Thermal barrier coatings for diesel engine exhaust applications

Abstract: The strive to increase the engine efficiency in terms of fuel consumption and lower emissions have lead to higher demands on materials. In this thesis five different thermal barrier coatings applied using air plasma spraying to three materials commonly used for exhaust application are evaluated. This thesis work was done at Scania CV in Södertälje with main focus on evaluation during thermal cycling. The goal of this thesis is to evaluate the coatings and correlate their behaviour to their characteristic microstructure. The coatings were evaluated through their stability in thermal conductivity, fracture toughness, hardness, porosity and failure modes. The parameters where obtained using laser flash, Vickers indentation, Vickers indentation fracture toughness and microscopic evaluation methods. The evaluation shows that conventionally used zirconia based materials exhibits low thermal conductivity, high hardness, and stable fracture toughness compared to other evaluated materials. One material that can be applicable in diesel exhaust application is mullite, which showed similar performance to zirconia based materials. For the use of TBC together with SiMo51 a different bondcoat than conventional NiCrAlY needs to be evaluated.