Coating of niobium and niobium alloys with aluminium. Part II. Hot-dipped coatings

Abstract

Coupons of niobium and niobium alloys were hot-dipped in molten aluminum. For niobium, a critical temperature of 1200 ° C was found. Above this temperature an adherent coating is formed. This coating consists of a thick layer of NbAl3, a thin layer of Nb2Al and, for prolonged dipping times, a very thin layer of Nb3Al. Below this temperature, a biphase zone of NbAl3 grains in an aluminum matrix is formed at the niobium surface. For niobium alloys, the critical temperatures vary with the composition of the alloy. As in the case of pack-cementation of niobium and niobium alloys, the mechanical characteristics of the substrate determine the structure of the coating and therefore the critical, temperature. The growth kinetics of the coatings were also studied. © 1971.