CRYSTALLIZATION AND STRUCTURE OF HIGH BORON CONTENT IRON-BORON ULTRAFINE AMORPHOUS ALLOY PARTICLES

Amorphous to crystalline transformation of chemically prepared Fe64B36 ultrafine amorphous alloy particles has been investigated by Mossbaue r spectroscopy, Brunauer-Emmett-Teller surface area measurements and t ransmission electron microscopy. Structural relaxation was observed be low 350 degrees C, which resulted in narrowing the full width at half maximum for the hyperfine field distribution from 13.0 to 10.6 T, whil e the average hyperfine field kept unchanged, to be about 20.3 T. Crys tallization started on the surface at about 300 degrees C and proceede d into the bulk at about 400 degrees C. Partial crystallization betwee n 400 and 450 degrees C resulted in increasing the average hyperfine f ield for the remaining Fe-B amorphous matrix to 21.6 T. alpha-Fe and F e2B were the only iron containing phases related to bulk crystallizati on, with the latter as a predominant component, accompanied by the seg regation of about 19% boron atoms. Above 500 degrees C, sintering of t he particles became very remarkable and a solid state reaction between diffusing iron and boron atoms to form Fe2B took place making the spe ctral area ratio for Fe2B to alpha-Fe components increase accordingly. A locally distorted non-stoichiometric Fe2B quausicrystalline structu re for the high boron content sample was proposed.