Evaluation of modifications induced on pore network and structure of partially stabilized zirconia manufactured by hybrid plasma spray process

Abstract

Thermal barrier coatings (TBCs) constituted by yttria partially stabilized zirconia (i.e. Y-PSZ, ZrO 2+7wt.% Y 2O 3) and a metallic bond layer (i.e. usually MCrAlY where M represents a combination of Ni and Co) are extensively used to improve the performance of hot-section components of gas turbines. Air plasma spray (APS) and in-situ laser irradiation by diode laser processes are combined to modify structural characteristics of TBCs. The existence of interconnected porosity and segmented cracks in APS·TBCs not only influences their mechanical properties, but also deteriorates the oxidation and corrosion resistance of the component. One of the purposes of combined laser treatments is so to architecture differently the pore networks. The dependence between the microstructure of TBCs, which was modified by laser treatment, and corrosion resistance has been evaluated by an electrochemical test. Results show that, for a laser energy density ranging from 1.7 to 1.9 J mm −2, the pore network connectivity level decreases. Scanning electron microscopy observation revealed also that laser treatment induces a change of the microstructure from lamellar to columnar dendritic. Intensive image analysis was also performed to further quantify the pore characteristics (i.e. nature, orientation, percentage, etc.). Moreover, no phase transition was noticeable: the metastable tetragonal phase still remains the predominant phase after laser treatment.