Oxide phases and residual stresses in scales formed at early stages of oxidation of β-NiAl at 1473 K and the effect of implanted yttrium

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• 作者：J. Jedliński ; R. Gołdyn ; J.-L. Grosseau-Poussard ; G. Bonnet ; K. Kowalski ; A. Bernasik ; G. Smoła ; J. Dąbek and M. Nocuń
• 刊名：Materials and Corrosion
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：68
• 期：2
• 页码：235-248
• 全文大小：2340K
• ISSN：1521-4176

文摘

Oxide phases formed at early oxidation stages on unmodified and yttrium-implanted β-NiAl intermetallic compound were studied with the aid of photoluminescence spectroscopy in scales developed at 1473 K for oxidation periods of up to 4 h. Two-stage-oxidation exposures with up>18up>Oub>2ub>-tracer were applied. The PLS method was also used to assess the residual stresses in α-Alub>2ub>Oub>3ub> scale at consecutive stages of its development. It was found that scale formation occurs in a very local way, related to inhomogeneous distribution of Cr in substrate: sometimes distances as short as 10–15 μm were sufficient to observe entirely different phases in the scale. In general, implanted yttrium was found to retard the formation of a stable and protective layer of α-Alub>2ub>Oub>3ub>. Oxidation for 4 h was necessary for no transient aluminum oxides (mostly θ and/or δ) to be detected, while on non-implanted material they were not found after only 26 min exposure. Only compressive stresses were found in α-alumina scales. They were rather high, reaching even 5 GPa. However, their dependence on the regions in the scale and the scale evolution stage was observed. The results indicate that patches frequently observed in scales on β-NiAl are regions where the phase transformation of transient aluminas to the α phase occurs preferentially. Ridges, which fill the transformation-related cracks, consisted only of α-Alub>2ub>Oub>3ub>. Combination of these results with those obtained using SIMS distribution analyses of oxygen isotopes as well as with SEM/EDX, enabled very precise conclusions to be inferred concerning the scale growth mechanism. In particular, the local nature of the scale development can be described in more detail.