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Cyclic long-term testing of gas turbine burner materials in reducing environments at 700 °C

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Abstract

Gas turbines operating under fuel-rich conditions may suffer from material degradation and metal dusting. To evaluate this cyclic exposures have been done at 700 °C during 5000 h in two synthetic environments having a carbon activity of 0.26 and above unity. It was found that the common stainless steel 304L is incapable of withstanding either of the environments, while the stainless steel 253MA performs well because a protective silica layer is formed. The ferritic alumina formers Kanthal APM and Kanthal APMT perform well, together with several commercial chromia forming Ni-base alloys. As a general trend the material degradation is slower in the environment with the higher carbon activity, but pre-oxidised samples of chromia forming alloys did experience sudden and rapid carburisation after scale failure. Also a TBC system failed earlier in this environment, because graphite formation at the top coat/bond coat interface caused spalling of the top coat. Further the MCrAlY bond coat cracked and caused carburisation of the underlying Ni-based substrate. A silicon modified aluminide coating showed good degradation resistance, but stimulated excessive carbon deposition in the environment of high carbon activity.

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