Preparation of large-size Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod by laser directed energy deposition and its microstructure homogenization mechanism

Laser 3D printing based on melt growth has great potential in rapid preparation of Al_(2)O_(3)-based eutectic ce ramics.In this work,la rge-scale Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod with diameter of 4-5 mm and height higher than 250 mm was additively manufactured by laser directed energy deposition.Especially,heat treatment was applied to eliminate the microstructure heterogeneity in the as-deposited eutectic ceramic,and the microstructure homogenization mechanism was studied in depth.The results indicate that colonies and banded structures completely disappear after the heat treatment,producing a homogeneous network eutectic structure.The microstructure homogenization is revealed to experience three stages of discontinuous coarsening,continuous coarsening and microstructure coalescence.Additionally,it is found that the eutectic spacing linearly increases with the heat treatment time,meaning that the coarsening behavior of the laser 3D-printed Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)eutectic ceramic satisfies well with the Graham-Kraft model.

Formation mechanism and roles of oxygen vacancies in melt-grown Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) eutectic ceramic by laser 3D printing

Laser three-dimensional(3D)printing has become a significant technique to fabricate high-performance Al_(2)O_(3)-based eutectic ceramics based on melt growth.However,oxygen vacancies are inevitable crystal defects during this process,and their formation mechanism and roles in the as-deposited ceramics are still unclear.In this paper,Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) ternary eutectic ceramics were prepared by laser 3D printing,and the formation mechanism of the oxygen vacancies was revealed by conducting a well-designed annealing experiment.In addition,the effects of the oxygen vacancies on the structure and mechanical property of the as-solidified eutectic ceramic were investigated.The formation of oxygen vacancies is revealed to be a result of the transfer of oxygen atoms from the oxide ceramic to the oxygen-deficient atmosphere by means of vacancy migration mechanism.Besides,the presence of oxygen vacancies has no obvious effects on crystalline structure and microstructure of the additively manufactured eutectic ceramic.However,the chemical bond property changes to some extent due to the formation of these crystal defects,which may affect the mechanical property of the as-deposited eutectic ceramic.It is found that the hardness decreases by 3.9%,and the fracture toughness increases by 13.3%after removing the oxygen vacancies.The results may provide a potential strategy to regulate the mechanical property of the oxide ceramic materials.