Journal of Advanced Materials in Engineering

Journal of Advanced Materials in Engineering

Over-Temperature Degradation of CVD Germanium-Modified Aluminide Coatings on Hastelloy X at 1400 °C

Document Type : Original Article

Authors
Reza Etemadi Kafash 1
Mohamad Javad Eshraghi 1
Keivan Asadian 1
Seyed Mohammad Mehdi Hadavi 2
1 Department of Materials Engineering, Materials and Energy Research Center (MERC), Karaj, Iran
2 Semiconductor Research Institute, Materials and Energy Research Center (MERC), Karaj, Iran
10.47176/jame.46.1.1196
Abstract
Introduction and Objectives: This study redefines the 1400 °C experiment as an over-temperature degradation test rather than a conventional service-temperature oxidation test, and evaluates the microstructural stability limit of conventional and germanium-modified aluminide coatings on Hastelloy X.
Materials and Methods: Ge-containing precursor layers were produced by CVD using 600 °C/4 h and 900 °C/2 h routes, followed by CVD aluminizing at 1020 °C for 3 h. The coated specimens were exposed at 1400 °C for 55 h and then characterized by mass-change measurement, cross-sectional BSE observations, semi-quantitative EDS, elemental mapping, and XRD.
Results: In the available dataset, ‎Al‎ and Ge900-Al showed net mass changes of -0.09687 and -0.09421 mg/cm², respectively, whereas Ge600-Al retained a positive net mass change of +0.05971 mg/cm². Ge900-Al showed clearer XRD evidence of retained β-NiAl, while Ge600-Al showed the most favorable mass-change response within the present 55 h window.
Conclusion: The results should be interpreted as a short-window over-temperature degradation response. The behavior of the coatings is controlled not only by Ge addition but also by the initial coating architecture, the continuity of Ge/Cr-bearing barrier-like regions, and the relative retention of β-NiAl. Because the test temperature exceeds the nominal melting range of Hastelloy X, the results are not intended to represent normal service oxidation behavior.
Keywords
Hastelloy X, Aluminide coating, Germanium modification, Over-temperature degradation, Mass change, Microstructural stability, &‌beta
-NiAl
Subjects
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Journal of Advanced Materials in Engineering
Volume 46, Issue 1
Winter 2027
Pages 67-83

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