Abstract

The impact of small deposits of calcium–magnesium–aluminium silicates (CMAS) on the top of thermal barrier coatings (TBCs) made of yttria-stabilised zirconia (YSZ) produced via electron-beam physical vapour deposition (EB-PVD) is shown to play a role in the microstructural and chemical stability of the coatings; hence, it also affects the thermal insulation potential of TBCs. Therefore, the present work investigates the degradation potential of minor CMAS deposits (from 0.25 to 5 mg·cm−2) annealed at 1250 °C for 1 h on a novel Er2O3-Y2O3 co-stabilised ZrO2 (ErYSZ) EB-PVD TBC, which is compared to the standard YSZ coating. Due to the higher reactivity of ErYSZ coatings with CMAS, its penetration is limited in comparison with the standard YSZ coatings, hence resulting in a better thermal insulation of the former after ageing.

Highlights

  • Thermal barrier coatings (TBCs) allow both better performance and an extension of component durability via the protection of superalloy components in the hottest sections of gas turbines [1,2]. These multilayer coatings comprise a metallic bond coating (BC) that provides resistance to oxidation while growing a thin oxide known as the thermally grown oxide (TGO), which is responsible for the adherence of the ceramic top coating (TC)

  • This study investigated the degradation potential of minor calcium–magnesium–aluminium silicates (CMAS) deposits

  • CMAS did not fully penetrate the coatings, which resulted in the partial coverage of the surface of the coatings

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Summary

Introduction

Thermal barrier coatings (TBCs) allow both better performance and an extension of component durability via the protection of superalloy components in the hottest sections of gas turbines [1,2] These multilayer coatings comprise a metallic bond coating (BC) that provides resistance to oxidation while growing a thin oxide known as the thermally grown oxide (TGO), which is responsible for the adherence of the ceramic top coating (TC). To reach higher efficiencies and performance of turbine engines, the inlet gas temperature must increase further This ever-increasing demand leads to the constant need to search for new solutions with, for instance, an interest in developing top coatings with even greater thermal insulation potential [5]. To some extent, doping YSZ with several other additives such as NiO, Nd2 O3 , Er2 O3 , Yb2 O3 , and Gd2 O3 allowed an enhancement of TBCs performances via Materials 2020, 13, 4382; doi:10.3390/ma13194382 www.mdpi.com/journal/materials

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