PHASE-STABILITY IN BE-NB AND BE-NB-ZR INTERMETALLICS

Sputter deposition of Be-Nb alloys at low temperatures (30-degrees-C) produces an amorphous phase for compositions of greater than 5 at.% Nb. A metastable crystalline phase which can be considered a highly faulted form of the Be12Nb occurs at higher deposition temperatures or by low temperature annealing of the amorphous phase. Because of structural similarities, this metastable phase is a precursor to the formation of either Be12Nb or Be17Nb2 upon high temperature annealing. There was no evidence of the Be5Nb phase which has been postulated on some phase diagrams. The Be12Nb phase can accommodate considerable zirconium in the structure and the Be13Zr can accommodate niobium in its structure. The Be13Zr becomes the predominant phase when the Zr/Nb composition ratio is greater than unity. High temperature annealing of the ternary results in dual-phase regions of Be12(Nb,Zr)+Be17(NbZr)2 or Be13(Zr,Nb)+Be17 (Zr,Nb)2, but the coexistence of Be12(Nb,Zr)+Be13(Zr,Nb)has not been observed.