Suspension plasma sprayed thermal barrier coatings for internal combustion engines

Sammanfattning: The upward trend in internal combustion engine efficiency is likely driven by the depletion of fossil fuels. Since no replacement in sight can deliver energy comparable to the conventional oil, there is a need to use it more rationally and effectively. Thermal barrier coatings have been seen for a long time as a solutionto increase the thermal efficiency of gas turbine engines but suffer from the lackof strong applicability in internal combustion engines. This is due to the different restrictions when comparing the environment on the gas turbines and in internal combustion engines. To overcome this problem and, at the same time, expand the application field of thermal barrier coatings, more efforts need to be devoted.In this work, different top coat materials using various deposition techniques were evaluated and categorized in three different thermal barrier coating (TBC) architectures. The first was the lamellar yttria-stabilized zirconia (YSZ) top coat deposited by atmospheric plasma spray (APS), used as a reference sample. The second architecture was a columnar suspension plasma spray (SPS) TBC with YSZ and gadolinium zirconate (GZO) top coat. The SPS process can produce avariety of microstructures, and they were, for the first time, tested in an internal combustion engine. The third architecture was an SPS top coat, with an additional layer on the top, called a sealing layer of either metallic or ceramic material, both never investigated in a diesel engine application earlier.For the thermophysical properties investigation, a combination of laser flashanalysis (LFA) and modeling with object-oriented finite element (OOF) was employed to understand the properties in all the applications. The performance of the coatings was evaluated in two different ways, by thermal cyclic tests, basedon the TBCs behavior under cyclic thermal loads and by single-cylinder engine experiment. The characterization of the coatings was done by scanning electron microscope (SEM) before and after the thermal cyclic tests.The performance properties were correlated with coatings microstructure and thermophysical properties. It was shown that a columnar TBC produced by SPS had a superior engine efficiency in the single cylinder engine experiment.