Laser additive manufacturing of melt-grown Al₂O₃/GdAlO₃ eutectic ceramic composite: Powder designs and crack analysis with thermo-mechanical simulation

Directed energy deposition method is an efficient one-step laser additive manufacturing technology to achieve eutectic ceramic composite with high property and ultra-fine microstructures. In this paper, melt grown dense Al₂O₃/GdAlO₃(GAP) eutectic ceramic composites have been directly fabricated from the spherical powder reconstructed by an optimized spray granulation method. Effects of the powder size distribution, feeding rate, and heat treatment on the morphology and microstructure of the as-solidified eutectic ceramic composites have been investigated. Results show that the powder fluidity plays an important role in the heat conduction of the laser process. Finer powder (imperfect spherical powder with diameter less than 10 µm) gives rise to the disturbance of molten pool. Moreover, this powder greatly aggravates the phenomenon of powder’ sticking on surface of the specimen, which subsequently induces the leading growth of coarse dendrite-like GAP primary phases (higher interface temperature of dendrite tip for GAP phase) and sintered eutectic phases at the specimen edge. The finite element modeling (FEM) method is used to analysis the coupled thermal dynamic during the process after verification with infrared thermal image. It shows that longitudinal maximum principal stress exhibits a steep gradient at the edges of the as-solidified ceramic, making the specimen susceptible to cracking along the deposited direction at the first few layers. By optimizing the feedstock powder characteristics and the directed energy deposition process, completely solidified cylindrical and thin-walled Al₂O₃/GAP eutectic ceramic composites with the maximum dimensions of ϕ 4 × 95 mm³ and 10 × 4 × 44 mm³ have been successfully fabricated. The solidified specimens present smooth glossy surface and fine microstructures with the average eutectic spacing of 0.31 µm. The average micro-hardness and fracture toughness of 15.16 ± 0.29 GPa and 4.3 ± 0.09 MPa·m^1/2 have been obtained, respectively.