Materials Transactions Online

Materials Transactions, Vol.51 No.01 (2010) pp.2-7
© 2010 The Japan Institute of Metals

Microstructural Evolution in Pure Aluminum in the Early Stages of Processing by High-Pressure Torsion

Cheng Xu1, Zenji Horita2 and Terence G. Langdon1,3

1Departments of Aerospace & Mechanical Engineering and Materials Science University of Southern California, Los Angeles, CA 90089-1453, U.S.A.
2Department of Materials Science and Engineering, Faculty of Engineering Kyushu University, Fukuoka 819-0395, Japan
3Materials Research Group, School of Engineering Sciences University of Southampton, Southampton SO17 1BJ, U.K.

Measurements were taken to evaluate the evolution of homogeneity in disks of high-purity aluminum in the early stages of processing by high-pressure torsion. The results demonstrate that samples processed through 1/4 or more whole revolutions exhibit microhardness values which are generally higher in the centers of the disks than at the edges whereas after 1/8 turn the hardness is higher at the edge than in the center. It is shown that all of the hardness measurements are mutually consistent and they scatter around a unique curve when plotted against the equivalent strain. The measurements of hardness are supplemented by microstructural observations which provide evidence of a gradual evolution in the microstructure with increasing strain from an initial formation of subgrains to an array of ultrafine grains separated by boundaries having high angles of misorientation.

(Received 2009/8/3; Accepted 2009/10/2; Published 2009/11/26)

Keywords: hardness, high-pressure torsion, homogeneity, severe plastic deformation, ultrafine grains

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