Characterization of microstructural effects in a percussion laser-drilled powder metallurgy Ni-based superalloy

Excerpt

In the combustion zone of gas turbine engines for aircraft, it is essential to maintain a large temperature differential between the combustion gases and the Ni superalloy components so that fuel is used efficiently while avoiding degradation of the turbine blades, rotors, casings, etc. This is typically achieved using a combination of thermal barrier coatings (TBCs) and cooling holes [1‐3]. In the latter case, air from the compressor section is forced through internal channels in the components and this emerges from arrays of fine (<500 μm in diameter) cooling holes, establishing a thin air layer between the combustion gases and the TBC. Current generation engines can contain in excess of 10⁶ cooling holes and most of these are produced by electro-discharge machining (EDM) or laser drilling. The use of laser drilling is increasing because it enables holes to be drilled through components with TBCs (e.g. [4, 5]); this is a significant advantage over EDM where the holes must be formed in uncoated components and the subsequent application of a TBC can cause cooling-hole blockage. …