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Effect of YCl3 addition on chromium pack diffusion type coating of an Ni-Co-ThO2 composite material

par Ghodsi, Mehdi ;Beatse, Teddy ;Vandenberg, Don
Référence Surface & coatings technology, 45, 1-3, page (179-183)
Publication Publié, 1991-05

Article révisé par les pairs

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Résumé :

A chromium-rich zone was obtained at the surface of an Ni-Co-ThO2 composite material using a pack diffusion type coating process with NH4Cl as activator and the addition of 16-30 wt.% YCl3 to the pack composition. We have shown that the alumina powder, serving as diluent in the pack, induced the dissociation of YCl3 by the formation of an AlYO3 mixed oxide above 800 °C. This reaction thus produced a complementary source of chlorine, leading to the formation of another chromium carrier (CrCl3) by a process similar to the decomposition of NH4Cl at lower temperatures. The addition of YCl3 enables the material to be used in severe oxidizing and wearing conditions, or allows a Cr2O3 protective layer, which can be destroyed by spalling in thermal cycling conditions, to be restored. © 1991.