Insights into the influence of powder particle shape on forming process and mechanical properties of Al₂O₃ ceramic fabricated by laser directed energy deposition

Laser directed energy deposition (LDED) is a promising technology for preparing complex-shaped melt-grown Al₂O₃-based ceramics which are important candidates for new high-temperature structural materials. The characteristics of ceramic powder particle significantly affect the stability of LDED process and the forming quality of ceramic samples. In this study, rod-like and thin-walled Al₂O₃ ceramics were one-step fabricated by LDED by using the plasma spheroidized alumina powder (PSAP) and irregular alumina powder (IAP), respectively. The differences in forming quality and mechanical properties of the specimens prepared by the above two powders were analyzed and discussed. Both powders achieved high-quality forming of rod-like samples with high relative densities of more than 99% and 98%, respectively. The flowability of IAP met the fundamental forming requirements of LDED technology. The microhardness and fracture toughness of the Al₂O₃ ceramics obtained by using IAP were 17.77 ± 0.97 GPa and 4.58 ± 0.50 MPa·m^1/2, respectively. Due to the angular shape and narrow particle size distribution of IAP, there were lack-of-fusion (LOF) pores at the grain boundaries. Intergranular oxide impurities and LOF pores reduced the flexural strength. In contrast, the flexural strength of Al₂O₃ ceramics prepared by PSAP reached 276.6 ± 22.9 MPa due to the columnar crystals with highly consistent growth orientation. Combining the reduction of line energy density and the supplement of additional laser energy input, crack-free thin-walled Al₂O₃ ceramics with a width of 30 mm were successfully manufactured using PSAP. Its relative density was close to 99%, and the forming error of width direction was only 5.7%. The study demonstrates the profound influence of powder particle shape on the forming quality of LDED, which provides an essential reference for laser additive manufacturing of high-quality Al₂O₃-based ceramics.