Thermal history and stress redistributions achieving reduced crack susceptibility in laser-directed energy-deposited Al₂O₃/GAP/ZrO₂ eutectic ceramics by circular oscillation scanning

Crack control remains a major challenge in laser-directed energy deposition (LDED) of oxide eutectic ceramics because of their intrinsic brittleness and thermal-stress accumulation. In this work, emissivity-calibrated in-situ infrared thermometry and thermo-mechanical simulation were used to reveal how circular oscillation scanning (COS) reduces the crack susceptibility of LDED Al₂O₃/GAP/ZrO₂ eutectic ceramics. Compared with linear reciprocating scanning, COS produced a wider high-temperature zone, stronger interlayer reheating, and milder recooling. At the representative mid-height location, the average cooling rate from peak temperature to melting point decreased from 330.91 to 173.82 °C/s, while the reheating-induced temperature rise increased from 167.38 to 1076.03 °C. Stress analysis showed that COS reduced crack susceptibility mainly by weakening the continuous bottom-centered tensile-stress band and localizing higher-stress regions near the side areas, rather than by simply lowering the local stress peak. This stress redistribution was consistent with the observed transition from bottom-initiated vertical cracking to side-localized, laterally limited cracking. The COS parameter study further revealed a trade-off between thermal coverage and tensile-stress concentration. These findings provide guidance for scan-path design and crack control in LDED of oxide eutectic ceramics.