Microstructural characteristics of ultrafine-grained aluminum produced using equal-channel angular pressing
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I.
INTRODUCTION
THERE is considerable current interest in the processing procedure of equal-channel angular (ECA) pressing in which an intense plastic strain is introduced into a sample through simple shear.[1] It is now established that this procedure provides the capability of producing an ultrafine grain size, in the submicrometer or nanometer range, in large-grained polycrystalline samples.[2,3] To date, there have been numerous reports describing the use of ECA pressing for the fabrication of a wide range of ultrafinegrained materials.[4–17] Most of the investigations of ECA pressing to date have concentrated primarily on examining the microstructures and properties of selected materials after pressing to a relatively large strain. Recently, an investigation was reported in which transmission electron microscopy (TEM) was used to monitor the microstructural evolution as a function of strain in samples of pure aluminum.[15] However, there have been no similar investigations using optical microscopy. The present investigation was initiated in order to alleviate this deficiency. Experiments were conducted on pure aluminum with the objective of examining, using optical microscopy, the macroscopic characteristics of ECA pressing as a function of the total imposed strain. The results from these experiments are described in this report and, in addition, it is demonstrated that there is a very good correlation between the experimental observations and the pre-
YOSHINORI IWAHASHI, formerly Research Assistant with the Department of Materials Science and Engineering, Kyushu University, is Staff Engineer, Mitsubishi Fukahori, Heavy Industries, Ltd., Nagasaki Shipyard and Machinery Works, Munakaka, Nagasaki 851-03, Japan. MINORU FURUKAWA, Associate Professor, is with the Department of Technology, Fukuoka University of Education, Fukuoka 811-41, Japan. ZENJI HORITA, Associate Professor, and MINORU NEMOTO, Professor, are with the Department of Materials Science and Engineering, Kyushu University, Fukuoka 812-81, Japan. TERENCE G. LANGDON, Professor, is with the Departments of Materials Science and Mechanical Engineering, U.S.C., Los Angeles, CA 90089-1453. This article is based on a presentation made in the symposium ‘‘Mechanical Behavior of Bulk Nanocrystalline Solids,’’ presented at the 1997 Fall TMS Meeting and Materials Week, September 14-18, 1997, in Indianapolis, Indiana, under the auspices of the Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees. METALLURGICAL AND MATERIALS TRANSACTIONS A
dicted shearing patterns introduced into the samples during the ECA pressing procedure. II.
EXPERIMENTAL MATERIAL AND PROCEDURES
The experiments were conducted using samples of aluminum of 99.99 pct purity. An aluminum ingot was rolled into a plate at room temperature and samples were cut for ECA pressing with dimensions of 10 3 10 3 75 mm3. Each sample was annealed for 1 hour at 773 K and the longitudinal surfaces were prepared for ECA pressing using 800grit SiC
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