A framework for modeling creep in pure metals

Abstract

The process of creep in pure metals is modeled as the cooperative interaction of three phenomena: the thermally activated, force-dependent release of dislocation segments from obstacles; the substructrual refinement of the microstructure due to plastic deformation; and the diffusion-controlled coarsening of the substructure. Key parameters are given as approximate generic values which can be varied. It is shown that for a wide range of parameters, the model reproduces the key features of the creep of pure metals: a steady-state stress exponent near 5 is recovered, and the key microstructural-length scale is related by a power law close to the reciprocal of stress (this dependence is not a strong function of temperature at a given stress). In addition, the activation energy of steady-state creep is nearly that of self-diffusion. Thus, the model reproduces the well-known phenomenology of puremetal steady-state creep. However, the present model is based on separate microstructural phenomena, which can be independently refined and studied.

Application of a modified jogged-screw model for creep of TiAl and α-Ti alloys

“…These route to modeling 5-power-law creep in subgrain-forming diffusional-transport models concern conditions of higher metals is described in a companion article in this volume. [9] temperature and low stresses in which the stress exponents…”

Electron Backscatter Diffraction Mapping of Microstructural Evolution of Pure Magnesium during Creep

“…[18] The relationship between flow stress and subgrain size and its contribution to the creep rate is summarized by Sherby et al [6] and remains an area of interest in the study of creep mechanisms. [17,19] Examples of low-temperature power-law creep microstructure can be observed in the compilation by Gandhi and Ashby [20] of creep at high-stress levels, and more recently a similar microstructure is also exhibited in the work by Liu and Wu [21] on creep of AZ31 at a very fast strain rate.…”

“…Microstructurally, the hightemperature low-stress power-law creep is believed to exhibit an ordered arrangement of dislocation substructures resulting in the formation of subgrains that resemble slip lines. [6,11,16] On the other hand, lowtemperature high-stress creep has been shown to be dominated by more localized clustering of dislocation cells or subgrains, [17] which eventually break down into fine grains. In this article, adjacent grain misorientations of 5 to 15 deg are considered subgrains and misorientations greater than 15 deg are considered grain boundaries.…”

Computational Methods for Microstructure-Property Relationships

“…This has been developed into an approximate model elsewhere (Daehn et al 2004). Alternately, fewer assumptions can be made and dislocation generation by plastic flow, recovery and the release from obstacles can be considered simultaneously (Brehm and Daehn 2002). So long as the assumptions in the postulates listed are adhered to, this produces results similar to the very simple model.…”

“…The following section gives an account of a model that can reproduce the salient features of pure metal creep that are described in the introductory section of this paper with a very simple model. This is a somewhat abbreviated and simplified version of a model that has appeared elsewhere (Daehn et al 2004;Brehm and Daehn 2002). For simplicity's sake, it is assumed that one type of obstacle (represented by s 1 and s 2 ) is present in the structure.…”