Microstructure and composition of multi-layered oxide scale evolved during isothermal exposure of ZrB₂–SiC–LaB₆ composite to air at 1500°C

ABSTRACT

The ZrB₂–SiC–LaB₆ composite prepared by spark plasma sintering with B₄C and C as additives was isothermally exposed in air at 1500°C for 24 h and the evolved oxide scale examined by scanning and transmission electron microscopy. It was found that a glassy borosilicate (BSG) layer with a thin film of La₂Si₂O₇ had formed on the outermost surface of oxide scale, contributing to protection against oxidation. The detailed investigation of the cross-section of the oxide scale has revealed the formation of a layered microstructure formed by growth involving partial crystallisation of BSG forming ZrSiO₄ along with re-precipitation of La₂Si₂O₇ and ZrO₂ after prior dissolution of La₂O₃ and ZrO₂ in the glassy matrix.

KEYWORDS:

• ZrB₂–SiC–LaB₆ composite
• ultra-high temperature ceramics
• oxidation
• FIB
• TEM

Acknowledgements

Technical assistance received from Mr. Mithun Das, Mr. B. Santu Mudliyar, and Mr. Subhabrata Chakraborty, Staff members of Central Research Facility, IIT Kharagpur for characterisation of specimens, is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).