Ion channeling and TEM studies of pulse melted Fe(Pd) alloys

Abstract

Metastable Fe(Pd) surface alloys formed by deposition of layers of Pd on (100) Fe and subsequent pulsed (≈70 ns, 1.9 J/cm 2) electron beam melting into the bcc substrate have been investigated by ion backscattering/channeling and TEM. Repeated pulsed melting allowed examination of the epitaxial growth of the bcc substrate phase into the alloyed region for successively lower Pd concentrations. This procedure permitted detailed examination of the conditions for solidification with the fcc or bcc crystal structure and for metastable phase formation during rapid solidification. Bcc epitaxy is absent at Pd concentrations ≳30 at.%, where an fcc surface layer forms. Channeling of the Pd and Fe signals was observed at Pd concentrations ≲16.5 at.%, where a single-phase, supersaturated bcc alloy is observed. At an intermediate Pd concentration of 22–23 at.%, both epitaxial bcc and fcc materials are formed. The observed maximum substitutional Pd concentration in the bcc phase is about a factor of 5 greater than the maximum equilibrium solid solubility.