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  • 1
    Electronic Resource
    Electronic Resource
    Simulations of reactive sputtering with constant voltage power supply (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 6399-6408 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reactive sputtering in an Al–O2/Ar system equipped with a dc power supply in constant voltage mode was simulated using a kinetics model in this article. This work showed that reactive sputtering under reactive gas flow rate control and with a constant voltage power was much different from that with a constant current power both in time-dependent and parameter-dependent behaviors. Numerical analysis predicted the continuous, N-shaped V–I characteristics curves, which agreed with the experimental curves reported by other researchers in a system which was equipped with a dc constant current power but operated under voltage control [R. McMahon et al., J. Vac. Sci. Technol. 20 376 (1982); K. Steenbeck et al., Thin Solid Films 92, 371 (1982)] and in a system with a modulated power supply [H. Ohsaki et al., Thin Solid Films 281-282, 213 (1996)]. The continuous parameter-dependent functions indicated that there is no hysteresis effect in constant voltage reactive sputtering, which is a well-known feature of dc constant current magnetron sputtering of an Al–O2/Ar system. According to the simulated kinetics curves using the same simulation parameters, the initial values of oxide coverage on the target surface had no influences on the final parameters at steady state in a constant voltage system, whereas different initial coverage may lead to different steady states (hysteresis behaviors) in a constant current system. This article showed that the films of any reactive gas contents, i.e., the M1−θ−(MOx)θ films (M=metal, MOx=compound of metal) with full range of 0≤θ≤1, could be produced in constant voltage reactive sputtering which is a system simpler than those under partial pressure control.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368966
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  • 2
    Electronic Resource
    Electronic Resource
    Oxidation behavior of TiAl coated with a fine-grain Co-30Cr-4Al film (1993)
    Springer
    Oxidation of metals 39 (1993), S. 457-473 
    Details
    ISSN: 1573-4889
    Keywords: high temperature ; oxidation behavior ; TiAl ; Co-Cr-Al coating ; alumina scale ; pore formation
    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 behavior of TiAl coupons coated with a fine-grain Co-30Cr-4Al (mass %) film of about 30-μm thickness has been studied at 1100–1400 K in a flow of purified oxygen at atmospheric pressure for up to 500 ks. Three oxidation stages were recognized: initial transient, parabolic, and accelerated stages. However, at 1100 K a parabolic stage continues for more than 800 ks. The activation energy for parabolic oxidation agrees with reported values for the oxidation of alumina-former alloys, although the mass gains during the parabolic stages are relatively small at 1200 and 1300 K. Micropores developed mainly at the scale/coating and coating/substrate interfaces as oxidation proceeded. This is attributable to recrystallization of the coating during oxidation and a Kirkendall effect due to preferential diffusion of Co into the substrate. The accelerated oxidation can be explained in terms of the formation of rutile mounds on the scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00664666
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  • 3
    Electronic Resource
    Electronic Resource
    Rehealing ability of oxide scales formed on microcrystalline K38G coatings (1995)
    Springer
    Oxidation of metals 43 (1995), S. 317-328 
    Details
    ISSN: 1573-4889
    Keywords: microcrystalline ; rehealing ; oxide scales ; superalloys ; coating ; 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 rehealing ability of the protective oxide scales formed on a microcrystalline coating of the Ni-base superalloy K38G has been studied. The results indicated that the oxide scales on the coating may be rehealed when the original scales are destroyed, and the coating still has excellent resistance against high-temperature oxidation. When the original Al2O3 oxide scales spall, mixed-oxide scales of both (Al, Cr)2O3 and TiO2 can form on the surface. The mixed scales are very protective and adherent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01047033
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  • 4
    Electronic Resource
    Electronic Resource
    The oxidation resistance of a sputtered, microcrystalline TiAl-intermetallic-compound film (1995)
    Springer
    Oxidation of metals 43 (1995), S. 395-409 
    Details
    ISSN: 1573-4889
    Keywords: microcrystalline film ; TiAl intermetallic compound ; 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 behavior of a cast TiAl intermetallic compound and its sputtered microcrystalline film was investigated at 700–900°C in static air. At 700°C, both the cast alloy and its sputtered microcrystalline film exhibited excellent oxidation resistance. No scale spallation was observed. However, at 800–900°C, the oxidation kinetics for the cast TiAl alloy followed approximately a linear rate law, which indicates that it has poor oxidation resistance over this temperature range. The poor oxidation resistance of TiAl was due to the formation of an Al2O3+TiO2 scale which spalled extensively during cooling. Nevertheless, the sputtered, TiAl-microcrystalline film exhibited very good oxidation resistance. The oxidation kinetics followed approximately the parabolic rate law at all temperatures. Although the composition of the scales was the same as that of scales formed on the cast alloy, the scales formed on the sputtered microcrystalline-TiAl film are adherent strongly to the substrate. No scale spallation was found at 700–850°C, while a small amount of spallation was observed only at 900°C. This indicates that microcrystallization can improve the oxidation resistance of the TiAl alloy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046890
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  • 5
    Electronic Resource
    Electronic Resource
    Hot-Corrosion Behavior of TiAl-Base Intermetallics in Molten Salts (1999)
    Springer
    Oxidation of metals 51 (1999), S. 235-250 
    Details
    ISSN: 1573-4889
    Keywords: TiAl ; INTERMETALLICS ; HOT-CORROSION ; MELTS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The hot-corrosion behavior of Ti-50Al,Ti-48Al-2Cr-2Nb, and Ti-50Al10Cr alloys was investigatedin (Na, K)2SO4 andNa2SO4 + NaCl melts. TiAlintermetallics showed much better hot-corrosionresistance in (Na, K)2SO4 at900°C than the Ni-base superalloy K38G. Two types ofcorrosion products formed on Ti-50Al: some areas werecovered with a continuous Al2O3 scale, whereas otherareas formed a mixed Al2O3 +TiO2 scale; TiS existed at the scale-alloyinterface. A mixed Al2O3 +TiO2 scale formed on Ti-48Al-2Cr 2Nb, and nosulfide was found beneath the scale. An adherentAl2O3 scale, however, formed onTi-50Al-10Cr, which provided excellent hot-corrosionresistance. All three alloys suffered severe hotcorrosion in Na2SO4 + NaCl meltsat 850°C. A mixed Al2O3 +TiO2 scale formed on all three alloys andmany voids and pits existed in the scale-alloy interface. Thehot-corrosion mechanisms are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018818622547
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  • 6
    Electronic Resource
    Electronic Resource
    The mechanism of scale adhesion on sputtered microcrystallized CoCrAl films (1996)
    Springer
    Oxidation of metals 45 (1996), S. 39-50 
    Details
    ISSN: 1573-4889
    Keywords: CrCrAl ; microcrystalline coating ; oxidation mechanism ; scale adhesion
    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 mechanisms of sputtered microcrystalline Co−30Cr−5Al coatings were investigated by an acoustic emission technique, scatch test, transmission electron microscope (TEM), which was compared with CoCrAlY alloy. The results indicated that the beneficial effects of microcrystallization on the scale adhesion of Co−30Cr−5Al alloy are as follows: (1) The sputtered CoCrAl coating possesses a columnar structure, and oxidation along the columnar grains may form many micropegs which can anchor the scale to the metallic substrate, enhancing bonding of the scale. (2) The grain size of the sputtered coating is several orders of magnitude smaller than that of the cast alloy, and the grain size of oxide scales formed on the former is finer than that of the latter. The finer oxide scale may relieve the growth stresses during isothermal oxidation and partial thermal stresses during cooling by plastic deformation through grain sliding. The microcrystalline coating is more plastic than the cast alloy, which may relieve a certain amount of thermal stresses of the oxide scales. On the basis of oxide adhesion and plasticity, microcrystallization is more beneficial than the addition of reactive elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046819
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of nanocrystallization on the selective oxidation and adhesion of Al2O3 scales (1997)
    Springer
    Oxidation of metals 48 (1997), S. 215-224 
    Details
    ISSN: 1573-4889
    Keywords: nanocrystallization ; oxidation ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Many mechanisms for the effect of reactive elements on the selective oxidation and scale adhesion of alloys have been proposed. However, nanocrystallization (or microcrystallization) has recently been found to have almost the same effect as that of reactive elements. This note reviews the effect of nanocrystallization on the selective oxidation and adhesion of Al2O3 scale with particular reference to the author's own results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01670500
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of chromium on the oxidation resistance of TiAl intermetallics (1997)
    Springer
    Oxidation of metals 48 (1997), S. 381-390 
    Details
    ISSN: 1573-4889
    Keywords: TiAl intermetallics ; chromium ; oxidation kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The effect of 10 at.%Cr on the oxidation resistance of TiAl intermetallic compound at 800–1100°C in air was investigated. The results indicated that 10 at.%Cr equally substituting for Ti and Al in TiAl alloy had duplex effects on the isothermal kinetics of DAL At lower temperatures (800–900°C), Cr increased the oxidation rates as a result of the doping effect of Cr in the scale and at higher temperatures (1000–1100°C), especially at 1100°C, Cr significantly reduced the oxidation rates as a result of the formation of a continuous Al2O3 film on the surface. 10 at.%Cr only substituting for Ti in TiAl alloy remarkably reduced the oxidation rates at all temperatures by about two orders of magnitude. Moreover, 10 at%Cr significantly improved the cyclic-oxidation rsistance of TiAl alloy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02153457
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of nanocrystallization on the corrosion resistance of K38G superalloy in CO + CO2 atmospheres (1997)
    Springer
    Oxidation of metals 48 (1997), S. 497-509 
    Details
    ISSN: 1573-4889
    Keywords: corrosion ; CO + CO2 ; K38G alloy ; grain-boundary diffusion
    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 resistance of the cast superalloy K38G and a sputtered nanocrystalline coating of the same material was investigated in pure CO in the temperature range, 850–1000°C and in CO-20 vol.% CO2 at 900°C. The cast K38G alloy formed Cr2O3 and TiO2 scales, and a zone of internal Al2O3 precipitation. Weight-gain kinetics followed the parabolic rate law under all conditions investigated. The sputtered K38G nanocrystalline coating, however, formed a single-phase Al2O3 scale and no internal-oxidation zone. The parabolic rate constants for nanocrystalline coating oxidation were about one order of magnitude smaller than those of the cast alloy. The changes in reaction morphology and rate are attributed to the more rapid grain-boundary diffusion of aluminum in the nanocrystalline material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02153462
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of a sputtered TiAlCr coating on the oxidation resistance of TiAl intermetallic compound (1997)
    Springer
    Oxidation of metals 48 (1997), S. 511-525 
    Details
    ISSN: 1573-4889
    Keywords: TiAl intermetallic compound ; isothermal/cyclic oxidation ; TiAlCr coating ; MCrAlY coating ; interdiffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The effect of a sputtered TiAlCr coating on the oxidation resistance of TiAl intermetallic compound was investigated in static air. The bare TiAl alloy exhibited poor isothermal and cyclic-oxidation resistance at 800–1000°C due to the formation of TiO2-base scales which tend to spall during cooling. A sputtered Ti-50Al-10Cr coating remarkably improved the oxidation resistance of TiAl, due to the formation of an adherent Al2O3 scale at 800–1000°C. After long-term oxidation (at 900°C for 1000 hr), TiAlCr coating still provided excellent protection for the TiAl alloy. Minor interdiffusion occurred due to the inward diffusion of Cr, while no Kirkendall voids were found at the coating/ substrate interface. In contrast, NiCrAlY and CoCrAlY coatings reacted extensively with the TiAl alloys. Moreover, the TiAlCr coating alloy is based on γ-TiAl and TiAlCr Laves phases, which may offer improved mechanical properties. The TiAlCr coating exhibited a better combination of oxidation resistance and substrate compatibility than conventional aluminide and MCrAlY coatings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02153463
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