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  • 11
    Digitale Medien
    Digitale Medien
    The high-temperature oxidation of Ni-20%Cr alloys containing various oxide dispersions (1975)
    Springer
    Oxidation of metals 9 (1975), S. 275-305 
    Details
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Ni-Cr alloys ; rare-earth oxide dispersion ; dispersion-strengthened alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of Ni-20%Cr alloys containing approximately 3 vol.% Y2O3, ThO2, and A12O3 as dispersed particles has been examined in the temperature range 900 to 1200° C in slowly flowing oxygen at 100 Torr. The results show that the oxidation behavior of the Y2O3-, ThO2-, Al2O3-, and Ce02-containing alloys is very similar and that some anomalies in the behavior of the ThO2-containing alloy might be explained by the slower rate of chromium diffusion in this coarse-grained alloy. Two Al2O3-containing alloys were studied. One with a relatively coarse dispersoid size behaved in a manner analogous to a dispersion-free Ni-30% Cr alloy at 1100°C. The other alloy contained a dispersion of fine Al2O3 particles and behaved exactly like the Y2O3-containing alloy at 1000 and 1100°C, but at 1200° C oxidized at a faster rate. It has been shown that the adherent scales on dispersion-containing alloys have a stabilized fine grain size, whereas the nonadherent scales on dispersion-free alloys undergo grain growth.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00613277
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  • 12
    Digitale Medien
    Digitale Medien
    The high-temperature oxidation of cobalt-21 wt.% chromium-3 vol.% Y2O3 alloys (1972)
    Springer
    Oxidation of metals 5 (1972), S. 59-84 
    Details
    ISSN: 1573-4889
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Alloys of Co-21 wt. % Cr-3 vol. % Y 2 O 3 have been prepared by a mechanical alloying method, and oxidized in oxygen at 100 Torr in the temperature range 900–1200°C. The general effects of the dispersed oxide phase are similar to those reported for nickel-base alloys: the selective oxidation of chromium to form a continuous protective Cr 2 O 3 scale is promoted; the rate of growth of Cr 2 O 3 is reduced compared to dispersoid-free alloys; the adhesion of the Cr 2 O 3 is greatly improved; and the scale-forming reaction is probably at the scale-metal interface in the alloys containing the dispersoid, whereas it is at the scale-oxygen interface in dispersoid-free alloys. This last point has not been positively demonstrated. The improvement in adhesion is of particular significance, since the scales on cobalt-base alloys are prone to spallation, and it has been possible to study the mechanism of adhesion in more detail. It appears that in dispersoid-free material the metal recedes from the scale-metal interface, leaving the scale supported on the tops of metal “peaks” but this does not happen in the alloy containing the dispersoid, either because the growth direction of the scale has been changed, or because of changes in the substrate grain size. In general, the observations support the model proposed in an early study for the oxidation of Ni-20 wt.% Cr alloys containing oxide dispersions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00614619
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  • 13
    Digitale Medien
    Digitale Medien
    Observations on the role of oxide scales in high-temperature erosion-corrosion of alloys (1986)
    Springer
    Oxidation of metals 25 (1986), S. 175-199 
    Details
    ISSN: 1573-4889
    Schlagwort(e): high-temperature oxidation ; erosion ; erosion-corrosion mechanisms ; high-temperature alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The results are presented of exposure to a controlled high-temperature erosive gas stream of a series of alloys, which were selected to represent the range of microstructures and mechanical properties available in commercial high-temperature alloys. Analysis of the kinetic and morphological data suggested that the high-temperature oxidation behavior of a given alloy plays a very important role in determining its erosion-corrosion behavior under the conditions studied. In terms of relative behavior, alloys which are weak but ductile at temperature, and which form tenacious oxide scales, exhibited the highest resistance to high-temperature erosion-corrosion. Simple models were developed to describe the expected interaction between high-temperature oxidation and erosion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00655896
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  • 14
    Digitale Medien
    Digitale Medien
    Influence of solid-state CaS-CaO-CaSO4 deposits on corrosion of high-temperature alloys in simulated FBC environments (1989)
    Springer
    Oxidation of metals 31 (1989), S. 325-340 
    Details
    ISSN: 1573-4889
    Schlagwort(e): sulfidation ; nickel-base alloys ; iron-base alloys ; fluidized-bed combustion ; deposit-related attack
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract This study addresses questions concerning the likelihood of sulfidation attack of heat-exchanger alloys beneath deposits of sulfur-sorbent material in fluidized-bed combustors. Alloy specimens were exposed at 900°C in calcium sulfate-calcium oxide and calcium sulfide-calcium oxide mixtures, in environments in which the oxygen partial pressures were fixed at values corresponding to the equilibrium values for each solids mixture, using controlled ratios of CO and CO2. The only source of sulfur in these systems was the calcium sulfate or sulfide. Sulfidation attack of nickel-base alloys occurred in both mixtures, the calcium sulfide-calcium oxide mixture being the more aggressive. Iron-base alloys were less susceptible to attack, although susceptibility increased with increasing nickel content. FeCrAlY-type alloys were resistant to attack. Comparison with corrosion behavior under conditions in which the oxygen and sulfur partial pressures were the same as those used here, but in which the sulfur source was in the gas phase, indicates that the form of the sulfidation attack is similar but that its progress is much slower under solid deposits.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00846692
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  • 15
    Digitale Medien
    Digitale Medien
    Sulfidation and sulfidation-oxidation of nickel- and cobalt-base alloys containing dispersions of stable oxides (1974)
    Springer
    Oxidation of metals 8 (1974), S. 361-377 
    Details
    ISSN: 1573-4889
    Schlagwort(e): sulfidation ; sulfidation/oxidation ; hot corrosion ; nickel alloys ; cobalt alloys ; oxide dispersions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The presence of a fine dispersion of a stable oxide is known to have a beneficial effect on the oxidation resistance of nickel- and cobalt-base heat-resisting alloys. This paper presents some preliminary experimental results relating to the hot-corrosion resistance of these alloys. Alloys forming Cr 2O3 scales appear to be resistant to oxidation when coated with sodium sulfate, whereas an alloy normally forming an Al 2O3 scale suffers accelerated attack. During sulfidation some of the alloys suffer an accelerated degradation, with sulfur penetrating rapidly along what appear to be grain boundaries. The same effect is noted in sulfidation-oxidation experiments, when the Cr 2O3-forming alloys suffer accelerated oxidation, the effect of the dispersoid being apparently removed. An Al 2O3-forming alloy resists this form of attack well. The sodium sulfate-coated test is probably a good guide to the behavior under weakly corroding conditions, whereas the sulfidation-oxidation test may give a better indication of the behavior under highly aggressive conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00603387
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  • 16
    Digitale Medien
    Digitale Medien
    The isothermal oxidation of Co-Cr alloys in 760 Torr oxygen at 1000°C (1977)
    Springer
    Oxidation of metals 11 (1977), S. 163-191 
    Details
    ISSN: 1573-4889
    Schlagwort(e): cobalt-chromium ; oxidation ; oxygen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The isothermal oxidation of Co-Cr alloys containing 0–30% Cr in 760 Torr oxygen at 1000° C has been studied kinetically and by appropriate physical techniques. Chromium additions to cobalt increase the parabolic oxidation rate to an almost constant level from 2 to 15% Cr, while further additions to 20–30% Cr decrease the rate. All the alloys produce a virtually pure CoO layer outside a layer containing Co-Cr spinel particles in a Cr3+ -doped CoO matrix. The variation of oxidation rate with alloy chromium content is explained in terms of the complex interplay of doping, blocking of cation transport by voids and spinel particles and short circuiting by transport of dissociative oxygen across these voids and other processes, internal oxidation making a negligible direct contribution to weight gain. Complete spinel layers are never quite developed under the conditions studied, although formation of spinel does slow the oxidation rate. The improved protection eventually obtained at higher chromium levels is produced by the tendency to form a Cr2O3 healing layer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00606542
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  • 17
    Digitale Medien
    Digitale Medien
    Hot Corrosion of an EB-PVD Thermal-Barrier Coating System at 950°C (2000)
    Springer
    Oxidation of metals 54 (2000), S. 401-424 
    Details
    ISSN: 1573-4889
    Schlagwort(e): hot-corrosion testing ; MCrAlY-type bond-coat alloys ; EB–PVD thermal barrier coatings ; oxide-scale fluxing ; biomass-derived fuel combustion atmosphere
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Model thermal-barrier coating (TBC) systems consisting of cast NiCrAlYsubstrates and electron-beam, physically vapor-deposited (EB–PVD)partially yttria-stabilized zirconia (PYSZ) coatings with three differentmicrostructures were tested in 1-hr cycles at 950°C under hot-corrosionconditions (sodium and sodium/potassium sulfates) likely to occur inbiomass-derived fuel-fired gas turbines. In contrast to conditionsinitiating Type I hot-corrosion attack, a modified test procedure wasused in this study where periodically salt-coated specimens were subjectedto an oxygen atmosphere while SOx was omitted, thus taking into account theessentially sulfur-free biomass fuel-combustion atmosphere. For comparison,similar tests were conducted on bare MCrAlY-type alloys. TBC failure byspallation of the PYSZ coating was observed between 300 and 500 1-hrcycles. Irrespective of PYSZ microstructure and deposit chemistry, failurewas primarily induced by crack formation and propagation within thevoluminous oxide scale formed as a result of hot-corrosion attack of themetal, rather than degradation of the ceramic layer. Since the major attackmode of the TBC seemed to be hot corrosion of the bond coat, this paperhighlights degradation mechanisms and microstructures of uncoated bond-coatcompositions. On the basis of the present results, implications of thefailure mode of EB–PVD PYSZ on in-service components are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004634400479
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  • 18
    Digitale Medien
    Digitale Medien
    The oxidation of Fe-Cr alloys containing an oxide dispersion or reactive metal additions (1974)
    Springer
    Oxidation of metals 8 (1974), S. 283-301 
    Details
    ISSN: 1573-4889
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of an iron-16% chromium alloy containing a dispersion of yttria particles and of iron-16 to 18% chromium alloys containing small additions of yttrium or zirconium has been studied at 1100 and 1200°C in 100 Torr oxygen. The yttria-containing alloy exhibited the excellent oxidation resistance usually associated with oxide-dispersion-containing alloys, having a thin, adherent, virtually iron-free scale which resisted the breakaway rapid oxidation behavior commonly found in Fe-Cr alloys in this composition range. Of the alloying additions intended to form a fine oxide dispersion during oxidation, only zirconium affected the oxidation behavior in a beneficial way, the scale on the yttrium-containing alloy being possibly less protective than that on the equivalent binary alloy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00609945
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  • 19
    Digitale Medien
    Digitale Medien
    Effect of Experimental Procedures on the Cyclic, Hot-Corrosion Behavior of NiCoCrAlY-Type Bondcoat Alloys (2000)
    Springer
    Oxidation of metals 54 (2000), S. 255-276 
    Details
    ISSN: 1573-4889
    Schlagwort(e): hot-corrosion testing ; NiCoCrAlY-type bond coats ; contaminant flux rate ; biomass fuels
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A simplified test procedure was established to assess the hot-corrosion behavior of MCrAlY-type nickel-base alloys under the influence of molten sodium sulfate as well as sodium sulfate/potassium sulfate salt blends. Salt-coated specimens were exposed to 1-hr thermal cycles at 950°C in flowing oxygen for up to 500 cycles. Mass-change data of the specimens revealed a significant dependence of the corrosion attack not only on the average contaminant flux rate, as expected, but also on the initial amount of salt deposited during each recoating cycle. Furthermore, deposit removal before salt recoating markedly influenced the corrosion attack of the alloys. This was apparently related to changes in salt chemistry by the dissolution of elements such as Cr from the alloy, which can shift the basicity of the salt and thus affect the extent of attack. Substituting Na for K in sodium sulfate/potassium sulfate salt blends generally resulted in decreased attack. For K-containing salt deposits, increasingthe gross amount of alkali compared to sulfur resulted in increased sample weight losses due to scale spallation. In contrast, decreasing the amount of sulfur in such deposits which contained exclusively Na as the alkali resulted in a significantly reduced corrosion attack compared to stoichiometric sodium sulfate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004698211940
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  • 20
    Digitale Medien
    Digitale Medien
    Indentation fracture of WC-Co cermets (1985)
    Springer
    Journal of materials science 20 (1985), S. 1873-1882 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Indentation fracture of a series of well-characterized WC-Co cermets was studied with a Vickers diamond pyramid indenter. The resulting crack length-indentation load data were analysed in terms of relations characteristic of radial (Palmqvist) and fully developed radial/median (half-penny) crack geometries. The radial crack model gave a better fit to the data on all the alloys studied. Crack shapes determined by repeated surface polishing confirmed the radial nature of the cracks. An indentation fracture mechanics analysis based on the assumption of a wedge-loaded crack is shown to be consistent with the observed linear relation between the radial crack length and the indentation load. The analysis also predicts a simple relation among the fracture toughness (K lc), the Palmqvist toughness (W) and the hardness (H) of the WC-Co alloys.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00555296
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