Kinetics and formation mechanism of amorphous Fe52Nb48 alloy powder fabricated by mechanical alloying

A single phase amorphous Fe,,Nb,, alloy has been synthesized through a soli d state interdiffusion of pure polycrystalline Fe and Nh powders at room te mperature, using a high-energy ball-milling technique. The mechanisms of me tallic glass formation and competing crystallization processes in the mecha nically deformed composite powders have been investigated by means of X-ray diffraction, Mossbauer spectroscopy, differential thermal analysis, scanni ng electron microscopy and transmission electron microscopy. The numerous i ntimate layered composite particles of the diffusion couples that formed du ring the first and intermediate stages of milling time (0-56 ks), are inter mixed to form amorphous phase(s) upon heating to about 625 K by so-called t hermally assisted solid state amorphization, TASSA. The amorphization heat of formation for binary system via the TASSA, Delta H-a, was measured direc tly as a function of the milling time. Comparable with the TASSA, homogeneo us amorphous alloys were fabricated directly without heating the composite multilayered particles upon milling these particles for longer milling time (86 ks-144 ks). The amorphization reaction here is attributed to the mecha nical driven solid state amorphization. This single amorphous phase transfo rms into an order phase (mu phase) upon heating at 1088 K (crystallization temperature, T-x) with enthalpy change of crystallization, Delta H-x, of -8 .3 kJ mol(-1). (C) 1999 Elsevier Science S.A. All rights reserved.