The formation ans structure of aluminide base protective coatings on Nb and its alloys

Protective coatings of niobium and its alloys have been produced using two aluminization processes: activated cementation and immersion in liquid aluminum. The structures and formation mechanisms of the coatings have been studied. The coatings are primarily composed of the compound NbAl3, but they can consist of a layer of equiaxed grains, a layer of grains oriented perpendicular to the interface, or a combination of an outer layer of equiaxed grains and an inner layer of oriented grains. The appearance of the different structures depends on the formation process (immersion or activated cementation), the treatment temperature, the structural state of the niobium, or the additions made to this metal. The main result of this study is to demonstrate that, for fixed deposition conditions, these parameters influence the deformation capacity of the substrate and consequently the modes of stress relaxation that occur during the growth of the layers.