Towards Manufacturing High-Quality Film-Cooling Holes Using Femtosecond Laser Combined with Abrasive Flow

Film-cooling holes are the key cooling structures of turbine blades, and there are still great challenges in manufacturing high-quality film-cooling holes. Although abrasive flow machining can be used as a post-processing technique to optimize the quality of film-cooling holes, its action process and influence mechanism have not been systematically studied. Herein, the drilling method of femtosecond laser combined with abrasive flow is studied in detail. Moreover, for comparison, the drilling methods of single femtosecond laser, single electrical discharge machining, and electrical discharge machining combined with abrasive flow are also discussed. The microstructure and composition distribution of the hole walls before and after abrasive flow machining were systematically characterized, indicating that abrasive flow can effectively remove the recast layer and cause local plastic deformation. Due to the surface hardening and non-uniform residual stress caused by abrasive impact, abrasive flow machining can increase the high-temperature endurance time of film-cooling holes while reducing the elongation. The combination of femtosecond laser and abrasive flow machining demonstrates the best high-temperature mechanical properties, with the endurance time and elongation reaching 136.15 h and 12.1%, respectively. The fracture mechanisms of different drilling methods are further discussed in detail. The research results provide theoretical guidance for the manufacturing of high-quality film-cooling holes through the composite processing of femtosecond laser and abrasive flow.