Corrosion behaviour of gas turbine alloys under high velocity burnt fuels

The aim of alloy development in the field of nickel based super alloys for flying and land based gas turbines is to enhance significantly the mechanic al properties at high temperatures thus leading to a higher temperature cap ability. The higher temperature capability of the structural elements of ga s turbines results in an increased efficiency, a lowered fuel consumption a nd less emissions. To achieve an increased high temperature capability, however, surface degra dation of the material must be adjusted adequately, hence corrosion resista nce has to be improved. Additional to the isothermal and cyclic oxidation t ests which are performed in stagnant air the oxidation behaviour of alloy 2 100 GT and alloy C-263 was investigated by means of burner-rig-experiments under high velocity burnt fuels. Tn the burner rig test facility the sample is exposed to a hot gas stream of burned natural gas with gas velocities i n the range of 60 m/s to 150 m/s. The metal temperature of the sample can b e adjusted in the range of 900 degreesC to 1200 degreesC. In the tests described in this paper the gas velocities were chosen to be 6 0 m/s, 100 m/s and 140 m/s. The test duration was 1 h and 10 h. The test te mperature was kept constant at 1000 degreesC. After 1 h of testing both all oys showed mass gain which was significantly higher for alloy C-263. After 10 h of testing the mass loss of alloy C-263 was enhanced with increasing g as velocity. Alloy 2100 GT showed only at the highest gas velocity a mass l oss. The examinations by means of SEM and light-optical microscopy of the oxide scale and of the microstructure showed that alloy 2100 GT has a dense adher ent alumina scale and suffers no internal oxidation even under burner-rig-t est conditions. Alloy C-263 forms a mixed chromia and Cr-Ti-mixed oxide scale. The chromia is evaporated with increasing gas velocity, leaving (Cr-Ti)Oz-needles on th e surface. In the isothermal and cyclic oxidation tests alloy 2100 GT shows an excelle nt oxidation behaviour up to 1200 degreesC with a corrosion rate of less th an 0.1 mm/a. The aluminium content of app. 3 wt.-% which is remarkably high for a wrought alloy leads to the formation of a thin dense and adherent al umina scale. Alloy C-263 is a chromia former which is not suitable for temperatures high er than 1000 degreesC.