Optical Monitoring of Periodical Structure Formation on Light Metals During a Single Laser Pulse in the Nanosecond Regime

Additive manufacturing (AM) is an interesting technique to produce parts with light metal alloys such as Ti-6Al-4V and Scancromal® for aerospace applications. The generated surfaces often require post-processing to improve their quality or be conferred new functionalities. Direct laser interference patterning (DLIP) is a flexible laser-based technique capable of tailoring surface properties by generating structures in the micro/nano range. This study experimentally investigates the dynamics of single-pulse nanosecond DLIP (ns-DLIP) surface structuring on these AM alloys using time-resolved reflectivity measurements. Periodic line-like features with a 6.0 μm spatial period are fabricated by applying single ns laser pulses with fluences ranging from 0.18 to 1.39 J/cm². The material's reflectivity is monitored by analyzing the temporal evolution of the zeroth diffraction order intensity. It is found that the time the material is in the liquid state increases with the pulse fluence, spanning 91 to 154 ns for Ti-6Al-4V and 62 to 115 ns for Scancromal®. By correlating reflectivity variations with structure depths, the growth rates of the periodic features are estimated, reaching maxima of ~35 nm/ns for Ti-6Al-4V and ~50 nm/ns for Scancromal® at the highest fluences investigated. This time-resolved reflectivity approach provides insights into the single-pulse formation dynamics of laser induced periodic surface structures on these additively manufactured alloys relevant for aerospace applications.