High-temperature dislocation-precipitate interactions in Al alloys: An in situ transmission electron microscopy deformat
- PDF / 1,996,385 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 43 Downloads / 269 Views
D.C. Ahn and P. Sofronis Department of Theoretical and Applied Mechanics, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801 (Received 19 December 2004; accepted 2 March 2005)
The fundamental processes controlling the high-temperature interaction of dislocations with precipitates in Al-alloys were investigated in real time by deforming specimens in situ in the transmission electron microscope at elevated temperature. The observations support a bypass mechanism involving the interaction of lattice dislocations with the precipitate–matrix interface dislocations, where the rate-limiting step in the interaction is the release of the dislocation from the particle. These observations are discussed in relation to high-temperature deformation processes and models.
I. INTRODUCTION
At low temperatures, strengthening due to secondphase particles is governed by the dislocation either cutting through or looping around the particle.1 The former process occurs predominantly for small coherent particles, and the latter for incoherent particles and large coherent particles. At higher temperatures, dislocation climb introduces other bypass mechanisms, which are classified as either local or general climb.2,3 Local climb refers to the situation in which the dislocation remains in the glide plane, except at the particle where it is confined to the particle–matrix interface, giving rise to a sharp bend in the dislocation line. On the other hand, general climb refers to a relaxed configuration where the portion of the dislocation undergoing climb extends well away from the interface to minimize the line energy. The nature of the climb process influences the resistance associated with the particle, with the resistance being in general higher for local climb when the particles are coherent. For incoherent particles, the dislocations undergo local climb and then detachment.4,5 The stress associated with the detachment depends on the increase in strain
a)
Address all correspondence to this author. e-mail: [email protected] This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www. mrs.org/publications/jmr/policy.html. DOI: 10.1557/JMR.2005.0224 1792
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 7, Jul 2005 Downloaded: 16 Mar 2015
energy associated with the lattice dislocation being released from the particle–matrix interface and may be greater than the stress associated with dislocation climb.5,6 For dislocation interactions with incoherent particles, it is assumed that the incoherent interface allows the core of the lattice dislocation to spread, which makes it easy for the dislocation segment to move to the exit side of the particle. Alternatively, the lattice dislocation can interact with the interfacial dislocations to become incorporated into the interface much in the same way they are incorporated into a grain boundary.7 These interfacial dislocations can, through a pro
Data Loading...
