The Effect of Coating Composition and Geometry on TBC Lifetime

Several factors are being investigated that affect the performance of thermal barrier coatings (TBC) for use in land based gas turbines where coatings are mainly thermally sprayed. This study examined high velocity oxygen fuel (HVOF), air plasma sprayed (APS) and vacuum plasma sprayed (VPS) MCrA1YHfSi bond coatings with APS YSZ top coatings at 900 degrees-1100 degrees C. For superalloy 247 'substrates and VPS coatings tested in 1-h cycles at 1100 degrees C, removing 0.6wt.%Si had no effect on average lifetime in 1-h cycles at 1100 degrees C, but adding 0.3%Ti had a negative effect. Rod specimens were coated with APS, HVOF and HVOF with an outer APS layer bond coating and tested in 100-h cycles in air+10%H2O at 1100 degrees C. With an HVOF bond coating, initial results indicate that 12.5 mm diameter rod specimens have much shorter 100-h cycle lifetimes than disk specimens. Longer lifetimes were obtained when the bond coating had an inner HVOF layer and outer APS layer.