About this Journal Submit a Manuscript Table of Contents
Journal of Metallurgy
Volume 2012 (2012), Article ID 290873, 7 pages
http://dx.doi.org/10.1155/2012/290873
Research Article

Effect of Mechanical Milling and Cold Pressing on Co Powder

1Department of Engineering Metallurgy, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, South Africa
2Council for Scientific and Industrial Research (CSIR), Materials Science and Manufacturing, Meiring Naude Road, Brummeria, P.O. Box 395, Pretoria 0001, South Africa
3DST/CSIR Nanotechnology Innovation Centre, National Centre for Nano-Structured Materials, Council for Scientific Industrial Research, P.O. Box 395, Pretoria 0001, South Africa

Received 29 August 2011; Revised 28 October 2011; Accepted 2 November 2011

Academic Editor: Qian Zhao

Copyright © 2012 A. S. Bolokang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Cold pressing (CP) of the amorphous-like Co powder suppressed most of the XRD peaks, in particular the peak along (100) plane. The DSC curve of unmilled CP Co powder has shown a distinct sharp exothermic peak at 615C°. Upon annealing at 700C°, only the FCC phase with lattice parameter of 3.51 Å was detected by XRD. Our results implied that the exotherm at 615C° corresponds to compaction-pressure-assisted HCP to FCC first-order phase transition. The XRD analysis of 30 h milled powder revealed for the first time the FCC phase with a=3.80 Å. However, due to presence of (100) and (210) peaks, this phase is thought to be FCT with lattice parameters a=b=3.80 and c=3.07 Å. Consequently, the high-energy milling carried out in the current work induced for the first time HCP to FCT transition in Co. Upon CP of milled powder, the lattice parameter a shrunk from 3.80 to 3.75 Å. However, during annealing of the CP milled Co powder at 750C°, the FCT to FCC transition occurred, yielding the FCC phase with a=3.51 Å.