Amorphous Alumosilicophosphate Coatings for Niobium Alloys
In the proposed study the less known kinds of thermal barrier coatings used to protect niobium or its alloys against the oxygen corrosion at temperatures above 6000C are discussed. Coatings were obtained from glass in the system BaO(MgO)- Al2O3- SiO2-P2O5 with the softening temperature above 7000C. The development of amorphous coatings from glass includes the preparation of it, deposition on surface of niobium alloy Nb+1% Zr and high-temperature annealing process. The coating can be represented as a multilayer system – top glassy layer (20-25 µm), glasscrystalline (8-10µm) and crystalline interfacial layer (~ 5-8 µm). The interfacial layer forms in the result of diffusion of Nb in a narrow layer close to substrate. Interfacial layer is crystalline and is composed from fine NbP crystals. This layer is the determinative barrier for oxygen diffusion into the substrate at the maximum of operating temperature 950 0C.
Masaaki Naka and Toshimi Yamane
G. M. Sedmale and V. P. Kobyakov, "Amorphous Alumosilicophosphate Coatings for Niobium Alloys ", Materials Science Forum, Vol. 502, pp. 237-242, 2005