Abstract
Furnace cycling has been widely used to study the failure of EB-PVD thermal barrier coatings. This contribution compiles TBC furnace cyclic lives over a broad literature base to highlight optimum systems and generalized trends not always apparent in one study. Systems included typical bond coats (Pt-modified aluminides, diffused Pt-only γ/γ′, and NiCoCrAlY (±Pt, Hf) overlays) and superalloy substrates (1st, 2nd, 3rd generation single crystals, directionally solidified, or conventionally cast). Pretreatments included controlled low p(O2) bond coat pre-oxidation and grit blasting (or none). The aggregate lives (~70) suggest a general trend with temperature, ~10-fold decrease for every 100°C increase. Measured alumina scale thicknesses (~30) were, on average, ~6.1±1.8μm at failure and independent of temperature for conventional systems. Most failures thus occurred in less time than that predicted to grow 7μm of alumina scale (as estimated from separate TGA studies of a Pt-modified aluminide coated 2nd generation single crystal superalloy). A tentative activation energy indicated from the broad distribution of failure times was ~280kJ/mol, while that from homogeneous TGA testing was ~380kJ/mol, with regression coefficients of r2=0.57 and 0.98, respectively.
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