Molecular dynamics study of femtosecond laser ablation of titanium

Femtosecond laser ablation offers exceptional precision for titanium processing, yet the atomistic origins of crystallographic anisotropy in ultrafast material removal remain poorly understood. Here, molecular dynamics simulations coupled with a two-temperature model were used to determine how crystallographic orientation and microstructure govern the thermal response, defect evolution, and ablation behaviour of hexagonal close-packed (HCP) titanium as a reference material. Basal (0001), prismatic (10–10 and 11–20), first-order pyramidal (10–11), second-order pyramidal (11–22), and polycrystalline configurations of HCP titanium were subjected to two representative laser fluences (0.109 and 0.545 J cm −2 ) with temperature-dependent electronic properties. The second-order pyramidal orientation consistently generated the highest average temperature within the laser-interaction region. At absorbed fluences of 0.109 and 0.545 J cm − 2 , its temperature was approximately 30–36% higher than those of the basal and prismatic orientations, but only approximately 12% higher than that of the first-order pyramidal orientation. Single crystals developed comparatively organised dislocation networks that followed the evolving melt-pool geometry, whereas the polycrystalline model exhibited heterogeneous defect nucleation at grain boundaries, which acted simultaneously as dislocation sources and barriers to propagation. Laser-induced defects also developed a characteristic sixfold arrangement reflecting the underlying symmetry of the titanium lattice. These findings establish a direct atomistic link between crystallographic structure, local temperature evolution and defect-mediated material removal, providing a mechanistic basis for controlling crater morphology, thermal damage and surface integrity during precision femtosecond-laser processing.