Direct atomistic simulations of metastable state destruction in titanium (β-α martensitic transition) caused by external influences

Pavel V Chirkov,Roman M Kichigin,Vladimir V Dremov,Alexey V Karavaev,F Gálvez Díaz-Rubio,D.A Cendón Franco

doi:10.1051/epjconf/202125002011

Abstract

Large-scale classical molecular dynamics (CMD) is utilized to simulate the β→α phase transition in pure titanium. Samples with a metastable polycrystalline bcc structure are prepared using crystallization from liquid state and subsequent recrystallization at elevated temperatures. Controlling the heating-cooling regimes we prepared two different kinds of samples with coarse and fine grain structures. The metastable bcc samples were relaxed at temperatures noticeably lower than the equilibrium β-α transition temperature. During the following cooling of the samples down to room temperature, transitions to the α phase start. With the prepared metastable bcc samples of two kinds we perform the CMD study of the β→α transition under plain shock wave loading and imposed shear deformations. From the CMD simulations we obtain information about the transformation barriers, mechanisms, and kinetics. Results of CMD simulations suggest that grain boundaries hamper the hcp phase growth.

Highlights

Martensitic phase transitions have a great influence on the properties of such materials as steels, shape-memory alloys, and titanium based alloys
Classical Molecular Dynamics (CMD) samples with fine and coarse metastable polycrystalline bcc structures are prepared through crystallization from a liquid state and subsequent recrystallization at elevated temperatures
The metastable bcc samples were relaxed at temperatures noticeably lower than the equilibrium β-α transition temperature

Summary

Introduction

Martensitic phase transitions have a great influence on the properties of such materials as steels, shape-memory alloys, and titanium based alloys. CMD simulations are performed using the LAMMPS code [2] with the Embedded Atom Model (EAM) interatomic potential for pure Ti [3] which reasonably well describes many properties of hcp, bcc and liquid Ti including the equilibrium phase diagram at relatively low pressures (see Table 1). We employ the OVITO [4] software to visualize the resulted atomic configurations and the Polyhedral Template Matching method (PTM) [5] to distinguish between different structure types. Such settings allow us to perform simulations and postprocessing of sufficiently large systems containing hundreds millions of atoms

Polycrystalline CMD sample generation

Summary