Unstable Motion of an Edge Dislocation in a Solute Atom Atmosphere Studied by Kinetic Monte Carlo Simulations
- PDF / 88,147 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 39 Downloads / 164 Views
Unstable Motion of an Edge Dislocation in a Solute Atom Atmosphere Studied by Kinetic Monte Carlo Simulations X. M. Gu and Y. Q. Sun Department of Materials Science and Engineering University of Illinois, Urbana, IL 61801, USA ABSTRACT The discontinuous yielding of a model material, which contains an edge dislocation moving in the atmosphere of solute atoms, is studied by Kinetic Monte Carlo (KMC) simulations. The stress-strain curves for a constant strain rate were obtained at different temperatures. The dislocation moves discontinuously, producing three types of serrated yielding behavior at intermediate temperatures for different imposed strain rates. Positive dependence of flow stress on temperature and negative strain rate sensitivity were observed in the regime of discontinuous motion. The present model, though highly simplified and not taking into account the collective behaviors of dislocations in real materials, does exhibit some of the basic features observed in experiments. INTRODUCTION Discontinuous yielding, commonly referred to as the Portevin-Le Chatelier (PLC) effect, occurs in many dilute alloys within certain regimes of temperature and strain rate. Such an effect, characterized by temporal and spatial inhomogeneity in slip, has been investigated extensively by both theoretical and experimental studies [1-9]. One of the most successful theories, first proposed by Penning [1] and later developed by Kubin, Estrin and their coworkers [2-3], explains the temporal inhomogeneity by phenomenological descriptions of deformation with a constitutive equation. A condition for temporal inhomogeneity, according to this theory, is the existence of negative strain rate sensitivity. The physical mechanisms of the negative strain rate sensitivity are based on the dynamic interaction between diffusing solute atoms and mobile dislocations that are temporarily arrested by localized obstacles [6-7]. Later developments have taken into account the effect of strain softening by using the second derivative of local strain as an additional term in the constitutive equation [3,8], and further progress has been made by introducing a non-linear theory [5,9]. In the present paper, Kinetic Monte Carlo simulation is used to study the motion of an edge dislocation moving in a solute atmosphere without explicit assumptions about strain rate sensitivity, work hardening or work softening. Nor are there strong localized obstacles in the simulation. The Monte Carlo method has been used recently by Wang et al. [10] to study the behavior of an edge dislocation interacting with solute atoms under a constant stress. We study a more relevant situation, where the net machine strain rate, consisting of elastic and plastic contributions, is kept constant, and the stress and dislocation velocity are both allowed to vary under the constraint of the constant net strain rate. The approach therefore mimics the usual tensile test. Although the model is a highly simplified one, it is shown to possess some of the basic features found in experiments.
Z
Data Loading...
