The effect of cycle frequency, H2O and CO2 on TBC lifetime with NiCoCrAlYHfSi bond coatings

Abstract

Furnace cycle testing of superalloy 1483 and X4 substrates with high velocity oxygen fuel (HVOF) NiCoCrAlYHfSi bond coatings and air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) top coatings was conducted at 1100°C in various environments. Average thermal barrier coating (TBC) lifetimes were 5–6 times longer when 100h cycles were used to simulate base-load power generation operation, compared to the 1h aero-engine standard cycle. Longer exposure times for 100h cycles increased the interdiffusion resulting in no clear effects of H2O and CO2 additions on average TBC lifetime for the 1483 substrates, contrary to the results with 1hcycles where the addition of H2O reduced TBC lifetime. The lower Al content and perhaps the higher Ti content in 1483 compared to X4 resulted in lower TBC lifetimes for 1483. Photo-stimulated luminescence piezospectroscopy (PLPS) and 3D microscopy were used to measure residual stress in the alumina scale and surface roughness, respectively, on specimens with and without a YSZ top coating.