High Temperature Surface Engineering PDF

Platinum aluminide coatings act as a remedy against certain aggressive conditions in which modern aero-gas turbines operate. High aluminium activity coatings, such as RT22LTt, provide excellent protection for turbine blades from oxidation and hot corrosive attack. This is due to the formation of an alumina-based scale which acts as an environmental barrier. The integrity or scale can however, be undermined by the diffusion of damaging elements from both within the coating and the substrate to the oxide/ coating interface. High activity coatings are particularly susceptible to this type of degradation as they are formed by an inward diffusion process, resulting in substrate elements being present in the as-processed coating.

In contrast, as low activity coatings are formed by an outward diffusion process, the coating should be free from the potentially dangerous elements. This study investigated the oxidation resistance of a low aluminium activity platinum aluminide coating developed by Chromalloy United Kingdom Ltd. The ability of the coating to maintain a protective oxide was assessed, relative to RT22LT, after isothermal soaks at 11aoec, using SEM and XRD analysis to identify changes in coating morphology and degradation modes within the system. In comparison to RT22LT, the low activity coating was shown to have a superior performance, producing a complete and compact oxide scale and was less susceptible to both contamination and substrate elements.

Edited by: J. Nicholls, D. Rickerby