Phase equilibria and lattice distortion X-ray diffraction characterization of multicomponent alloys selected by a genetic algorithm

Abstract

The BEPE internship project proposed here aims to improve Caroline's work by performing advanced X-Ray characterization of previously designed multicomponent alloys selected by a genetic algorithm partly developed, implemented, and used by Caroline in her FAPESP project. The algorithm designs strong MPEAs by combining different models to find optimized compositions. One crucial step is use empirical thermodynamic criteria to estimate if a composition will be single-phase and its crystal structure, to do so, in the present work, the parameters "phi" and "VEC" are used. Furthermore, one of the main used strengthening models calculates the expected lattice distortion which is converted into a solid solution strengthening term. As will be shown in the present BEPE project, the students preliminary results point in the direction that the algorithm was able to find interesting single-phase compositions with large lattice distortions and consequently promising calculated mechanical properties. However, to do so, some compositional restrictions were added to correct discrepancies between the values calculated by these models and predictions by CALPHAD softwares (Pandat and Thermo-Calc) used to validate the calculations.In the current BEPE project these discrepancies will be investigated by comparing experimental data to the predictions from the "phi" and "VEC" criteria, Pandat/CALPHAD and ThermoCalc/CALPHAD. The experimental data will be acquired at a state-of-the-art X-Ray diffractometer available at Colorado School of Mines (CSM) that allows acquiring high quality X-Ray Diffraction patterns using a high energy Mo source. This diffractometer is equipped with in-situ heating at different temperatures which will be used to evaluate the phase equilibria of the selected alloys as a function of temperature. The diffractometer also allows acquisition of pair-distribution function (PDF) to assess local atomic environments, which will be used in the current project to evaluate the average lattice distortion. (AU)