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 solid state interdiffusion of pure polycrystalline Fe and Nh powders at room temperature, using a high-energy ball-milling technique. The mechanisms of metallic glass formation and competing crystallization processes in the mechanically deformed composite powders have been investigated by means of X-ray diffraction, Mossbauer spectroscopy, differential thermal analysis, scanning electron microscopy and transmission electron microscopy. The numerous intimate layered composite particles of the diffusion couples that formed during the first and intermediate stages of milling time (0-56 ks), are intermixed to form amorphous phase(s) upon heating to about 625 K by so-called thermally assisted solid state amorphization, TASSA. The amorphization heat of formation for binary system via the TASSA, Delta H-a, was measured directly as a function of the milling time. Comparable with the TASSA, homogeneous 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 mechanical driven solid state amorphization. This single amorphous phase transforms 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.