LASER DRILLING OF AIR-FILM COOLING HOLES IN AIR AND WITH COAXIAL WATERJET ASSISTANCE

Air-film cooling holes were drilled into a turbine blade with a 532-nm Nd:YVO4 nanosecond laser in air and with coaxial waterjet assistance. The drilling quality of the sidewalls of the holes was investigated comparatively by means of a 3D confocal laser scanning microscope, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy. Results have shown that the maximum thickness of the processing-induced defects around the air-film cooling holes drilled by the laser in air is up to 100 µm, while the holes obtained by means of the asynchronous operation of laser drilling in air and coaxial waterjet assistance indicate no spatter, oxide layer, recast layer or cracks. Compared with laser drilling in air, the minimum size of the heat-affected zone around the air-film cooling holes induced by asynchronous processing is decreased down to the sub-micrometer scale. The main phases in the oxide layer, recast layer and heat-affected zone are α-Al2O3, γ-Ni, and β-NiAl, respectively. Asynchronous processing can help us achieve high position precision and it will have wide application. are α-Al2O3, γ-Ni, and β-NiAl, resp