A multiscale approach to understand the role of dislocation motion on carbon mobility and the breakup of carbides in martensitic bearing steels.

金属的塑性主要是由位错运动引起的。钢中碳的存在阻碍了位错的运动，导致了更强的材料，这种强化效果取决于碳留在原处。马氏体在滚动接触疲劳(RCF)下的衰变被认为是由于碳的迁移，这是本项目的目标，以了解位错运动在滚动接触疲劳下的碳再分布中所起的作用。来自原子模拟的结果，如碳的位错结合能，将用于下一阶段的多尺度方法，其特征是位错的动力学蒙特卡罗(KMC)模拟。从这些模拟中可以提取位错运动规律，即位错速度与外加应力、温度和溶质浓度有关的函数。KMC模拟还将包括溶质扩散，以确定碳在不同应力、温度和浓度范围内如何随位错移动。KMC模拟的结果可以用于一种称为离散位错动力学(DDD)的更细粒度的方法，在这种方法中可以模拟多个位错及其相互作用。通过这种方法，可以计算晶体在各种应变条件下产生的应力。然而，如果本项目中开发的KMC程序成功地模拟了多个位错，则可能没有必要使用DDD。

Plasticity in metals is mainly due to dislocation motion. The presence of carbon in steels hinders dislocation motion, leading to a stronger material and this strengthening effect depends on the carbon staying where it is. The decay of martensite under rolling contact fatigue (RCF) is thought to be due to carbon migration - it is the goal of this project to understand the role that dislocation motion plays in the redistribution of carbon under RCF.Results from atomistic simulations such as carbon dislocation binding energies will be used in the next stage of a multiscale approach featuring kinetic Monte Carlo (kMC) simulations of dislocations. From these simulations dislocation mobility rules can be extracted; i.e. functions that relate dislocation velocity to applied stress, temperature and solute concentration. The kMC simulations will also incorporate solute diffusion to ascertain how carbon moves with dislocations in different stress, temperature and concentration regimes. The results of the kMC simulations can be used in a more course-grained approach called discrete dislocation dynamics (DDD) where multiple dislocations and their interactions are simulated. From this approach it is possible to calculate the stress produced in a crystal under a variety of straining conditions. However, it may not be necessary to use DDD if the kMC code developed in this project is successful in simulating multiple dislocations.