The Research On Picosecond Laser Machining Of Holes In Ni-base Single Crystal Superalloys DD6

The laser drilling technology with its high efficiency, high quality and non-contact has been widely applied in many fields. Laser drilling technology in turbine blades is an important application,but there are inevitably recast layer and micro cracks on the hole wall drilled by millisecond and nanosecond laser. With the rapid development of laser technology, especially the promotion of research and development of picosecond(ps) laser, the precision and quality of laser drilling have been greatly improved. However, there have been very limited studies regarding the mechanisms and applications of ps laser drilling in turbine blades, especially the research about interaction effect among appearance, quality and efficiency. Hence, the systemic and substantial investigation will be very helpful for potential applications in the field of industrial ps laser fabrication of aerospace materials.In this study, DD6 Ni-base single crystal superalloys, which have been used extensively for turbine blades, were mainly used to investigate. And a ps laser was used to do experiment. The detailed analyses of ps laser ablation for bulk superalloys were carried out. Further, the process optimization for ps laser fabrication of cooling hole in superalloy components was investigated.The study of ps laser-induced damage morphologies and ablation thresholds indicates that two distinctive ablation regimes including unmelted ablation and melted ablation existed in DD6 Ni-base single crystal superalloys. The diameters of these two ablation regimes were characterized as a function of laser fluence. In addition, the melted ablation threshold was determined to be 0.11J/cm2. There was no recast layer and micro cracks on the hole wall.The study of ps laser drilling on the DD6 Ni-base single crystal superalloys indicates that there was nearly no spatter on the surface of the micro-hole and there were some microcrack and discontinuous recast layer in the wall of micro-holes. Due to the coaxial blowing nitrogen gas, there was no heat defects and the efficiency was the fastest. The trepanning technique had distinctive advantages in shape, size, quality and ablation rate of cooling holes. In addition, micostructural investigation for ps laser processing of superalloys through thermal barrier coating(TBC) indicated a complete absence of laser-induced defects or delamination along interfaces of the TBC system.