Experimental evidence for non-thermal sintering of Ti nanoparticles under femtosecond laser irradiation

Titanium (Ti) and its alloys are widely used in aerospace and biomedical applications, yet their high melting point and strong reactivity make them difficult to process using conventional methods. Laser-based additive manufacturing typically relies on melting, which can introduce porosity, cracking, and uncontrolled microstructures. In this work, we provide evidence supporting a fundamentally different sintering pathway in Ti nanoparticles under femtosecond laser irradiation that is consistent with non-thermal atomic transport. Because fs pulses deposit energy faster than electrons can transfer it to the lattice, they generate intense, localized electronic excitations that can drive atomic motion without reaching the melting point. These ultrafast non-thermal pathways—particularly field-enhanced diffusion and electromigration-like transport—enable densification at greatly reduced thermal budgets. Experiments show that fs irradiation at room temperature produces fragmented features dominated by ablation, whereas moderate substrate heating to 220 °C suppresses ablation and yields well-connected nanoparticle networks, despite peak lattice temperatures remaining below the Ti nanoparticle melting point. The results indicate that substrate heating enhances non-thermal atomic mobility and enables a controllable transition from ablation to densification. This study provides strong evidence that fs-induced non-thermal mechanisms can be harnessed for processing high-melting-point metals and suggests a promising pathway for manufacturing lightweight, fine particle-domain Ti structures with minimal thermal damage.