Hot Cracking in the Heat-Affected Zone of Laser-Drilled Turbine Blades Made from the Nickel-based Superalloy Rene 80

摘要

Advanced film-cooling technologies for hot-gas exposed components of gas turbines featuring inlet temperatures which continue rising now as before necessitate specialized manufacturing methods. Meanwhile, the laser has become the preferred tool for the manufacture of a large number of small-sized film-cooling bores in turbine components made from nickel-based superalloys. Most of such materials admittedly are heat crack sensitive in the heat-affected zone adjoining the remelted layer. Wide-scale metallographic examinations which were made to optimize parameters exhibited a marked micro-structural effect on hot crack sensitivity for the Rene 80 material, i.e. equal laser parameters may result in different hot crack lengths depending on the local microstructural configuration in the close vicinity of the bores. The grain size, grain boundary morphology and orientation and the configuration of primary carbides seem to play a substantial part. These internal conjunctions should be taken into account in specifying admissible heat crack lengths since it does not appear realistic to take an influence on local microstructural parameters in conventional investment casting processes with an economically acceptable expenditure.