Atomistic insights into ultrafast phase transitions driving nanoparticle formation in femtosecond laser–irradiated nickel-based superalloys

Abstract

Femtosecond laser machining of specialty alloys has evolved into a high-precision, low-damage technology with extensive applications in micro- and nano-scale fabrication. However, the lack of atomic-scale underlying mechanisms significantly hinders the efficiency of process optimization. This study investigated the electron dynamics and ultrafast phase transitions of nickel-based superalloys at the atomic level using pump–probe microscopy and molecular dynamics coupled with the two-temperature model (MD-TTM). Within the first 2 ps, electron excitation and scattering increased the transient differential reflectivity (TR). Beyond this timescale, the onset of mechanical relaxation and phase transitions in lattice system decreased the TR. Spatiotemporal analysis of TR micrographs identified thresholds for spallation and phase explosion and confirmed the coexistence of these two-phase transition mechanisms. The experimental observations were further demonstrated by atomic-scale insights from MD-TTM simulations, which capture the evolution of electron–lattice energy transfer, lattice density variations and, material ejection dynamics. Based on the identified mechanisms, the morphology of both the ejected materials and the processed surface can be tuned by precisely adjusting the laser fluence. This study offers fundamental insights into the complex ultrafast processes governing femtosecond laser–alloy interactions and establishes a theoretical foundation for material ejection and surface morphology regulation, enabling high-precision micro/nanostructure fabrication.