Thermomechanical fatigue characterization of zirconia (8%Y2O3-ZrO2) and mullite thermal barrier coatings on diesel engine components: effect of coatings on engine performance

8%Y2O3-stabilized zirconia (8YPSZ) and mullite (3Al(2)O(3)-2SiO(2)) powders , which were made plasma sprayable by using an organic binder (polyvinyl al cohol), have been plasma spray coated on to the piston head, valves and cyl inder head of a 3.8 kW single-cylinder diesel engine, previously coated wit h Ni-Cr-Al-Y bond coat. The engine with components coated with 250 mu m thi ck 8YPSZ and 1 mm thick mullite thermal barrier coatings has been evaluated for fuel efficiency and for endurance during 500 h long rigorous tests. Im proved fuel efficiency was shown by the engine with coated components and t he results are discussed. The coatings and the coated components have also been examined for phases, microstructure and chemical composition by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispers ive X-ray analysis (EDAX). Mullite coatings were found to exhibit increased resistance to microcracking compared with 8YPSZ during the 500 h endurance test.