Effects of bond-coat preoxidation and surface finish on isothermal and cyclic oxidation, high temperature corrosion and thermal shock resistance of TBC systems

A systematic study of the effects of bond-coats surface modifications prior to ceramic deposition is presented. TBC systems have been made and tested with most combinations of the following parameters: 1/substrate: IN100 or AM3 (single crystal) Ni-based superalloys; 2/ bond-coat: VPS NiCoCrAlYTa or CoNiCrAlY, (Ni,Pd)Al, (Ni,Pt)Al; 3/ bond-coat surface finish: as deposited, machined, grit blasted, preoxidized; 4/ top coat: APS or EB-PVD Y2O3 stabilized ZrO2. The preoxidation treatments of bond-coats were determined from the results of a study (TGA-GIXRD-SEM-SIMS) of their short-term (6 hours) isothermal oxidation behavior as a function of temperature (900 to 1100 degreesC), oxygen partial pressure and heating rate. Under these conditions all bond-coats are alumina formers, but depending on the oxidation conditions, transition aluminas may be formed. The characterization of complete TBC systems was also performed, including isothermal oxidation (TGA), cyclic oxidation at 1100 degreesC, cyclic corrosion at 900 degreesC and thermal shock (fast cooling from 1200 degreesC).