Characterization of a Ceramic Matrix Composite coated with an environmental barrier under multiphysical loadings
Topic(s) : Experimental techniques
Co-authors :
Louane RONTEIX (FRANCE), Yannick PANNIER (FRANCE), Florent MAUGET (FRANCE), Nicolas GUEL , Thomas VANDELLOS (FRANCE), Jonathan CORMIERAbstract :
Silicon Carbide (SiC) Ceramic Matrix Composites (CMC) are promising materials for use in aircraft engine turbines. They have a lower density and better properties at high temperature than superalloys, but the engine environment is critical for CMC structures. In fact, the high temperatures coupled with water vapor degrade quickly CMCs mechanical properties and decrease their lifetime. So, using an environmental coating on these materials is necessary for this type of application.
The Environmental Barrier Coating (EBC) studied here is a 3rd generation type. It is made with a Silicon (Si) bond coat deposited by thermal spray on the SiC/SiC CMC substrate and an Ytterbium DiSilicate (YbDS) top coat layer. The deposition methods of both layers allow a thin EBC (<100µm). It is known that this kind of EBC is sensitive to mechanical and thermomechanical loadings and to oxidizing species that exists within aircraft engine turbines. Nevertheless, there is only a few studies concerning the behavior under multiphysical loadings of this system with thin EBCs.
The aim of the study is to characterize damage mechanisms of the CMC/EBC system under thermomechanical loadings by coupling thermal gradients and mechanical stresses. On one hand, experiments are conducted on SiC/SiC CMC/Si/YbDS samples with a electromechanical machine, using induction to heat up the sample and generate a thermal gradient upon the length. For each test, multiple instrumentations are used (infrared camera, pyrometer and acoustic emission sensors) in order to measure thermal field and to detect acoustic events like cracking within the sample. Extensometry is also used to measure the strain evolution. Moreover, shrinkage cracks have been observed on the YbDS surface. To determine their influence on the coating damage mechanisms, surface and bulk observations of the samples are realized, before and after the tests, using optical microscopy and micro-tomography acquisitions. Other characterizations using a Scanning Electron Microscope (SEM) are made on the fracture surfaces and within the substrate and the coating using cuts in the tested sample to understand the damage mechanisms. On the other hand, simulations of the thermal gradient and the mechanical loadings generated during tests have been implemented using Abaqus simulations to evaluate the strain and stress states within the CMC/EBC system. These simulations allow a better understanding of the mechanical response of the samples depending on the thermomechanical solicitations applied.
The Environmental Barrier Coating (EBC) studied here is a 3rd generation type. It is made with a Silicon (Si) bond coat deposited by thermal spray on the SiC/SiC CMC substrate and an Ytterbium DiSilicate (YbDS) top coat layer. The deposition methods of both layers allow a thin EBC (<100µm). It is known that this kind of EBC is sensitive to mechanical and thermomechanical loadings and to oxidizing species that exists within aircraft engine turbines. Nevertheless, there is only a few studies concerning the behavior under multiphysical loadings of this system with thin EBCs.
The aim of the study is to characterize damage mechanisms of the CMC/EBC system under thermomechanical loadings by coupling thermal gradients and mechanical stresses. On one hand, experiments are conducted on SiC/SiC CMC/Si/YbDS samples with a electromechanical machine, using induction to heat up the sample and generate a thermal gradient upon the length. For each test, multiple instrumentations are used (infrared camera, pyrometer and acoustic emission sensors) in order to measure thermal field and to detect acoustic events like cracking within the sample. Extensometry is also used to measure the strain evolution. Moreover, shrinkage cracks have been observed on the YbDS surface. To determine their influence on the coating damage mechanisms, surface and bulk observations of the samples are realized, before and after the tests, using optical microscopy and micro-tomography acquisitions. Other characterizations using a Scanning Electron Microscope (SEM) are made on the fracture surfaces and within the substrate and the coating using cuts in the tested sample to understand the damage mechanisms. On the other hand, simulations of the thermal gradient and the mechanical loadings generated during tests have been implemented using Abaqus simulations to evaluate the strain and stress states within the CMC/EBC system. These simulations allow a better understanding of the mechanical response of the samples depending on the thermomechanical solicitations applied.