Solid-state reactions in mechanically alloyed Al-V powders

Abstract

High-energy ball milling has been performed on Al _x V_1−x powder mixtures in the Al-rich range of composition (x = 0.61, 0.70, 0.75, 0.85 and 0.90). The structural evolution and the thermal stability of the samples was followed by X-ray diffraction and differential scanning calorimetry. We have observed that, similar to other Al-transition metal binary systems, the reaction rate decreases with increasing Al content and that milling promotes diffusion of both elements into each other; in fact for short times of milling Al(V) and V(Al) solid solutions have been observed at all investigated compositions. With the exception of the Al-richest composition, several metastable phases have been observed to nucleate in the early stages of milling. In a broad range of composition around the stoichiometric ratio extended milling promotes the formation of the Al₃V intermetallic compound in a heavily strained nanocrystalline state. Upon heating of pre-milled samples to 360°C the disappearance of the metastable phases and the formation of a significant amount of the compound Al₃V has been observed at every composition and for all investigated milling times. The formation of Al₈V₅, Al₂₃V₄ and Al₁₀V has been observed upon heating to higher temperatures pre-milled samples containing 61, 85 and 90 at. % Al.