Phase stability at high temperatures in the Nb-Al system

The phases present in the Niobium-Aluminum system were investigated by X-ray diffraction and scanning electron microscopy on jelly-roll composites of 23.5, 27.5 and 35.0 at% Al, quenched after being heated in various time intervals (0.3 sec-5 min) to temperatures in the vicinity of the bcc formation temperature. In the present configuration, at concentrations around 27.5 at% Al the bcc phase is the product of an eutectoidal reaction between A15-structure Nb/sub 3/Al and sigma-phase Nb/sub 2/Al. This eutectoid has not been found in any of the published equilibrium phase diagrams, a revised equilibrium phase diagram is proposed.