Phase-Field Simulation of Microstructure Changes in Ni<SUB>2</SUB>MnGa Ferromagnetic Alloy Under External Stress and Magnetic Fields

Abstract

Since the factors that influence microstructure formation are extensive (e.g., alloy composition, applied stress, external magnetic field, etc.), quite a lot of experimental trial-and-error is often necessary when searching for the best combination of desired microstructure and material properties, even when the basic mechanism of microstructure formation is understood. During the last decade, the phase-field method has emerged across many fields in materials science as a powerful tool to simulate and predict complex microstructure evolution. Since the phase-field methodology can model complex microstructure changes quantitatively, it is possible to search for the most desirable microstructure by using this method as a design simulation, i.e., through computer trial-and-error testing. In order to establish this methodology, first of all, quantitative modeling of complex microstructure changes using the phase-field method is required. The objective of this study is to model the twin macrostructure developments in Ni2MnGa ferromagnetic alloy under external stress and magnetic field. This alloy has been actively investigated in the field of the magnetic induced shape memory effect, recently. Through the computer simulation, we show that it is possible to model the macrostructure changes in Ni2MnGa quantitatively using the phase-field method. This modeling method may also be applicable to another alloy systems that the magnetic shape memory effect will take place. The simulation result also suggests that the mobility of twin boundary motion is enhanced just below the Ms temperature. Using the phase-field method to model the microstructure evolutions is thought to be a very effective strategy in predicting and analyzing the complex microstructure formation where the magnetic and stress fields should be considered simultaneously.