Crystallization kinetics, microstructure evolution, and mechanical responses of Cr-Co alloys

Abstract

Understanding the crystallization kinetics of Cr-Co alloys and providing a quantitative characterization of the microstructure evolution during quenching are of practical significance to their industrial applications. Using molecular dynamics simulations, we investigate the solidification of Cr30Co70 and Cr70Co30 subjected to different cooling rates. Besides, the outcomes are examined for their mechanical responses under uniaxial tensile loading. It is disclosed that slower cooling (≤ 1 K/ps) is beneficial to crystallization, while faster quenching generally leads to disordered structures. In the solidified outcomes, regardless of composition ratios and cooling rates, Co-Co bonding is the most favorable compared with that of Co-Cr and Cr-Cr. As for structural order, the Co-rich alloys exhibit a hexagonal close-packed (hcp) dominant crystalline order, while face-centered cubic (fcc) becomes more advantageous in the remaining cases. Among all the samples, the Cr30Co70 obtained with 0.5 K/ps is an exception since it abnormally adopts fcc as a major crystalline order and realizes lower energy than expected. Additionally, under uniaxial tensile loading, a phase transition from fcc or hcp to body-centered cubic (bcc) is identified in the Cr30Co70 samples, while it is absent in the Cr70Co30 ones. These findings can aid in the design, manufacturing, and utilization of Cr-Co alloys in the field of material industry.