Development of Aluminide Coatings for Mo and Nb Alloys Using by Lamination Cladding

In order to improve the oxidation resistances of Mo and Nb alloys, aluminide coatings were developed by lamination cladding. Mo, Nb, and Al sheets with a purity of 99.99 wt% and dimensions of 15 mm x 10 mm x 0.5 mm were prepared by cutting, followed by the development of a specimen piece by holding the At sheet between two sheets of Mo or Nb. The specimen wrapped with a Ta foil to prevent oxidation was heated at temperatures of the order of the melting point of Al in a pure At atmosphere. On the basis of the elemental analysis by characteristic X-rays, the laminated layers formed on the Mo substrates were found to be composed of MoAl5, MoAl4, and Mo3Al8. It was also found that the main phase constituting the laminated layers changed from MoAl5, to Mo3Al8 on increasing the temperature from 973 K to 1473 K. In contrast, NbAl3 was singly formed on the Nb substrate, irrespective of the heating temperatures. However, since NbAl3 grains have a spherical shape, the NbAl3 layer was not formed on the Nb substrate.