Femtosecond laser additively manufactured crack-resistant alumina

Laser additive manufacturing (AM) of ceramics is severely hindered by the material’s intrinsic brittleness and the intense macroscopic thermal gradients inherent to continuous-wave (CW) laser processing, which inevitably induce macro-scale thermal stresses, cracks, and pores. To fundamentally resolve this limitation, this study proposes a novel approach utilizing femtosecond laser additive manufacturing for wide-bandgap alumina (Al₂O₃) ceramics. The ultra-high peak power of the femtosecond laser triggers nonlinear absorption, facilitating highly localized energy deposition and significantly mitigating thermal diffusion. The effects of laser energy density and repetition rate on the forming quality are systematically investigated. In situ high-speed imaging demonstrates that the instability of the melt pool and pore formation can be effectively suppressed by optimizing the pulse repetition rate. Furthermore, the interaction process between a femtosecond laser and alumina was investigated using ultrafast reflection pump-probe spectroscopy. Ultimately, the ultrafast melt-pool dynamics and morphology formation mechanism during femtosecond laser additive manufacturing of alumina are elucidated. Under optimal parameters (132 J/mm² energy density and 800 kHz repetition rate), we successfully fabricated near-fully dense (>99%), crack-lean Al₂O₃ components. The femtosecond laser promotes a non-equilibrium process, yielding refined grain structures that result in exceptional mechanical properties, including a microhardness of 21.4 GPa, a compressive strength of 969.7 MPa, and a fracture toughness of 5.1 MPa⸱m^1/2. Moreover, the successful fabrication of complex, thin-walled architectures with feature sizes below 250 μm demonstrates the potential of femtosecond lasers for the direct, defect-lean additive manufacturing of high-precision ceramic components.