Abstract
Nb (niobium) and Nb-based alloys are promising refractory materials for use at high temperatures. However, due to the weak resistance to high temperature oxidation, a dramatic modification in oxidation resistance is required to use Nb-based refractory materials. Alloying Nb with other elements improves its mechanical properties and oxidation resistance to some extent. An improvement in oxidation resistance by forming Al (aluminum) based coating with dense Al 2 O 3 by utilizing different methods seems a prospective way for developing Nb-based refractory materials. In the current study, halide activated pack cementation (HAPC) and subsequent plasma electrolytic oxidation (PEO) were combined to form an oxidation-resistant coating on niobium base metal. Prospective Al 2 O 3 phases in amorphous or various kind of crystalline forms at the top were formed by anodic oxidation of cementation layer and modified to oxidation resistant a -Al 2 O3 by subsequent annealing at 1000 o C for 2 hours in argon gas. Comparing weight changes after oxidation tests shows that formed protective oxide film has a noticeable positive effect on the protection of Nb metal at high temperatures.
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