A NEW TECHNIQUE TO REPAIR LOCALISED COATING DEFECTS FOR GAS TURBINES BLADES AND VANES

The protection against corrosion and oxidation of the blades and vanes of gas turbines has been successfully obtained by depositing overlay coatings of MCrAlY with vacuum plasma spray (VPS) technique. However it is necessary to qualify repair processes, even for localised coating defects produced during the manufacturing process or after service.Ansaldo and Atla have developed a technique to repair such localised defects.This process consists in:• localised stripping with two different techniques,• depositing new coating on the removed zone by plasma spray with special device,• diffusing of the new coating with vacuum thermal treatment,• non destructive evaluating to examine the repaired zone.This process guarantee good quality with economical advantages comparing with the traditional method which removes all the coating and repeats the VPS process.Copyright © 1995 by ASME