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  • 1
    Electronic Resource
    Electronic Resource
    Further aspects of the oxidation of binary two-phase alloys (1993)
    Springer
    Oxidation of metals 39 (1993), S. 197-209 
    Details
    ISSN: 1573-4889
    Keywords: oxidation ; binary alloys ; two-phase 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 corrosion behavior of binary, two-phase alloys is considered in which the matrix contains mostly the less-noble metal that forms a fast-growing oxide, while the second phase is rich in a component that forms a more stable but slowly-growing oxide. It is assumed that the second phase exists as a dispersion of isolated, rod-like particles. It is further assumed that both phases form external films with no internal oxidation. It is shown that the oxidation behavior of this type of alloy depends on both the oxidation time and the size of the second-phase particles. In particular, for short oxidation times and large second-phase particles the matrix will oxidize faster than the dispersed phase, so that the dispersed particles will be only partly corroded or even incorporated into the matrix-oxide scale as unoxidized islands, forming an irregular alloy-scale interface. On the contrary, for long times and small particle sizes the two phases will tend to oxidize at approximately the same rate, leading to the formation of regular alloy-scale interfaces. The time for the transition between the two corrosion regimes depends not only on the ratio between the rate constants for the growth of the two oxides but also on the size of the dispersed-phase particles, smaller sizes producing shorter transition times. Eventually, under favorable conditions the formation of the fast-growing oxide may even stop, leading to the formation of a protective layer of the most-stable oxide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665611
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  • 2
    Electronic Resource
    Electronic Resource
    The possible scaling modes in the high-temperature oxidation of two-phase binary alloys. Part I: High oxidant pressures (1994)
    Springer
    Oxidation of metals 42 (1994), S. 409-429 
    Details
    ISSN: 1573-4889
    Keywords: two-phase alloys ; oxidation ; scale structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The main possible modes of the high-temperature corrosion of binary twophase alloys by a single oxidant under gas-phase pressures sufficient to corrode both alloy components are examined to highlight the differences in their behavior with respect to single-phase alloys. It is shown that in the absence of important diffusion processes of the metal components in the alloy the expected scale structures are significantly different from those typical of single-phase alloys. The effects due to the existence of different degrees of deviation from equilibrium as a result of kinetics hindrances for the formation of the most stable oxide and in the absence of alloy diffusion are then examined. It is also shown that when diffusion in the alloy becomes important the alloy may develop an outer single-phase layer depleted in the most-reactive component, which may lead to various possible scale structures. The conditions for the transition between the various oxidation modes as well as the effect of the various parameters of kinetics, thermodynamic and structural nature over the corrosion behavior of two-phase alloys are also examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046758
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  • 3
    Electronic Resource
    Electronic Resource
    Possible scaling modes in high-temperature oxidation of two-phase binary alloys. II: Low oxidant pressures (1995)
    Springer
    Oxidation of metals 43 (1995), S. 379-394 
    Details
    ISSN: 1573-4889
    Keywords: two-phase alloys ; oxidation ; scale structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The main possible modes of the high-temperature corrosion of binary two-phase alloys by a single oxidant under gas-phase pressures sufficient to corrode only the most-reactive alloy component are examined to compare their behavior with that of single-phase alloys. In the absence of important diffusion processes of the metal components in the alloy, the scale structures expected are different from those typical of single-phase alloys. Moreover, when diffusion in the alloy becomes important, these systems may develop an outer single-phase layer depleted in the most-reactive component, which may lead to different possible scale structures. The conditions for the transition between the various oxidation modes as well as the effect of the various parameters of kinetic, thermodynamic, and structural nature over the corrosion behavior of two-phase alloys are also examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01047037
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  • 4
    Electronic Resource
    Electronic Resource
    The oxidation of Co−Nb alloys under low oxygen pressures at 600–800°C (1995)
    Springer
    Oxidation of metals 43 (1995), S. 527-542 
    Details
    ISSN: 1573-4889
    Keywords: Co−Nb alloys ; high temperature ; oxidation
    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 two Co−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600°C and 10−20 atm at 700 and 800°C, below the dissociation pressure of cobalt oxide. At 600 and 700°C both alloys showed only a region of internal oxidation composed, of a mixture of alpha cobalt and of niobium oxides (NbO2 and Nb2O5) and at 700°C also the double oxide CoNb2O6, which formed from the Nb-rich Co3Nb phase. No Nb-depleted layer formed in the alloy at the interface with the region of internal oxidation at these temperatures. Upon oxidation at 800°C a transition between internal and external oxidation of niobium was observed, especially for Co−30Nb. This corrosion mode is associated with the development of a single-phase, Nb-depleted region at the surface of the alloy. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in cobalt and to the relation between the microstructures of the alloys and of the scales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046897
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  • 5
    Electronic Resource
    Electronic Resource
    The air oxidation of two-phase Cu-Cr alloys at 700–900°C (1997)
    Springer
    Oxidation of metals 48 (1997), S. 357-380 
    Details
    ISSN: 1573-4889
    Keywords: chromium ; copper ; binary alloys ; two-phase alloys ; oxidation ; high temperatures
    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 in air of three two phase Cu-Cr alloys with nominal Cr contents of 25, 50, and 75 wt. % was studied at 700–900°C. The alloys corroded nearly parabolically, except at 900°C, when the corrosion rates decreased with time more rapidly than predicted by the parabolic rate law. The corrosion rate decreased for higher Cr contents in the alloy under constant temperature and generally increased with temperature for the same alloy composition. The scales were complex and consisted in most cases of an outermost copper oxide layer free from chromium and an inner layer composed of a matrix of copper oxide or of the double oxide Cu2Cr2O4, often containing particles of chromium metal surrounded by chromia and then by the double oxide. Metallic copper was also frequently mixed with chromia. Cr-rich regions tended to form continuous chromia layers at the base of the scale, especially at the highest temperature. No chromium depletion was observed in the alloy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02153456
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  • 6
    Electronic Resource
    Electronic Resource
    The oxidation of Ni-Nb alloys at low-oxygen pressures at 600–800°C (1995)
    Springer
    Oxidation of metals 44 (1995), S. 399-415 
    Details
    ISSN: 1573-4889
    Keywords: Ni−Nb alloys ; high temperature ; oxidation
    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 two Ni−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600° C and 10−20 atm O2 at 700 and 800° C, these pressures being less than the dissociation pressure of nickel oxide. The scales formed on both alloys at 600 and 700° C show only a region of internal oxidation composed of a mixture of alpha nickel and niobium oxides (Nb2O5 or/and NbO2), which formed from both the metal phases present, i.e., Ni8Nb and Ni3Nb. Only small, or even no, Nb depletion was observed in the alloys close to the interface with the zone of internal oxidation at these temperatures. On the contrary, samples of both alloys corroded at 800° C produced a continuous external scale of niobium oxides without internal oxidation. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in nickel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01058244
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  • 7
    Electronic Resource
    Electronic Resource
    An improved treatment of the conditions for the exclusive oxidation of the most-reactive component in the corrosion of two-phase alloys (1994)
    Springer
    Oxidation of metals 42 (1994), S. 465-483 
    Details
    ISSN: 1573-4889
    Keywords: binary alloys ; two-phase alloys ; oxidation ; high temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The conditions for the exclusive oxidation of the most-reactive component during the corrosion of binary, two-phase alloys by a single oxidant are reexamined by using a more correct form of the mass balance for this component. Moreover, the previous treatment is extended to include the case in which the transition falls in the range of alloy compositions corresponding to the stability of the single phase rich in the most-reactive component. The limiting conditions for the transition in the single and two-phase fields are examined and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046761
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  • 8
    Electronic Resource
    Electronic Resource
    The corrosion of pure niobium in oxidizing, sulfidizing, and oxidizing-sulfidizing gas mixtures at 600–800°C (1996)
    Springer
    Oxidation of metals 46 (1996), S. 287-297 
    Details
    ISSN: 1573-4889
    Keywords: pure niobium ; oxidation ; sulfidation ; oxidation-sulfidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of pure niobium has been studied at 600–800°C in various environments as part of a study of the corrosion resistance of its alloys with iron, cobalt, and nickel to atmospheres of low-oxygen and/or high-sulfur activities. The results have shown that not only the sulfidation but also the corrosion in mixed atmospheres and particularly the oxidation under low oxygen pressures of pure niobium are quite slow, with kinetics rather similar in the three types of gas mixtures used. The good corrosion resistance of niobium to attack by oxygen under low pressures is quite interesting because this element is corroded very rapidly by oxygen under high oxygen pressures, due to the formation of the nonprotective highest oxide Nb2O5 as a main corrosion product.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01050800
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  • 9
    Electronic Resource
    Electronic Resource
    An analysis of the internal oxidation of binary M-Nb alloys under low oxygen pressures at 600–800°C (1996)
    Springer
    Oxidation of metals 46 (1996), S. 441-463 
    Details
    ISSN: 1573-4889
    Keywords: niobium alloys ; oxidation ; high temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of M−Nb alloys based on iron, cobalt, and nickel and containing 15 and 30 wt% Nb has been studied at 600–800°C under low oxygen pressures (10−24 atm at 600°C and 10−20 atm at 700–800°C). Except for the Co−Nb and Ni−Nb alloys corroded at 800°C, which formed external scales of niobium oxides, corrosion under low O2 pressures produced an internal oxidation of niobium. This attack was much faster than expected on the basis of the classical theory. Furthermore, the distribution of the internal oxide in the alloys containing two metal phases was very close to that of the Nb-rich phase in the original alloys. These kinetic, microstructural, and thermodynamic aspects are examined by taking into account the effects of the limited solubility of niobium in the various base metals and of the two-phase nature of the alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048640
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  • 10
    Electronic Resource
    Electronic Resource
    The air oxidation of two-phase Cu-Ag alloys at 650–750°C (1997)
    Springer
    Oxidation of metals 47 (1997), S. 21-52 
    Details
    ISSN: 1573-4889
    Keywords: copper ; silver ; high temperature ; oxidation ; two-phase 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 corrosion of three two phase Cu-Ag alloys containing 25, 50, and 75 wt% Ag has been studied at 650 and 750°C. In all cases the alloys formed external scales of copper oxides. At the same time, an internal precipitation of Cu2O within a silver matrix was also produced, with an oxide volume fraction larger for the alloys richer in Cu. Beneath this mixed layer a region of single-phase solid solution of Cu in silver formed for Cu-50Ag and especially for Cu-75Ag. Silver metal remained in the metal-consumption zone, acting essentially as an inert marker, except for a few particles with were incorporated into the growing scales. Both pure Cu and the alloys corroded parabolically, but the rate constants for the alloys decreased with increased Ag content under constant temperature. The various aspects of the corrosion of these alloys are examined by taking into account the possible effects associated with the presence of two metal phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01682370
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