Processing and microstructural study of surface laser remelted Al2O3–YSZ–YAG eutectic plates

Surface modification of ternary Al2O3–Zr2O3–Y2O3 eutectic oxides was produced by laser melting. Preheating the ceramics and using a protecting atmosphere, we obtained homogeneous eutectic surface layers of 7 mm × 25 mm and 400 μm thick. The remelted layers were dense using processing rates below 500 mm/h but showed bubble porosity at faster processing rates. The phases in the resultant material were cubic zirconia (YSZ), α-Al2O3 and Y3Al5O12 (YAG). At 20 mm/h, the remelted layer presented a Chinese-script like microstructure formed by an interpenetrating network of Al2O3 and YAG. At travelling speeds greater than 500 mm/h colonies were formed. At the largest processing rates the microstructure becomes fibrous like, the YSZ phase locating at the interface between Al2O3 and YAG phases. The chemical composition was independent of position into the layer. The very fine microstructure allows an in-line optical transmittance in the NIR of 60% for a 380 μm thick layer processed at 3500 mm/h.