The Corrosion Resistance of Two Coatings Applied to Allison 250-C20b Blades

摘要

Blades made of 17-4 PH steel were coated with A-12 and with Sermetal 735. The coated blades were tested with neutral and acid salt sprays and in a compressor rig. These studies were undertaken as a result of the disintegration of an Allison 250-C20B compressor from a BO-105C helicopter. Corrosion pits were found on the concave sides of the rotor blades and in the vane root areas nominally covered by a plastic coating. The salt spray tests did not simulate real conditions as they did not produce the observed pitting. The compressor rig test did simulate operational conditions. It also demonstrated the ability of the coatings to protect the blades.