Performance Metrics and Experimental Testing of Erosion-Resistant Compressor Blade Coatings

Abstract

A durability test rig for erosion-resistant gas turbine engine compressor blade coatings was designed and commissioned. Bare and coated 17-4PH steel modified NACA 6505-profile blades were spun at an average speed of 10 860 rpm and exposed to garnet sand-laden air for 5 hours at an average sand concentration of 2.5gm3of air and a blade leading edge (LE) Mach number of 0.50. The rig was designed to represent a first stage axial compressor. Two 16μm-thick coatings were tested: Titanium Nitride (TiN) and Chromium-Aluminum-Titanium Nitride (CrAlTiN), both applied using an Arc Physical Vapour Deposition technique. A composite scale, defined as the LAZ score, was devised to compare the durability performance of bare and coated blades based on mass-loss and blade dimension changes. The bare blades’ LAZ score was set as a benchmark of 1.00, with the TiN-coated and CrAlTiN-coated blades obtaining respective scores of 0.69 and 0.41. A lower score identified a more erosion-resistant coating. Major locations of blade wear included: trailing edge (TE), LE and rear suction surface (SS). TE thickness was reduced, the LE became blunt, and the rear SS was scrubbed by overtip and recirculation zone vortices. The erosion effects of secondary flows were found to be significant. Erosion damage due to reflected particles was absent due to a low blade solidity of 0.7. The rig is best suited for durability evaluation of erosion-resistant coatings after being proven worthy of consideration for gas turbine engines through ASTM standardized testing.