Laser-assisted surface melting of Al2O3-YSZ eutectic ceramics

A procedure for surface densification and/or texturing of Al2O3-YSZ (yttria stabilised zirconia) ceramics with eutectic composition by means of laser surface melting is presented. By scanning a high-power laser beam on a ceramic surface, we achieve a textured and fully dense surface layer from 30 to 1000 microns thick. For example, using a thin diode laser line with fluence 1.23 kW/cml and 0.14 mm/s scan rate, the solidified layer has 560 pm depth. We get a low roughness and dense surface. The microstructure is fine (micron size) due to the eutectic composition. The orientation of the microstructure is determined by the shape of the solid-liquid interface in the solidification process. We study the shape of this interface in transverse and longitudinal cross-sections in single as well as overlapping scans, which are required to process large surfaces. From the macroscopic point of view, the transition between adjacent scans is smooth. However, the microstructure presents discontinuity in the interphase spacing due to microstructural evolution in the heat affected region as well as the nucleation of an Al2O3 layer at the beginning of the crystal growth. The thermal shock inherent to the procedure generates cracks longitudinal and transverse to the scanning direction, as well as delaminating cracks. We analyse different possibilities to reduce this thermal shock. The best results are obtained by preheating the substrate, allowing us to process surfaces of Al2O3-YSZ eutectic ceramics 99% dense.