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  • 11
    Electronic Resource
    Electronic Resource
    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
    Keywords: sulfidation ; nickel-base alloys ; iron-base alloys ; fluidized-bed combustion ; deposit-related attack
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00846692
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  • 12
    Electronic Resource
    Electronic Resource
    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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00609945
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  • 13
    Electronic Resource
    Electronic Resource
    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
    Keywords: hot-corrosion testing ; NiCoCrAlY-type bond coats ; contaminant flux rate ; biomass fuels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004698211940
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  • 14
    Electronic Resource
    Electronic Resource
    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
    Keywords: sulfidation ; sulfidation/oxidation ; hot corrosion ; nickel alloys ; cobalt alloys ; oxide dispersions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00603387
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  • 15
    Electronic Resource
    Electronic Resource
    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
    Keywords: cobalt-chromium ; oxidation ; oxygen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00606542
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  • 16
    Electronic Resource
    Electronic Resource
    Factors affecting the high-temperature oxidation behavior of some dilute nickel- and cobalt-base alloys (1977)
    Springer
    Oxidation of metals 11 (1977), S. 141-150 
    Details
    ISSN: 1573-4889
    Keywords: nickel alloys ; cobalt alloys ; oxidation rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Oxidation of nickel- and cobalt-base alloys, containing small additions of a higher valent second metal, in oxygen or air at high temperatures results in the formation of relatively complicated scale morphologies which change subtly with increasing additions of the second element and its characteristics. The various factors that can influence the oxidation behavior of such alloys are assessed and correlated with the oxidation kinetics and scale morphology types. For very dilute alloys the increase in oxidation rate compared with that of the corresponding pure metal (nickel or cobalt) is largely due to doping of the external oxides. However, once the solubility limit of the second metal in this oxide is exceeded, additional increases in second metal content of the alloy can either increase further or decrease the oxidation rate. The exact behavior depends on the relative interplay of factors such as internal oxide formation and coalescence, blocking effects of incorporated internal oxide or pores in the scale, short-circuit paths through the scale, doping, and the relative diffusion rates of the two metals in the scale. Probable rate-determining steps for oxidation of different alloy composition ranges are proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00606401
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  • 17
    Electronic Resource
    Electronic Resource
    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
    Keywords: high-temperature oxidation ; erosion ; erosion-corrosion mechanisms ; high-temperature alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00655896
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  • 18
    Electronic Resource
    Electronic Resource
    An approach to modeling simultaneous high-temperature oxidation and erosion (1991)
    Springer
    Oxidation of metals 35 (1991), S. 89-106 
    Details
    ISSN: 1573-4889
    Keywords: high-temperature oxidation ; erosion ; corrosion-erosion ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An approach is suggested for describing the rate of degradation of alloys subjected to the combined effects of high-temperature oxidation and erosion. The basis for this approach is essentially empirical, and is drawn from observations of the kinetics and scale morphologies of alloys in laboratory tests. The two major assumptions used are that the alloy surface is always covered by an oxide layer, and that only oxide (not alloy substrate) is removed by the erosion process. The mode of erosion is not explicitly defined. The rate of erosion, that is, the amount of oxide lost in a given erosion event, is taken to be proportional to the thickness of the oxide layer. The relationships developed have been found capable of accurately describing the shapes of oxidationerosion kinetic curves, and the predicted thickness of the steady-state oxide layers remaining on the alloys agreed reasonably with experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00666502
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  • 19
    Electronic Resource
    Electronic Resource
    Indentation fracture of WC-Co cermets (1985)
    Springer
    Journal of materials science 20 (1985), S. 1873-1882 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00555296
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  • 20
    Electronic Resource
    Electronic Resource
    On estimating fracture toughness of cemented carbides from Palmqvist crack sizes (1986)
    Springer
    Journal of materials science 5 (1986), S. 365-368 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01748108
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