Oxidation at 1250 degrees C of {Cr, Ta}-rich carbides-strengthened {Ni, Co}-based alloys

摘要

Thermogravimetry tests were performed for 70 h at 1250 degrees C in the air for six TaC-strengthened alloys with different values of the Ni/Co ratio. The oxidation and chromia volatilization rates were specified, and the formed oxides were characterized. Metallographic observations show that the alloys rich in Ni (from approximate to 70 to approximate to 25 wt. Ni) stayed chromia-forming until the end of the 70 h. In contrast, catastrophic oxidation locally started in the case of the Co-based alloys, which are too poor in Ni. The numerical exploitation of the mass gain files was done taking into account the mass loss induced by the chromia volatilization phenomenon. Results clearly showed a regular increase in oxidation parabolic constant when Ni is more and more replaced by Co.