Laser micro-hole drilling in thermal barrier coated nickel based superalloy

This investigation deals with laser drilling of micro holes in yttria stabilised zirconia coated nickel based superalloy using a power modulated fiber laser. The parameters taken into account are assist gas pressure, modulation frequency, pulse on time and hole inclination angle. These parameters affect the important geometrical characteristics of holes, e.g., hole diameter, hole wall smoothness, taper angle and recast layer thickness. It has been found that the assist gas pressure has a significant effect on hole entry and exit diameter, taper angle and hole wall smoothness. It has also been observed less number of pulses of higher energy produces a hole with smaller entry and exit diameter, smaller taper angle, smoother hole wall and a thin stretched recast layer (∼ 15μm). The minimum achieved hole entrance diameter, exit diameter and taper was 342 μm, 200 μm and 3.54° respectively. Off normal drilling produces a hole with elliptical entrance. The eccentricity of such holes increases with inclination angle. Thick recast layers are produced at high inclination angles.