Rapid production of pillar structures on the surface of single crystal CMSX-4 superalloy by femtosecond laser machining

CMSX-4 nickel superalloy specimens, in single crystal form, were prepared for in-situ machining trials using femtosecond pulse laser processing in a focussed ion beam scanning electron microscope. Preliminary laser ablation trials were carried out to establish the optimum focus distance. Various pillars were then prepared using the femtosecond laser, varying rectangular hatch pattern, scan speed, laser line separation and frequency. Polishing trials used helical laser hatch patterns to refine pillar shape and produce circular pillars with high aspect ratio. Example pillars were characterised by FIB-SEM cross-sectional examination to assess microstructural changes and re-deposition of vaporised material. The final selected laser parameters were able to produce a stable high-aspect ratio pillar in 4501 s, 1600 µm high with tip diameter 138 µm. An area 655 × 656 µm was cleared around the pillar with over 0.65mm³ of metal removed.