Strain-induced grain growth of cryomilled nanocrystalline Al in trimodal composites during forging

Authors

B. Yao; B. Simkin; B. Majumdar; C. Smith; M. van den Bergh; K. Cho;Y. H. Sohn

Comments

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Abbreviated Journal Title

Mater. Sci. Eng. A-Struct. Mater. Prop. Microstruct. Process.

Keywords

Strain-induced grain growth; Nanocrystalline; Al; Trimodal composites; TENSILE PLASTIC-DEFORMATION; BOUNDARY MOTION; NANOSTRUCTURED MATERIALS; THERMAL-STABILITY; ALUMINUM; ALLOY; MECHANISMS; STRENGTH; SIZE; MIGRATION; Nanoscience & Nanotechnology; Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering

Abstract

Grain growth of nanocrystalline aluminum (Al-nc) in trimodal Al metal-matrix-composites (MMCs) during hot forging was investigated. The Al-nc phase formed through cryomilling of inert gas-atomized powders in liquid nitrogen has an average grain size down to 21 nm, exhibits excellent thermal stability. However, substantial grain growth of Al-nc up to 63 nm was observed when the Al MMCs were thermo-mechanically processed even at relatively low temperatures. Grain growth of the cryomilled Al-nc phase in trimodal Al MMCs after hot forging was documented with respect to temperature ranging from 175 degrees C to 287 degrees C, true strain ranging from 0.4 to 135 and strain rate ranging from 0.1 to 0.55 s(-1). Hollow cone dark field imaging technique was employed to provide statistically confident measurements of Al-nc grain size that ranged from 21 to 63 nm. An increase in forging temperature and an increase in true strain were correlated with an increase in grain size of Al-nc. Results were correlated to devise a phenomenological grain growth model for forging that takes strain, strain rate and temperature into consideration. Activation energy for the grain growth during thermo-mechanical hot-forging was determined to be 35 kJ/mol, approximately a quarter of activation energy for bulk diffusion of Al and a half of activation energy for static recrystallization.

Journal Title

Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing

Volume

536

Publication Date

1-1-2012

Document Type

Article

Language

English

First Page

103

Last Page

109

WOS Identifier

WOS:000301319300015

ISSN

0921-5093

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