Microstructure formation of silicide coating on Nb–W–Mo–Zr alloy

ABSTRACT

Silicide coatings were deposited on the Nb–5W–2.5Mo–1Zr alloy by pack cementation method. The microstructure, phase distribution, growth kinetics and oxidation behaviour of the coatings were studied. The results show that the coatings were mainly composed of an outer NbSi₂ layer, an acicular Nb₅Si₃-dispersed NbSi₂ two-phase layer and a Nb₅Si₃ inner layer, exhibiting a three-layer structure. The temperature and holding time both have a significant effect on the coating formation. It was found that the coating growth kinetics at 1250°C followed a parabolic law. The coating exhibited a relatively good short-term protection to the substrate in static air at 850 and 1250°C. Both scales formed at the two oxidation temperatures consisted mainly of a mixture of SiO₂, Nb₂O₅ and NbO.

KEYWORDS:

• Nb-based alloy
• silicide coating
• pack cementation
• oxidation

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China (grant numbers 51401166, 51431003 and U1435201) and Natural Science Basic Research Plan in Shaanxi Province of China (grant number 2017JM5086).