Andre Malie

Microstructure of Pt-modified aluminide coatings on Ni-based superalloys

Abstract This study deals with the microstructure of a Pt-modified aluminide coating as a function of the treatment parameters. IN 100 (polycrystalline) and AM 1 (single crystal) superalloys have been used as substrates and coated by an Aluminizing Phase Vapor Snecma ® low-activity treatment developed by Snecma-Services. By using the Fisher experiment design method, we have shown that the aluminum quantity incorporated in the coating depends essentially on the donor, and that the presence of important amounts of platinum at the surface allows a better incorporation of this aluminum through the reaction Pt+2Al→PtAl 2 . This latter phase then transforms into (Ni, Pt)Al during the aluminizing treatment. The results of this investigation allow to describe the microscopic aluminizing mechanisms.

Transition in high-temperature oxidation kinetics of Pd-modified aluminide coatings: Role of oxygen partial pressure, heating rate, and surface treatment

The isothermal oxidation of Pd-modified Ni aluminide coatings was studied as a function of P o 2 and temperature (900–1200 °C). A kinetic transition was observed between 900 and 1000 °C. Grazing incident x-ray diffraction, thermogravimetric analysis, x-ray photoelectron spectroscopy, scanning electron microscopy/energy dispersive spectroscopy, and secondary ion mass spectrometry analyses are consistent with the growth of δ-alumina or α-alumina below or above this transition temperature. Moreover, because P o 2 was established before specimen heating, an effect of heating rate was observed and analyzed. More importantly, no kinetic transition was observed for sand-blasted specimens oxidized at low P o 2 . Thus conditions for the direct growth of an α-alumina scale could be determined from the reported results.

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: IN 100 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 Y 2 O 3 stabilized ZrO 2 . 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°C), 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°C, cyclic corrosion at 900°C and thermal shock (fast cooling from 1200°C).