Session: Research Posters

Paper Number: 120240

120240 - Femtosecond Laser Sintering of Ti Nanoparticles 

Titanium (Ti) has been widely utilized in the aerospace, automobile, and biomedical industries due to its beneficial properties, such as high strength, wear resistance, light weight, corrosion resistance, and biocompatibility. Despite its many favorable properties, the manufacturing of Ti has been challenged due to its high strength. In order to fabricate Ti, selective laser sintering (SLS) can be utilized. SLS is a branch of laser powder bed fusion (LPBF) additive manufacturing (AM), utilizing a powder bed and laser irradiation. Femtosecond (fs) lasers have received attention in the field of SLS due to their high peak power and ultra-short irradiance time, which is less than the electron-phonon coupling time, resulting in high precision and minimized heat-affected zones. One of the challenges of using fs lasers for SLS is the high possibility of ablation caused by hot electron blast effects. Once a material is illuminated by the ultrafast pulsed laser, electrons within the optical penetration depth first absorb the photon energy and become a hot electron gas at an electron temperature of several thousand Kelvins. The large gradient of hot electrons induces a strong blasting force, which is proportional to the square of the hot electron temperature. Additionally, when the energy gained by hot electrons is high enough to overcome the work function of the material, the electrons flow out from the surface. The unbalance of positive and negative charges will form an electric field, and eventually, material explosion can be caused by the repulsive Coulomb force due to the electric fields. To address the ablation issues, we propose a double-pulse sintering strategy for manufacturing Ti nanoparticles (NPs). By dividing the original single pulse train into a double pulse train with a delay time, the high peak electron temperature can be reduced to avoid ablation. During the delay time, some of the energy from the first pulse can be transferred to the nearby lattice before the second pulse approaches. For this reason, the delay time is chosen to be comparable to the electron-phonon coupling time so that the highest electron temperature would not be too high to cause ablation. By having a delay time longer than the electron-phonon coupling time, ablation of Ti NPs can be avoided, and smooth sintering can be achieved. By adopting the double-pulse sintering, we expect advancements in surface roughness and the strength of the printed part. By suppressing the ablation of Ti NPs, a decrease in pores or defects in Ti sintered parts is expected, resulting in high strength and relative density. A decrease in surface roughness of the sintered parts is also expected by having the relaxation delay time in the double pulse.

Presenting Author: Janghan Park The University of Texas at Austin

Presenting Author Biography: Janghan Park is a PhD student at The University of Texas at Austin majoring in Mechanical Engineering. His research interests are selective laser sintering and light-matter interactions using ultrafast optics.

Authors:

Janghan Park The University of Texas at Austin
Yaguo Wang The University of Texas at Austin