Femtosecond Laser Ablation Regimes in a Single-Crystal Superalloy

摘要

Femtosecond (fs, 10−15 second) laser ablation of single-crystal nickel-base superalloy CMSX-4 under laser fluences ranging from 0.1 to 160 J/cm2 has been investigated. For comparison, the ablation behaviors of Ni and Ni3Al as individual components of the superalloy have also been studied. Two distinct ablation regimes were observed, dependent on the incident laser fluence. The ablation threshold fluences for these two ablation regimes were determined to be $ phi _{{th1}} $ = 0.30 ± 0.03 and $ phi ^{{}}_{{th2}} $ = 5.3 ± 0.5 J/cm2 in the superalloy. Ablation thresholds for the single-phase Ni and Ni3Al alloys were close to those measured for two-phase superalloy. The two distinct surface morphologies produced by ablation in these regimes were characterized in detail by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The ablation rate equations for the two regimes are presented and the corresponding ablation mechanisms are discussed. The implications for application of fs pulsed lasers to machining of superalloys are also discussed.