TY  - JOUR
AU  - Bakan, Emine
AU  - Sohn, Yoo Jung
AU  - Vaßen, Robert
TI  - Microstructure and Phase Composition Evolution of Silicon-Hafnia Feedstock during Plasma Spraying and Following Cyclic Oxidation
JO  - Acta materialia
VL  - 214
SN  - 1359-6454
CY  - Amsterdam [u.a.]
PB  - Elsevier Science
M1  - FZJ-2021-02465
SP  - 117007 -
PY  - 2021
AB  - 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.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000663791200010
DO  - DOI:10.1016/j.actamat.2021.117007
UR  - https://juser.fz-juelich.de/record/892966
ER  -