Formation and stability of E93-type phases in the Ni-Nb alloy system studied by X-ray and neutron diffraction

By analyzing the phase states formed in Ni60-30Nb40-70 alloys under melt quenching and amorphous alloy crystallization, some researchers have revealed the formation of two E93-type phases (η′ and η″) with different crystal-lattice periods: 1.120 ± 0.001 and 1.164 ± 0.002 nm, respectively. To obtain more accurate information on the structure of these phases and explain the reasons of their formation during the non-equilibrium crystallization of a supercooled melt and an amorphous alloy, X-ray and neutron diffraction methods, as well as crystal-chemical criteria from the formation and stability theory for intermediate phases and metal glasses in transition-metal systems, are used. It is experimentally demonstrated that the η′ and η″ phases belong to different structural types, namely, Fe6W6C and Ti2Ni, respectively. The formation of the phases mentioned above is correlated with the corresponding crystal-chemical parameters: the size factor and the electron concentration.