Bulk nanostructured materials by large strain extrusion machining
- PDF / 191,592 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 92 Downloads / 207 Views
M.R. Shankar Department of Industrial Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
J.B. Mann, W.D. Compton, and S. Chandrasekara) Center for Materials Processing and Tribology, School of Industrial Engineering, Purdue University, West Lafayette, Indiana 47907-2023 (Received 27 May 2006; accepted 4 October 2006)
Large strain extrusion machining (LSEM) is presented as a method of severe plastic deformation for the creation of bulk nanostructured materials. This method combines inherent advantages afforded by large strain deformation in chip formation by machining, with simultaneous dimensional control of extrusion in a single step of deformation. Bulk nanostructured materials in the form of foils, plates, and bars of controlled dimensions are shown to result by appropriately controlling the geometric parameters of the deformation in large strain extrusion machining.
I. INTRODUCTION
There has been significant interest in developing methods for production of bulk nanostructured metals and alloys with the objective of exploiting their enhanced mechanical properties for structural applications.1,2 Most of these methods have relied on the use of severe plastic deformation (SPD) for effecting microstructure refinement. SPD methods such as equal channel angular extrusion (ECAE),1–4 high-pressure torsion (HPT),1 and more recently, chip formation in machining,5,6 have been particularly effective in imposing large plastic strains in a variety of materials. Among these methods, chip formation in machining offers a simple route for the production of nanostructured and ultra-fine grained (UFG) materials by the imposition of very large plastic strains in a single pass of the cutting tool.5–7 While shear strains in the range of 1–15 can be imposed in a variety of materials, including those of moderate to high initial strength, by the use of a tool of appropriate geometry, the geometry of the deformation and resulting chip is not determined a priori. Herein, a variant of the machining process—large strain extrusion machining (LSEM)—is described that, in a single-step deformation process, combines microstructure refinement by large-strain machining with shape and
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0021 J. Mater. Res., Vol. 22, No. 1, Jan 2007
http://journals.cambridge.org
Downloaded: 12 Mar 2015
dimensional control of the chip by “extrusion.” The LSEM process produces bulk UFG and nanostructured materials at small deformation rates that suppress in situ heating and microstructure coarsening. The controllability of deformation strain and the resulting microstructure is demonstrated in foils and plates of copper. Transmission electron microscopy (TEM) and hardness measurements are used to track the formation of high-strength, UFG microstructures as a function of deformation for shear strains in the range of 2–11. This LSEM is analogous to an earlier extrusion-cutting process; however, these early studies were motivated by the production of
Data Loading...
