High-Speed Laser Patterning of YSZ Ceramic Substrates for Plasma Spraying: Microstructure Manipulation and Adhesion of YSZ Coatings

This paper introduces novel possibilities of using recently developed high-power lasers for high-speed surface periodic structuring/patterning of the ceramic substrates for the subsequent thermal spray coating deposition, which may be difficult to pattern using conventional methods. Yttria-stabilized zirconia (YSZ) was selected as model ceramic for both substrates and coating. Three different types of patterns were produced by three different laser technologies: dimples with nominal depth of 15 and 30 mu m (pulsed nanosecond laser), grids with nominal depth of 15 and 30 mu m (continuous wave laser), and pillars with nominal depth 30 mu m (ultrashort pulsed femtosecond laser). All surface patterns were thoroughly periodical and their surface roughness ranged from Sa = 4.5 to 10.3 mu m, significantly surpassing conventional grit-blasting. Pulsed and continuous wave lasers showed very high process rates (up to 54.5 mm2/s and 323.6 mm2/s, respectively) and tendency to develop network of shallow surface cracks. Ultrashort pulsed laser technology was slower (process rate 1.65 mm2/s) but the surface was crack-free with desirable miniature anchoring points. Plasma spraying was carried out with powder, solution, and suspension feedstocks providing an experimental matrix demonstrating potential benefits and risks of each pattern-feedstock combination. Not all combinations led to successful coating deposition, but results show that microstructure of the coating may be deliberately controlled by laser texturing, in particular periodic substrate pattern led to periodic coating microstructure in the case of suspension spraying. Also adhesion/cohesion of the coating to the substrate may be in many cases significantly improved by laser patterning of the substrate. The highest coating adhesion/cohesion strength (26.2 +/- 4.8 MPa) was achieved for the coating deposited from solution on pillar patterns. Finally, a possibility to combine the high-speed and advanced surface morphology produced by continuous wave and femtosecond lasers, respectively, and direct patterning of plasma sprayed coating were also demonstrated.