Fabrication and characterization of thermal barrier coatings for internal combustion engines via suspension plasma spray with high solid loading

Suspension plasma spraying (SPS) technique producing thermal barrier coatings (TBCs) with high porosity and good thermal shock resistance has great potential to improve the thermal efficiency of internal combustion (IC) engines. However, its wide usage is limited by the immature fabrication technology and low spraying efficiency. Therefore, this study optimized the SPS process with high solid loading and characterized the properties of the coating to obtain TBCs suitable for IC engines. Suspension composition optimization revealed that polyethylenimide (PEI) has the best dispersion effect, and a suspension with high solid loading of 35 wt% was obtained. Furthermore, the effects of the spraying distance, feeding speed and spraying power on the coating microstructure were investigated, and the porosity and thermal shock resistance of the coatings were characterized to determine the optimal spraying process. Thermal shock failure of SPS coatings primarily arises from the propagation of horizontal cracks originating from vertical intercolumn cracks. The SPS coating with a feathery columnar structure has the best thermal shock resistance. By optimizing the spraying process, a coating with porosity up to 24.16 %, bonding strength of 41.69 MPa, and good thermal shock resistance is successfully achieved.