Correlation of Process Conditions, Porosity Levels and Crystallinity in Atmospherically Plasma Sprayed Yb2Si2O7 Environmental Barrier Coatings

Robert Vaßen,Doris Sebold,Yoo Jung Sohn,Emine Bakan

doi:10.3390/jcs5080198

Abstract

Environmental barrier coatings are necessary to protect fibre reinforced ceramics from high recession rates in fast and hot water vapor-containing gases as they typically are found in the hot gas sections of gas turbines. A standard material to protect SiC/SiC composites is atmospherically plasma sprayed (APS) Yb2Si2O7. For this material, it is difficult to obtain at reasonable substrate temperatures both low porosity and high crystallinity levels during APS. In this paper results of coatings prepared by a so-called high velocity APS process and also more conventional processes are presented. All coatings have been prepared by a single layer deposition method which avoids inter passage porosity bands. Furthermore, the samples were heat-treated in air at 1300 °C for 100 h and the influence of the topcoat density on the growth of the silica scale on the used silicon bond coat was studied.

Highlights

The efficiency of many energy conversion processes, as for example gas turbines, increases with the operation temperature
A breakthrough was the development of long fibre reinforced ceramics, which give largely improved damage tolerance of the materials [1] and so different components have been produced with such ceramic matrix composites (CMCs)
In this paper Yb2Si2O7 environmental barrier coatings on silicon bond coats have been produced by an atmospheric plasma spraying process using single layer deposition

Summary

Introduction

The efficiency of many energy conversion processes, as for example gas turbines, increases with the operation temperature. One attractive class of materials for this application is ceramics as they offer often high temperature capability in combination with high specific strength which is of special importance for aero-engines. A breakthrough was the development of long fibre reinforced ceramics, which give largely improved damage tolerance of the materials [1] and so different components have been produced with such ceramic matrix composites (CMCs). In a gas turbine, the oxidative atmosphere contains fast flowing water vapor. This water vapor leads to the formation of volatile (oxy) hydroxides, which remove the scale and can lead to massive damage to the whole component [4,5]: Licensee MDPI, Basel, Switzerland

Methods

Results

Conclusion