Papers by Author: Yannik Cadoret

Abstract: Aluminide diffusion coatings are widely used in aeronautic domain. Nickel based superalloys present good mechanical properties and creep resistance at high temperature but their corrosion resistance is somewhat poor. In order to enhance their lifetime at high temperature, aluminide coatings can be applied on alloy surface. Aluminium present on material surface can form, at high temperature, alumina scale which is a protective oxide scale. In the present study, nickel aluminide coatings were carried out by aluminisation in a single step pack cementation process on nickel based superalloys 600 and AM1. Ni-Al intermetallic was obtained in each case. Oxidation tests were carried out at 900°C in air under atmospheric pressure. At this temperature, transient alumina as γ-Al2O3 and θ-Al2O3 appear on surface and are less protective than the stable α- Al2O3. Reactive elements can enhance α-Al2O3 nucleation and change diffusion mechanism during oxidation leading to a better adherence of alumina scale. In the present work, yttria was introduced by Metal-Organic Chemical Vapour Deposition (MOCVD) prior to the aluminisation. Yttria doped and undoped sample behaviours were compared under oxidising atmospheres.

Abstract: The present work, performed on nickel aluminides deposited on a single Ni-based superalloy AM1, focuses on the effect of the following several parameters on the microstructural and chemical changes occurring during isothermal heat treatment at 1100°C for 50h : -oxygen pressure by comparing heat treatment under ambient air (PO2 = 0.2 bar) and under secondary vacuum (PO2 = 0.2x10-6 bar). -cooling rate after isothermal heat treatment by comparing furnace cooling (3°C/min) and water quenching (500°C/min). -Pt addition in the coating by comparing NiAl and NiPtAl coatings. Characterizations were performed using SEM, analytical TEM and electron microprobe analyses. The results show that these parameters have a strong influence on both the microstructural evolution and the oxidation of the thermal barrier coating (TBC) system. Appropriate heat treatments are essential to improve interfacial resistance and increase the durability of TBC systems.