ELEVATED TEMPERATURE DIFFUSION IN THE SYSTEMS Nb-Pt, Nb-Se, Nb-Zn, Nb-Co, Ni-Ta, and Fe-Mo

摘要

The electron probe microanalyzer has been used to determine the composition and extent of phases occurring in bimetal diffusion couples at 1100°C. A total of eighteen phases were determined in six binary systems: Nb-Pt,Nb-Se, Nb-Zn, Nb-Co, Ni-Ta, and Fe-Mo. In all cases the phases are stoichiometric and expressible in small whole numbers. The Nb-Se and Nb-Zn systems are somewhat alike in their phase formations in that Nb-Se exhibits Nb-Se, Nb2Se3, and Nb-Se2 while Nb-Zn produces Nb-Zn, Nb2Zn3, NbZn, and NbZn3. Diffusion between niobium and platinum to form Nb3Pt, NbPt, NbPt,, and NbPt3 would seem to preclude prolonged use of platinum thermocouples in contact with niobium at 1100°C. The only phases produced in the Nb-Co system are previously unreported in the literature and areNb3Co2 andNbCo4. This system also exhibited an extended region containing about 5 weight per-cent niobium in cobalt in agreement with the solubility limit shown in existing phase diagrams. Ni-Ta diffusion produced zones which showed strong cracking and grain formation. The phases TaNi3, TaNi2,TaNi, andTa3Ni2 comprised the zones, with pure tantalum precipitating in the TaNiz phase on cooling from 1100°C. Fe-Mo produced only one phase: Mo2Fe3.