THE IN-SERVICE DEGRADATION OF CORROSION-RESISTANT COATINGS

As part of work to extend the operating life of turbine blades, rainbo w testing was performed to evaluate the effects of cooling-hole design modifications and the impact of a top aluminide on M-Cr-Al-Y coating on insevice coating deterioration. Cooling design modifications consid ered include a camberline-cooling-hole design, a peripheral-cooling-ho le design with a turbulated leading-edge hole, and a peripheral-coolin g-hole design with all turbulated holes. The results in this article s how that a top aluminide coating and peripheral cooling-hole design ex tend the M-Cr-Al-Y coating's service life. Additionally, the coating-d eterioration results are correlated with the beta-NiAl-depleted zone i n the coating and the oxide thickness at the cooling-hole surfaces. Va riations of coating degradation and cooling-hole surface oxidation amo ng the blades are discussed in terms of estimated service temperatures measured from gamma' particle size.