Insights into high thermal stability of laser additively manufactured Al2O3/ GdAlO3/ZrO2 eutectic ceramics under high temperatures

Laser additive manufacturing techniques have been considered to be the most promising methods to fabricate melt-grown Al2O3-based eutectic ceramics which are potential candidates for high temperature structural applications. In this paper, Al2O3/GdAlO3/ZrO2 ternary eutectic ceramic was additively manufactured based on one-step melt-growth by laser directed energy deposition, and its thermal stability under high temperatures was studied. The results indicate that the as-solidified eutectic composite consists of ultrafine phases of alpha-Al2O3, GdAlO3 and t-ZrO2, and presents an irregular eutectic morphology with amounts of terminations and branches. The 3D-printed eutectic ceramic exhibits a superior thermal stability that no mass variation and no phase transition occur even after annealed at 1500 degrees C for 200 h. In addition, the submicron-scaled eutectic microstructure and the polished surface topography can maintain stability up to 1400 degrees C which is higher than 80% of its melting point (>0.8 Tm). With further increasing the temperature, obvious microstructure coarsening, and surface holes formation occur, leading to the severely deterioration of the mechanical property. The hardness of the as-deposited eutectic ceramic rapidly decreases from 15.84 +/- 0.61 GPa to 13.01 +/- 0.40 GPa after 200 h annealed at 1500 degrees C. The results indicate that the additively manufactured Al2O3-based eutectic ceramics have great potential to be long-time high-temperature structural materials applied at elevated temperatures.