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Formation of corrosion pockets in FeNiCrAl at high temperatures investigated by 3D FIB‐SEM tomography
Materials and Corrosion ( IF 1.6 ) Pub Date : 2020-06-26 , DOI: 10.1002/maco.201911386 Katrin Jahns 1 , Ulrich Krupp 2 , Gustav Sundell 3 , Christine Geers 4
Materials and Corrosion ( IF 1.6 ) Pub Date : 2020-06-26 , DOI: 10.1002/maco.201911386 Katrin Jahns 1 , Ulrich Krupp 2 , Gustav Sundell 3 , Christine Geers 4
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A recently published study of high temperature nitridation of iron chromium aluminum alloys (FeCrAl) at 900°C in N2–H2 has redundantly shown the formation of locally confined corrosion pockets reaching several microns into the alloy. These nitrided pockets form underneath chromia islands laterally surrounded by the otherwise protective alumina scale. Chromia renders a nitrogen‐permeable defect under the given conditions and the presence of aluminum in the alloy. In light of these findings on FeCrAl, a focused ion beam–scanning electron microscope tomography study has been undertaken on an equally nitrided FeNiCrAl sample to characterize its nitridation corrosion features chemically and morphologically. The alloy is strengthened by a high number of chromium carbide precipitates, which are also preferential chromia formation sites. Besides the confirmation of the complete encapsulation of the corrosion pocket from the alloy by a closed and dense aluminum nitride rim, very large voids have been found in the said pockets. Furthermore, metallic particles comprising nickel and iron are deposited on top of the outer oxide scale above such void regions.
中文翻译：
通过3D FIB-SEM断层扫描研究了高温下FeNiCrAl中腐蚀腔的形成
最近发表的研究在900°C的N 2 -H 2中对铁铬铝合金（FeCrAl）进行高温氮化的研究已经多余地显示了局部封闭的腐蚀腔的形成，该腐蚀腔延伸到合金中几微米。这些渗氮的囊袋在氧化铬岛的下方形成，该氧化铬岛在横向上被原本具有保护性的氧化铝垢包围。在给定条件下以及合金中存在铝时，铬会产生氮可渗透缺陷。根据在FeCrAl上的这些发现，对同等氮化的FeNiCrAl样品进行了聚焦离子束扫描电子显微镜断层扫描研究，以化学和形态表征其氮化腐蚀特征。大量的碳化铬沉淀强化了合金，这些沉淀也是优先的氧化铬形成部位。除了通过封闭且致密的氮化铝边缘确认了合金完全密封了腐蚀腔外，还在所述腔中发现了非常大的空隙。此外，包含镍和铁的金属颗粒沉积在这些空隙区域上方的外部氧化物垢的顶部上。
更新日期：2020-06-26
中文翻译：
通过3D FIB-SEM断层扫描研究了高温下FeNiCrAl中腐蚀腔的形成
最近发表的研究在900°C的N 2 -H 2中对铁铬铝合金（FeCrAl）进行高温氮化的研究已经多余地显示了局部封闭的腐蚀腔的形成，该腐蚀腔延伸到合金中几微米。这些渗氮的囊袋在氧化铬岛的下方形成，该氧化铬岛在横向上被原本具有保护性的氧化铝垢包围。在给定条件下以及合金中存在铝时，铬会产生氮可渗透缺陷。根据在FeCrAl上的这些发现，对同等氮化的FeNiCrAl样品进行了聚焦离子束扫描电子显微镜断层扫描研究，以化学和形态表征其氮化腐蚀特征。大量的碳化铬沉淀强化了合金，这些沉淀也是优先的氧化铬形成部位。除了通过封闭且致密的氮化铝边缘确认了合金完全密封了腐蚀腔外，还在所述腔中发现了非常大的空隙。此外，包含镍和铁的金属颗粒沉积在这些空隙区域上方的外部氧化物垢的顶部上。
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