| 1. |
- Axelson, Olav, 1937-, et al.
(författare)
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Regulatory toxicology and pharmacology.
- 2003
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Ingår i: International journal of occupational and environmental health. - 1077-3525 .- 2049-3967. ; 9, s. 386-389
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Tidskriftsartikel (refereegranskat)
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| 2. |
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| 3. |
- Das, D. K., et al.
(författare)
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Effect of Al content on microstructure and cyclic oxidation performance of Pt-aluminide coatings
- 2002
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Ingår i: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 57:3-4, s. 245-266
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Al content, i.e., the amount of Al picked up during aluminizing, on the microstructure and cyclic oxidation properties of Pt-aluminide coatings has been investigated. The cast Ni-base superalloy CM-247 was used as the substrate material and a single-step, high-activity pack aluminizing process was used to produce the Pt-aluminide coatings. The Al content of these coatings was varied by using packs with different compositions of the Al source. Pt-aluminide coatings having three different Al contents, namely 6.5, 16, and 21 mg cm-2, were evaluated for their cyclic oxidation resistance at 1200°C in air. It was found that the Pt-aluminide coatings, irrespective of their Al contents, evolve in the same manner during aluminizing and result in a three-layer structure with an outer PtAl2 + NiAl two-phase layer, an intermediate NiAl layer, and the inner interdiffusion layer. The stability of this three-layer coating structure over long periods of aluminizing, however, is dependent on the availability of Al from the pack during this period. Below a certain threshold Al availability, the two-phase outer layer transforms to a single-phase NiAl structure causing the coating to change from its three-layer structure to a two-layer one. Cyclic oxidation results indicate that, while a minimum Al content in Pt-aluminide coatings is essential for deriving the best oxidation performance, increasing the Al content beyond a certain level does not significantly enhance oxidation behavior. The effect of Al content on aspects, such as coating degradation and nature of coating-surface damage during cyclic oxidation, is also discussed.
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| 4. |
- Das, D. K., et al.
(författare)
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Effect of prealuminizing diffusion treatment on microstructural evolution of high-activity pt-aluminide coatings
- 2000
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Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 31:8, s. 2037-2047
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Tidskriftsartikel (refereegranskat)abstract
- The effect of prealuminizing (or prior) diffusion treatment on the evolution of Pt-aluminide coatings on the Ni-based superalloy CM-247 has been studied by using a single-step, high-activity aluminizing process. Coatings generated without any prior diffusion treatment, as well as those formed by adopting two extreme prior-diffusion schedules (at 850 °C for 0.5 hours and at 1034 °C for 5 hours), were investigated by analyzing the coating structures at various stages of aluminizing. When the dilution of the Pt layer, caused by its interdiffusion with the substrate during the prior diffusion treatment, is only marginal (as in the case of no prior diffusion and diffusion at 850 °C for 0.5 hours), the equilibrium Pt-aluminide coating structure evolves through the formation of two transient layers during the initial stages of aluminizing. In contrast, for diffusion at 1034 °C for 5 hours, which results in extensive dilution of the Pt layer, the two-phase equilibrium structure (PtAl2 in a matrix of NiAl) in the outer layer of the coating is found to develop during very early stages of aluminizing and remains unchanged, even over extended periods of aluminizing. Further, in the case of prior diffusion at 1034 °C for 5 hours, Pt is found to remain distributed to a greater extent over the entire thickness of the coating than in the cases of limited prior diffusion treatment. The present findings underline the significance of the nature of the prior-diffusion schedule on the microstructural evolution of Pt-aluminide coatings. It has also been found that a prealuminizing diffusion treatment is particularly important for Pt-aluminide coatings from the point of view of coating adhesion to the substrate.
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| 5. |
- DAS, D.K., et al.
(författare)
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High temperature oxidation behaviour of directionally solidified nickel base superalloy CM–247LC
- 2003
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Ingår i: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 19:6, s. 695-708
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Tidskriftsartikel (refereegranskat)abstract
- The present paper describes the isothermal and cyclic oxidation behaviour of the technologically important nickel base directionally solidified superalloy CM-247LC in air in the temperature range 1000-1200°C. This superalloy behaves as a transition nickel base alloy under isothermal oxidation conditions and exhibits a fairly long transient oxidation period (~20 h at 1100°C). Irrespective of the temperature of exposure and nature of oxidation (isothermal or cyclic), a composite oxide scale develops on CM-247LC. While the outer portion of the oxide scale consists of either spinel (NiAl2O4) or a mixture of spinel and NiO, depending on oxidation temperature, the inner portion is always constituted of alumina. Beyond the transient period, the alloy is found to follow parabolic oxidation kinetics. The oxide layer that forms is invariably very non-uniform in thickness, and is dispersed with two types of oxide particles. While tantalum rich oxide particles are found scattered in the outer zone of the oxide layer, hafnium rich oxide particles lie close to the oxide/metal interface. Results also reveal that the nature of oxidation associated with the CM-247LC superalloy causes entrapment of metal islands in the oxide layer.
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