Journal Article

FZJ-2021-02465

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Microstructure and Phase Composition Evolution of Silicon-Hafnia Feedstock during Plasma Spraying and Following Cyclic Oxidation

Bakan, E. (Corresponding author)FZJ* ; Sohn, Y. J.FZJ* ; Vaßen, R.FZJ*

2021
Elsevier Science Amsterdam [u.a.]

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Please use a persistent id in citations: http://hdl.handle.net/2128/27909  doi:10.1016/j.actamat.2021.117007

Abstract: In this work, silicon–hafnia (Si-HfO2, 80/20 mol. %) feedstock was plasma sprayed for Environmental Barrier Coating bond coat application. In the as-sprayed coating, hafnium disilicide (HfSi2), HfO2 tetragonal (t), and cubic (c) phases with a total volume of ~20 % were detected together with Si and HfO2 monoclinic (m). The temperature-dependent evolution of these phases was analyzed and paired with microstructural observations. It was found that above 700 °C, HfSi2 oxidizes and HfO2 (t) and (c) transforms into (m) polymorph. Up to this temperature, as-sprayed coating showed a non-linear expansion behavior. Estimated volume expansion at ~750 °C was 3.6 % based on dilatometry measurement. The primary and secondary mechanisms leading to the expansion in the coating were identified as oxidation of HfSi2 and polymorphic phase transitions in HfO2, respectively. As a consequence of the volume expansion, the coating was extensively cracked during cyclic oxidation and hence not protective anymore. After 100 h at 1300 °C, the volume fraction of oxidation product SiO2 was significant in the coating (0.34), while HfO2 was largely consumed (0.1) in the formation of HfSiO4 (0.56). This result suggested that reversible α↔β phase transitions in SiO2-cristobalite could be another factor contributing to the cracking in the coating during cyclic oxidation.

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Contributing Institute(s):

1. Werkstoffsynthese und Herstellungsverfahren (IEK-1)

Research Program(s):

1. 124 - Hochtemperaturtechnologien (POF4-124) (POF4-124)

Appears in the scientific report 2021

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Database coverage:
; ; ; Clarivate Analytics Master Journal List ; Current Contents - Engineering, Computing and Technology ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF >= 5 ; JCR ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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