Femtosecond laser ablation and nanoparticle formation in intermetallic NiAl

The ablation behavior of a stoichiometric intermetallic compound beta-NiAl subjected to femtosecond laser pulsing in air has been investigated. The single-pulse ablation threshold for NiAl was determined to be 83 +/- 4 mJ/cm(2) and the transition to the high-fluence ablation regime occurred at 2.8 +/- 0.3 J/cm(2). Two sizes of nanoparticles consisting of Al, NiAl, Ni3Al and NiO were formed and ejected from the target during high-fluence ablation. Chemical analysis revealed that smaller nanoparticles (1-30nm) tended to be rich in Al while larger nanoparticles (>100 nm) were lean in Al. Ablation in the low-fluence regime maintained this trend. Redeposited material and nanoparticles remaining on the surface after a single 3.7 J/cm(2) pulse, one hundred 1.7 J/cm(2) pulses, or one thousand 250 mJ/cm(2) pulses were enriched in Al relative to the bulk target composition. Further, the surface of the irradiated high-fluence region was depleted in Al indicating that the fs laser ablation removal rate of the intermetallic constituents in this regime does not scale with the individual pure element ablation thresholds. (C) 2015 Elsevier B.V. All rights reserved.