A mechanism for the negative strain-rate sensitivity of dilute solid solutions

A new mechanism is proposed for dynamic strain ageing and the negative strain-rate sensitivity (SRS) exhibited by dilute solid solutions containing mobile solute atoms. The mechanism is based on the strength variation of dislocation junctions due to the presence of solute clusters on forest dislocat...

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Bibliographic Details
Published in:Acta materialia 2004-07, Vol.52 (12), p.3447-3458
Main Author: Picu, R.C
Format: Article
Language:English
Subjects:
Applied sciences
BINDING ENERGY
Condensed matter: structure, mechanical and thermal properties
DIFFUSION
Dislocation junctions
DISLOCATIONS
Exact sciences and technology
MATERIALS SCIENCE
Mesoscopic modeling
Metals. Metallurgy
ORIENTATION
Physics
Portevin–LeChatelier effect
SENSITIVITY
SIMULATION
SOLID SOLUTIONS
STRAIN AGING
STRAIN RATE
Strain-rate sensitivity
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Summary:A new mechanism is proposed for dynamic strain ageing and the negative strain-rate sensitivity (SRS) exhibited by dilute solid solutions containing mobile solute atoms. The mechanism is based on the strength variation of dislocation junctions due to the presence of solute clusters on forest dislocations. The strength of a Lomer–Cottrell lock in which the mobile dislocation is free of solute, while the forest dislocation is clustered, is studied by using an orientation-dependent line tension model. It is shown that the junction strength increases with the size of the cluster on the forest dislocation (binding energy of the forest dislocation to its cluster). The cluster forms by lattice diffusion and its size depends on the time lapsed from the formation of the respective dislocation segment. Therefore, the average size of clusters on new forest dislocations is smaller the larger the imposed strain rate. Consequently, the average strength of junctions decreases (after a transient) upon an increase of the strain rate, which leads to negative SRS. A model including the results of the mesoscopic analysis is developed to capture this mechanism. The model reproduces qualitatively a number of key features observed experimentally at the macroscopic scale. The new mechanism does not require solute diffusion to take place sufficiently fast for clustering of mobile dislocations to happen during their arrest time at obstacles, as assumed in previous models of the phenomenon.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2004.03.042