Non-isothermal nano-crystallization kinetics in amorphous Ni55Nb35Si10 alloy
(1. Department of Metallurgy and Materials Science, Shahid Bahonar University, Kerman, Iran;
2. Department of Material Engineering, Nanotechnology and Advanced Material Institute, Isfahan University of Technology (IUT), Isfahan, Iran;
3. Department of Nanomaterials Engineering, Chungnam National University, Daejeon 305-764, Korea)
2. Department of Material Engineering, Nanotechnology and Advanced Material Institute, Isfahan University of Technology (IUT), Isfahan, Iran;
3. Department of Nanomaterials Engineering, Chungnam National University, Daejeon 305-764, Korea)
Abstract: The non-isothermal crystallization kinetics of Ni55Nb35Si10 amorphous alloy, prepared by mechanical alloying, was studied using differential scanning calorimetry. The amorphous alloy showed one-stage crystallization on heating, which led to the formation of nano-intermetallic crystals in amorphous matrix. The apparent activation energy for the crystallization of the alloy, determined by the Kissinger equation, was relatively high (468 kJ/mol), indicating that this amorphous alloy has high thermal stability. Changes in the activation energy during the crystallization process, were also evaluated by iso-conversional methods. The results showed that it decreases slowly from the beginning to crystallized fraction α=0.35 and it remains almost constant to the end of the process. The nano-crystallization mechanism for the non-isothermal crystallization of the amorphous alloy was explained by determining Avrami exponents. Transmission electron microscopy studies revealed the microstructural modification of amorphous alloy via nano- crystallization during annealing. The results suggest that the nucleation rate decreases with increasing time and the crystallization mechanism is governed dominantly by a three-dimensional diffusion-controlled growth. A predictive equation was obtained based on the Sestak-Berggren autocatalytic model to describe quantitatively the non-isothermal crystallization kinetics.
Key words: amorphous alloy; kinetics; nano-crystallization; DSC; activation energy