Actes du 3ème Colloque International sur la Corrosion et la Protection des Matériaux à Haute Température
J. Phys. IV France 03 (1993) C9-531-C9-538
Kinetic and morphologic study of the pack-aluminization of a series of refractory alloysD. Claves and A. Galerie
Laboratoire Science des Surfaces et Matériaux Carbonés, URA CNRS n° 413, ENS d'Electrochimie et d'Electrométallurgie de Grenoble, Institut National Polytechnique de Grenoble, BP 75, Domaine Universitaire, 38402 Saint Martin d'Hères, France
Five refractory alloys, Fe-20Cr-20Ni, Fe-20Cr-36Ni, Fe-20Cr-45Ni, Fe-20Cr-60Ni and Ni-20Cr, were submitted to pack aluminization at 850 °C for different durations in a NaF-activated pack. After a short period to achieve steady state, the coating kinetics were shown to be linear. The rate of aluminization was the same for the four alloys containing iron (about 1 mg.cm-2.h-1) and notably higher (1.8 mg.cm-2.h-1) in the case of the Ni-20Cr alloy. The nature of the formed products and the morphology of the layers were shown to depend on the alloy composition. The most important feature was the presence of external FeA13 on the four Fe-containing alloys, whereas a mixture of Ni2Al3 +NiAl was observed on the Ni-20Cr alloy. Kinetic experiments and thermodynamic calculations allowed a derivation of the value of the Al-activity at the gas-substrate interface. The mechanisms involved in the aluminization were shown to depend on the Al-concentration in the pack, on gaseous diffusion for low Al concentration and on interface reaction for high Al concentration.
© EDP Sciences 1993