Recrystallization without High Temperature or Deformation
Abstract
Recrystallization is one of the most impactful phenomena in materials processing. It is the science of removing defect and residual stress from metals and alloys. The outcome often includes control of grain size, texture, grain boundary character distribution parameters that influence the materials properties. Since pre-historic era, recrystallization has been achieved with heat treatment and external deformation. State of the art processes use very high temperature, otherwise the defects do not have sufficient mobility to nucleate the recrystallization process. Deformation is also critical for recrystallization since it is the stored energy that drives the dynamics. Residual deformation leads to static recrystallization, while dynamic recrystallization requires externally applied deformation (such as drawing or extrusion). The process is very time consuming, requiring anywhere from hours to days.In this project, we propose a non-thermal process that also does not need any externally applied deformation. We will exploit the electron wind force (EWF), which originates from passage of electrical current in metals. When very high momentum electrons impinge on defects, they transfer their momentum to the defects ? giving rise to the EWF that is extremely localized to the defects. In the defect-free lattice, electrons scatter to generate Joule heating only. We remove the Joule heat to allow the EWF to dominate the phenomena. We hypothesize that EWF acts `just in place?, (i.e., on the defects) while leaving the defect-free lattice alone. This makes the EWF induce at least 10x faster recrystallization dynamic at temperatures near or below 100 ?C. Our core objective is to discover the fundamental mechanisms behind the room temperature and ultrafast recrystallization process. We hypothesize that the EWF dissociates complex and immobile defect structures to highly mobile defects, such as the Shockley partial dislocations. We also hypothesize that EWF is an internally generated mechanical force field, thereby self-sustaining dynamic recrystallization without any external deformation. This poses an intriguing contrast with the conventional wisdom that the rate and magnitude of concomitant external deformation dictates dynamic recrystallization. The highly localized and dynamic impact of the EWF may contribute to generation of high density of annealing twins without any external deformation. Any externally applied strain can strongly influence the proposed mechanism. A major challenge in recrystallization research is its prejudice to the localized distributions of stored energy and misorientation; essentially the gradients of the microstructural parameters. To pinpoint nucleation and growth, one needs to map localization in microstructures continuously. This is a roadblock for the current art, where analytical microscopy is performed either on as-received or post-processed specimens. We propose a combined experimental-computational effort to shift the current experimental philosophy. Our experiments will be performed inside high resolution analytical microscopes that can map highly localized variation in strain, phase composition, grain size, texture, defect type and density, solute/precipitate clustering and grain boundary character distribution.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 01, 2023
- Source ID
- W911NF2310359
Entities
People
- Haque
Organizations
- Army Contracting Command
- Pennsylvania State University
- United States Army