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  • 1
    Electronic Resource
    Electronic Resource
    Behavior of oxide scales on 2.25Cr-1Mo steel during thermal cycling. II. Scales grown in water vapor (1989)
    Springer
    Oxidation of metals 31 (1989), S. 35-69 
    Details
    ISSN: 1573-4889
    Keywords: cyclic oxidation ; water vapor ; 2.25Cr-1Mo steel ; acoustic emission technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The acoustic emission (AE) technique has been applied to identify scale cracking during thermal cycling of tubes of 2.25Cr-1Mo steel. The scale morphology and failure mode were investigated by light and electron optical methods. The scale formed at 600°C in water vapor consists of an outer magnetite and an inner, chromium-containing spinel layer. Cooling leads to tensile stresses in the scale that cause macro and microcrack formation in the scale. At constant-cycle parameters, a characteristic set of crack length and crack density is established. Changes in the cycle parameters also change the crack length and crack density. The experimental results can be described by a model developed by Hasselmann assuming a large number of noninteracting microcracks in a ceramic plate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665486
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  • 2
    Electronic Resource
    Electronic Resource
    Behavior of oxide scales on 2.25Cr-1Mo steel during thermal cycling. I. Scales formed in oxygen and air (1989)
    Springer
    Oxidation of metals 31 (1989), S. 1-34 
    Details
    ISSN: 1573-4889
    Keywords: cyclic oxidation ; 2.25-1Mo steel ; acoustic-emission technique ; oxide-scale buckling and cracking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The acoustic-emission (AE) technique has been applied to study scale-damage processes during thermal cycling of a tube, preferentially between 600 and 300°C in air, oxygen, and air + 0.5% SO2. The AE measurements were accompanied by optical and electron-optical investigations on tube rings exposed to the same cycling conditions. During the first period of cycling, a scale rich in hematite is formed. It suffers compressive stresses during cooling. The result is a buckled multilayered scale with separated lamellae. The scaling rate is lower than under isothermal conditions. AE signals start after 175°C cooling. After longer exposure times, the scale contains an increasing amount of magnetite and becomes more compact. The scaling rate increases and is comparable to that under isothermal conditions. AE signals are already observed after 50°C cooling and are correlated with crack formation in the magnetite caused by tensile stresses there. The addition of SO2 to air enhances the crack-healing process due to higher Fe diffusion in FeS. The scale is more compact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665485
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  • 3
    Electronic Resource
    Electronic Resource
    The cyclic-oxidation behavior of several nickel-base single-crystal superalloys without and with coatings (1994)
    Springer
    Oxidation of metals 41 (1994), S. 271-300 
    Details
    ISSN: 1573-4889
    Keywords: cyclic oxidation ; single-crystal superalloys ; coating, reactive-element effect ; acoustic emission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Several commerical single-crystal superalloys (CMSX-2, CMSX-3, CMSX-4, CMSX-6, SRR 99) and some laboratory versions of one of them (CMSX-4) with various Y additions were investigated concerning their cyclic-oxidation resistance in air at 1000 and 1150°C. The investigations also included two materials (CMSX-6, SRR 99) with an RT-22 coating. Weight changes and acoustic emission were recorded up to 1000 cycles and scales, coatings, and substrates were characterized by metallography, SEM, and microprobe in postexperimental investigations. The best cyclic-oxidation behavior and excellent resistance to spalling even at 1150°C were shown by a laboratory version of CMSX-4 containing between 10 and 60 ppm Y. While at 1000°C interdiffusion can be taken as tolerable for the coated alloys, there is rapid degradation of the coating by interdiffusion at 1150°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01080784
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  • 4
    Electronic Resource
    Electronic Resource
    Cyclic-oxidation behavior of TiAl and of TiAl alloys (1993)
    Springer
    Oxidation of metals 39 (1993), S. 93-106 
    Details
    ISSN: 1573-4889
    Keywords: cyclic oxidation ; TiAl ; TiAl alloys ; scale spallation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The cyclic-oxidation behavior of (in w/o) Ti-36Al, Ti-35Al-0.1C, Ti-35Al-1.4V-0.1C and Ti-35Al-5Nb-0.1C was studied between 800 and 1000° C in air. A few experiments were also performed in oxygen. Scale spallation after oxidation in air occurs during cooling on TiAl, TiAl-C, and TiAl-V at or close to the metal/scale interface when a critical scale thickness has been achieved. This process repeats and can lead to a stratified scale. These three materials form scales composed of an inward-growing fine-grain mixture of TiO2-Al2O3 and an outward-growing coarse-grain TiO2 layer or TiO2+Al2O3 mixture. The TiAl-Nb alloy had a significantly different behavior. The scale on this material grew very slowly because a protective Al2O3 layer formed at the metal/scale interface. This behavior resulted in much better resistance to spallation because the critical scale thickness was reached only after a much longer time, and is different from the behavior of the other three alloys. Oxidation in air leads to slight nitridation of the subsurface zone beneath the scale. In comparison to oxidation in air, oxidation in oxygen improves the cyclicoxidation behavior. Whereas the scale formed in air was uniformly thick over the entire surface, the scale grown in oxygen varied locally in structure and thickness. A large fraction of the surface was covered with a thin Al2O3 layer, while the remaining part formed a two-layer scale similar to that formed in air. The results are discussed briefly in the light of a recently published model for scale spallation under compressive stress, however, quantitative estimations are not possible due to a lack of relevant data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00666612
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  • 5
    Electronic Resource
    Electronic Resource
    Behavior of oxide scales on 12Cr-1Mo steel during thermal cycling (1993)
    Springer
    Oxidation of metals 39 (1993), S. 389-410 
    Details
    ISSN: 1573-4889
    Keywords: cyclic oxidation ; 12Cr-1Mo steel ; acoustic emission ; oxide-scale failure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Soot-blower operation leads to thermal-cyclic-oxidation conditions of heat-resistant steels in conventional power stations. The consequence may be failure of the protective oxide scales and increased corrosive attack. The behavior of protective oxide scales on 12Cr-1Mo steel was investigated under isothermal conditions at 650°C and under thermal cycling conditions between 650 and 300°C (200°C). The tests were performed in air, air + 0.5%SO2, simulating the fire side, and Ar-5% H2-50% H2O, simulating the steam side. Complete heat-exchanger tubes were used as specimens. The main instrument for the detection of scale failure was acoustic-emission analysis. In air and air + 0.5% SO2 the M2O3 scales with M = Fe, Cr were very thin and did not show significant failure either during isothermal or during cyclic oxidation. The thicker scales formed in Ar-5% H2-50% H2O, consisting of several partial layers, failed even during isothermal oxidation due to geometrically-induced growth stresses in the scale. Thus, in the thermal-cycling cooling periods there was only very little additional scale cracking. The scale behavior can be explained consistently by applying the existing quantitative models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00664663
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  • 6
    Electronic Resource
    Electronic Resource
    Behavior of oxide scales on alloy 800 H and HK 40 during thermal cycling (1993)
    Springer
    Oxidation of metals 40 (1993), S. 37-63 
    Details
    ISSN: 1573-4889
    Keywords: cyclic oxidation ; alloy 800 H ; HK 40 ; acoustic emission ; oxide-scale failure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Cyclic oxidation causes degradation of alloys used in the chemical and petrochemical industries. In this paper, the behavior of the protective oxide scales formed on Alloy 800 H and HK 40 was investigated under thermalcycling conditions with upper-hold temperatures of 900°C (Alloy 800 H) and 950°C (HK 40). The atmospheres in the tests were air, air+0.5% SO 2 and Ar-5%H 2 -50%H 2 O. Tests were accompanied by acoustic-emission measurements in order to detect scale failure in situ during the experiments. During cooling the scales were under compression which led to spalling when critical stress values were reached in the scales. The outer-spinel partial layers are more prone to spallation, and the presence of SO 2 increases the amount of acoustic-emission activity (scale damage). In the case of HK 40 the oxide scales on the as-cast surfaces showed better spallation resistance than those on the ground surfaces. Quantitative model considerations were able to describe the spallation behavior of the protective scales investigated, and critical-temperature-drop diagrams for scale failure are given. The model approach was supported by results from the acoustic-emission measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665258
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