APS TBC performance on directionally-solidified superalloy substrates with HVOF NiCoCrAlYHfSi bond coatings

•The effect of substrate on TBC lifetime was studied using 1483, X4 and 247 alloys.•Substrates with HVOF NiCoCrAlYHfSi bond coatings and APS–YSZ top coatings were studied.•Photo-stimulated piezospectroscopy stress maps were collected on oxide scales on bare bond coatings and with a YSZ coating.•X-ray fluorescence was used to measure chemical changes in the bond coating.

Directionally-solidified (DS) superalloy components with advanced thermal barrier coatings (TBC) to lower the metal operating temperature have the potential to replace more expensive single crystal superalloys for large land-based turbines. In order to assess relative TBC performance, furnace cyclic testing was used with superalloys 1483, X4 and Hf-rich DS 247 substrates and high velocity oxygen fuel (HVOF)-NiCoCrAlYHfSi bond coatings at 1100 °C with 1-h cycles in air with 10% H2O. With these coating and test conditions, there was no statistically-significant effect of substrate alloy on the average lifetime of the air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) top coatings on small coupons. Using photo-stimulated luminescence piezospectroscopy maps at regular cycling intervals, the residual compressive stress in the α-Al2O3 scale underneath the YSZ top coating and on a bare bond coating was similar for all three substrates and delaminations occurred at roughly the same rate and frequency. X-ray fluorescence (XRF) measurements collected from the bare bond coating surface revealed higher Ti interdiffusion occurring with the 1483 substrate, which contained the highest Ti content.