As the advance of gas turbine engines, turbine entry temperature has been continuously enhanced, which demands for high performance thermal barrier coatings and improved cooling arrangement on turbine blades. In recent years, for the purpose of improving film cooling efficiency on a turbine blade while reducing the total volume of cooling air, film cooling holes are designed with three-dimensional shaped diffuser openings, such as chevron and trapezoid shaped holes. Precise manufacturing of such shaped hole-openings is a challenge especially when the metal blades are coated with ceramic thermal barrier coating (ZrO_2). Compared with traditional millisecond pulsed laser drilling or micro-EDM process, high frequency short pulsed laser combined with high speed galvoscanner has demonstrated unique advantages in micromachining directly on ceramics or metals with high quality. In this study, a ns pulsed Ytterbium fiber laser is used to study the physical interactions between pulsed laser beam and ceramic coating and base metal materials. Thermal ablation model was established to determine the ablated material volume and dimensions subjected to stationary pulses and a moving laser beam. Results are compared between modeling and experimental data. Optimized machining parameters are recommended with the aim of maximum process efficiency with minimum thermal effects such as spatters, microcracks and spallation.
展开▼
