High temperature behaviour of NbSi₂ coating on the Nb-1Zr-0.1C alloy

ABSTRACT

High temperature behaviour of NbSi₂ coatings on the Nb-1Zr-0.1C alloy, developed using the molten salt technique, has been investigated. For this purpose, samples were aged at different temperatures under vacuum and in the ambient atmosphere. High temperature annealing between 1200 and 1400°C of the coating under vacuum led to the formation of a layered structure comprising various silicide phases and porous microstructures. The formation of the porous structure was rationalised on the basis of differential diffusion mechanism of elemental species. The high temperature annealing in an ambient atmosphere showed that the single layer of NbSi₂ coating formed on the Nb alloy was found insufficient to provide protection at high temperatures under oxidising environments. By introducing intermediate coating, concentrations and effective size of pores were reduced. Based on the EDS analysis, density of the pores and their size distribution, a mechanism involving diffusion of Nb/Si in the formation of Nb₅Si₃ has been proposed.

KEYWORDS:

• Molten salt
• Nb alloy
• silicide coating
• high temperature behaviour
• porosity

Acknowledgements

The assistance provided by Dr. Naveen Kumar N, MSD, BARC in FESEM characterisation is gratefully acknowledged. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Disclosure statement

No potential conflict of interest was reported by the authors.