Industrial gas turbine components are subject, in the course of their operating life, to various kinds of damages, requiring repair processes during periodical overhauling operations. Blades, in particular, suffer from creep, corrosion, wear phenomena.
The majority of blade damage is currently repaired by means of manual TIG welding, with a filler metal which is often different from the blade alloy. This leads to an inferior metallurgical and mechanical condition of the repaired area as compared to the base metal. Besides, the nickel superalloys of the blades are often subject to cracking during welding operations.
A process of laser welding for the repair of the airfoil tip has been introduced and optimized, to improve the characteristics of the repaired component. Powder of the same alloy of the part is used as filler metal, and the process is carried out using a Nd:YAG laser, equipped with a 6–axis CNC motion control. The original blade geometry is rebuilt by multi–layer cladding, then the blade is submitted to machining operations, NDT testing and heat treatment.
The optimizing activity has been performed with the aid of microstructural characterization, chemical composition checking (by EDX microanalysis), hardness and stress rupture testing of the welded specimens.