Objective This study systematically investigates the damage mechanisms of diamond-silicon carbide （SiC） composites during femtosecond laser cutting with a focus on how laser power affects surface morphology， roughness， and crystallographic structure.By correlating laser parameters with the material response， the study aims to offer theoretical insights for optimizing processing conditions， thereby balancing cutting efficiency and surface quality in ultrahard composites.

Methods Diamond-SiC composites were synthesized via silicon vapor infiltration （SVI）. A porous diamond preform with an average particle size of 50 μm， was infiltrated with silicon vapor at 1 600 ℃ under vacuum， resulting in a dense composite with a final density of 3. 05 g/cm³. Specimens were polished to a surface roughness （R_a ）≤1 μm before laser processing. Femtosecond laser cutting was performed under four power levels （0 W，2 800 W，3 000 W，3 200 W） with fixed parameters： a wavelength of 1 064 nm， repetition frequency of 3 kHz， pulse width of 30 μs， and scanning speed of 50 mm/min. For post-processing characterization， X-ray diffraction （XRD） was employed for phase analysis， scanning electron microscopy （SEM） was utilized for surface morphology evaluation， and atomic force microscopy （AFM） was applied for 3D roughness quantification.

Results and Discussion

The initial surface roughness （R_a ） of unprocessed samples was measured as 52. 9 nm. At 2 800 W laser power，R_a slightly decreased to 49. 4 nm due to localized laser-induced smoothing effects. However， when the power exceeded 3 000 W，R_a surged to 122 nm （3 000 W） and 375 nm （3 200 W）， which was attributed to intensified melting， sputtering， and thermal stress-induced irregularities. AFM analysis revealed the formation of wave-like textures and deep grooves on

surfaces processed at higher powers， confirming severe surface degradation. XRD analysis identified diamond （C）， SiC， silicon （Si）， and graphite （GCB）. Unprocessed samples showed dominant peaks corresponding to diamond （111，220） and SiC （002，111，200）. At 2 800 W， minor graphite peaks emerged， indicating partial diamond-to-graphite transformation （sp³→sp2）. At 3 000 W， graphite content increased significantly， accompanied by weakening SiC diffraction intensities. At 3 200 W， graphite became the dominant phase while certain SiC peaks disappeared， suggesting phase decomposition or amorphization. SEM images of unprocessed surfaces displayed uniform microtextures. At 2 800 W， fine grooves and localized melting were observed.At 3 000 W， melt pools expanded， and irregular trenches formed. At 3 200 W， extensive sputtering and non-uniform material removal resulted in chaotic surface structures. AFM further highlighted re-solidified molten regions with blurred grain boundaries that correlated with increased roughness. Low-power cutting （≤2 800 W） achieved “cold processing” via confined energy deposition， minimizing thermal diffusion. In contrast， high-power cutting （>3 000 W） induced significant thermal mismatch between diamond （thermal conductivity of 2 000 W/（m·K）） and SiC （490 W/（m·K））， generating interfacial stresses that promoted delamination. Excessive heat accumulation also accelerated diamond graphitization and SiC decomposition， ultimately degrading the material’s mechanical and thermal properties.

Conclusion The surface quality and structural integrity in diamond-SiC composites are controlled by laser power levels. Optimal surface smoothing is achieved at 2 800 W （Ra=49. 4 nm）， while higher powers exceeding 3 000 W lead to significantly increased roughness （Ra>120 nm） due to thermal damage mechanisms. Phase transformations， particularly diamond graphitization and SiC decomposition， intensify with increasing power， fundamentally altering material functionality. These findings highlight the delicate balance required in laser processing parameters， and the trade-off between cutting efficiency and surface precision is influenced by the interplay between thermal stress， phase dynamics， and gas-assisted melt removal.