Femtosecond Laser Micromachining of Single-Crystal Superalloys

摘要

Continuous advances in turbine engine temperature capability have been enabled by the development of multiple generations of Ni-base single crystal superalloys along with complex cooling schemes for blades and vanes. Modern aero-engines contain up to 100,000 cooling holes and drilling requires significant time and expense. Recently, laser machining has become an accepted process for drilling closely-spaced cooling holes in turbine engine hot-section components, such as combustion chambers, nozzle guide vanes and turbine blades. Some negative effects may occur with the use of common nanosecond and picosecond lasers, including microcracking, excessive melting and tapering of the drilled holes, These defects can potentially degrade the performance of a component in Service and limit the application of lasers for micromachining. Recently developed femtosecond (l fs = 10~(-15)s) pulse length lasers are attractive for high quality micromachining. Ultrafast laser pulses (~100 fs) at intensities above the ablation threshold for a material can remove surface layers by inducing a rapid solid to vapor phase transition. Importantly, there is negligible heat dissipation into the bulk material. Thus, collateral damage to the surrounding area is limited and high precision machining is permitted. The objective of the present work was to study the characteristics of damage induced by femtosecond laser micromachining in a single-crystal superalloy with and without thermal barrier coating. Damage was studied as a function of processing conditions and examined via scanning electron microscopy (SEM) and transmission electron microscopy (TEM).