Abstract
Environmental/thermal barrier coatings (E/TBCs) of yttria partially stabilised zirconia (YSZ), gadolinium zirconate (GZO) and a combination of Y2SiO5 and GZO were applied on a Nb/Nb5Si3‐based alloy with the nominal composition of Nb‐25Ti‐8Hf‐2Cr‐2Al‐16Si (at%). A B‐containing M7Si6‐based (M = Ti, Nb, Fe, Cr) layer produced by pack cementation was used as bond coat. The ceramic topcoats were manufactured by electron‐beam physical vapour deposition (YSZ and GZO) and magnetron sputtering (Y2SiO5). The different E/TBC systems were tested under cyclic oxidation conditions in air at 1100 and 1200 °C. Lifetimes exceeding 1000 cycles of 1 h dwell time at 1100 °C were determined. The YSZ, GZO and combined Y2SiO5 + GZO topcoats did not spall off during the maximum exposure time, exhibiting good adherence to the thermally grown oxide scale which consisted of mixed oxides of Fe, Ti, Cr and Nb embedded in silica. For the E/TBC systems with YSZ and GZO which were thermally cycled at 1200 °C, lifetimes up to 850 cycles were measured; that of the system with a combined Y2SiO5 + GZO topcoat exceeded again 1000 cycles.
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