Providing the technology to achieve an efficiency of 65 % in natural gas-fired combined cycle power plants is the aim of the German Collaborative Research Center 561 “Thermally highly loaded, porous and cooled multi-layer systems for combined-cycle power plants” at RWTH Aachen University, Germany. For this purpose the fluid temperatures in the gas turbine cycle have to be raised considerably. Therefore a more effective cooling of the thermo-mechanically highly-loaded parts has to be realized, which is achieved by a newly developed effusion cooling requiring cooling holes with a diameter of 0.2 mm at an acute inclination angle of up to 30°.
Within this paper the influences of the process gas sort and pressure on the drilling are investigated concerning drilling velocity, hole quality (recast layer thickness and closures within the hole), and hole geometry (diameter and taper). For the experiments the process gases oxygen, argon, nitrogen, and compressed-air are used with the pressure being varied from 5 to 20 bar. At fixed laser parameters the process gas is determined to have a significant influence on the drilling result.