Melt-grown alumina-based composites are receiving increasing attention due to their potential for aerospace applications; however, the rapid preparation of high-performance components remains a challenge. Herein, a novel route for 3D printing dense (< 99.4%) high-performance melt-grown alumina-mullite/glass composites using directed laser deposition (DLD) is proposed. Key issues on the composites, including phase composition, microstructure formation/evolution, densification, and mechanical properties, are systematically investigated. The toughening and strengthening mechanisms are analyzed using classical fracture mechanics, Griffith strength theory, and solid/glass interface infiltration theory. It is demonstrated that the composites are composed of corundum, mullite, and glass, or corundum and glass. With the increase of alumina content in the initial powder, corundum grains gradually evolve from near-equiaxed dendrite to columnar dendrite and cellular structures due to the weakening of constitutional undercooling and small nucleation undercooling. The microhardness and fracture toughness are the highest at 92.5 mol% alumina, with 18.39±0.38 GPa and 3.07±0.13 MPa·m^1/2, respectively. The maximum strength is 310.1±36.5 MPa at 95 mol% alumina. Strength enhancement is attributed to the improved densification due to the trace silica doping and the relief of residual stresses. The method unravels the potential of preparing dense high-performance melt-grown alumina-based composites by the DLD technology.

Al₂O₃/Al₆Ti₂O₁₃ composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based (DED-LB) technology. However, the wider application of DED-LB technology is limited due to the inadequate understanding of process conditions. The shaping quality, microstructure, and mechanical properties of Al₂O₃/Al₆Ti₂O₁₃ (6 mol% TiO₂) composite ceramics were systematically investigated as a function of energy input in an extensive process window. On this basis, the formation mechanism of solidification defects and the evolution process of microstructure were revealed, and the optimized process parameters were determined. Results show that high energy input improves the fluidity of the molten pool and promotes the uniform distribution and full growth of constituent phases, thus, facilitating the elimination of solidification defects, such as pores and strip gaps. In addition, the microstructure size is strongly dependent on the energy input, increasing when the energy input increases. Moreover, the morphology of the α-Al₂O₃ phase gradually transforms from cellular into cellular dendrite with increasing energy input due to changing solidification conditions. Under the comprehensive influence of solidification defects and microstructure size, the fracture toughness and flexural strength of Al₂O₃/Al₆Ti₂O₁₃ composite ceramics present a parabolic law behavior as the energy input increases. Optimal shaping quality and excellent mechanical properties are achieved at an energy input range of 0.36−0.54 W*min² g⁻¹ mm⁻¹. Within this process window, the average microhardness, fracture toughness, and flexural strength of Al₂O₃/Al₆Ti₂O₁₃ composite ceramics are up to 1640 Hv, 3.87 MPa m^1/2, and 227 MPa, respectively. This study provides practical guidance for determining the process parameters of DED-LB of melt growth Al₂O₃/Al₆Ti₂O₁₃ composite ceramics.