Actes du 3ème Colloque International sur la Corrosion et la Protection des Matériaux à Haute Température
J. Phys. IV France 03 (1993) C9-85-C9-97
Microstructure influence on the oxidation behaviour at 750°C of astroloyC. Mons1, C. Lineau2, C. Haut1, G. Rautureau3, E. Beauprez3 and G. Moulin3
1 Laboratoire de Métallurgie Structurale, ISMA, URA 1107, Bâtiment 413, Université Paris XI, 91405 Orsay, France
2 Laboratoire de Métallurgie Structurale, ISMA, URA 1107, Bâtiment 413, Université Paris XI, 91405 Orsay, France
3 ETCA, CREA/PS-LA, 16 bis Avenue Prieur de la côte d'Or, 94114 Arcueil, France
γ-γ' nickel base alloy, as Astroloy is sensitive to environment for fatigue crack propagation at 750°C. Two main oxides are obtained, especially enriched with Ni, Al (+Cr) in the outer zone and with Al, Cr in the inner one. The oxide scale growth is mainly controled by oxygen bulk difision, expect in the case of rolled sample where a linear diffusion of oxygen can also intervene for the growth of inner oxide layer. The inner oxide scale grows 103 times faster than the outer one. On account of the different diffusivities of metal and oxygen together with the dissolution of oxygen and formation of suboxides, (containing Ni, Cr in γ phase and Al, Ti in γ' islands) at the oxide scale-alloy matrix interface, an accumulation of mechanical constraints occurs in the alloy during oxidation. With a model based on "a solutal elastic effect when the concentration of solute varies" [l] a depth corresponding to a maximum stress was estimated between 3.4 x 10-8 cm to 1154 x 10-8 cm in front of the oxide scale-alloy matrix interface. Local enrichment in oxygen on induced defects (vacancies, holes) or precipitates then disturb the 18O diffusion profile versus alloy's depth.
© EDP Sciences 1993