The Effect of Coating Composition and Geometry on Thermal Barrier Coatings 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) MCrAlYHfSi bond coatings with APS YSZ top coatings at 900-1100 -C. For superalloy 247 substrates and VPS coatings tested in 1 h cycles at 1100 -C, removing 0.6 wt %Si had no effect on average lifetime in 1 h cycles at 1100 -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 -C. With an HVOF bond coating, initial results indicate that 12.5mm diameter rod specimens have much shorter 100 h cycle lifetimes than disk specimens. Much longer lifetimes were obtained when the bond coating had an inner HVOF layer and outer APS layer.