Mechanical Properties and Thermal Shock Behavior of Al2O3-YSZ Ceramic Layers Obtained by Atmospheric Plasma Spraying

Abstract

Ceramic coatings have many advantages for industrial and medical applications due to their exceptional properties. Ceramic coatings with a thickness of approximately 45 μm, after grinding, were grown using a robotic arm that used the atmospheric plasma spraying procedure. The thermal shock stresses—a common situation in applications but difficult to reproduce under laboratory conditions—of the ceramic layers on top of the metal substrate was achieved using solar energy focused by a concentrating mirror, based on experiments conducted in the CNRS-PROMES laboratory, UPR 8521, belonging to the French National Centre for Scientific Research (CNRS). The ceramic layers showed excellent stability at 1000 °C, even at high heating or cooling rates. At high temperatures (above 1800 °C), the exfoliation of the complex ceramic layer was observed. No differences in the structural, phase, mechanical or adhesion properties of the ceramic layer were observed after the thermal shock cycles (in the literature, there have been quite few reports regarding the properties of the ceramic layers after the thermal shock application). Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques were used to characterize the complex ceramic coating and the effects of thermal shock cycling. The phases and chemical composition of the complex coatings remained similar, insensitive to thermal shock at 1000 °C, consisting of a mixture of crystalline yttrium zirconium oxide and α and γ alumina. For all cases, the main residual stress state was tensile. After 5 or 10 cycles of thermal shocks, a smoothing of the residual stress state was observed in the investigated area. A higher temperature (above 1800 °C), applied as thermal shock, led to higher residual stresses and resulted in large cracks and the spallation of the coating layer.