Internal oxidation

[traytown]

Hi All,
Is it possible for a aluminide coated superalloy (Tubine blade) to outwardly oxidize into the coating during the coating process?

 

[kumkumvijay]

Hello
Yes, its possible. Aluminide process can be done in two method in pack cementation technique. Low Aluminium or high aluminum content on the surface.

Generally high Al content is inwards process where beta NiAl and Ni2Al3 forms. so we need to do additional diffusion Heat Treatment to convert all Ni2Al3 as beta NiAl. Inward process is low temperature process ie.700-950 oC. the layer is rich in Al and during service the Al will further diffuse into parent metal.

At low Al content on reaction surface, the outward process will take place. This process need high temperature. Aluminum diffusion inward is faster than Nikel outward process due to Ni diffusion through the aluminide inter metalic layer. But in the outward diffusion process, Ni rich beta NiAl forms which may not be as prefered as inward process due to no al diffusion during service.

Based on the Ni and Al concentration on the reaction surface the complete process cycle & micro structure will be affected.

Thanks,