Determining Interface Fracture Toughness in Multi Layered Environmental Barrier Coatings with Laser Textured Silicon Bond Coat

Markus Wolf,Hideki Kakisawa,Fabia Süß,Robert Vaßen,Daniel Emil Mack

doi:10.3390/coatings11010055

Abstract

In the high temperature combustion atmosphere inside of aircraft turbines, the currently used ceramic matrix composites require a protective environmental barrier coating (EBC) to mitigate corrosion of the turbine parts. Besides thermomechanical and thermochemical properties like matching thermal expansion coefficient (CTE) and a high resistance against corrosive media, mechanical properties like a high adhesion strength are also necessary for a long lifetime of the EBC. In the present work, the adhesion between an air plasma sprayed silicon bond coat and a vacuum plasma sprayed ytterbium disilicate topcoat was aimed to be enhanced by a laser surface structuring of the Si bond coat. An increase in interface toughness was assumed, since the introduction of structures would lead to an increased mechanical interlocking at the rougher bond coat interface. The interface toughness was measured by a new testing method, which allows the testing of specific interfaces. The results demonstrate a clear increase of the toughness from an original bond coat/topcoat interface (8.6 J/m2) compared to a laser structured interface (14.7 J/m2). Observations in the crack propagation indicates that the laser structuring may have led to a strengthening of the upper bond coat area by sintering. Furthermore, in addition to cohesive failure components, adhesive components can also be observed, which could have influenced the determined toughness.

Highlights

IntroductionThe currently used nickel-based alloys inside of the turbines, are limited in their operation temperature and require complex cooling and protection systems to operate at high temperatures
Gas turbines are commonly used in the field of power generation and aero engines.The currently used nickel-based alloys inside of the turbines, are limited in their operation temperature and require complex cooling and protection systems to operate at high temperatures
After the laser structuring of the specimen ST2 and ST3, the roughness was measured for all three specimen types. 3D illustrations of an unstructured bond coat (ST1) and

Summary

Introduction

The currently used nickel-based alloys inside of the turbines, are limited in their operation temperature and require complex cooling and protection systems to operate at high temperatures For this reason, new materials like SiC/SiC ceramic matrix composites (CMCs) are in focus of the turbine development to achieve higher fuel efficiencies and to simultaneously reduce the release of environmentally harmful by-products [1,2,3,4]. New materials like SiC/SiC ceramic matrix composites (CMCs) are in focus of the turbine development to achieve higher fuel efficiencies and to simultaneously reduce the release of environmentally harmful by-products [1,2,3,4] These materials offer some advantages against the nickel-based alloys, such as much higher operation temperatures, lower weight, and superior mechanical properties [5,6,7]. It is necessary to protect the CMCs with environmental barrier coatings (EBCs)

Methods

Results

Conclusion