ISSN:
0947-5117
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Description / Table of Contents:
Ein gemeinsamer Ansatz: Isotopische Exposition/SIMS-Analyse/REM zur Untersuchung des Anfangsstadiums der Oxidation von β-NiAL bei 1473 KDas Anfangsstadium der Oxidation von β-NiAl wurde bei 1473 K an unmodifiziertem Material und nach Y-Implantation untersucht. Hierzu wurde die 16O/18O-Zwei-Stufen-Oxidation in Kombination mit hochauflösender Sekundärionenmassenspektrometrie (SIMS) sowie Rasterelektronenmikroskopie (REM) eingesetzt. Es zeigt sich, daß die gebildeten Oxidschichten hinsichtlich der Zusammensetzung und des Gefüges nicht homogen sind. Deswegen war es erforderlich, analytische Methoden (SIMS und REM) mit sehr hoher Ortsauflösung bei höchstmöglicher Empfindlichkeit zu verwenden. Dadurch konnten die unterschiedlichen Wachstumsmechanismen in den einzelnen Bereichen der Oxidschicht auf den beiden verschiedenen Substrattypen identifiziert werden.
Notes:
The early oxidation stages of unmodified and yttrium-implanted β-NiAl have been studied at 1473 K using sequential isotopic exposure (so-called two-stage oxidation) combined with low and high resolution SIMS analysis and SEM characterization.The scales growing on unmodified material comprised typically a cracked morphology with oxide ridges growing outward from the cracks. Some ridges were formed at the reaction temperature during the first oxidation stage and continued growing during the second stage. This resulted in a network of ridges on the outer surface of the scale.Two regions: non-cracked areas and cracked round patches were observed in the scale on yttrium-implanted β-NiAl. No ridges but thin lace-like oxide was formed in cracks and round particles extruded from some crack centres. No network was formed by the lace-like oxide. Inward oxygen transport contributed significantly to the overall matter transport in the patches, while its contribution in the remaining scale was much less pronounced. The very thin outermost layer of most patches was enriched in Cr, which was present at a level of ca. 90 ppm only in the starting material. This finding is discussed in terms of the effect of Cr on the phase transformation of unstable aluminas into the stable β-Al2O3.The results showed that the scales were inhomogeneous regarding both composition and microstructure. Therefore, only analytical methods having respectable sensitivity and resolution might be used to give reliable information regarding the growth mechanisms of scales. This applies to SIMS as well as to the electron microscopy methods.
Additional Material:
14 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/maco.19950460505
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