Predicting Coating Degradation Under Variable Peak Temperatures

Abstract

The cyclic oxidation behavior of a CoCrAlY coating on a GTD-111 substrate was characterized by thermal cycling between ambient temperature and a variable peak temperature. The initial peak temperature of the thermal cycle was 954°C (1750°F) and tested for n1 cycles. The peak temperature was then increased to 1010°C (1850°F) for n2 cycles. Finally, the peak temperature was raised again to 1066°C (1950°F) for n3 cycles, where n1, n2, and n3 are in the range of a few hundred to a few thousand cycles. In all three cases, thermal cycles consisting of 55 minutes at the peak temperature and 5 minutes heating/cooling were used. Weight change of the test specimens was measured as a function of thermal cycle. The results were compared against a coating life model that treats coating degradation mechanisms including oxidation, spallation, and aluminum loss due to both inward and outward diffusion. Using this model, the influence of the variable peak temperature on coating life was predicted in accordance with experimental results.

Contribution of High Mechanical Fatigue to Gas Turbine Blade Lifetime during Steady-State Operation

“…The effects of fatigue on gas turbine lifetime have been comprehensively studied to understand the degradation mechanisms and failure modes of HGPCs [28][29][30][31] and to assess their remaining useful lifetime (RUL) [32][33][34]. These studies enable one to accurately estimate the operational lifetime of HGPCs and their coating layers in a gas turbine.…”