The effects of grain size and temperature on mechanical properties of CoCrNi medium-entropy alloy

Abstract

In this paper, the molecular dynamics method was used to analyze mechanical properties and microscopic deformation mechanisms of CoCrNi medium-entropy alloy with different average grain sizes at various temperatures. Its elastic modulus and Poisson's ratio were first calculated by the constant pressure molecular dynamics method. It is found that the elastic modulus increases with the average grain size increasing and is reduced at elevated temperatures. However, its Poisson's ratio decreases with the average grain size increasing and is not sensitive to temperatures.Simulations of simple tension were carried out and the results show that: (1) when the average grain size exceeds 15.2 nm, its yield stress and maximum flow stress decreased with the average grain size raising (Hall-Petch relationship), in this situation it is speculated that the dislocation slips and deformation twins within the grains dominate the plastic deformation; (2) when the grain size is smaller than 15.2 nm, the two stress parameters instead increase with the average grain size increasing (Inverse Hall-Petch relationship), such a plastic deformation mechanism is understood mainly due to grain boundaries migrations and grain rotations. In the end, as temperature effects on microscopic deformation mechanisms are concerned, it is found that more dislocations tend to be plugged near grain boundaries which have lower mobility at lower temperatures. Accordingly, the two stress parameters increase as the temperature decreases.

Properties of radiation-induced point defects in austenitic steels: a molecular dynamics study

“…The interatomic potential between Fe, Cr, Ni, and Mn atoms was described using the 2NN MEAM (modified embedded-atom method) potential reported by Choi et al [40]. This potential has been shown to provide reliable results in studies of atomistic-level phenomena, including NiCo, NiFe [41], CoCrNi [42], CrFeCoNi [43], and FeMnCrNi [44]. Since the potential function applicable to the five-element alloy is generally adapted to its subsystem, a quaternary MEAM potential function degenerated from the five-element potential function was used in our MD simulations.…”