Effect of laser focus shift on the forming quality, microstructure and mechanical properties of additively manufactured Al2O3-ZrO2 eutectic ceramics

Melt-grown Al2O3-ZrO2 eutectic ceramics have attracted extensive attention for harsh environment applications. In this work, Al2O3-ZrO2 eutectic ceramic is additively manufactured via one-step laser powder bed fusion (LPBF). The effect of laser focus shift on the relative density, phase formation, microstructure evolution, and mechanical properties was systematically investigated. The as-fabricated specimens are dominated by alpha-Al2O3 and t-ZrO2. The m-ZrO2 phase increases with increasing the laser defocus shift. The cellular-like structure formed when convection dominated at focal plane, while colony eutectic structure occurred when eutectic growth dominated at higher defocus shift. The deformation of cellular-like structure and needle-like ZrO2 into concave cells and dendritic structures is principally determined by the evolution of solid/liquid (S/L) interfaces. With the formation of needle-like or dendritic ZrO2 ductile phase, the crack propagation is prevented, leading to progressively enhanced fracture toughness with a maximum value of 8.04 MPa m1/2.