Influência da temperatura de pré-aquecimento sobre a morfologia e ciclos térmicos de revestimentos YSZ

Abstract

High temperature resistant coatings, such as thermal barrier coatings (TBC), are composed of a ceramic layer (Top Coat) deposited on a metallic layer Bond Coat, these coatings are normally applied by thermal spray techniques to protect these components. In order to improve the coating properties, it is necessary to analyze the influence of the different processing parameters on the performance of the coatings, for example, the preheating temperature of the substrate. The general objective of this research was to study the influence of preheating temperature of the substrate on the morphology and behavior of ytrria stabilized zirconia (YSZ) ceramic coatings, submitted to thermal cycles. The ceramic coating deposition was carried out by air plasma thermal spraying process (APS) on a Ni substrate.alloy pre-coated with a Bond Coat constituted of a Ni superalloy thermally sprayed by high velocity oxy-fuel process (HVOF). Preheating temperature influence was analyzed on the YSZ porosity, as well as the coating morphology, microhardness, tensile adhesion resistance and interface fracture toughness of the Top Coat, before and after thermal cycling oxidation tests. It was observed that increasing the preheating temperature decreases the YSZ porosity, improving the coating adhesion and microhardness increase. This pre heating temperature increase promoted a greater fracture toughness on the YSZ/Bond Coat interface. The cyclic oxidation reduced the porosity of the Top Coat and promoted some metallurgical changes on the Bond Coat, resulting in the fracture toughness increase in the Top Coat/Bond Coat interface. This effect was more pronounced on samples with minor substrate preheating temperature.