Phase formation and stability in sputter deposited Be–Nb compounds

Abstract

The phase relations and thermal stabilities of phases in sputter deposited Be–Nb alloys (3–14% Nb) have been studied. An amorphous phase forms during deposition at ambient temperatures (30 °C) for compositions >5% Nb. Metastable crystalline phases form during deposition at 350–450 °C as well as during annealing of the amorphous phase. One metastable bcc phase designated as Be 12 Nb′ can be explained by an extremely high fault density in the Be 12 Nb structure and is a precursor phase to the formation of both Be 12 Nb and Be 17 Nb 2 . Another metastable bcc phase also forms during high temperature deposition. Transformation to the equilibrium phases occurs at temperatures >800 °C. A stoichiometric range of about 5.5–7.8% is indicated for the Be 12 Nb phase and is probably due to vacancies on the Nb sublattice. No evidence of a Be 5 Nb phase was found and the Be 17 Nb 2 phase is stable to room temperature.