On the Use of JMAK Theory to Describe Mechanical Amorphization: A Comparison between Experiments, Numerical Solutions and Simulations

Javier Blázquez,Clara Conde,Alejandro Manchón-Gordón,Alejandro Conde,Jhon Ipus

doi:10.3390/met8060450

Abstract

The kinetics of amorphization during ball milling is generally analyzed using two different approaches: the classical Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory and Delogu and Cocco’s model for which a region deterministically transforms after it reaches a certain number of collisions. The application of JMAK analysis to the latter model predicts Avrami exponents to be higher than the experimental ones (typically close to one). We develop simulations based on the probabilistic character of the nucleation phenomenon and concave growth of the amorphous phase in the core of a nanocrystal. The predictions of our simulations are in good agreement with the low Avrami exponents and with the size evolution of the remaining crystallites found experimentally. From these values, the parameters involved in the simulated model (growth rate and probability of nucleation) can be estimated.

Highlights

IntroductionRapid quenching is the standard method used to achieve an amorphous structure in which a strongly disordered, high temperature, liquid-like structure is frozen
The development of amorphous alloys in the 1960s by Paul Duwez [1] opened a new branch of research about the properties, microstructures and kinetics of these metastable systems [2,3].Rapid quenching is the standard method used to achieve an amorphous structure in which a strongly disordered, high temperature, liquid-like structure is frozen
In order to test the predictions of the different models here described, besides literature data, two binary compositions, Fe70 Zr30 and Fe70 Nb30, were prepared from mechanical alloying by ball milling in a planetary mill Fritsch Pulverrisette 4 Vario (Fritsch GmbH, Idar-Oberstein, Germany) from elemental powders (>99%)

Summary

Introduction

Rapid quenching is the standard method used to achieve an amorphous structure in which a strongly disordered, high temperature, liquid-like structure is frozen. The production of amorphous systems via mechanical alloying and/or milling (in a much broader compositional range than that obtained by rapid quenching methods [6]) has been widely found in the literature [2]. It is evident that the mechanisms that induce amorphization from mechanical milling are completely different to those that preserve the liquid-like structure by rapid quenching. Different microstructural and thermal analyses have shown equivalent behaviors of the obtained amorphous structures (e.g., glass transition temperature, amorphous halo observed by diffraction techniques, etc.) [2,3,7,8]

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Conclusion