In-situ microwave–laser hybrid additive manufacturing of nano Al₂O₃/YAG/ZrO₂ ternary eutectic melt-growth ceramics: control of microstructural homogeneity and high densification

The fabrication of melt-growth ceramics (MGCs) via laser-directed energy deposition (LDED) is highly attractive because of its ability to directly fabricate net-shaped components in a single step, eliminating the need for molds or binders. However, the complex and rapid solidification dynamics inherent to the LDED process lead to directional microstructural growth, periodic coarse banding, and high porosity, severely limiting the components’ mechanical properties and reliability. To overcome these limitations, an innovative in situ microwave-assisted LDED process for the fabrication of Al₂O₃/YAG/ZrO₂ (AYZ) ternary eutectic ceramics was developed to allow precise control over the entire solidification and fabrication of the component. The results show that with high-adsorption microwave assistance, the global structural homogeneity of the as-fabricated samples is significantly improved, with the interlayer banded structure transitioning from an irregular morphology to a lamellar and periodic structure. Furthermore, ZrO₂ exhibits texture randomization evolution under high microwave absorption fabrication conditions. The simulation results reveal the physical mechanisms driving the material’s enhanced integrity. The microwave field suppresses the maximum thermal gradient by up to 55.3%, which homogenizes the solidification conditions. Simultaneously, it substantially prolongs the melt pool lifetime. This extended duration, combined with a critically important in situ plasma ignited by frequent collisions between laser-provided seed electrons and gas molecules, promotes dramatic densification. This dual-mechanism approach significantly reduces the internal porosity—decreasing the void fraction by 85.5% to a minimum of 0.11% and decreasing the average pore size by 49.3%. These improvements in material integrity directly translate to superior mechanical performance. While maintaining the intrinsic hardness and fracture toughness of the AYZ eutectic ceramic, the microwave-assisted process significantly reduces the anisotropy of these properties compared with those of components fabricated at room temperature. In addition, the flexural strength of the microwave-assisted sample is 22.2% greater than that of the nonmicrowave-assisted sample, reaching a maximum of 373.8 MPa, indicating synergistic control of strength and toughness. This research, therefore, establishes a novel methodology for defect mitigation and performance modulation in the laser additive manufacturing of high-quality MGCs.