Fabrication of functionally-graded yttria-stabilized zirconia coatings by 355 nm picosecond dual-beam pulsed laser deposition

Abstract

This article presents the design, fabrication, and characterization of functionally-graded yttria-stabilized zirconia (YSZ) coatings by using a novel dual-beam pulsed laser deposition method based on a 355 nm ps laser. Graded coatings were fabricated by mixing YSZ and the substrate material (stainless steel). The two materials were ablated and deposited on a substrate inside a vacuum chamber, in a way that the mixture composition gradually changes from stainless steel to YSZ, along the coating's growth direction, following a predesigned linear composition profile. The Rockwell indentation method was employed for the adhesion strength analysis based on the interfacial crack radius (c) and indentation load (P). When a load P is applied on the sample surface, a crack with a radius c will be formed. Hence, by using more than one loads and measuring the generated crack diameters, dP/dc can be estimated, which is considered as a critical parameter and is proportional to the coating's adhesion strength. The graded coating was found to provide improved adhesion strength (dP/dc = 9.41 N/μm) over pure YSZ coatings (dP/dc = 8.35 N/μm and 8.43 N/μm). In this study, the thermal barrier effects of the coatings were examined by measuring the thermal conductivity values of the coatings using a high-power multi-mode fiber laser as an impulsive heat source and an infrared camera, and the deposited YSZ coatings showed a low thermal conductivity (∼1.14 W/m·K).