metal interface that alters the gradient of oxygen potential within the scale. 相似文献
14.
The influence of superficially applied oxide powders on the high-temperature oxidation behavior of Cr2O3-forming alloys 总被引:1,自引:0,他引:1
The effects of superficially applied CeO2, mixed rare earth oxides, Co3O4, and Cr2O3 powders on the isothermal and cyclic oxidation of Ni-Cr alloys and the effects of CeO2 and MgO powders on the isothermal oxidation of Fe-25 wt.% Cr have been studied over the temperature range 940–1150°C in pure oxygen and dry air. The rates of oxidation of both the Ni- and Fe-base alloys were markedly reduced by the application of CeO2 powder. The presence of CeO2 also improved the scale adherence and resulted in marked changes in the oxidation morphology. The presence of Co3O4 or Cr2O3 powders on Ni-Cr alloys or MgO on Fe-Cr also produced changes in the oxidation morphology but did not decrease the rate of oxidation. These results are interpreted in terms of the influence of the oxide powders on the development of scale microstructure and their effectiveness in decreasing grain boundary transport in Cr2O3.This paper is based in part on the Ph.D. thesis of G. M. Ecer (1975) and in part on the M.S. thesis of R. B. Singh (1977). 相似文献
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16.
采用铜板空冷和铜辊甩带的方法,研究元素Y对Mg-Cu合金的组织结构和室温硬度的影响。研究表明:元素Y形成的化合物最终富集于枝晶网胞间。随着元素Y的添加,Mg-Cu二元合金试样的晶粒显著细化,显微硬度大幅提高。另外,在快速冷却条件下,Mg90 Cu5Y5试样的微观结构为微晶和非晶的夹杂,形成非晶的能力大大增强。 相似文献
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18.
This study investigated the influence of silicon content and pouring temperature on the shape of eutectic silicon in the hypoeutectic Al-Si strips produced by an unequal-diameter twin-roller strip caster. The strips had three different silicon contents; 6.35wt%, 8.89wt% and 10.67wt%. They were poured at various temperatures from 600 °C to 650 °C.The results indicate equiaxed cells in the central zone of the strips. While both acicular and granular eutectic silicon can be observed in this equiaxed-cell zone, the area of the zone with granular particles increases with decreasing pouring temperature in the strips of higher silicon content. Al-10.67wt% Si strip, having the highest silicon content, can obtain completely granular particles when poured at the lowest temperature of 600 °C.Acicular eutectic silicon particles which lead to crack initiation largely account for the elongation deterioration. Nonetheless, if the particles in the equiaxed-cell zone are partly or all granular, the elongation can be enhanced. Hence, increasing silicon content and lowering pouring temperature to modify the eutectic silicon in the equiaxed-cell zone from acicular to granular can improve the ductility. 相似文献
19.
1 INTRODUCTIONChromium, aluminum, and silicon can formsatisfactory protective scales on Ni based alloys.Chromium is expensive and not suitable for use attemperatures above 1 000℃ due to the evaporationof CrO3. It has also been well established that theincorporation of Si in many alloy systems has abeneficial effect on their oxidation resistance[1, 2].In addition, silicon is abundant and cheap. More over, Si has one of the largest solubility in Ni3Alwhere it … 相似文献
20.
The influence of strontium addition and solidification rate on eutectic grain structure in a near-eutectic AI-Si alloy was investigated. The characteristic temperature of eutectic nucleation (TN),minimum temperature prior to recalescence (TM),and the growth temperature (TG) during cooling were determined by quantitative thermal analysis. All characteristic temperatures were found to decrease continuously with increasing Sr content and solidification rate. Microstructural analysis also revealed that the eutectic grain size decreases with increasing Sr content and solidification rate. Such eutectic grain refinement is attributed to the increased actual under-cooling ahead of the liquid/solid interface during solidification. 相似文献