Surface remelting strategy for enhancing forming quality in laser directed energy deposition of Al₂O₃/GdAlO₃/ZrO₂ eutectic ceramics: Defect suppression and microstructure evolution

The intrinsic brittleness of ceramic materials and the complex temperature field used during laser directed energy deposition (LDED) inevitably lead to the formation of surface and internal defects in the fabricated components, which significantly affect their subsequent deposition accuracy and mechanical properties. This study systematically investigates the influence of the laser surface remelting (LSR) process on the forming quality of Al₂O₃/GdAlO₃/ZrO₂ eutectic ceramics prepared via LDED and reveals the underlying mechanisms with the support of finite element method (FEM) simulations and an infrared thermal imager. The new LSR strategy achieves a remarkable reduction of up to 82% in surface roughness by forming a secondary molten pool and mitigating heat accumulation effects. Moreover, the internal crack density and porosity are reduced by 41% and 86%, respectively. Through redistribution and precise control of the energy input, the originally incomplete eutectic microstructure is successfully transformed into an ultrafine eutectic microstructure, thereby effectively mitigating microstructural inhomogeneity, with the eutectic spacing refined to as small as 102 nm. Additionally, the reduction in surface and internal defects increases the relative density of the samples from 89.3% to 95.9%, whereas the microhardness shows maximum improvements of 18% and 11% in the transverse and longitudinal sections, respectively. On this basis, by integrating the LSR process, this study successfully prepared a bulk eutectic ceramic free of obvious macroscopic defects, with dimensions of 45 mm × 20 mm × 30 mm. The results provide critical insights into the scientific mechanism of the LSR in terms of defect suppression, microstructure evolution regulation, and mechanical property enhancement of eutectic ceramics. This approach is expected to offer a new technical pathway for improving the formation quality of LDED-ed large-size complex oxide eutectic ceramics, as well as other brittle material systems.