Solid-state reactions upon mechanical alloying of an Fe32Al68 binary mixture

Abstract

The sequence of solid-state reactions that occur upon mechanical alloying of powder mixtures of Al and Fe taken in an atomic ratio of 68: 32 has been studied by the methods of X-ray diffraction analysis, Mossbauer spectrometry, and Auger spectrometry. Upon the formation of a nanocrystalline state (<10 nm), there takes place a mutual penetration of Al atoms into Fe and Fe atoms into Al particles. The rate of consumption of the fcc Al is substantially higher than that of the bcc Fe. The process of the mechanical alloying (MA) was found to be two-stage. At the first stage, up to 2 at % Fe is dissolved in the fcc Al, and an amorphous Fe25Al75 phase is formed in the interfaces, whose amount reaches 70 at % at the finish of the initial stage. In the interfaces of the α-Fe phase, a disordered bcc phase of composition Fe66Al34 is formed, which contains up to 12 at % Al segregates. At the second stage, the amorphous phase crystallizes into an orthorhombic intermetallic compound Fe2Al5. The residual α-Fe, bcc Fe66Al34, and segregated Al form a bcc phase of composition Fe35Al65.